Seismic Hazard Assessment for the Kingdom of Saudi Arabia

Tom BrocherDirector, Earthquake Science Center

U.S. Geological SurveyJune 1, 2014

The Goal

• Provide a state-of-the-art seismic hazard assessment for the Kingdom

• Focus on characterizing earthquake faults within the Kingdom – earthquake chronology, slip per event, slip rates, magnitudes, style of faulting

• Another focus will be ground motion prediction equations and site response within the Kingdom

• Assessing extreme wave hazard along the coasts• Training is a major goal of the work

Characterizing Earthquake Faults

• Identifying and mapping young faults– Quaternary Geologic maps– Photos and Imagery– LiDAR– InSAR– Aeromagnetic mapping– Seismic reflection profiling

Characterizing Earthquake Faults

Conducting field and laboratory studies of faults– Field mapping– Geomorphic analysis– Trenching– Age dating of offset soils

Predicting Strong Ground Motions

• Compile existing strong ground motion data within the Kingdom and nearby regions

• Derive ground motion prediction equations• Characterize crustal structure to regionalize the

ground motion data• Characterize site response (Vs30) in the Kingdom• Imaging sedimentary basins for long period

response

Characterize strain rates in the Kingdom

• Use GPS and InSAR data to estimate strain rates in the Kingdom

• Compile earthquake catalog and generate a smoothed seismicity map for the Kingdom

PSHA Analysis

• Earthquake faults• Smoothed seismicity• Strain rates• Ground motion predictions• Site response (Vs30)

Pascucci, Free, Lubkowski, 2008

Who are we?

• The Earthquake Science Center has many years of experience performing seismic hazard assessments in California and the US

• Expertise in: – Paleoseismic investigations of faults– Geophysical characterization of faults– Prediction of strong ground motions– Geodesy and strain measurements– Earthquake monitoring– Probabilistic Seismic Hazard Analysis

Earthquake Science Center Organization

• Earthquake Monitoring (53 staff)– Earthquake Monitoring Project (28 staff)– Southern California Seismic Network (14 staff)– Deformation (13 staff)

• Earthquake Hazard Assessment (48 staff)– Shaking, Damage, Failure (Earthquake Effects) (20 staff)– Southern California Earthquake Hazards Assessment (11 staff)– Pacific Northwest Hazards Project (10 staff)– Bay Area Earthquake Hazards (7 staff)

• Earthquake Research (22 staff)– Earthquake Processes Probabilities and Occurrence (13 staff)– Induced Seismicity (9 staff)

Hazard Methodology Procedure Cartoon

a bEarthquake SourcesGround motion

d1

d2

d3

d4

r1

r2

r3

San Andreas fault

high seismicityzone

peak ground acceleration (pga)

Hazard curve

annu

al p

roba

bilit

y of

ex

ceed

ing

pga

0.25g

a

M 7.6

distancepeak

gro

und

acce

lera

tion

M7.6

0.5g

The first step in making hazard maps: construct a hazard curve at each site

Source B

Source A Site

M7.

5, T

r=20

0 yr

M5.5, Tr=10 yr

50km

10km

Annual probability that earthquake occurs:

Source A: 1/10 = 0.10Source B: 1/200 = 0.005

Constructing a hazard curve: a real example

Consider the uncertainty in motions from GMPEs

Consider the uncertainty in motions from GMPEs

Combine the source and ground-motion uncertainties

Plot the resulting FOE for the PSA value

Do this for all possible ground motions from Source A to make a hazard curve for Source A

Combine hazard curves for all source t make the final hazard curve

Pick off value for hazard map

Make a map of the ground-motion values for a given FOE; this is the hazard map that is the basis for the design maps included in building codes

Note: different M and R limits than on slide for Anchorage

4

Interferograms Used Spokane, Washington

5

We invert for the Vertical and East components of deformation using the interferograms (2-5) shown in the previous slide.

8

Comparison of best-fit model to data

9

Comparison of best-fit model to data – Cross-Sections

11

Model fault line in downtown Spokane, GoogleEarth

Looking NE