GROUND MOTION CHARACTERISTICS DURINGTHE 2011 OFF THE PACIFIC COAST OF TOHOKUEARTHQUAKE
Transcript of GROUND MOTION CHARACTERISTICS DURINGTHE 2011 OFF THE PACIFIC COAST OF TOHOKUEARTHQUAKE
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GROUND MOTION CHARACTERISTICS DURING
THE 2011 OFF THE PACIFIC COAST OF TOHOKUEARTHQUAKE
Hiroyuki Gotoi) and Hitoshi Morikawaii)
i) Assistant Professor, Disaster Prevention Research Institute,Kyoto University, Japan.
ii) Associate Professor, Department of Built Environment,Tokyo Institute of Technology, Japan.
ABSTRACT
The 2011 off the Pacific coast of Tohoku Earthquake (MW 9.0) caused
severe damage not only because of the great tsunami, but also because of
the ground motions. In the present paper, we report some details of the
source mechanism and the ground motions during the earthquake, and dis-
cuss the ground motion characteristics related to the damage in the Tsukidate
and Furukawa areas. Damage grades in Tsukidate, where the largest peak
ground accelerations were observed, are not severe in comparison to those in
Furukawa. The pseudo-velocity response spectrum for the ground motions
observed in the Furukawa area is similar to that in the JR Takatori records
for the 1995 Kobe earthquake.
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Key words: The 2011 off the Pacific coast of Tohoku Earthquake, earth-
quake, ground motion, peak ground acceleration, pseudo velocity response
spectrum, frequency contents (IGC: A-01, C-00)
INTRODUCTION
On 11 March 2011, a large earthquake hit the eastern part of mainland
Japan. The earthquake, and particularly the great tsunami caused by it,
resulted in the death of more than ten thousand persons. Structures were
also damaged not only due to the tsunami, but also due to the ground mo-
tions, e.g., elevated bridges of the Tohoku Shinkansen (Takahashi, 2011) and
geotechnical structures (Tohata et al., 2011). Strong ground motions during
the earthquake were observed over almost the entire county of Japan. At
least 18 stations observed peak horizontal accelerations of over 980 cm/s2,
and two stations observed seismic intensities of over 6.5 on the Japan Mete-
orological Agency (JMA) scale. It should be noted that the damaged areas
do not correspond to the locations observing the large accelerations and in-
tensities.
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Residential damage, due to the ground motions, was concentrated in the
Furukawa area of Osaki City and the Sanuma area of Tome City, which are
both located in inland areas of Miyagi Prefecture (Goto, 2011a). The seismic
intensities observed at the seismic stations located in these areas were in the
range of 5.5-6.5. On the other hand, no significant damage was reported in
the Tsukidate area of Kurihara City, where a seismic intensity of over 6.5
was observed (Goto, 2011a). This means that the damage grades are not
consistent with the JMA intensities.
In this article, we review the source process and the ground motions
during the earthquake, and then discuss the ground motion characteristics
related to the damage in the Tsukidate and Furukawa areas.
CHARACTERISTICS OF SOURCE PROCESS
The earthquake, officially named The 2011 off the Pacific coast of To-
hoku Earthquake by JMA, occurred at 14:46 (JST, GMT+9) on 11 March
2011. The hypocenter was located in the offshore region of the eastern part
of mainland Japan, and the depth was 24 km. The Moment magnitude (MW)
was 9.0 (Hirose et al., 2011), making it the largest earthquake observed in
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Japan since 1900, and the 4th largest earthquake in the world since 1900. Fig-
ure 1 shows the distribution of aftershocks occurring within 24 hours after
the main shock, which almost covers the fault zone of the main shock. This
implies that the dimensions of the fault zone were about 500 km in length
along the coast line by about 200 km in width. Figure 1 also shows the
centroid moment tensor (CMT) solutions estimated by JMA (Hirose et al.,
2011) and F-net organized by the National Research Institute for Earth Sci-
ence and Disaster Prevention (NIED). They indicate that the mechanism was
a reverse fault with a compressional axis in an almost east-to-west direction,
which is estimated as N103E by JMA and N110E by NIED, respectively.
The location of the seismic fault and the mechanism imply an inter-plate
earthquake on the plate boundary between the North American plate and
the Pacific plates.
The Headquarters for Earthquake Research Promotion had warned of
the occurrence of an earthquake in offshore Miyagi Prefecture with a prob-
ability of 99% and a scale of MJMA 7.5 within 30 years. The event was
expected to be similar to Miyagi-oki earthquake (MW 7.6) of 1978. However,
the events corresponding to the Tohoku earthquake were not evaluated. The
earthquake ruptured over several segments, which had been evaluated as
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independent earthquakes.
Figure 2 shows the distribution of seismic intensities on the JMA scale.
Intensities over 6.5 were recorded at K-NET MYG004, located in Kurihara
City of Miyagi Prefecture, and at KiK-net TCGH16, located in Haga Town
of Tochigi Prefecture. Intensities over 6.0 were widely recorded in Miyagi,
Fukushima, Ibaraki, and Tochigi Prefectures (see Figure 1) (Hoshiba et al.,
2011). The observation of an intensity over 6.5 occurred for only the second
time since the 1995 Kobe earthquake in Japan; the other was the record
in Kawaguchi during the Mid-Niigata Prefecture earthquake of 2004. The
intensity distribution is not simply attenuated from the east coast, but also
varies strongly along the coast line. This implies that the source rupture
process was not spatially uniform.
Figure 3 shows the envelopes of the borehole accelerograms observed
by KiK-net (NIED). In order to highlight the high frequency components,
the accelerograms are filtered in the range of 0.5-10 Hz, and the envelopes
are averaged with moving windows of 2.0s. Stations were selected to be al-
most parallel to the strike direction of the seismic fault estimated by JMA
(N193E). First and second wave groups, with an interval of about 50 sec-
onds, were mainly observed at the northern stations, e.g., wave groups being
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observed at the earliest time at IWTH05. The wave groups are not clear at
the southern stations, but a third wave group was mainly observed at the
southern stations, e.g., wave groups being observed at the earliest time at
TCGH13. This implies that the rupture process of the earthquake involved
at least three significant events radiating high-frequency energy. The first
two pulses mainly affected the ground motions observed in Iwate and Miyagi
Prefectures, while the third pulse affected the ground motions observed in
Ibaraki and Tochigi Prefectures.
Several research groups have reported on the source process during the
earthquake. GPS data and low-frequency ground motions imply that a large
slip region is located on the shallower side of the seismic fault (e.g. Miyazaki
et al., 2011; Suzuki et al., 2011; Yoshida et al., 2011). They estimated a max-
imum slip of about 35-50 m, which is almost in the same order as the geodetic
data observed just above the hypocenter (Sato et al., 2011). On the other
hand, ground motions corresponding to the frequency components higher
than 0.1 Hz imply that several strong motion generation areas (SMGAs) are
located on the deeper side of the seismic fault (e.g. Asano and Iwata, 2011;
Kurahashi et al., 2011). A high-frequency radiation area is also estimated by
the back-projection method to be located on the deeper portion of the fault
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(e.g. Ishii, 2011; Wang and Mori, 2011; Zhang et al., 2011). This implies
that the locations of seismic wave radiation areas depend on the frequency
band (Koper et al., 2011); the high-frequency radiation is generated along
the deeper side, while low-frequency radiation and a large slip are generated
on the shallower side. The full rupture process, considering both the high-
and low-frequency radiation is estimated by Ide et al. (2011).
The ground motions observed in Miyagi and Iwate Prefectures consist of
two major wave groups with an interval of about 50 seconds (see Figure 3).
The origins are estimated to be on the deeper side of the hypocenter, and
to be located close to each other (Asano and Iwata, 2011; Kurahashi et al.,
2011). This means that a time lag of about 50 seconds was required between
the events. Goto et al. (2011c) suggest that reflection waves from the free
surface affected the generation of the latter event.
CHARACTERISTICS OF GROUND MOTIONS
Ground motions during the earthquake were observed by several seismic
networks organized by NIED, JMA, Port and Airport Research Institute
(PARI), Building Research Institute (BRI), National Institute for Land and
Infrastructure Management (NILIM), and other organizations. Figures 4 and
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5 show the distributions of peak ground accelerations (PGA) and peak ground
velocities (PGV), respectively, in the horizontal components calculated from
the available records of the ground motion, respectively. PGA values do
not simply attenuate from the east coast; they vary strongly along the coast
line, similar to the seismic intensity distribution. Large PGAs were mainly
observed in the regions of 1) Miyagi Prefecture, and 2) Tochigi and Ibaraki
Prefectures, which are close to the locations of the SMGAs. Si et al. (2011)
compared the observed PGA and PGV to the ground motion prediction
equation by Si and Midorikawa (1999), which was developed using data from
earthquakes with MW 5.8-8.3. They summarized that PGAs observed within
100 km of the seismic fault are consistent with the equation for MW 9.0,
whereas PGVs within 300 km are weaker than that.
Table 1 lists the top 8 records of PGA in horizontal components, and Fig-
ure 6 shows the accelerograms of the top 4 PGA records: K-NET MYG004,
K-NET MYG012, PARI Onahama-G, and K-NET IBR003. The largest
PGA, 2765 cm/s2, was observed at K-NET MYG004. It is almost three times
larger than the gravitational acceleration. Even the second largest PGA ob-
served at K-NET MYG012 is about twice larger than the gravitational ac-
celeration. K-NET MYG004 and MYG012 are located in Miyagi Prefecture,
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while PARI Onahama-G and K-NET IBR003 are located in Fukushima and
Ibaraki Prefectures, respectively (see Figure 4). As discussed in the previ-
ous section, waveforms of K-NET MYG004 and MYG012 contain two wave
groups because of the two SMGAs located downdip of the hypocenter. On
the other hand, waveforms of PARI Onahama-G and K-NET IBR003 contain
one wave group.
The frequency contents of the ground motions are discussed via the
pseudo-velocity response spectrum (pSv), which is defined by dividing the
acceleration response spectrum (Sa) by angular natural frequency :
pSv(T) =1
Sa(T) =
T
2Sa(T) (1)
The pseudo-velocity response spectrum gives the same information as plot-
ting the acceleration response spectrum when the oblique line has a gradient
of 1/2, a so-called tri-partite plot (e.g. Chen and Scawthorn, 2002). It is
not theoretically equal to the velocity response spectrum (Sv), whereas sta-
tistically it is very close, except for the long natural periods (Hudson, 1962).
The acceleration and displacement response spectra are flat in the shorter
and longer natural periods, respectively, while the pseudo velocity response
spectrum gives a clear peak around the transition periods. We focus on the
peak value and the corresponding period of pSv to discuss the frequency
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contents.
Figure 7 shows the pseudo velocity response spectra of the K-NET
MYG004 and the MYG012 records. The lines corresponding to each record
are EW and NS components. The damping coefficient is set to be 0.05. The
response spectra are compared to the JR Takatori records taken during the
1995 Kobe earthquake, which were observed in the damage belt, the area
with a seismic intensity of 7 on the old JMA scale. In the area, more than
30% of the wooden houses were reported as having collapsed on the basis
of field reconnaissance (e.g. Kawase, 1996; JMA, 1997). pSv values of K-
NET MYG004 and MYG012 exceeded the JR Takatori records at periods
shorter than 0.5s, whereas those in the range of 1.0-2.0s were almost 1/4 of
those of the JR Takatori records. This means that the frequency content of
the records with the large PGAs is not similar to that of the JR Takatori
records. Figure 8 shows the distribution of the peak periods of the pSv ex-
ceeding 50 cm/s, which are categorized into either periods of either less than
or greater than 1.0s. Most of the records show peak periods of less than 1.0s.
This means that the high-frequency radiation less than 1.0s was significant
during the earthquake and caused the large PGAs. On the other hand, sev-
eral peak periods of over 1.0s were observed, although the PGAs were not
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very large.
Figure 9 shows the distribution of the peak values and periods of pSv in
its maximum component. The color of the symbols highlights the periods in
1.0-2.0s in order to emphasize the records similar to the JR Takatori records.
Large pSv values with periods in the range of 1.0-2.0s are concentrated in
the northern part of Miyagi Prefecture. We focus on the typical records with
the large pSv values and the period range of 1.0-2.0s, JMA Furukawa and
K-NET TCG006, as indicated in Figure 9. PGAs of JMA Furukawa and K-
NET TCG006 are 568 cm/s2 and 421 cm/s2, respectively, which are almost
half of the gravitational acceleration. Figure 10 shows the pSv of the JMA
Furukawa and the K-NET TCG006 records compared to the JR Takatori
records. Both peak periods are almost similar to the peak period of the JR
Takatori records. The peak value of JMA Furukawa is almost similar to that
of the JR Takatori records, whereas that of K-NET TCG006 is a little less.
In the following section, we discuss the differences in structural damage
around the seismic stations of K-NET MYG004 and JMA Furukawa, which
are typical of the stations observing the largest PGA and the significant
characteristics of pSv, respectively.
Long-duration ground motion is also a typical characteristic of this
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earthquake, because the generation of the seismic waves continued about
160s (Suzuki et al., 2011) due to the rupture propagation of such a large
scale seismic fault. This caused liquefaction damage, especially in the Tokyo
Bay area (Tohata et al., 2011). Figure 11 shows accelerograms at K-NET
CHB008 and CHB024 located in the Tokyo Bay area. An acceleration of over
50 cm/s2 acceleration continued for about 50s at CHB008. CHB024 shows a
drastic change in amplitude, a reduction in high-frequency components, and
spike-like phases after about 100s, which all corresponds to the characteris-
tics of the records on the liquefied ground (e.g., Holzer et al., 1989; Iai et al.,
1995).
DAMAGES DUE TO GROUND MOTIONS IN TSUKIDATE
AND FURUKAWA AREAS
We focus on the detailed damages due to the ground motions in two
typical areas of Miyagi Prefecture, Tsukidate and Furukawa. The largest
PGA site, K-NET MYG004, is located in the Tsukidate area, and the re-
markable site in terms of pSv, JMA Furukawa, is located in Furukawa area.
We performed damage reconnaissances not only for residential structures,
but also for Japanese shrines and temples in both areas. Focus was placed
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on the elements common to the shrines and gravestones at temples, because
these are almost uniformly distributed in all of Japan. In the case of the
shrines, the several elements are addressed; such as torii, a Shinto gate made
of wood and/or stones, suibansha, a basin containing water for ritual pu-
rification of mouth and hands before entering the shrine grounds, komainu,
statues of lions or lion dogs that guard the shrine, honden, the Main Hall
or kami hall where the kami (god) is enshrined, and sando, the approach to
the shrine or honden, lined with trees or lanterns (Young et al., 2004). The
difference in damage patterns emphasizes the relative difference in damage
grades between the areas, although the quantitative research has been lim-
ited in the damage grade of the honden at the Japanese shrine (Yamada et
al., 2008), and for the damage ratio of the gravestones (e.g. Ishiyama, 1982;
Midorikawa and Fujimoto, 1996; Kaneko and Hayashi, 2000). Therefore, we
compare the actual damages to the honden and the gravestones with the es-
timation curves developed quantitatively in previous studies quantitatively,
and introduce patterns of the other damages developed qualitatively.
Tsukidate area
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The Tsukidate area is located in Kurihara City, Miyagi Prefecture, which
is about 60 km north of Sendai City. There is one seismic station, K-NET
MYG004, which observed the largest PGA of 2765 cm/s2 and a seismic in-
tensity of 6.6 on the JMA scale.
Damage reconnaissance around the seismic station was performed on 2
April 2011. Figure 12 shows the location of K-NET MYG004 and the damage
along the reconnaissance trails. The trails cover the downtown of Tsukidate.
We observed a few fallen pieces of block walls, peeled off exterior faces of
stores, cracks on the columns of residential houses, broken windows, and the
caving in roads, which are marked as squares in Figure 12. There were no
collapsed or severely damaged houses along the reconnaissance trails.
One shrine, Tsukidate Hachiman Shrine, and one temple, Sorinji Tem-
ple, are located in the area. At Tsukidate Hachiman Shrine , only one ko-
mainu fell down, and the damage of the honden was categorized into D1 in
the damage rank by Okada and Takai (1999) (Figure 13). At the Sorinji
Temple, the gravestones were classified into three categories: a) collapse of
the main gravestone, b) movement of the gravestone or the other damage,
and c) no damages. The number of gravestones corresponding to each cat-
egory was a) 36, b) 111, and c) 457. Ratios of the collapsed and damaged
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gravestones are 0.06 and 0.24, respectively. Collapsed gravestones around
the observed station in the JR Takatori records from the Kobe earthquake
were reported in the ratio of 0.70 by Midorikawa and Fujimoto (1996), which
is higher than the ratio for the Tsukidate area.
Furukawa area
The Furukawa area is located in Osaki City, Miyagi Prefecture, which is
in between the Tsukidate area and Sendai City. Furukawa Station of the JR
Tohoku Shinkansen and JR Riku-u-tosen is located at the center of down-
town. There are four seismic stations, K-NET MYG006, JMA Furukawa,
Furukawa Gas, and NILIM Furukawa. However, the records for the main
shock at Furukawa Gas were unfortunately missed (Goto et al., 2011b). K-
NET MYG006, JMA Furukawa and NILIM Furukawa observed PGAs of
583 cm/s2, 568 cm/s2, and 483 cm/s2, and seismic intensities of 6.1, 6.2, and
6.1, respectively.
Damage reconnaissance in the area around the seismic stations of K-
NET MYG006 and JMA Furukawa was performed on 4 days, namely, 14, 15,
29, and 31 March 2011. Figure 14 shows the location of the seismic stations
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and the significant damage along the reconnaissance trails. Furukawa Gas
is located about 1 km west of the area, and NILIM Furukawa is located
about 2 km east of the area. Uplifted manholes and uneven walkways due
to liquefaction were observed in the western area of JR Furukawa Station.
Severe residential damage was observed in the area nearby the liquefaction
area. We classified the residential damage into four categories, namely, 1)
totally collapsed houses, 2) severely damaged houses, 3) raw land, and 4)
other. The total number of houses in categories 1)-3) was 37.
Three shrines and three temples are located in the area. Figures 15-17
show the details of the shrine damage to the shrines. The marked squares
indicate collapsed stone monuments, while the arrows show the collapse direc-
tions. Several stone monuments, i.e., stone lanterns and komainu, collapsed
at the shrines. Wooden honden at the Konpira and Nishinomiya Shrines,
and the suibansha of the Nishinomiya Shrine were severely damaged. The
damage to the honden at Konpira, Kanaya, and Nishinomiya Shrines was
categorized into D3, D1, and D3 in the damage rank by Okada and Takai
(1999), respectively. We classified the damage levels of the gravestones at
the Zuisenji Temple into the same categories as the Sorinji Temple, and the
number of graves corresponding to each category was a) 193, b) 64, and c)
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93 in the half-yard of the gravestone garden. The ratios of the collapsed
and damaged gravestones are 0.55 and 0.73, respectively, which are higher
than for Sorinji Temple. Although gravestones at Ichijyoji Temple were also
severely damaged, the number of damaged gravestones at Seiganji Temple
was very few.
The aspect ratios for 10 samples randomly selected from the gravestones
at Zuisenji Temple averaged 0.44, defined by the ratio of width to height of
the stone. It is similar to the form of typical Japanese gravestones, averaging
0.40 of the aspect ratio. Several researcheres proposed a relation between the
ground motion indices and the damage ratio of the typical gravestones as a
damage curve, based on the actual damages during the historical earthquakes
(e.g., Midorikawa and Fujimoto, 1996; Kaneko and Hayashi, 2000). The
damage curve proposed by Kaneko and Hayashi (2000) is as follows;
R = [(ln PGV ln76)/0.4], (2)
where R is the damage ratio, and denotes the cumulative distribution
function of the normal distribution. The unit for the PGV is cm/s. The
observed PGVs at K-NET MYG004 and JMA Furukawa are 106 cm and
84 cm/s, respectively, and they estimate the damage ratios as 0.80 and 0.60
using Equation (2), respectively. The value is consistent with the one for
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Zuisenji Temple, whereas it is larger than the actual damage ratio for Sorinji
Temple.
Yamada et al. (2008) proposed the damage curve for the honden cali-
brated by the damages during the 2007 Niigataken Chuetsu-oki earthquake.
It is defined by a ratio of higher than D3 in the damage rank within a 2 km
radius of the observation site;
R = [(ln PGV ln 100)/0.31]. (3)
The observed PGVs at K-NET MYG004 and JMA Furukawa lead to estima-
tions of damage ratios of 0.57 and 0.28, respectively. In the Tsukidate area,
only one sample, D1, is available. In the Furukawa area, three samples, D3,
D1, and D3, indicate the ratio of 0.67, which is larger than the estimation.
The quantitative values imply that the damage is not exactly consistent
with the observed PGVs. In addition, the damage patterns for the structures
and the shrines suggest that the ground motions in the Tsukidate area. At
least, the patterns imply that the ground motion characteristics should not
be discussed only based on PGAs and PGVs.
DISCUSSION
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Figure 18 shows the velocity waveforms observed at K-NET MYG004
in the Tsukidate area, and K-NET MYG006 and JMA Furukawa in the
Furukawa area. The waveforms contain two wave groups with an interval of
about 50s. The peak velocities are about 100 cm/s, 90 cm/s, and 80 cm/s,
respectively. PGAs and PGVs of K-NET MYG004 are larger than the records
for the Furukawa area, whereas the indicies seem to contradict the damage
patterns in both areas. This implies that PGAs and PGVs were not indicative
of the damage grade around the seismic stations.
Figure 19 shows the pseudo response velocity spectra (h=0.05) of K-
NET MYG004, MYG006, and JMA Furukawa. Periods at the peak values
for K-NET MYG006 and JMA Furukawa are in the range of 1.0-1.5s, whereas
those for K-NET MYG004 are less than 0.5s. As shown in Figures 7 and 10,
the spectrum shapes of JMA Furukawa are more similar to those of the JR
Takatori records than K-NET MYG004. The ground motions observed at the
damaged sites during the Kobe earthquake and also in Furukawa area contain
similar frequency components. Sakai (2009) suggests that the components
in the period ranging from 1.0-1.5s affect the structural damages, and this is
consistent with the observations in the Furukawa area.
In Furukawa, the damage grades around the seismic stations were slightly
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different; K-NET MYG006 is not located in the severely damaged region,
while JMA Furukawa is (see Figure 14). The ratios of the horizontal com-
ponent of the ground motions observed at JMA Furukawa to the horizontal
component of the ground motions observed at K-NET MYG006 during the
same event, namely H/H spectrum ratios, are calculated. Figure 20 shows
the H/H spectrum ratios during the main shock and the other significant
earthquakes: 1) a MW 7.0 intra-slab earthquake that occurred in the Pacific
plate on 26, May 2003, 2) a MW 7.1 inter-plate earthquake that occurred on
the plate boundary between the Pacific and North American plates on 16,
August 2005, and 3) a MW 7.0 intra-crust earthquake that occurred on 14,
June 2008. The spectrum ratio is calculated after filtering with a moving
window of length 0.2s in width. The periods at the peaks of the H/H spec-
trum ratios are about 0.5s for the other events, whereas those for the main
shock are larger than 0.5s, especially about 1.0s in the NS component. PGAs
at K-NET MYG006 were 268 cm/s2 during the 2003 earthquake, 151 cm/s2
during the 2005 earthquake, and 315 cm/s2 during the 2008 earthquake, re-
spectively, which are about a half the PGA during the main shock, 583 cm/s2.
The longer peak periods during the main shock imply the nonlinear behaviors
of the shallow soils. The peak period of the H/H spectrum ratios is almost
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close to the peak period of pSv at K-NET MYG006 and JMA Furukawa.
This means that ground motions in 1.0-1.5s around JMA Furukawa were
emphasized because of the soil nonlinearity compared to those at K-NET
MYG006.
CONCLUSION
The 2011 off the Pacific coast of Tohoku Earthquake caused severe dam-
age not only because of the great tsunami, but also because of the ground
motions. The observed ground motions imply at least three significant events
generating high-frequency radiation, which are consistent with the location
of the SMGAs. They gave rise to two wave groups in the waveforms at the
northern stations, and a third wave group at the southern stations.
PGAs observed during the earthquake were extraordinarily large. The
largest PGA observed at K-NET MYG004 was about three times larger than
the gravitational acceleration. The pseudo-velocity response spectra of the
records are different from those of JR Takatori because the ground motions
with large PGA give shorter peak periods than 1.0s. On the other hand,
several peak periods over 1.0s were observed, although the PGAs were not
large. The pseudo-velocity response spectrum of the JMA Furukawa records
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was similar to that of the JR Takatori records with the peak period of 1.3s.
We have emphasized that the spectrum shapes recorded in the damaged areas
during this earthquake and the Kobe earthquake are similar, and that the
results are consistent to those in the summary by Sakai (2009). We have
also pointed out that the ground motions in 1.0-1.5s at JMA Furukawa were
emphasized because of the soil nonlinearity.
ACKNOWLEDGMENTS
We thank the anonymous reviewer as well as the editor, Professor Akira
Murakami for their thorough comments. We also thank many organizations
for their contributions to the strong ground motion observations, namely,
K-NET, KiK-net organized by NIED, JMA, PARI, BRI, NILIM, ERI of
the University of Tokyo, and AIST. Damage investigations were conducted
in collaboration with Associate Professor Yasuko Kuwata, Associate Profes-
sor Akihiro Takahashi, Associate Professor Yoshikazu Takahashi, and the
geotechnical team of the JSCE Great Tohoku Earthquake damage reconnais-
sance members. We appreciate the information from and the discussions with
many researchers, and also the kind cooperation of the people of Furukawa
and Tsukidate.
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Table 1: Top 8 records of PGA in horizontal components
PGA [cm/s2] Station
2765 K-NET MYG004
1970 K-NET MYG012
1913 PARI Onahama-G
1844 K-NET IBR003
1807 K-NET MYG013
1614 K-NET IBR013
1425 K-NET TCG009
1425 K-NET FKS016
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138 140 142 144
36
38
40
100 km
CMT solution (NIED)
CMT solution (JMA)
0 25 50
depth [km]
Iwate Prefecture
Miyagi Prefecture
Fukushima Prefecture
Ibaraki Prefecture
Tochigi Prefecture
Figure 1: Aftershock distribution within 24 hours after the main shock, and
CMT solutions estimated by JMA and F-net (NIED).
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138 140 142 144
36
38
40
100 km 4.5
5.0
5.5
6.0
6.5
7.0JMA intensity
Figure 2: Distribution of seismic intensities on the JMA scale.
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0
100
200
300
400
500
[km]
0 50 100 150 200
time [s]
0.510Hz envelope (smoothing in 2s window)
IWTH08
IWTH13
IWTH02
IWTH04
IWTH05
MYGH06
MYGH08
MYGH09
FKSH17
FKSH18
FKSH09
FKSH11
IBRH12
TCGH13
TCGH16IBRH11
IBRH19
140 142
36
38
40
100 km
IBRH19
IBRH11
TCGH16
TCGH13
IBRH12
FKSH11
FKSH09
FKSH18
FKSH17
MYGH09
MYGH08
MYGH06
IWTH05
IWTH04
IWTH02
IWTH13
IWTH08
Figure 3: Envelopes of borehole accelerograms in EW component observed
by KiK-net (NIED). Stations are selected to be almost parallel to the strike
direction of the seismic fault.
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138 140 142 144
36
38
40
100 km
KNET MYG004
KNET MYG012
PARI OnahamaG
KNET IBR003
0
300
600
900
PGA [cm/s/s]
Figure 4: Distribution of peak ground accelerations (PGA) in horizontal
components.
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138 140 142 144
36
38
40
100 km 0
25
50
75
100
PGV [cm/s]
Figure 5: Distribution of peak ground velocities (PGV) in horizontal com-
ponents.
-2000
0
2000
0 50 100 150 200
acceleration[cm/s2]
time [s]
K-NET MYG004 N161oE
K-NET MYG012 N92oE
PARI Onahama-G N127oE
K-NET IBR003 N323oE
(Max. 2765 cm/s2)
(Max. 1970 cm/s2)
(Max. 1913 cm/s2)
(Max. 1844 cm/s2)
Figure 6: Accelerograms of top 4 PGA records of the maximum component.
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10
100
1000
0.1 0.5 1 2 5
pSv(h=0.0
5)[cm/s]
period [s]
K-NET MYG004K-NET MYG012
1995 JR Takatori
Figure 7: Pseudo-velocity response spectra (h=0.05) of K-NET MYG004 and
MYG012, compared to JR Takatori records during 1995 Kobe earthquake.
The two lines plotted together for each event correspond to EW and NS
components.
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138 140 142 144
36
38
40
100 km
peak period of pSv
(> 50cm/s)
< 1.0s
> 1.0s
Figure 8: Distribution of peak periods of pSv over 50 cm/s categorized into
periods of either less than or greater than 1.0s.
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138 140 142 144
36
38
40
100 km
KNET TCG006 (359cm/s, 1.3s)
JMA Furukawa (423cm/s, 1.2s)
0.1 1 10
sec.
pSv (h = 0.05)
300cm/s
150cm/s
Figure 9: Distribution of peak pSv and periods. Color of the marks highlights
the periods in 1.0-2.0s.
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10
100
1000
0.1 0.5 1 2 5
pSv(h=0.0
5)[cm/s]
period [s]
JMA FurukawaK-NET TCG006
1995 JR Takatori
Figure 10: Pseudo-velocity response spectra (h=0.05) of JMA Furukawa and
K-NET TCG006, compared to JR Takatori records during 1995 Kobe earth-
quake. The two lines plotted together for each event correspond to EW and
NS components.
0
500
0 50 100 150 200
acceleration[cm/s
2]
time [s]
K-NET CHB008 EW
(Max 157 cm/s2)
K-NET CHB024 EW
(Max 203 cm/s2)
Figure 11: Accelerograms in Tokyo Bay area
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K-NET MYG004
Sorinji temple
Tsukidate hachiman shrine
evidence of ground motion
200m
reconnaissance trail
Osaki city hall
Figure 12: Location of seismic station, K-NET MYG004, and the significant
damages observed in Tsukidate area.
N
Figure 13: Damage to Tsukidate Hachiman Shrine. Symbol of gate is the
location oftorii, squares are komainu, symbol of house is honden, and shaded
area is sando.
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200m
Zuisenji temple
Nishinomiya shrine
Konpira shrine
Kanaya fudoson shrine
JMA Furukawa
collapsed residence
severe damaged residence
raw land
sand boiling
uplifted manhole
K-NET MYG006
reconnaissance trail
JR Furu
Ichijyoji temple
Seiganji temple
Figure 14: Location of seismic stations, K-NET MYG006 and JMA Fu-
rukawa, and the significant damages in Furukawa area.
N
Figure 15: Damage to Konpira Shrine. Symbol of gate is the location of torii,
squares are komainuand stone monuments, symbols of house are honden and
suibansha, and shaded area is sando.
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N
Figure 16: Damage to Kanaya Shrine. Symbol of gate is the location of torii,
squares are komainu and stone monuments, symbol of house is honden, and
shaded area is sando.
N
Figure 17: Damage to Nishinomiya Shrine. Symbol of gate is the location of
torii, vertical markers are wooden lanterns, symbol of house is honden, and
shaded area is sando.
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0
100
200
300
0 30 60 90 120 150 180
velocity[cm/s]
time [s]
K-NET MYG004 EW
K-NET MYG006 EW
JMA Furukawa EW
(Max. 49.2 cm/s)
(Max. 91.9 cm/s)
(Max. 76.7 cm/s)
0
100
200
300
0 30 60 90 120 150 180
velocity[cm/s]
time [s]
K-NET MYG004 NS
K-NET MYG006 NS
JMA Furukawa NS
(Max. 104.8 cm/s)
(Max. 58.5 cm/s)
(Max. 81.1 cm/s)
Figure 18: Velocity waveforms of K-NET MYG004, MYG006, and JMA
Furukawa.
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10
100
1000
0.1 0.5 1 2 5
pSv(h=0.0
5)[cm/s]
period [s]
K-NET MYG004K-NET MYG006JMA Furukawa
Figure 19: Pseudo-velocity response spectra (h=0.05) of K-NET MYG004,
MYG006, and JMA Furukawa. The two lines plotted together for each event
correspond to EW and NS components.
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0.5
1.0
2.0
0.2 0.5 1 2 5
H/H
spectrumr
atio
period [s]
JMA Furukawa / MYG006
main shock
other events
Figure 20: H/H spectrum ratios between JMA Furukawa and K-NET
MYG006 during the main shock and the other significant events on 26, May
2003, 16, Aug. 2005, and 14, Jun. 2008.
44