Seismic Hazard Assessment for the Kingdom of Saudi Arabia Tom Brocher Director, Earthquake Science Center U.S. Geological Survey June 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 The first step in making hazard maps: construct a hazard curve at each site Hazard Methodology Procedure Cartoon a Earthquake Sources b a Ground motion Hazard curve r1 M 7.6 d1 d4 annual probability of exceeding pga r2 d2 peak ground acceleration M7.6 d3 high seismicity zone San Andreas fault distance 0.25g 0.5g peak ground acceleration (pga) r3

Constructing a hazard curve: a real example 1/200=0.005 Source B M7.5, Tr=200 yr 50km 10km Site Source A M5.5, Tr=10 yr 1/10=0.10 Annual probability that earthquake occurs: Source A: 1/10 = 0.10 Source B: 1/200 = 0.005

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

Interferograms Used Spokane, Washington Interferogram 1 and 2 are from the ERS-2 satellite. Interferograms 3-5 are from the RADARSAT-1 satellite. Interferogram 6 is from the ENVISAT satellite. DEM is from SRTM, used in topographic corrections. Satellite flight direction labeled AZ, look direction labeled LOS. 4

We invert for the Vertical and East components of deformation using the interferograms (2-5) shown in the previous slide. The freeway (I 80) and major US routes (2 and 395) are shown in each panel. The city streets are shown in the top panel. 5

Comparison of best-fit model to data Cross-section A-A’ and B-B’ shown in next slide. 8

Comparison of best-fit model to data – Cross-Sections 9

Model fault line in downtown Spokane, GoogleEarth Hanging-wall is on the left and Foot-wall is on the right. Spokane was a Native American meeting place because of the Falls. Europeans were attracted to Spokane because of the Falls. Spokane was founded in 1873 as the city of Spokane Falls. After the Spokane Fire of 1889 destroyed the downtown, wooden buildings were prohibited during the rebuild. From historicalspokane.org: “Spokane's rebirth resulted in about 100 new elaborate brick, masonry, and terra cotta commercial buildings in the downtown in the year immediately following the fire.” Over 50% of the buildings in Spokane are designated historic, many of them brick buildings built just after the fire. Looking NE 11