1

10% chance in 50 years

Let’s go through the steps that yield hazard risk maps like these.

Hazard Assessment• Monitoring, data collection: to determine

magnitude / frequency relationships (thus probability)– Often extrapolate to higher magnitudes

– Some modeling and simulation may help, especially for rare events, few observations

– May also include historical and pre-historic reconstructions for more time depth (old fault scarps of events centuries before)

• Translate into hazard elements, e.g.:

– Eq mag (ML) = ground shaking (%g accel) at some probability

(Not unlike effort to create a better historical hurricane data set)

Hazard Assessment (cont)

• Calculate damage / loss curves---or refer to current engineering practice to choose “standard” event or risk threshold (g with 10% chance in 50 years)

• This standard risk allows you to create a map: very important in EQ where local conditions affect ground motions, but difficult-requires lots of field work, geo-data.

• Map populations and property at risk

• Apply loss curves

• Go to Risk/hazard ManagementMatch ground shaking probability (left) with population (right), giving rough idea of risk

(prob. X consequence), and you see areas of high risk and low risk: So Cal and Bay area

are high risk; Central Valley (even with significant pop) is low risk.

Fortunately, seismology has provided lots of observations, so frequency/magnitude

relationships are getting well established, esp. modest event magnitudes. The data pours

in, and over just ten years, thousands of epicenters show where the eq action is in So.

Calif. (often but not always along surface expression of fault, the blue lines).

Fault scarps: sometimes obvious!

Aerial view of the San Andreas fault

slicing through the Carrizo Plain in the

Temblor Range east of the city of San Luis

Obispo. (Photograph by Robert E.

Wallace, USGS.)

Hebgen Lake, MT, 1959 eq

Death Valley, CA

Geographical risk is also ascertained by mapping the faults, some are obvious!

2

Aerial surveys right after eq’s can reveal fault patterns not mapped before because

they had no sfc expression. Surface rupture, 1992 Landers EQ, San Bernardino

County, CA. –ranged from 2 inches to 20 ft

Not all faults are created

equal, or offer equal risk:

some that are “locked”

may not have ruptured in

modern times, but show

pre-historic evidence of

fewer, big ruptures.

SO

Different contributions to

a point’s risk of shaking by

an ensemble of different

faults

Ground motions for known magnitudes and relationship b/w ML and shaking can be

established, and then linked to frequency of seismic activity. Here are peak velocity

contours for the magnitude 6.7 1994 Northridge earthquake. Contours of velocity are in

cm/sec, measured by accelerometers. Red star is epicenter, note peak motions off-set to

north along foothills.

Another step in risk assessment is to map actual damage, here expressed by the

Modified Mercalli eq intensity scale, and link it to ground shaking, and thus be able to

project damage into the future.

Damage

ProjectionsYou can also link ground

motions to rough ideas, or

categories, of damage and the

Mercalli scale is typically used

as an anchor for such

comparisons (Box. 5.1 in

textbook).

Add it all up!

• Run lots of simulations

• Add new data all the time (M and accelerations to let you know how each signature of a fault plays out across a varied topography)

• Look for hidden, quiescent old faults

• Up-date risk assessment

• Up-date hazard reduction efforts

• Improve disaster preparedness

3

OK, next step is

mitigation:

Damage and Loss

Reduction

OK: so you know the risk,

now you can you design

and retro-fit the built

environment to reduce

loss (at least you start

trying, within limits of

costs and benefits).

EQ Resistant Design/Code• Global problem: URM: adobe, brick, stone

• Good: “weak” structures like pole/thatch

• Good: wood frame construction (80% houses in U.S.)

• Two main approaches in engineered structures:

– Bracing, and shock-absorbing bases, “strong, flexible, ductile materials (e.g., steel framing)– allow motions to move thru the building w/ less damage.

– “Base Isolation,” is most extreme and expensive mitigation (see next slide): prevent motions form transmitting form ground to the building.

– Base Isolation is very expensive, so: Maybe not every bldg, but schools, hospitals, nuclear power plants, dams, etc. Also: gas, water, electric lines

• Avoid glass; facades; parapets; balconies, etc. that fall away from structures (often into streets on people!)

• Interior design: anchor everything!

• Choose safer locations: e.g., bedrock often better than clay, alluvial sediments, or man-made fill (especially fill)

Base isolation in Martin Luther King Jr. civic center

in Berkeley—this was an expensive retro-fit! Does

not work for tall bldgs.

Other approaches add bracing to transmit motions

though bdlgs, see next slide

See more seismic design specs at:

http://www.wbdg.org/design/seismic_design.php

?r=resist_hazards

Bracing: structural members that transmit waves

thru the structure safely:

Can be tested on “shaking tables”: see:

http://peer.berkeley.edu/testing/index.html

http://www.ecs.csun.edu/~shustov/000-EPF.html

Replacement of the Bay bridge after

1989 Loma Prieta EQ, with seismic

design. Long Term Problem

• Still: majority of structures, even in EQ zones, not resistant (CA code improved in 1933; strengthened dramatically in 1970s and 1980s) still most bldgs are at risk.

• So, there’s a lot to accomplish in terms of emergency preparedness! Especially since there’s no skill in EQ predictions, though it is known that catastrophic EQ events will eventually occur in American and other cities. More on that later.

4

Tsunami• Caused by earthquakes: Large, shallow

focused EQ on sea bed.

• Essentially seismic sea wave: long wave

length (100-200km!) and low amplitude

(<.5M); fast: 500-6000 Km/h

• Slow and build height near shore, measured

by height of wave (trough to crest), and run-

up zone or distance above normal high tide

• H and run-up vary greatly along coastline:

shallow/deep; bays vs. points, etc.

• Can be quite deadly: 5,500 deaths during

1982-2002 (2,000 from one event—Table

5.4)

• Perhaps 50,000 deaths in 21st century

(then there was 2004 Tsunami!)

• Geographically most frequent in Pacific and

Indian oceans

• Japan/Taiwan (Honshu 10 m wave R = 10

years!); 1933 event along Japan’s Sanriku

coast (24 m) was r = 70 years---killed 3,000+

• Alaska and US West Coast

• Indian ocean/SE pacific:

Dec. 26, 2004 Sumatran

EQ/tsunami killed some

186,000 with 42,000 “missing”

or some 230,000.

http://iri.columbia.edu/~lareef/tsunami/#Tsunami_Animation:_National_Institute_of

http://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake

9.0 EQ, 4th most powerful since 1900!

Matched most deadly modern EQ (1976 Tangshan EQ

in China)

Large area affected, large height (4m+), and little

warning, even w/ 2 hrs travel time to Indian/Sri Lanka

2004 Tsunami travel time (hrs)

5

Warning System (Pacific)

• Tsunami Warning / Watch / Advisory Warnings

issued by the National Weather Service's tsunami

warning centers

• Actions:

– a) locate and size major earthquakes in the Pacific basin,

– b) determine their tsunamigenic potential,

– c) predict tsunami wave arrival times and, when possible,

run-up on the coast, and

– d) provide timely and effective tsunami information and

warnings to the population of the Pacific to reduce the

hazards of tsunamis, especially to human life

• New systems going in Atlantic ocean and Indian ocean

http://www.pmel.noaa.gov/tsunami/pugetsound/pre2/movie/ps.html

Predicting magnitude is challenge: height and run-up/inundation Preparedness: Tsunami inundation and

evacuation maps now available for West Coast

Tsunami preparedness along US Pacific coasts.