Application of GPS Data to UCERF3 and Seismic Hazard Assessment in California

1. Application of GPS Data to UCERF3 and Seismic Hazard Assessment in California Yuehua Zeng & Wayne Thatcher U. S. Geological Survey With Major Contributions from: David Sandwell, Kaj Johnson & Liz Hearn

2. Issues for April 2010 SCEC Sponsored Workshop to Incorporate Geodetic Surface Deformation Data into Probabilistic Seismic Hazard Assessments 1. Strain Rate Map Methodologies & Issues 2. Block Modeling Methodologies & GPS Fault Slip Rate Estimation 3. Earthquake Cycle Deformation & Influence of Postseismic Transients

3. GOALS & DESIRED OUTCOMES The purpose of the workshop is to begin scientific consideration of how to incorporate GPS & InSAR constraints on strain rates and fault slip rates into the next generation California earthquake hazard assessment ("UCERF3"). Desired outcomes of the meeting are: 1. Assessment of secure science ready for UCERF3 applications 2. Agenda of new research objectives for SCEC and others in support of UCERF3 and related probabilistic hazard assessments.

4. Preliminary Combined Western US Velocity Field • On this map there are 2026 unique sites with horizontal velocity sigma less than 1 mm/yr • In region shown, the number of sites with velocity sigmas less than value shown for horizontal or vertical rates are: s mm/yr # Horizontal #Vertical 0.1 294 - 0.2 717 148 0.3 965 285 0.4 1125 375 0.5 1338 515 1.0 2026 987 1.5 2247 1244 2.0 2317 1475 UNAVCO Working Group (Chair, Tom Herring)

5. 1. Strain Rate Mapping Methologies & Issues Science of making strain rate maps Results of community modeling exercise What’s next? (Leader: David Sandwell)

9. Conclusions • strain rate = velocity/locking depth; moment rate = velocity X locking depth • strain rate looks like UCERF2 (best correlation .76) • strain rate not well resolved by GPS • deformation models are best for resolving strain along faults • how do we decompose strain into elastic and inelastic (e.g. creep)? • need targeted campaign GPS; need L-band InSAR (e.g. DESDynl

10. 2. Fault Slip Rate Estimates from Block Models Block modeling methodologies Results of community modeling exercise Open discussion (Leader: Kaj Johnson) McCaffrey 2009

15. Slip Rate Estimation Exercise • Provided to participants: • Part of CMM4 GPS velocity field • 2. Simplified fault geometry • (segment locations and dips) • “geologic” slip rate constraints for each segment (not used in any models reported here) • Results reported by participants: • Strike-slip, dip-slip, and tensile components of velocity • discontinuities across segments • 2. Predicted surface velocities • Estimated or prescribed locking depths (if applicable)

16. Challenges in kinematic modeling: • Do we need more physics? • What constraints/data to use? • Consider off-fault and on-fault long-term deformation? • Earthquake cycle effects (transients)? • Rigid-body block motions sufficient for describing long-term kinematics? • Is the microplate (blocks) model adequate? • Do we need to include lateral variations in properties? Nonlinear rheology? Fault friction?

17. 3. Eq Cycle & Other Effects on Interseismic Deformation Influence on fault slip rate estimation Results of community modeling exercise Open discussion (Leader: Liz Hearn) Hearn et al 2009 JGR

20. Workshop Report Complete 23 pp report was available on SCEC website from May 2010 • Short version published 21 September 2010 in Eos (AGU weekly newspaper)

21. Plans for 2011 • 4 Proposals submitted to SCEC on 5 November -to support workshop + 3 academic Pis • Conveners’ Meeting March 2011, USGS/Golden Wrap-up, Consensus Workshop, June 2011 • Final Reports & Recommendations by Late 2011 -3 disciplinary reports by Johnson, Hearn & Sandwell - consensus fault slip & strain rate estimates provided