March 7, 2008NGA-East 2nd Workshop1 RECENT DEVELOPMENTS IN STRONG MOTION SIMULATIONS FOR CEUS Paul Somerville and Robert Graves URS Pasadena MOTIVATION: CEUS ground motion models are based on simulations validated against sparse data

March 7, 2008NGA-East 2nd Workshop2 OUTLINE Strong ground motion simulation & validation Seismic wave propagation Effect of crustal structure on ground motions Review of EPRI ground motion modeling Review of CEUS ground motion model (USGS), and modeling of NSN data (NRC) Improvement of simulations and models

March 7, 2008NGA-East 2nd Workshop3 NGA-E NGA-East

March 7, 2008NGA-East 2nd Workshop4 Broadband Ground Motion Simulation Elastodynamic Representation Theorem: Ground motion U(t) can be calculated from the convolution of the slip time function D(t) on the fault with the Green's function G(t) for the appropriate distance and depth, integrated over the fault rupture surface U(t) =  D(t) * G(t) Combine long period and short period simulations to generate broadband time history

March 7, 2008NGA-East 2nd Workshop5 Validation of Ground Motion Simulations Against Strong Motion Recordings Measure the difference between recorded and simulated ground motion (response spectral residuals) Bias: Do the simulations systematically under- or over-predict the recorded ground motions? Standard Error: What is the average difference between recorded and simulated values?

March 7, 2008NGA-East 2nd Workshop6 Validation against Arleta recording of Northridge earthquake Validation against a large set of Northridge earthquake recordings Recording Simulations

March 7, 2008NGA-East 2nd Workshop7 Validation against WUS earthquakes

March 7, 2008NGA-East 2nd Workshop8 Wave Propagation Critical reflections from the lower crust Contributions of different wave arrivals to ground motion attenuation

March 7, 2008NGA-East 2nd Workshop9 Critical Reflections from the Lower Crust 30 km 40 km Direct, upgoing: becomes weak with increasing distance Reflected, downgoing: becomes strong beyond the critical distance

March 7, 2008NGA-East 2nd Workshop10 Long duration – due to scattering This simulation has no scattering Direct (S) fades as downgoing (ScS, SmS) strengthens DataSimulation

March 7, 2008NGA-East 2nd Workshop11 Direct (upgoing) waves are strongest at close distances but their amplitudes fade at larger distances Reflected (downgoing) waves are weak at close distances but dominate at larger distances (beyond about 50 km)

March 7, 2008NGA-East 2nd Workshop Saguenay earthquake

March 7, 2008NGA-East 2nd Workshop13 Harvard data and simulation SmS etc.sSms, SmSSmS recorded simulated Simulations work well at long periods

March 7, 2008NGA-East 2nd Workshop14

March 7, 2008NGA-East 2nd Workshop15 Contributions of Different Waves Individual body waves Combination Complete simulation

March 7, 2008NGA-East 2nd Workshop16 Review of EPRI (1993) Ground Motion Modeling Survey of crustal structure in CEUS Simulation analysis of the effect of crustal structure on ground motion attenuation

March 7, 2008NGA-East 2nd Workshop17 GrenvilleN. Appalachian granite Conrad interface gabbro Moho interface

March 7, 2008NGA-East 2nd Workshop18 Crustal Structure Regions Northern Appalachian Grenville

March 7, 2008NGA-East 2nd Workshop19 Simulated attenuation in 16 different regions

March 7, 2008NGA-East 2nd Workshop20 Crustal Structure Regions Northern Appalachian Grenville

March 7, 2008NGA-East 2nd Workshop21 Effect of Crustal Structure Grenville - NoConrad Layer N. AppalachiansConrad Layer Eq Depth 7 kmEq Depth 11 kmEq Depth 15 km

March 7, 2008NGA-East 2nd Workshop22 NRC Project (1998): Modeling Attenuation of NSN Data in the Grenville Province (5 yrs of data) o Data - Simulation -- Model

March 7, 2008NGA-East 2nd Workshop23 USGS Project (2001): CEUS Ground Motion Model from Simulations Earthquake Source Scaling and Ground Motion Attenuation Relations in Central and Eastern North America, Somerville et al. (2001) Comparison with results obtained using the stochastic model: Atkinson and Boore (1995); Toro et al. (1997)

March 7, 2008NGA-East 2nd Workshop24 Generating Ground Motion Models from Simulations Earthquake source scaling relations were derived from the source parameters of 3 eastern North American events (Hartzell, 1994) The source scaling relations were used to generate a large suite of ground motion simulations using a broadband Green’s function method The simulated ground motions were used to generate a ground motion prediction model

March 7, 2008NGA-East 2nd Workshop25 Hartzell (1994) Rupture Models

March 7, 2008NGA-East 2nd Workshop26 Rupture Area Scaling

March 7, 2008NGA-East 2nd Workshop27 Scaling of Rise Time (slip duration on fault)

March 7, 2008NGA-East 2nd Workshop28 Source Scaling Relations in the CEUS Rupture area is smaller (0.4) than for tectonically active regions Average slip is 2.5 times larger than for tectonically active regions Rise time is 1.85 times larger than for tectonically active regions Slip velocity is 35% larger than for tectonically active regions (higher dynamic stress drop)

March 7, 2008NGA-East 2nd Workshop29 Comparison of Simulation-Based Ground Motion Prediction Models M 6.5

March 7, 2008NGA-East 2nd Workshop30 Ways to Improve CEUS Ground Motion Prediction Models Use 15 years of NSN / ANSS data from CEUS to test earthquake source scaling and wave propagation models Apply broadband simulation methods, developed and validated in the WUS, to the CEUS environment Rigorously validate predictions against augmented CEUS data

March 7, 2008NGA-East 2nd Workshop31 Resources for Simulation SCEC Broadband Strong Motion Simulation Platform (Three Methods) USGS Golden: Set of Four Strong Motion Simulation Methods (Steve Hartzell)

March 7, 2008NGA-East 2nd Workshop32 SCEC Kinematic Broadband Ground Motion Simulation Platform Calculate Kinematic Broadband (0-10 Hz) Waveforms for Scenario Earthquakes Validation of simulations Verification of simulations Platform brings objectivity, transparency and repeatability to strong motion simulations

March 7, 2008NGA-East 2nd Workshop33 Source Description CFM, ERF M w, Dimension, Geometry … Kinematic Rupture Generator 1. Beroza 2. Archuleta 3. Graves 4. … Standard Rupture Format GF Libraries Site Lists Velocity Models … High Frequency Simulation (> 1 Hz) 1. 1D / Ray GF 2. Scattering 3. Site Effects 4. … Low Frequency Simulation (< 1 Hz) 1. 1D / 3D GF 2. 3D AWM 3. Site Effects 4. … Combine Low & High Frequency 1. Filters 2. Time Shift 3. … Broadband Time Histories (0 – 10 Hz) SCEC Broadband Simulation Platform

March 7, 2008NGA-East 2nd Workshop34 SUMMARY CEUS ground motion prediction models are based on simulations validated against sparse data We now have 15 years of high quality ground motion data from NSN / ANSS in the CEUS We have advanced broadband strong motion simulation procedures that have been validated in the WUS We have a platform for broadband strong motion simulation that brings objectivity, transparency and repeatability to strong motion simulations