Earthquake early warning for Israel: Recommended … · 2014-05-11 · Earthquake early warning for...
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GII 500/676/12
Earthquake early warning for Israel:
Recommended implementation strategy
Richard M. Allen (Chair)1, Gidon Baer (Coordinator) 2,4,
John Clinton3, Yariv Hamiel4, Rami Hofstetter5,
Vladimir Pinsky5, Alon Ziv6, Aldo Zollo7
1 - University of California, Berkeley, USA
2 - Earth and Marine Research Administration, Israel
3 - ETH Zurich, Switzerland
4 - Geological Survey of Israel
5 - Geophysical Institute of Israel
6 - Tel Aviv University, Israel
7 - University of Naples "Federico II", Italy
International advisory committee on earthquake early warning
GSI/26/2012 GII 500/676/12
Jerusalem, December 2012
Ministry of Energy and Water Resources
Geological Survey of Israel
The Geophysical Institute of Israel
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Table of Contents
Executive summary ................................................................................................................................ 3
Committee charge ................................................................................................................................... 5
Tectonic setting and seismic risk ...................................................................................................... 6
Guiding principles for the development of a warning system ............................................. 10
Approaches to early warning ........................................................................................................... 11
Regional EEWS ....................................................................................................................................... 13
Onsite EEWS ........................................................................................................................................... 14
Front detection or barrier EEWS (S-wave threshold EWS) ................................................... 15
The proposed Early Warning system for Israel ......................................................................... 16
Simulated early warning performance in Israel ....................................................................... 20
Assessment of alert times .................................................................................................................. 20
Simulations of P-wave approach .................................................................................................... 25
Recommendations for software implementation .................................................................... 29
Recommendations for early-warning capable network stations ....................................... 30
Proposed initial design ...................................................................................................................... 32
Timeline and budget for implementation ................................................................................... 36
Timeline ................................................................................................................................................... 36
Estimated budget .................................................................................................................................. 39
Important improvements beyond the initial 2-year plan ..................................................... 40
Building seismological capacity in Israel .................................................................................... 42
Bibliography ........................................................................................................................................... 43
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Executive summary
The purpose of this report is to recommend an optimal design and implementation plan
for an earthquake early warning system in Israel. The goal of the project is to provide
earthquake warning to schools around the nation within 2 years of project
commencement, and extend the warning nationwide beyond a period of 3 years. This
recommendation was prepared by an international advisory committee on Earthquake
Early Warning that was formed by the Earth and Marine Research Administration (EMRA),
Ministry of Energy and Water Resources of Israel and assembled in Jerusalem from
September 9th to 14th, 2012. The committee consisted of eight: Prof. Richard M Allen
(committee chair), Director of the seismological laboratory, University of California,
Berkeley, USA; Dr. John Clinton, Director of seismic networks, Swiss Seismological Service,
ETH, Zurich, Switzerland, Prof. Aldo Zollo, Seismologist,University of Naples "Federico II",
Italy; Dr. Gidon Baer (committee coordinator), acting General Director of the EMRA, Dr.
Yariv Hamiel, Geophysicist, Geological Survey of Israel; Dr. Rami Hofstetter and Dr.
Vladimir Pinsky, Seismologists, the Geophysical Institute of Israel, and Dr. Alon Ziv,
Seismologist, Tel Aviv University.
The infrastructure for providing earthquake early warning in Israel will be a state-of-the-
art seismic network that will provide the best possible early warning capability for the
entire state of Israel and its entire population, within the proposed budget and timeline,
while also allowing for improvements in the warning system as warning algorithms
continue to be developed and enhanced around the world. This new seismic system
should build on the existing monitoring capability in Israel in order to maximize the long-
term operability of the system. Specifically, the new seismic network stations that we
propose should be integrated into the Israeli Seismic Network (ISN), and the ISN should be
simultaneously upgraded.
There are two types of approach to earthquake early warning. The first is an S-wave
based threshold approach, which alerts when two or more seismic stations observe
ground shaking above a pre-defined strong shaking level. The advantage of this approach
is simplicity and that cheap low-quality accelerometers can be used. The challenges
include the fact that the first earthquake to trigger the system will be the big earthquake
for which an alert is needed so without lowering the threshold – often not possible for
low-quality sensors, only simulated testing is possible; alerts are only generated for events
close to the sensors; and there is currently no open source community supported
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processing system. These challenges all mean that there is no possibility of upgrade or
improvements to the system in the future without a significant investment.
The second approach is the P-wave based earthquake detection. This approach uses P-
waves—which travel about twice as fast as S-waves and cause little damage—to detect
earthquakes, characterize the source magnitude and location, and then issue an alert
based on predicted shaking. The approach requires higher quality equipment, but it
allows for location specific alerts (a dynamic grid approach) and regular testing through
detection of smaller (non-hazardous) earthquakes. This is the approach favored by early
warning groups around the world (e.g., Japan, Taiwan, California, Italy, Switzerland). For
this approach there is also an open source community supported software.
The committee recommends a hybrid approach for Israel that invests in the necessary
hardware for a P-wave based system, while also supporting an initial S-wave based
threshold approach which can be implemented very rapidly at little additional cost. We
propose the installation of high quality seismic instrumentation along the Dead Sea and
Carmel Faults, consisting of a mixture of accelerometers and broadband velocity
instruments. These new seismic sites should be integrated into the ISN, and existing ISN
stations should be upgraded to the same quality. Seismic network management software
should be installed at a hub at the Seismology Division where an open source community
supported earthquake monitoring system will collect data from all seismic sites and
perform real-time event characterization and alerting. A secondary back-up seismic
network hub should be installed at a geographically separate location after the evaluation
period of the system. We recommend to initially implementing an S-wave based threshold
algorithm which can be put into action within the tight timeline decided by the Israeli
Government. A P-wave based approach should then be added, and an initial version is
expected to be ready within two years. Further assessment of system performance should
continue beyond this period in order to improve and optimize the algorithms making full
use of advances made by the early warning community around the world.
The proposed seismic network to be installed is as follows (see Fig. 8). A total number of
49 accelerometer-only sites will be deployed close to the Dead Sea and Carmel Faults
(within 15 km) in a single array of stations every ~10 km, south of the Dead Sea, and in a
staggered geometry (two parallel echeloned arrays of stations ~10 km apart) from the
Dead Sea northward. Five additional sites with co-located seismometers and
accelerometers should be deployed at large spacing along the Dead Sea Fault.
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Recommended specifications for all the instrumentation is provided in this report. This
plan fits within the approved budget and timeline.
The committee also recommends some additional areas of development and network
improvements that do not fit into the initial two-year plan, but are believed to be
important and should be pursued once the initial system as described above has been
installed and is operating. These include densification of the network (if required),
construction of a secondary backup hub, the development of a user base beyond just
schools; the continued development of improved early warning algorithms for Israel; the
implementation of an onsite approach for schools; continued evaluation of system
performance (based on small earthquakes and system test events); an evaluation of
system robustness for redundancy and performance; development of other real-time
earthquake information products including ShakeMaps; and the possible inclusion of real-
time GPS.
Finally, it is critical that an effort is made to build seismological capacity in Israel. Success
with early warning requires ongoing and continuous efforts in both academic and applied
research that is occurring in the university and governmental earth science research
institutes. The new seismic network will provide a significant amount of geophysical data
that should be effectively mined to improve understanding of seismic hazard and
seismotectonics. This includes ground motion attenuation relations, site effects, fault
mapping and delineation using microseismicity, and probabilistic seismic hazard
assessment. In order to support the successful operation and development of the early
warning system the next generation of seismologists in Israel must also be educated,
supported, developed and trained. This must start with the encouragement of students in
seismology and continue with the development of fulfilling career paths for them in Israel.
To achieve this goal, mechanisms to encourage, promote and financially support exchange
of students, postdocs and experienced researchers from and to Israel for earthquake
research is necessary.
Committee charge
The principal objective of the committee is to recommend an optimal earthquake early
warning system for the State of Israel, which should meet high operational standards, will
be financially and technically feasible, and will be implemented within a two-year
timeframe. The committee is charged to propose the system’s geographical configuration,
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its hardware, and software. Evaluation and recommendations regarding the benefits of the
system during its operation, both from the seismic hazard and the scientific aspects are
also included in the mandate of this committee.
Tectonic setting, seismic risk, and existing NETwork
The Dead Sea fault (DSF) poses a seismic threat to the population centers in its vicinity.
The fault system accommodates the left-lateral motion between the Sinai subplate and the
Arabian plate (Fig. 1). It is about 1,200 km long and connects the Taurus-Zagros
compressional front in the north, to the extensional zone of the Red Sea in the south. Over
the past few million years tectonic movements have shaped the Dead Sea Fault system.
The Dead Sea fault comprises several major basins connected by large faults. The Dead
Sea basin is the largest one. The total tectonic motion is primarily left-lateral strike-slip
and estimated to be approximately 5 mm per year.
Figure 1. General tectonic map of the region. The Dead Sea Fault and the Carmel Fault (labeled
CFS) are believed to be the primary sources of seismic hazard.
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The Dead Sea Fault poses a major threat to the population of Israel, Jordan, Syria, Lebanon,
and the Palestinian Authority. Records of destructive earthquakes that occurred in the last
3,000 years—some of which were catastrophic—are mentioned in the Bible, in later books,
or as reports by pilgrims who came to the Holy Land. Some examples include: (1) The 31
BC catastrophic event as described by Josephus Flavius in Antiquities of the Jews. (2) The
so called Bet Shean earthquake of 18/1/749. (3) Several strong events in today’s northern
Israel and southern Lebanon in May 1202. (4) Two strong earthquakes in October and
December 1759. (5) A strong earthquake in January 1837. These devastating events
claimed up to 30,000 casualties, several tens of thousands of wounded people and a large
number of fully or partially destroyed buildings in various cities and villages over a large
area. We do not know the exact magnitudes of these events, however, based on various
indications they are estimated to be of M 7.0 and above.
Since the beginning of the 20th century, several moderate earthquakes occurred along the
Dead Sea Fault. The M 6.2 earthquake of July 11, 1927, resulted in 285 deaths, 940
wounded and extensive damage in many towns and villages on both sides of the Dead Sea
Fault. Throughout the 20th century, several other widely felt earthquakes occurred in 1928,
1956, 1970, 1979, and 2004 with magnitudes in the range of M 5.0-5.5, fortunately causing
little or no damage in neighboring regions. On a statistical basis, we expect one earthquake
with a magnitude of 4.5, 5.0 and 6.0 to occur every year, 10 years and 80 years,
respectively. The catastrophic magnitude 7 and above events might occur every several
thousands of years. A similar event to the 1927 earthquake which was magnitude 6.2
would be very harmful and destructive today considering that the total population on both
sides of the Dead Sea Fault has increased by a factor of 20 since that earthquake. Various
seismic scenarios have been explored to better understand the consequences of future
earthquakes in terms of casualties, injuries and damage as a result of moderate to strong
earthquakes along the Dead Sea fault or the Carmel fault (e.g., Levi et al., 2010).
Instrumental seismic monitoring in the Middle East started at the end of the 19th century
with the installation of station Helwan (HLW) in Cairo, Egypt. From 1898 until 1912
Helwan was the only seismological station that operated in the region, the closest stations
being more remote and including stations at Athens and Istanbul. Another important
station that started operating in 1912 was Ksara, which is located in central-east part of
Lebanon. Station JER of the WWSSN, located in the Hebrew University of Jerusalem,
started operating in 1954, and was later upgraded in 1963. During the middle of the 20th
century temporary stations operated for a short period of time in various parts of Israel
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enriching somewhat the seismological catalog. Two seismic networks, with up to 35 short
period stations in each network, were installed in 1983, one in Jordan (JSO, Jordan
Seismological Observatory) and the other in Israel (ISN, Israel Seismic Network). With
time these networks have been upgraded and several broadband stations and
accelerometers have been installed. Since that time the seismicity of the Dead Sea fault is
continuously monitored by the ISN and JSO. In 2000 the catalogs of both networks were
merged to create a common Dead Sea Fault catalog, which is shown in Fig. 2. In addition to
these permanent networks, several temporary networks were deployed along the Dead
Sea fault, typically for 1-2 years, which further increases the database.
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Figure 2. Seismic network (blue squares), active faults (blue lines), and seismicity (purple, red and
green dots) in Israel and adjacent regions from 1900 to 2011. Data from the Geophysical Institute of
Israel. The Dead Sea fault on the east poses the main seismic threat.
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Given the seismic hazard in the region of the Dead Sea and Carmel Faults it is critical that
the surrounding populations remain vigilant to the risk of earthquakes. There are
multiple approaches available to mitigate the impact of inevitable future events. This
committee, and this report, focus on just one approach, that of earthquake early warning.
Guiding principles for the development of a warning system
The committee focused on designing an infrastructure for earthquake early warning that
can provide a flexible and durable state-of-the-art system within 2 years and beyond. This
basic philosophy has implications on the recommendations for both the seismic network
to be constructed, and the early warning algorithms that should be implemented.
In order to provide confidence in the warning system, early warning algorithms must be
rigorously testable and transparent. As such the alert algorithm must be openly available
to the scientific community. Such transparency ensures adjustments to the algorithm/alert
criteria that can be made as experience is gained.
The committee believes that although the expected source of large earthquakes are the
Dead Sea and Carmel faults, it cannot be discounted that seismic events producing
damaging ground motion will not occur away from these primary fault structures. From
the outset the system should be designed to issue alerts nationwide, from seismicity
occurring nationwide.
In the long term, we recommend that multiple warning algorithms should be considered.
This should include P-wave (providing information on both the location and magnitude)
and strong-shaking threshold based algorithms. The initial EEW system should use a
network-based approach, but having the option of introducing an onsite-type approach in
the future is an advantage (these various approaches are described in detail below). Also
in the long term, the alert information available should include the intensity of shaking
expected at a users’ location.
The EEW system should generate an informational alert for events smaller than are
expected to do damage. This is to exercise the system and provide informational alerts to
users. Without this ability to detect and generate informational alerts for smaller, more
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frequent events, it will be difficult to ensure the continued functionality of the system or
the ability of the population to respond to the alerts.
In order to meet these criteria, the seismic network monitoring infrastructure requires
major upgrade and densification. The existing high gain stations require upgrade in order
to be Early Warning capable, in particular because of their low bandwidth radio and high
latency satellite communication, and because not all are sufficiently broadband. The
accelerometer network also requires major overhaul, with instrumentation to be changed
and communication to be have real-time-capability. The committee believes there should
be a single high quality Israeli seismic network, combining both weak and strong motion
sensors, which can be used for both earthquake early warning and for other forms of
seismic hazard research. This will reduce seismic hazard in addition to providing a
warning capability. All new instrumentation and communication strategies should be
optimized for earthquake early warning applications. In addition to new network sites it is
critical that the existing ISN be upgraded to similar quality sites (including hardware and
communications).
Finally, the committee recommends that alerts should not be issued until the performance
of the system (in terms of false and missed alerts) reaches a performance standard to be
defined during the evaluation and aligned with performance standards defined by other
national public warning systems.
Approaches to early warning
The concept of earthquake early warning systems (EEWS) today is becoming more and
more prevalent as a mechanism to further reduce seismic hazard. EEWSs are real-time,
modern information systems that are able to provide rapid notification of the potential
damaging effects of an impending ground shaking, through rapid telemetry and processing
of data from dense instrument arrays deployed in the source region of the event, or
surrounding the target infrastructure such as a city.
There are two primary types of EEWS. A “regional” (or network-based) EEWS is based on
a dense sensor network covering a portion of, or the entirety of an area that is threatened
by earthquakes. Relevant source parameters, e.g. event location and magnitude, are
estimated from the early portion of recorded signals (initial P-waves) and are used to
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predict, with uncertainties, the ground motion intensity expected at a distant site where a
target structure of interest is located. Alternatively, a “site-specific” (or on-site) EEWS
consists of a single sensor or an array of sensors deployed at (or in the proximity of) the
target structure that is to be alerted, and whose measurements of amplitude and
predominant period of the initial P-wave motion are used to predict the ensuing peak
ground motion (mainly related to the arrival of S and surface waves) at the same site.
In the two cases, we expect differences in the lead-time, i.e. the time available for warning
before the arrival of strong ground shaking at the target sites. The maximum theoretical
lead-time for regional EEWS is often defined as the time difference between the S arrival at
the target and the first P arrival at the seismic network. However, an EEW system typically
requires a few seconds to detect the event, evaluate its severity, and decide whether to
issue the alert, so that the effective lead-time is always smaller. It is clear that, for such
systems, the lead-time increases with the distance of the target and with the rapidity of the
detection. If the target site is close to the epicentral area, the regional approach may not be
viable, since the lead-time may be zero, or can be too small for any application. For
regional EEWS the extent of the “blind zone”, e.g. the area within which destructive S-
waves may arrive before a warning can be issued, depends on the earthquake depth,
network coverage of the source, and the speed of the telemetry and processing system. Its
radius is typically 30km for shallow crustal earthquakes and a relatively dense network
(station spacing 20-30 km).
The onsite warning method uses the early part of the P-wave signal to predict the ensuing
peak ground motion (mainly S and surface waves) at the same site. In this case, the
theoretical lead-time can be defined as the time interval between the P and the S arrival at
the target, though, again, some seconds for detection and computation must be taken into
account. Similar to the case for the regional approach, the lead-time for the onsite
methodology increases with the epicentral distance due to the growing travel-time
difference between the slower S-phase and the faster P-phase. It is theoretically possible
that the onsite EEWS can provide a useful lead-time where a regional EEW system cannot,
due to a significantly smaller blind zone. However, the cost is the higher false alarm rates.
Still, when a regional strategy is possible, it generally provides a larger lead-time [Satriano
et al., 2010].
Earthquake Early Warning Systems have experienced a sudden improvement and a wide
diffusion in many active seismic regions of the world in the last three decades [e.g. Allen et
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al., 2009]. They are operating in Japan, Taiwan, Mexico and California. Many other systems
are under development and testing in other regions of the world such as Italy, Turkey,
Romania, and China. Most of these existing EEWS essentially operate in the two different
configurations described above, i.e. “regional” and “on-site”, depending on the source-to-
site distance and on the geometry of the considered network with respect to the source
area. A variant to these approaches is the “front detection” EEWS, such as the Seismic Alert
System for Mexico City, which can be particularly advantageous when the only potential
seismic sources are at some distance from a populated area. The seismic warning is issued
when several nodes of a “barrier-type” network of accelerometers deployed along the
Mexican coast, trigger on earthquakes occurring along the adjacent subduction zone,
providing about 60 sec warning to the city [Espinosa-Aranda et al., 2011].
Regional EEWS
The regional EEWS approach is based on the initial P-wave signal detection at a minimum
number of near-source stations (typically 4 to 6). The automatic picks of first P-arrivals at
few stations near the earthquake epicenter are used to determine a preliminary event
location, which is further refined upon the addition of readings from more distant
receivers. Several methodologies have been proposed for the real-time, evolutionary
estimation of the earthquake location which are now implemented in the EW algorithms
(ElarmS, Virtual Seismologist (Cua et al, 2009), PRESTo) running in California, Switzerland
and Italy. The real-time magnitude estimation is generally inferred from the measurement
of peak displacement and/or the predominant period measured in the first few seconds
(typically 3-4 sec) of the recorded P-signal. In some cases, especially for stations located
very close to the source, S-wave signals can also be usefully analyzed to get rapid
magnitude estimations along with P-wave signals. Several studies based on the off-line
analysis of near-source earthquake records from different seismic areas worldwide, have
indeed shown that magnitude correlates with distance-corrected, P-wave peak
displacement and predominant period over a relatively large magnitude range. Although
the saturation of the P-wave parameters has been observed for M > 6.5-7 earthquakes,
several methodologies making use of longer time windows of the P wave and/or the S
wave to update magnitude estimates have been shown to be efficient in minimizing the
problem (Colombelli et al., 2012). The source location and magnitude estimations, which
are continuously updated by adding new station data, as the P-wave front propagates
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through the regional EW network, are then used to predict the severity of ground shaking
at sites far from the source, through regional-specific, ground motion prediction equations.
Onsite EWWS
A different approach, the onsite techniques are generally aimed at estimating the expected
peak ground shaking, associated with S and surface waves, directly from the recorded
early P-wave signal. This is again accomplished through the use of empirical regressions
between measurements performed in the first few seconds of the P-wave signal and the
final peak ground motion. Nevertheless, there are certain onsite approaches (e.g.
Nakamura, 1988) that evaluate location (or hypocentral distance) and magnitude. They
are sometimes used as support for regional EEW systems, in order to reduce lead-times
and extend the region of applicability.
Wu and Kanamori (2005) showed that the maximum amplitude of a high-pass filtered
vertical displacement, measured on the initial 3 sec of the P-wave (namely Pd), can be used
to estimate the peak ground velocity, PGV at the same site, through a log-linear
relationship. This relationship does not depend on magnitude, in the sense that the same
values of Pd (and thus of PGV) could be due to a moderate but close earthquake or to a
large, distant event. Although initially observed for near-source records (distances < 30
km), further analyses on independent data-sets have confirmed that log PGV vs log Pd
scaling is still valid at relatively large distances, up to 300 km (Zollo et al., 2010, Colombelli
et al., 2012). Similar scaling relations have been observed between the initial P-wave
displacement/velocity/acceleration and final PGV or PGA, and implemented for onsite,
stand-alone warning systems, but the data scattering and uncertainty on peak motion
prediction generally increases passing from low- to high-frequency measurements of
ground motion quantities.
Most of the onsite EEWS currently operating are threshold-based, alert methodologies: the
alert is issued as the measured initial P-wave peak displacement/velocity/acceleration
overcomes a given amplitude threshold which is arbitrary set according to the predicted
peak ground motion value using the empirical scaling relations between P and S
amplitudes. Given that small magnitude earthquakes may have very large amplitudes but
high frequency spikes, such a basic threshold system can produce frequent false alarms. A
more robust approach is to combine the P-wave peak (which scales with distance and
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magnitude) and P-wave predominant period (which scales with the magnitude), into a
single indicator to be used for onsite warning (Wu and Kanamori, 2005). Based on this
idea, Zollo et al. (2010) and Colombelli et al. (2012) have proposed a threshold-based EW
method based on the real-time measurement of the period (τc) and peak displacement
(Pd) parameters at stations located at increasing distances from the earthquake epicenter.
The recorded values of early warning parameters are compared to threshold values, which
are set for a minimum magnitude 6 and instrumental intensity VII, according to the
empirical regression analyses of strong motion data from Japan, Taiwan and Italy. At each
recording site the alert level is assigned based on a decisional table with four alert levels
defined upon critical values of the parameters Pd and τc,. Given a real time, evolutionary
estimation of earthquake location from first P arrivals, the method furnishes an estimation
of the extent of potential damage zone as inferred from continuously updated averages of
the period parameter and from mapping of the alert levels determined at the near-source
accelerometer stations.
P-wave based, regional and onsite EW methods can be integrated in a unique alert system,
which can be used in the very first seconds after a moderate-to-large earthquake to
determine the earthquake location and magnitude and to map the most probable damaged
zones, using data from receivers located at increasing distances from the source.
Front detection or barrier EEWS (S-wave threshold EWS)
This is essentially a modified variant of the onsite approach, where a barrier-shaped,
accelerometric network is deployed between the ‘a priori’ identified source region and the
target site/region/infrastructure to be protected. The alert is issued when two or more
nodes of the seismic fence record ground acceleration amplitude larger than a default
threshold value. For typical regional distances, the peak acceleration at the barrier nodes
is expected to be associated with the S-wave train, so that the distance between the
network and the target is set to maximize the lead time, which is, in this case, the travel
time of S waves from the barrier to the target site. The most important examples of front
detection EW systems are the barrier-type, Seismic Alert System (SAS) for Mexico City and
the ring-type EW system for the Ignalina Nuclear Power Plant (INPP) in Lithuania.
There are few recent and contradictory reports about the performance of the Mexican
system. In a recent study, Iglesias et al, (2007) pointed out that SAS’s performance during
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1991–2004 revealed a surprisingly high rate of failure and false alerts. The authors
attribute this poor performance to an inadequate detection algorithm and a limited areal
coverage by the SAS. Nevertheless, the SAS, implemented in 1991, is the first public
warning system and continues to provide ~60 s warning to Mexico City.
The proposed Early Warning system for Israel
Based on the specific geographic distribution of the major earthquake causative fault
systems (Dead Sea and Carmel Fault Zones) two complementary, basic approaches for an
Early Warning System are feasible for the whole territory of Israel.
The first follows the “front detection”, early warning concept, by using the data from a
dense, nearly linear array of accelerometric sensors deployed parallel to the Dead Sea and
Carmel fault zones. S-waves radiated by moderate to large earthquakes (M > 5) occurring
along these fault zones, would trigger the closest nodes of the accelerometric network and
an alert is issued as the recorded peak acceleration passes a predefined threshold.
According to preliminary computations presented in a report entitled: “Assumptions and
guidelines for building an earthquake early warning system in Israel” by V. Pinsky
(Geophysical Institute of Israel), given an average station spacing of 5 kilometers and
requiring that the pre-determined acceleration threshold be exceeded at two adjacent
stations, results in warning times of about 10-14 seconds at an epicentral distance of
about 60 km, for events located up to 15 km from the array and whose epicenter is up to
25 km deep. Based on earthquake distribution analysis and extrapolation of ground
motion empirical relations (Boore et al., 1997), an average false alarm rate of 3 per year
has been inferred for a detection threshold of 70 gal and station spacing of 5 kilometers.
This value has to be finely calibrated in order to minimize the false alarms, which is the
severe weakness of this type of early warning approach. Inspection of the national
accelerometer network data set reveals that this threshold has been reached twice during
the past 2 decades: in Elat, 90 km from the Mw=7.2 Aqaba bay earthquake of 1995 and in
Yitav, 30 km from the Mw=5.1 Dead Sea earthquake of 2004. The latter may be considered
as a "false alarm".
Such a front detection, S-wave threshold-based early warning system has some
advantages: (a) it can be built with (relatively) cheap sensor technology using Micro
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Electro-Mechanical System (MEMS) accelerometers, (b) it by-passes the need to estimate
earthquake location and magnitude, which require the detection of the P-wave arrival and
sophisticated algorithms running in real-time. (c) As it provides only an approximation of
the earthquake severity based on the recorded ground motion, simple algorithms are
needed.
Nevertheless, several disadvantages should be carefully considered, if this option is
uniquely selected for an early warning system for Israel: (a) Since the system does not
provide information about the location and magnitude of the potential damaging
earthquake, when ground shaking above the threshold is observed over a wide section of
the seismic fence array, the only option would be to alert the entire nation. Similar to
current strategies for missile early warning, knowing the original position of the
earthquake source and its magnitude could greatly help into identify and select the areas
where the potential damage is expected to be more severe and therefore to be alerted with
a high priority. (b) If the earthquake occurs far from the seismic fence, within the Israel
territory, the S-wave threshold system would likely fail, since the recorded acceleration
may be below the threshold, depending on the distance from the array and on the event
magnitude. (c) Such a threshold-based approach would likely be set to activate only for
large events/amplitude triggers in order to reduce the number of false alarms due to low
magnitude events, occurring in proximity of the accelerometer array or due to moderate
earthquakes at regional distances. Selecting the appropriate threshold can be very difficult
to optimize. Also, given that the system should only trigger for big events, it cannot be
exercised and tested other than in major earthquakes.
A complementary early warning approach is the (integrated regional/onsite) P-wave
based method, which uses the initial P-wave information recorded by near-source, dense
accelerometer arrays deployed in the proximity of the active faults. P-waves travel about
twice as fast as S-waves, but have smaller amplitudes, thus making possible a more
complex, but still feasible real-time detection and analysis. Indeed a rich library of
algorithms and software packages are available for the automatic picking and association
of first P-wave arrivals from sparse digital networks. The use of accelerometers prevents
amplitude saturation and clipping, which are very likely at near-source distances of a
moderate to large earthquake (M>4). Moreover, the recent experience of real-time seismic
monitoring in Italy and Switzerland, using co-located velocity and accelerometer sensors,
confirms that high quality acceleration sensors can provide high quality P-wave
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recordings of small to large size earthquakes (M>2) at local distances (< 50 km), when
combined with wide dynamic range data-loggers (e.g. 24 bits).
The P-wave based, early warning approach has the main advantage to allow the
determination of the earthquake location and magnitude, which are used to predict the
peak ground motion at any distant locations through existing ground motion prediction
equations (GMPE). At the same time, onsite estimations of final peak ground motion can
also be inferred from the initial P-wave ground motion amplitude. When combined with
contemporary measurements of the P-wave characteristic period, the extent of the
potential damage zone can be rapidly assessed by using P-wave data from stations located
at increasing distances from the source (e.g., Colombelli et al., 2012).
We stress that, assuming continuous data-streaming from the near-source accelerometer
array, the information carried by P-waves does not replace information from PGA (or PGV)
associated with S-wave phases, but can complement it and can be used to
confirm/validate/cancel an issued alert at sites distant from the source.
Other important advantages of the P-wave based approach are that: (a) it allows detection
of events for a wide magnitude range, permitting regular testing and continual
optimization of algorithms using the frequently occurring earthquakes below alerting
thresholds, (b) it can provide location specific alert information (the so-called “dynamic
grid” for warning), (c) it would provide fewer false and missed alarms than an S-wave
based threshold system, and (d) the system is potentially able to provide warning for
earthquakes occurring throughout and outside the territory of Israel.
There are also drawbacks to the P-wave based approach: (a) It requires higher quality
seismic stations (more expensive than for the S-wave based threshold system), including
high sensitivity acceleration sensors and wide dynamic range data-loggers, with enhanced
capability of data processing, storage and transmission, (b) Such an approach needs to
operate a sophisticated system running real-time algorithms for detecting P-waves,
associating arrival from different stations to declare an event, providing an evolutionary
estimation of location and magnitude along with uncertainties, and predicting the peak
ground motion at the site and elsewhere by using local measurements and/or attenuation
relationships.
19
The challenges of greater complexity are balanced against the benefits of more complete
real-time earthquake information. It is for this reason that the P-wave based EEWS are the
most commonly used approach to early warning around the world. This also means that
there is a large supporting, open source and active community, which facilitates efficient
exchange of know-how and software.
Our proposal for an Israeli early warning system is to design and build a real-time, seismic
network, equipped with acceleration and velocity sensors, which operates integrated P-
wave based and S-wave based threshold methodologies. This can be realized through:
• The deployment of a dense array of accelerometers as close to the Dead Sea and
Carmel fault as possible, arranged as a staggered geometry (including pre-existing
ISN stations), with two parallel lines of sensors north of the Dead Sea and one line of
sensors south of the Dead Sea. The accelerometer array can be supplemented with
about ten seismometers co-located with the accelerometers and distributed along
the faults to improve the detection and analysis of background fault microseismicity.
After the system has been evaluated and proved operational, an additional ten
stations with co-located seismometers and accelerometers should be deployed
across Israel to create an even distribution when combined with the existing seismic
network (ISN) with the aim to (1) provide early warning for events that do not occur
on the main faults, (2) calibrate the P-wave based parameters for EEW, and (3)
develop intensity attenuation relationships that will be used to provide alerts that
include the predicted intensity. This deployment is shown in Fig. 8.
• The installation of uniformly high quality broadband and wide dynamic range
accelerometer and seismometer sensors that will allow for a full range of early
warning applications, i.e. both S-wave based threshold and also P-wave based
approaches.
• The implementation of a fast, robust and secure data transmission system
minimizing the data acquisition and transmission latency.
• The implementation of a (centralized) real-time, automatic, data processing and
management software platform (i.e. SeisComp3 or Earthworm) for the detection and
analysis of current microseismicity and continuous data streaming analyses running
P-wave based and S-wave based threshold algorithms.
20
Simulated early warning performance in Israel
Assessment of alert times
Here we assess the alert times for several approaches to early warning for several
network geometries in Israel. Note we only consider the delay due to the geometry of the
network and the type of waves being measured. In an operational early warning system,
there are other significant delays independent of these factors, including delays due to
data transmission, data processing, and alert dissemination. We consider 3 approaches:
(1) An S-wave based threshold method triggered by the S-wave arrival at the second
station, i.e. large amplitude shaking must be observed at 2 stations for the alert to be
generated.
(2) A P-wave method triggered by the P-wave arrival at the 4th station, i.e. required 4
station P-wave arrivals to alert. This is the number of stations required by several
early warning algorithms currently under testing around the world.
(3) A P-wave method triggered by the 6th P-wave arrival. This is also included as the
ability to generate alerts based on 6 P-wave triggers and will soon be available within
SeisComp3.
Two network geometries are considered in this analysis:
Network geometry A: The existing ISN network assuming all stations have been
upgraded and are early warning ready. The alerts times for the 3 EEW approaches are
shown in Fig. 3.
Network geometry B: A staggered array along the northern Dead Sea and Carmel faults
with spacing of 10 km in each line, a single array along the southern section of the fault
with 10 km spacing, and the upgraded existing ISN network (Fig. 8a). The alert times are
shown in Fig. 4. This is the minimal network geometry required for IEEWS (termed
"sparse" in the simulation figures) and the one proposed in this report.
Network geometry C: The final network geometry required for IEEWS (termed "dense" in
the simulation figures) includes a staggered array with ~10km spacing in each line along
the entire Dead Sea and Carmel faults, and the upgraded existing ISN network plus 10
additional stations across Israel (Fig. 8b). The comparison of this network performance
with the minimal network geometry (Network geometry B, Fig. 8a) is shown in Fig. 5.
In Figures 3 and 4, the sub-panels A, B and C show the delay in seconds (given by the
color) for the seismic waves (P-wave for A, B; S-wave for C) to arrive at the indicated
21
number of stations for an earthquake occurring at a depth of 10 km below that point in the
region of Israel. In subpanels D and E, for an earthquake occurring at that point, the color
indicates the difference in time for the S-waves to arrive at 2 stations and the P-wave to
arrive at 6 stations (D) and 4 stations (E). Hence (D) shows the difference in warning time
between the S-wave threshold solution and the robust P-wave solution using 6 picks; and
(E) shows the same threshold solution against a P-wave solution using 4 picks. In (D) and
(E), warm colors indicate regions where the P wave approach is faster than the S-wave,
and cold colors indicates places where the network geometry means the S-wave approach
will be faster than the P-wave. It should be noted that the delay times for the S-wave
approach are minimum estimates, as the ground acceleration is likely to exceed the pre-
determined threshold value some time after the arrival of the S-wave.
It is important to note that across most of Israel, and in particular the Dead Sea and Carmel
faults, the difference in arrival times between the S-wave threshold and P-wave at either 4
or 6 stations is under 2 seconds. This delay is comparable to delays that can be introduced
by data-logger packet size, communication, and processing. Note that the difference in
performance is near zero across the entire network for the preferred dense network
option, and in some areas along the Dead Sea and Carmel Faults, the P-wave algorithm
provides faster warning.
In A, B and C, it is clear that for the dense option the absolute delays are typically under 4s
across Israel for each method, and on the order of 2 seconds around the Dead Sea and
Carmel fault regions as well as the area near Lebanon. This is significantly better than
using the existing network of Israel alone.
Figure 5 shows the difference in alert times between the different network geometries.
The major improvements in alert times are focused along the 2 fault lines. With the
"dense" network geometry, alert times are lower across the nation.
We assume that all stations are operational all the time, earthquake depth is 10km, and P
and S-wave velocities are fixed (6 and 3.5km/s respectively). There is no consideration
given to delay in data transmission, or processing delay for an S-wave threshold or P-wave
EEW algorithm, and there is no discussion of the sensitivity of each method to various
magnitude sizes.
22
Figure 3. Alert time analysis for the existing ISN network upgraded to early warning capable
stations (network geometry A). Panels A-C: the color of each point on the maps illustrates the time
at which an alert would first be possible for an earthquake at that point according to the various
early warning approaches. For every location on the map, the color scale indicates the time
required for a P-wave to reach 4 stations (A), 6 stations (B), or an S-wave to reach 2 stations (C).
Panels D, E: the difference between the alert time for the various methods at any given location is
indicated by the color scale.
23
Figure 4. Alert time analysis for a ~10 km spaced array along the Dead Sea and Carmel Faults plus
the existing ISN network upgraded to early warning capable stations (network geometry B). See
Fig. 3 caption for explanation.
24
Figure 5. The differences in arrival times between the proposed network geometry ("sparse") and
the ISN geometry ("existing") for the 4 P-wave (A), 6 P-wave (B) and 2 S-wave (C) algorithms. The
main benefit of the proposed network is seen in the dramatic reduction in travel time for events
that would occur along the Dead Sea fault. The difference between the "dense" (network geometry
C) and the "sparse" network options are shown in panels D-F. The main benefit here is seen in the
reduction of travel time across the Arava Valley and other parts of the country away from the
known faults, which reflect the improved overall network density of the dense model.
25
Simulations of P-wave approach
The performance of a typical P-wave based, early warning system for Israel is studied
using the algorithm PRESTo (Probabilistic and Evolutionary Early Warning System)
(Satriano et al., 2010) presently implemented and operated by the ISNET network in
southern Italy (http://isnet.na.infn.it/presto_index.php). PRESTo is a software platform
for regional earthquake early warning that integrates recently developed algorithms for
real-time earthquake location and magnitude estimation into a configurable and portable
package. It has been very recently upgraded to evaluate alert levels and the extent of the
Potential Damage Zone, by combining real-time, evolutionary measurements of initial P-
peak displacement and predominant period at the network station sites (Zollo et al., 2010;
Colombelli et al., 2012).
We have performed a set of off-line simulations for potential Mw 6-6.5 events occurring
along the Dead Sea Fault north of the Dead Sea, north of the Sea of Galilee, and along the
Carmel Fault (Fig. 6). Two different network geometries have been used for the analysis,
network geometries B and C as described in the previous section. Synthetic accelerograms
have been computed assuming a point source, double couple earthquake source
mechanism, while the theoretical Green’s functions are obtained by the complete wave-
field, discrete wave number method (Bouchon, 1971; Coutant, 1989) for a 1-D layered
elastic/anelastic velocity model. The source time function of earthquakes has been
assumed to have a trapezoidal shape, whose duration and amplitude was compatible with
the one expected from a constant stress-drop source scaling relationship between moment
and duration. The 5-Hz low-pass filtered, three-component acceleration time series
simulated at the different network nodes have been played-back into the PRESTo system
as if they were real-time recorded and acquired by the EW network control server.
Animations of the output for all three events and the two network geometries may be
found in the following link:
http://people.na.infn.it/~zollo/Early Warning/EW Israel 2012/Report PRESTo.
Fig. 7 shows a snapshot of an output animation for the Mw 6 earthquake on the Carmel
Fault.
26
Figure 6. Map showing the locations of the three simulated earthquakes.
27
Figure 7. The left-hand panel shows the waveform time-series at the station of the new network
with the P-wave arrivals identified in yellow and the S-wave arrivals in red. The upper-right map
shows yellow and red circles indicated the distance that the P- and S-waves have travelled at this
point in time. The stations are indicated as yellow triangles and the numbers on the stations
indicate the strong shaking threat level, 3 representing intensities with MMI > 7. The lower right
figure shows the time history of the magnitude estimate.
28
Table 1 summarizes the main results of the simulation study. We have used all stations
with latitude greater than 31.5° and two network configurations, network geometries B
and C as described above. In the three analyzed cases, the first alert is available 3-4
seconds after the first P-wave pick, and 5-6 seconds after the origin time. This time
includes the arrival and detection of P-wave at minimum 5 closest stations, and the use of
a minimum of 2sec of the P-wave signal.
Table 1. Summary of performance for the three simulated earthquakes.
First
Alert
Minimum Lead
Times
Delta
Hypo
Delta
Mw
Mw
Error
Note
Carmel Fault
(Mw 6)
3 s after
1st pick
5 s after
OT
Jerusalem : 21s
Tel-Aviv: 16s
Haifa: 3s
< 2 km -0.1 ±0.1 Stable after
10 s from
OT
Dead Sea (Mw
6.5)
3 s after
1st pick
5 s after
OT
Jerusalem : 10s
Tel-Aviv: 14s
Haifa: 18s
< 0.1 km <0.1 ±0.05 Stable after
10 s from
OT
Sea of Galilee
(Mw 6.5)
4 s after
1st pick
6 s after
OT
Jerusalem : 26s
Tel-Aviv: 23s
Haifa: 10s
< 0.5 km <0.1 ±0.1 Stable after
10 s from
OT
Due to the proximity of the event epicenters to the seismic “fence” along the faults, no
significant differences are observed in the early warning system performance using the
“sparse” (network geometry B) or “dense” (network geometry C) configurations, so only
parameters for the “sparse” case are reported in the table. We expect that significant
improvements in the system performances should be observed using the “dense” seismic
fence for events located at larger distance from the array.
29
The minimum lead time, i.e. the time between the first S-arrival at the city and first alert
time, at three main cities depends on the earthquake location. It varies between 10 and 26
sec for Jerusalem, 14 to 23 sec for Tel Aviv and 3 to 18 sec for Haifa.
The simulation shows that we should expect relatively small errors in the earthquake
location and magnitude as provided by the P-wave based EEWS, so that reliable peak
ground motion predictions could be obtained by using attenuation relationships. The
extent of the potential damage zone, as determined by the area embedding the maximum
alert level nodes (e.g. alert level 3), is well defined in the three cases, corresponding to the
zone where instrumental intensity IMM > 7 is observed, the latter being derived from the
measured Peak Ground Velocity (Wald et al., 1999) (Fig. 7).
Recommendations for software implementation
In order to effectively manage the new seismic network architecture, and provide a
platform for EEW algorithm development and testing, we strongly suggest adoption and
operation of an open source, community supported package for seismic network data
operation. There are unfortunately only a few good options available to the monitoring
community at the moment, and Earthworm and SeisComP3 are the two strongest solutions.
The committee recommends using SeisComp3 for the following reasons:
- This is an open source network solution being adopted and developed by other
groups in Europe and across the globe
- The Geophysical Institute is already running it
- There is currently development of a Virtual Seismologist magnitude determination
module for SeisComp3
- The software includes fully tested and standard modules for data acquisition,
archival, automatic event detection and quantification, manual event review,
catalogue management and alert services - all using a single database – this
constitutes a full suite of features for managing the seismic network.
The committee recommends that the GSI will develop EEW modules on top and/or within
SeisComp3:
30
- The first (simplest) module is an S-wave threshold-based approach. This could be
designed by GSI and developed through a contract to GEMPA (software
consultants for SeisComP3).
- Components of the Virtual Seismologist algorithms will be available over the
course of the next year (from ETH)
- SeisComp3 provides a solid platform for further development to be made with new
algorithms based on research into early warning algorithms in Israel for Israel
- Other early warning groups are likely willing to share code for implementation but
this will require knowledgeable local support.
Recommendations for early-warning capable network stations
For stations within a seismic network to be capable of contributing to the types of early
warning systems being proposed in this project, each needs to be of a minimum standard.
An early warning ready station needs to continuously provide high quality data at high
sample rates, with a very high uptime, and minimum latency, to the seismic network
processing hub. It also needs to operate robustly for years to decades.
We break down the minimum requirements for the following station components: 1) the
sensor; 2) the data-logger; and 3) the peripheral station infrastructure, which includes
communications, power supply, and station housing.
Sensor: The new network will consist of (a) co-located high gain velocity sensors and low
gain strong motion accelerometers, and (b) stand-alone accelerometers. The goal for each
sensor is to provide on-scale, high quality records for both small earthquakes (to test and
calibrate the system, and collect high quality earthquake data with which to create a high
quality earthquake catalogue) and large earthquakes. Each sensor should reach the
following criteria:
- flat frequency response from
o 50Hz-50s for high gain sensors
o 100Hz-DC for strong motion sensors
- dynamic range of at least 120dB for each sensor
- sensor saturation of at least 1g for the strong motion sensor
Data-logger: The data-logger should be capable of
31
- Digitizing the full dynamic range of the signals recorded by the sensors. At
minimum the digitizer should be 21-bit, preferred is 24-bit.
- Sample rates of at least 100sps.
- Providing GPS timing with time resolution reaching or exceeding 1ms.
- Providing onsite recording of at least 3 months of continuous data at high sample
rates (in case communication is lost during a critical seismic sequence)
- Recording packets either natively in seed format and provide SeedLink
communications, or provide a well known format with durable software for
acquisition and conversion to mseed / SeedLink.
- Supporting multicast of the signal, so independent seismic processing hubs can
each receive the data.
Peripheral infrastructure:
- Communications: minimal latency, not greater than 3 seconds for 99% of packets
- Communications: bandwidth exceeding at least two times the average throughput
of the data.
- Communications: minimal gaps or out-of-sequence data packets
- Power: backup power supplying at least 2 weeks of independent power (typically
battery or solar)
- Security and robustness: the vault sensors, datalogger, and communications
should be secured from vandals and easy manipulation.
It should be noted that the station is not independent of the entire seismic network. The
datalogger and communications selected should be supported by appropriate acquisition
software at the network hub that allows rapid processing of the data packets so that the
overall latency of data is at an acceptable level. The entire system should be capable of
providing 99% of data to the EEW processing software with a latency of less than 5s.
Further, the overall noise measured by the seismic stations should be low enough to
ensure that the high quality instrumentation is being effectively used, and the station is
capable of recording with high signal-to-noise ratio the maximum number of earthquakes.
We recommend, for broadband high gain stations, that between 30Hz and 20s, the typical
station noise is at least 20dB below the High Noise model of Peterson (1993). Excellent
seismic stations should significantly exceed this level, and operate near the low noise
model at long periods out to 100’s of seconds. Strong motion stations should not exceed
the High Noise model across this same frequency band. We recommend that noise tests
32
lasting at least 1 week should be made at all candidate sites, with data processing via PQLX
to help interpret results in a homogenous manner. Achieving this noise level requires
careful site selection, and proper thermal insulation of each sensor.
It is important to reiterate the importance of reliable stations with high uptime. A crucial
component for having confidence in the seismic system is, at least for the sensor and
datalogger, having sensors that have demonstrated their successful performance in similar
networks. Independent confirmation of good performance by other network operators can
provide this confidence.
Both the datalogger and sensor must provide full system response in known format
(dataless Seed)
Proposed initial design
We propose a specific two-year plan for implementation of an early warning system in
Israel. This plan is obtainable within the budget and timeline provided and will achieve
the primary objective of delivering earthquake alerts to schools across Israel. The key
components of the initial two-year plan are as follows.
Install 55 new seismic station sites and integrate their operation with the existing ISN.
The recommended network design is “Network Geometry B” as described above, and is
shown in Fig. 8a. The network should consist of:
• Fifty (50) accelerometer-only sites as close as possible to the Dead Sea and Carmel
Faults (within 15 km) creating a staggered geometry (including pre-existing other
stations) with a spacing of 10km. This will create two parallel echeloned lines 10
km apart with stations every 10 km along each line, from the Dead Sea northward.
South of the Dead Sea there will be one line of sites spaced 10 km apart. This
configuration provides the very high-density network along known faults to
maximize warning time. Some of these stations can be installed in existing
bunkers where available.
• Five additional co-located seismometers and accelerometers along the Dead Sea
and Carmel Faults so that there will be a sufficient density of this type of stations
along the known hazardous faults.
33
There are also additional components and improvements to the system that are strongly
recommended but will not fit into the two-year plan and budget. These include deploying
additional seismometers (rather than just accelerometers) and densification of stations
across all of Israel (see network geometry C below, Fig. 8b). There are several reasons that
we recommend this network expansion. First, to calibrate the P-wave based parameters
for early warning using events with as wide a range of magnitude as possible. Second,
having high sensitivity stations and instrumentation across the country will facilitate the
development of intensity attenuation relationships that will be used to provide alerts that
include the predicted intensity. Third, having a dense network of stations across the
country will provide a warning capability for earthquakes occurring on faults anywhere in
Israel including unknown faults, or faults which are currently thought to be of low hazard.
Network operation and management software that can efficiently process all the data from
the existing and new seismic stations must be installed. This should be located at the
seismology division and should use an open source, community supported software
package. This system will perform all of the network operations that seismic networks
around the world operate including earthquake detection, location, magnitude
determination, catalog generation, data archival, data access etc. In addition, it will
provide earthquake alerts. Once the network hub at the seismology division is operating
satisfactorily, a second identical redundant hub at a separate geographical location should
be set up.
34
Figure 8a. Map of the recommended initial deployment plan (minimal requirement – configuration
B). The new stations are shown as blue triangles for the seismometer plus accelerometer stations
and red circles for the new accelerometer stations. The existing ISN sites are shows as green
triangles for seismometer sites and yellow circles for accelerometer sites.
35
Figure 8b. Map of the recommended final deployment plan (optimal requirement – configuration
C). The new stations are shown as blue triangles for the seismometer plus accelerometer stations
and red circles for the new accelerometer stations. The existing ISN sites are shows as green
triangles for seismometer sites and yellow circles for accelerometer sites.
36
The development, testing, and implementation of at least one early warning algorithm
should be undertaken. We recommend an initial implementation of an S-wave based
threshold system as this is the simplest possible approach and as such is the only one that
can be implemented within 2 years. It is important that development continues in order to
implement the preferred P-wave based approaches. An initial P-wave based approach
based on modules available for SeisComp3 will also likely be available within this two-
year timeframe.
Finally, we recommend upgrading all existing ISN sites to the same standards as the new
sites. This includes hardware at the sites, communication and integration of the data
streams with data from the new stations. The committee understands that this upgrade
will be financed from a separate budget. Completing this upgrade is critical.
Timeline and budget for implementation
Timeline
A preliminary timeline charting the development over the 2 years project duration for the
EEW system in Israel is presented in Fig. 9. We divide the project into two equally
important independent and parallel components: (a) the installation of the seismic
network and (b) the design and implementation of applications for seismic data
processing at the hubs.
(a) Installation of the Seismic network: The installation of the seismic network should
include two concurrent preliminary stages: (1) Procurement of seismic equipment
(including creating detailed requirements for equipment, requesting bids from
manufacturers, evaluating bids and testing candidate sensors, making final orders and
receiving the first equipment batches). This should last at least 6 months but not more
than 9 months. (2) Vault design and site selection including testing of background noise
levels and gaining permissions. The majority of sites should be selected within the first
year, but this stage can remain active for the duration of the project.
After the procurement stage is completed, the installation of accelerometers and
seismometers can begin. The proposed timeline assumes installation of about 4
37
accelerometer sites and 1 seismometer site per month. This is a very ambitious timeline,
but can be achieved with sufficient dedicated staff and solid planning.
(b) Creating the seismic data processing hubs: Prior to the design and installation of
EEW software applications at the hubs the preferred earthquake management software
should be configured (this software is likely SeisComP3). This will require a major effort at
the initial stage, and will also be an ongoing effort, with optimization continuing
throughout the life of the software. Once a high level of competence in SeisComP3 is
attained, investigation into the development and testing of the EEW algorithms should
begin. The preferred plan for the early warning system is to focus on building an S-wave
based threshold system immediately. The major first step is to develop the full
requirements for this as a SeisComP3 module and contract and work with the community
programmers to implement this module. Once installed, a period of testing is required to
observe the system, optimize the parameters and to minimize false alarms. After the
system is stable, the GSI should begin to introduce the software to the authorities
responsible for alerting and then begin sending alerts to downstream users.
At the same time as developments in the S-wave based threshold method are underway,
the early warning operations team should also become familiar with the on-going
community developments to include P-wave early warning algorithms into SeisComP3.
They should install existing modules, and understand how warning times can best be
reduced, locations and magnitudes be made more reliable, and alerts are best
disseminated to the user community.
As an earthquake service providing early warning, it is required to be robust, always
available and always operational. A careful investigation into the IT requirements for a
very high availability network hub, including possible redundancies, is required. Once a
plan for the hardware configuration to meet the security and high availability
requirements is developed, it should be installed at the first hub. Once the concept has
proven to be successful, an installation will follow at the second, geographically redundant
but identical processing hub. Monitoring software that continuously checks for problems
in hardware, software or communications should be installed.
38
Figure 9. Timeline for the development and implementation of an early warning system in Israel.
39
Estimated budget
The budget (Table 2) is based on the recommended system (configuration B).
Table 2. Budget outline for the construction of the new seismic stations
Item Number Price per
unit (NIS)
Total (NIS)
Site survey
Site selection and configuration
300,000
Site response testing
830,000
Sub-total site
survey 1,130,000
Site construction
Hardware
AB 38 95,000 3,610,000 AV 12 155,000 1,860,000 ASV 5 215,000 1,075,000 Personnel 4 800,000 3,200,000 Field expenses 2,000,000
Sub-total site
construction 11,745,000
Hubs
Hardware, security, monitoring, construction
1 2,900,000 2,900,000
Software 600,000 Personnel 5 800,000 4,000,000
Sub-total hubs 7,500,000
Estimated Total 20,375,000
40
The budget for site constructions will include:
(a) 38 accelerometers in existing IDF / Kibbutz bunkers, shelters or building basements
(AB), 12 accelerometers in new vaults (AV) and 5 combined accelerometers and
seismometers in new vaults (ASV).
(b) Personnel and field expenses
Hub construction will include:
(a) Hardware, security, monitoring, software contracts, and construction expenses.
(b) Personnel dedicated to the development and operation of the system.
Additional budget from separate sources should be allocated to the upgrade of the ISN
sites to standards similar to the new sites.
Important improvements beyond the initial 2-year plan
The strategy that the committee recommends for the initial 2-year development of the
early warning system in Israel is to create an advanced, real-time seismic monitoring
infrastructure, equipped with high quality velocity and acceleration sensors, deployed
along the most hazardous faults, i.e. the Dead Sea and the Carmel fault systems, and inside
the national territory. During this initial phase the committee recommends to install the
minimal number of stations (configuration B above, Fig. 8a) that will (1) provide the
requested early warning, (2) meet the approved budget. Regarding the early warning
approach, during this initial phase the priority is to implement the S-wave based threshold
algorithm, which should be a module in the software platform for the real-time data
acquisition, processing and storage. Having an initial P-wave based approach using
SeisComp3 modules that are currently under development should also be possible.
The committee highly recommends that scientific developments continue in the 2+ years
following the initial early warning system installation. Research should be focused on
improving the P-wave based regional methodologies available and installed for Israel.
Given the real-time, continuous data streaming from the early warning network, the
methods should be able to automatically detect and pick first P-arrivals from near-source
receivers, to declare an event, to estimate its location and magnitude along with
uncertainties, to predict the maximum ground shaking amplitudes at the target sites to be
protected and to broadcast the alerting message to end-users and decision makers. Several
41
different approaches are actually available from the research groups in USA, Italy,
Switzerland, Taiwan and Japan. A selection of these methods could be implemented and
run in parallel during a testing period of ~1 year. System thresholds should be set in order
that the early warning system can operate for small magnitude events (M>2.5), which will
ensure a sufficient number of events for calibrating and testing the different
methodologies.
The data analysis and performance evaluation during the testing period will allow
determination of whether to maintain/extend the existing early warning algorithms or to
develop new ones, specifically designed for the seismic hazard in Israel and incorporated
into the reality of the network geometry. After this evaluation period, the committee also
recommends to build a second backup hub, and to reexamine whether there is a need to
densify the network to its optimal, preferred shape (configuration C above, Fig. 8b).
A further possible development will concern the implementation of an “onsite” approach
that may provide alerts inside the blind zone of regional network warning system. This
can be initially tested using stations of the regional/ISN network that are close to schools.
If “onsite” warning proves valuable, additional stations would be needed at other schools,
which are the primary target buildings to be protected by the Israel EW system.
The continuous evaluation of system alert performance based on recordings of small to
moderate earthquakes will allow (a) identification of areas for prioritized improvement,
and (b) evaluation of the overall system robustness for redundancy and security and
consideration for dual communication paths, e.g. DSL and cellular.
Other real-time earthquake information products can also be developed as by-products of
the monitoring infrastructure. These may include methods for the fast mapping of the
strong ground shaking soon after an earthquake (e.g. ShakeMaps), estimating the location
and size of the potential damage zones, or to rapidly locate earthquakes which occur
outside the Israel territory, by using array analysis techniques.
In the line with recent advances in USA and Japan, further development should consider
the incorporation of real-time GPS into the early warning system. This will require both
the addition of real-time GPS stations and also the development of algorithms to make use
of the GPS data for early warning.
42
Finally, consideration should be given to the possibility of increasing the number of users
beyond schools, with the final destination of applying the system nationwide. Gathering
feedback from a range of users could be of great benefit for the improvement and durable
performance of the early warning system.
Building seismological capacity in Israel
Because it is located on the edge of the seismically active Dead Sea Transform, which is
known to have caused extensive damage and life losses over the past millennia, Israel
should excel in the field of earthquake science (as it does in several other prestigious
scientific disciplines). The planned upgrade and extensive expansion of the existing Israeli
seismic network should be viewed as a step towards fulfilling this vision.
We were happy to learn that the Israeli government has decided to build an earthquake
early warning system, but at the same time we wish to "alert" the decision makers that the
building and the long-term maintenance of such a system is a major seismological
undertaking that requires dedicated and extremely well trained personnel. Indeed, other
nations, that have implemented or are close to implement an effective earthquake early
warning system, are able to do so thanks to their excellent governmental and/or academic
earthquake research centers. Earthquake early warning is currently an area of intense
research, and it is vital that Israeli seismologists will become a dominant part of this
research group and be aware of new developments. In order to support the development
and the successful operation of the early warning system, a generation of Israeli
seismologists must be educated, supported and trained. This must start with the
encouragement of students in seismology, and continue with the development of fulfilling
career paths for them in Israel.
We strongly recommend that the Israeli government will encourage and financially
support exchange of students, post-docs and experienced researchers from and to Israel
for earthquake research including early warning. After the new seismic network is
installed, high quality seismic data will become available. These data should be effectively
mined to improve understanding of seismic hazard and seismotectonics, including ground
motion attenuation relations, site effects, fault mapping and delineation using
microseismicity and probabilistic seismic hazard assessment.
43
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Wald, D. J., V. Quitoriano, T. H. Heaton, and H. Kanamori (1999). Relationships between peak ground acceleration, peak ground velocity and modified Mercalli intensity in California, Earthq. Spectra 15, 557–564.
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46
אדמה חלשות שאינ� גורמות נזקי . זו גישה המקובלת היו בקרב קבוצות עבודה ומחקר בתחו
ווא�, קליפורניה, איטליה, שוויי�) וקיימת עבורה ההתרעה לרעידות אדמה בעול (למשל, יפ�, טאי
תמיכת תוכנה בקהילה הבינלאומית.
ע השלמת , ויאפשר (גלי לח� ותאוצות ס!) הועדה ממליצה על פתרו� המשלב את שתי הגישות
תקבל בשלב הראשו� התרעה התרעה ממוקדת לכלל תושבי המדינה. המערכת שתיבנה ההתקנה,
בשלב התרעה ה. תאוצת ס! בגדר הסיסמית, ובהמש ג התרעה באמצעות גלי לח�המבוססת על
בלבד, והיא מצריכה למוסדות חינו תכוו� #העלולה לגרו להתרעות שווא אחדות בשנה –הראשו�
אלגוריתמי פשוטי יותר שנית� לייש בפרק הזמ� הנדרש בהחלטת הממשלה, ללא תוספת כספית
ידע הקיי בעול ויכולות בתחו הסיסמולוגיה של האג! הל מערכת תסתמ עה רבה.
שישולב בעתיד הקרוב ע המכו� הגיאולוגי במסגרת מינהל המחקר למדעי האדמה ,לסיסמולוגיה
הידע בתחו מערכות ההתרעה בעול . שיורחבתשופר ככל והי . המערכת
כות גבוהה לאור שני קוי באיחדשי סיסמומטרי 5מדי תאוצה ו 50כ מער הגילוי יכלול
. תחנות אלו ישולבו ע הרשת הסיסמית של מדורגי בסמיכות לבקע י המלח ולהעתק הכרמל
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סמי וה� שתשמש ה� לניטור סי אחת מערכתתהיה במדינת ישראל סטנדרטי , כ שבסיו ההקמה
ק"מ בכל קו והמרחק 10יהיה כ לאור ה"גדר הסייסמית" המרחק בי� תחנות סמוכות התרעה.ל
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ותבצע ,תקלוט נתוני מכלל תחנות הרשת באמצעות תוכנות ייעודיות באג! לסיסמולוגיה, תוק
התרעה. ואבזמ� אמת אפיו� של כלל האירועי
למוסדות ימש שנתיי , ובסופו המערכת תחובר –המערכת תיבנה בשלושה שלבי : שלב ראשו�
ת, ייעשו בה שיפורי נדרשי , ובסופו ו תיבח� המערכמהלכימש כשנה, וב –שלב שני ;בלבד חינו
ביצועי ותדירות, רעידות אדמה חלשות הסתמ עלב מוסדות חינו .היא תהיה מבצעית עבור
ככל הנית� תו כדי ניצול הידע המערכת ייבדקו במש כל תקופת ההקמה ולאחריה, על מנת לשפר
. שלוש שני , המערכת תשודרג, מעבר ל –שלישי השלב ב וההתפתחות הטכנולוגית בתחו זה בעול
. במיקו גיאוגרפי שונה תחנות על פי הצור , ויוק מרכז שליטה ובקרה שני לגיבויבה וספו וית
ולאחר שתימצא אמינה בסטנדרטי המקובלי במערכות המתקדמות בעול ,המערכת תיבדק
אזרחי כלל ו גופי תשתית, היא תהפו למבצעית עבור ויצומצ המספר הצפוי של התרעות שווא
מלש"ח מעבר לתקציב הקיי 5לביצוע השלבי הראשו� והשני דרושה תוספת של כ .המדינה
מלש"ח. #7מלש"ח) ואילו לביצוע השלב השלישי יידרש תקציב נוס! של כ 15בהחלטת הממשלה (
למרות החריגות הללו ממסגרת התקציב, הועדה רואה חשיבות עליונה להקמת המערכת בהיק!
לשדרוג עתידי של מער התחנות ושיטות הגילוי, ולהקמת מערכת שליטה נוספת לגיבוי. המוצע,
יותקנו במוסדות שילוב יחידות התרעה מקומיות (ש :כוללי בי� השארנוספי שיפורי עתידיי
לצור קבלת תמונה , נזק משוערמפות יצור אוטומטי ומהיר של) ע המערכת הארצית, חינו
מערכות גילוי בשיטות נוספות, כגו� שילובבחדר המצב הלאומי בתו זמ� קצר, וראשונית של הנזק
GPS מערכת ההתרעה. ,בזמ� אמיתי ע
45
תקציר
על הקמת מערכת ,2012ביוני 7בישיבתה ביו ,החליטהועדת השרי להיערכות לרעידות אדמה
המשימה הוטלה על מינהל המחקר למדעי האדמה . התרעה קצרת מועד לרעידות אדמה בישראל
מית בעקבות ההחלטה הקי המינהל ועדת מומחי בינלאו. והי שבמשרד האנרגיה והמי
מידת ב ,שמטרתה לייע� למינהל ולהמלי� על המערכת האופטימלית שתענה על צרכי המדינה ותוק
הועדה כללה שלושה סיסמולוגי . פרק הזמ� ובגבולות התקציב עליה החליטה הממשלהב, האפשר
וחמישה סיסמולוגי , ל בעלי ש וניסיו� בהקמת מערכות התרעה לרעידות אדמה"מחו
להקמת שונות חלופות גישות ובחנה ו, חקר רעידות אדמהמישראל המתמחי בוגיאופיסיקאי
וסוגי , פיזור גיאוגרפי של המערכת, התרעההאלגורית , תרעההמבחינת צרכני ה, המערכת
.הנדרשי מכשירי ה
:חברי הועדה ה�
Prof. Richard M. Allen (Committee Chair), Director of the seismological laboratory, University of California, Berkeley, USA;
Dr. John Clinton, Director of seismic networks, Swiss Seismological Service, ETH, Zurich, Switzerland;
Prof. Aldo Zollo, Seismologist, University of Naples "Federico II", Italy;
גיאופיסיקאי, מנהל (בפועל), מינהל המחקר למדעי האדמה והי (מתא הועדה), ד"ר גדעו� בר
, גיאופיסיקאי, המכו� הגיאולוגיד"ר יריב חמיאל
, סיסמולוג, המכו� הגיאופיסיד"ר רמי הופשטטר
, סיסמולוג, המכו� הגיאופיסיד"ר ולדימיר פינסקי
, סיסמולוג, אוניברסיטת תל אביבד"ר אלו� זיו
מדידה מקומית יות להתרעה בפני רעידות אדמה. הראשונה מבוססת על קיימות שתי גישות עקרונ
(קו צפו! של תחנות לאור העתקי "גדר סיסמית" של תאוצת קרקע בשתי תחנות או יותר מתו
יוצרי רעידות האדמה), כ שהתרעה נשלחת א האות הנקלט גבוה מס! עוצמה מסוי שהוגדר
הול יחסית של מדי התאוצה הנדרשי להפעלתה. חסרונבפשטותה ובמחיר הז ואה ה. יתרונמראש
מהס! הנדרש להתרעה, נית� יהיה לבדוק אותה בס! עוצמות נמו יותרשאמנ בכ ואהשל השיטה
הפע הראשונה שבה היא תיבדק באופ� מבצעי תהיה ברעידה הגדולה אבל ,או על ידי סימולציות
התרעות יינתנו רק עבור ו� נוס! נובע מ� העובדה שחיסר. , או לחילופי� יתקבלו התראות שוואעצמה
ובמקרה של רעידות אדמה מרוחקות, למרות סבירות קרוב לתחנות הרשת, �שמוקד אדמה רעידות
תמיכת תוכנה היעדר נמוכה יחסית להתרחשות , לא נקבל התרעה נאותה. חסרו� בולט אחר הוא
יד ללא בעת התואפשרות לשדרג או לשפר אלמערכות מסוג זה בקהילה הבינלאומית, ולכ� לא תהיה
השקעה תקציבית משמעותית.
תחנות , אל S –מגלי ה , המהירי יותר(P-waves)גלי הלח� קליטתהגישה השנייה מבוססת על
בכל ותהצפוי תנודותסיסמית. ההתרעה מתקבלת על סמ חישוב עוצמת ומיקו הרעידה וההרשת ה
מכשור באיכות גבוהה יותר, א מאפשרת מת� התרעה מנ אנקודה באזור. גישה זו מצריכה
הזמ� באמצעות רעידות לאור דינאמי"), ובדיקה של המערכת שריג(" י ספציפיי אזורלממוקדת
47
המכון הגיאופיסי לישראל
: בישראל אדמה לרעידות מועד קצרת התרעה מערכת
ליישו� המלצות
5הופשטטר רמי, 4חמיאל יריב ,3קלינטו� ו�'ג, 2,4בר גדעו�, 1אל�. מ רד'ריצ
7זולו אלדו , 6זיו אלו�, 5פינסקי ולדימיר
ב"ארה, ברקלי, קליפורניה אוניברסיטת �1
והי� האדמה למדעי המחקר מינהל �2
שווי�, צירי�, ETH אוניברסיטת �3
הגיאולוגי המכו� �4
הגיאופיסי המכו� �5
אביב תל אוניברסיטת �6
איטליה, נאפולי אוניברסיטת �7
אדמה רעידות בפני להתרעה בינלאומית מייעצת ועדה
GII 500/676/12 GSI/26/2012
2012ירושלים, דצמבר
והמים האנרגיה משרד
יהגיאולוג המכון