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Source Inversion Validation (SIV): Quantifying Uncertainties in Earthquake Source Inversions

Source Inversion Validation (SIV): Quantifying Uncertainties in Earthquake Source Inversions. Martin Mai Morgan Page Danijel Schorlemmer. Earthquake rupture models.

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Source Inversion Validation (SIV): Quantifying Uncertainties in Earthquake Source Inversions

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  1. Source Inversion Validation (SIV): Quantifying Uncertainties in Earthquake Source Inversions Martin Mai Morgan Page Danijel Schorlemmer

  2. Earthquake rupture models • Finite-source inversion are done almost routinely today, using a variety of inversion / modeling approaches, different data sets and processing steps • We use the slip models to infer rupture dynamics, to devise source-characterization methods for ground-motion simulations, to perform Coulomb stress modeling, to …. • But: how “good”, i.e. reliable and robust, are these rupture models ?

  3. Intra-event variability • In cases where multiple slip-inversion solutions exist for a single earthquake we often find striking differences in the slip maps! • What drives the large differences between these slip models? A suite of models for the 1999 Izmit (M 7.5) earthquake

  4. Intra-event variability • In cases where multiple slip-inversion solutions exist for a single earthquake we often find striking differences in the slip maps! • What drives the large differences between these slip models? A suite of preliminary investigations of the large Chile earthquake

  5. Initial Project: SPICE BLIND TEST

  6. SPICE: Blind Test on Source Inversion • Source geometry and station distribution similar to the 2000 Tottori earthquake • Synthetic seismograms for 19 (33) near-fault sites (COMPSYN, fmax ~ 3 Hz) • Known: seismic moment: 1.43 x 1019 Nm, geometry (strike, dip, rake: 150°, 90°, 180°), hypocentral location and depth (Z= 12.5 km), velocity-density structure • Unknown: slip on fault plane, rupture velocity & rise time (both constant)

  7. SPICE: Blind Test on Source Inversion • 9 groups; the slip models from 5 groups are “visually” similar to the input model • waveform fits in all cases implied visually a “very good fit” ….

  8. Outcome of the blind test was unexpected • Despite the “simplicity” of the input model, inversions could not resolve slip very well; uncertainties in rupture velocity and rise time up to 20% • Despite differences among all inversion solutions, predicted waveforms are remarkably similar (f < 1 Hz), resulting in low misfit values (generally L2-norm) • 4 out of 9 inversion results are, statistically speaking, NOT better than a random model with somehow correlated slip! • Issues in the inversion method? • Issues in the parameterization? • Issues in the provided synthetics (“correct” solution) • Issues in the “basics”: Green’s function computation

  9. Source Inversion Validation

  10. Past Activities within the SIV Initiative • SPICE source inversion blindtest • March 2005 – Dec 2007; 9 participating groups • Special AGU session (Dec 2007) with invited speakers • Problems: short-lived; no funding; suggested data formats where not used, and hence lots of manual labor to generate comparisons • SCEC workshop on earthquake source inversion (Sept. 2008) • ~50 participants, 6 invited speakers, and ~3 hrs intense discussions • General consensus that SIV (Source Inversion Validation) has to continue • Collection of general ideas on how to setup the problems and how to organize ourselves … but no formal decisions or “constitution of a core group”

  11. Past Activities within the SIV Initiative • Proposal to SCEC for financial support for 2009 SCEC-SIV workshop • Dedicated webpage launched (March 2009) • Online platform to distribute the inversion problems and all relevant meta-data • General communication & exchange platform for everyone interested in SIV • Mini-workshop during SSA 2009 (April 2009) • ~20 participants for general ~2 hrs discussion on future activities • Step 0: Setup of Green’s function test and initial forward-modeling exercise • Workshop during the Annual SCEC meeting (Sept 2009) • Talks on uncertainty assessment, Bayesian modeling, robustness, source dynamics • Discussions on “Expectations from forward-modeling exercise” and “Simple inversion exercise” • Discussion on implementation (CSEP-like approach ?) http://siv.usc.edu

  12. Past Activities within the SIV Initiative • Workshop at KAUST, (March 22-24, 2010) • ~20 non-KAUST & 10 KAUST-affiliated participants • 3 days of talks and discussions on • Green’s function validation • New approaches to (source) inversion and validation • Addressing uncertainties and differences in source models • Using source models in subsequent work • Computational aspects & testing center • How to enjoy snorkeling and not to get sea-sick in unexpectedly rough waters in the Red Sea

  13. Program for this workshop • Saturday, September 11, 2010 (1:30-5:30pm) • Session I: Review of SIV Activities and Green's Function Test Results • 1:30 – 1:45 Mai, Page, Schorlemmer: SIV Introduction • 1:45 – 2:05 Causse, Mai, and all participants: Results from Green's function test • 2:05 – 2:35 Shao & Ji : What did the Exercise of SPICE Source Inversion Validation BlindTest not Tell You? • 2:35 – 3:45 Discussion of Green’s function Results • 3:45 – 4:00 break • Session II: Inversion Techniques & Slip Models • 4:00 – 4:20 Song: Does earthquake slip follow Gaussian statistics? • 4:20 – 4:50 Lavallee, Archuleta, Schmedes: Spectral analysis of slip spatial •   distributions • 4:50 – 5:30 Discussion of previous talks & plans for Sunday breakout groups

  14. Program for this workshop • Sunday, September 12, 2010 (8:00am-12:00pm) • Session III: Inversion Techniques and Seismic-Network Geometry • 8:00 – 8:30 Ellsworth: Source inversion with minimal assumptions • 8:30 – 9:00 Meng & Ampuero: Optimal network geometries for source inversion • 9:00 – 9:45 Discussion of previous talks, setting up the initial inversion test • 9:45 – 10:00 break • Session IV: Break-Out Session and Open Discussion • 10:00-10:45 Breakout groups meet • Preliminary breakout groups: • Input/Output formats, station geometry, • source models, forward model calculations, • misfit functions web tools & development • Where are we heading? What needs to be done? Who does what? • 10:45-12:00 Summaries from breakout groups, Open Discussion

  15. Step 0: Green’s Function Validation • Do all groups compute the Green’s function appropriately? • The SIV-project thus start with a zero-order test to verify GF-computations: • “point-source” at 10 km depth, parameterized as a 1 x 1 km2 slip patch with homogeneous slip and boxcar slip-function of duration τr = 0.2 sec • The shear-modulus at the given depth result in: Mw 4.992, M0 = 3.4992 x 1016 point-source depth

  16. Step 0: Green’s Function Validation • Two cases are considered for the Green’s function test • purely left-lateral strike-slip rupture on a vertical fault • purely thrust-motion on a 40° dipping fault • Stations at Y = 1 km parallel to surface projection of fault plane, and two arrays that are 30° and 60° rotated from the fault-parallel direction

  17. Details on Green’s function test in the next talk

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