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P. Martin Mai Institute of Geophysics, ETH Zurich mai@sed.ethz.ch and the SPICE Local Scale Group

Blindtest on Kinematic Source Inversion Initial (sobering) results. P. Martin Mai Institute of Geophysics, ETH Zurich mai@sed.ethz.ch and the SPICE Local Scale Group (Ampuero, Delouis, Festa, Holden, Madariaga, Moczo, Vilotte, Zarahdnik …). OUTLINE.

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P. Martin Mai Institute of Geophysics, ETH Zurich mai@sed.ethz.ch and the SPICE Local Scale Group

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  1. Blindtest onKinematic Source InversionInitial (sobering) results P. Martin Mai Institute of Geophysics, ETH Zurich mai@sed.ethz.ch and the SPICE Local Scale Group (Ampuero, Delouis, Festa, Holden, Madariaga, Moczo, Vilotte, Zarahdnik …)

  2. OUTLINE ► Goal: perform accurate kinematic finite-source inversion to estimate the rupture process during earthquake faulting ► Approach: test various source-inversion methods, and assess their resolution, strength and weaknesses to finally “design” the optimal inversion strategy ► Method: generate synthetic near-source motions for some source rupture model (with increasing complexity as the project progresses) that is known to only one person (M. Mai), while interested researchers can then apply their source-imaging technique “blindly”

  3. The Model Setup • Earthquake source geometry and station distribution chosen to be reminiscent of the 2000 Tottori earthquake (M = 6.9), but the details of the rupture process are not known.

  4. The Model Setup • Synthetic seismograms are then computed, assuming (unknown to modelers) constant rupture velocity, constant rise time, simple slip-velocity function, and heterogeneous slip. • A discrete wave-number integration method (0.01 < f < 3 .0 Hz) is used for wavefield calculations. • In the first step, no noise is added to the synthetics; later, also the above conditions on vr, tr will be relaxed. • The modelers are given; • seismic moment: 1.43 1019 Nm • dip = 90o • rake = 150o • hypocentral depth = 12.5 km • velocity-density structure

  5. INITIAL RESULTS • So far, four researchers have sent in their inversion solution to this initial problem: •  the results are remarkably diverse !!!!! • In alphabetical order … • Betrand Delouis: Non linear inversion by simulated annealing • Gaetano Festa: back-projection of the S -amplitudes along the rays • Catherine Holden: non linear inversion using the neighbourhood algorithm • Jiri Zahradnik: iterative moment-tensor deconvolution, combined with forward modeling

  6. INITIAL RESULTS • Betrand Delouis: Non linear inversion by simulated annealing vr = 3.1 km/s, tr = 1.0 s  NOTE THE GOOD DATA FITTING !!!

  7. INITIAL RESULTS • Gaetano Festa: back-projection of the S -amplitudes along the rays vr = 2.8 km/s, tr = 1.0 s  NOTE THE GOOD DATA FITTING !!!

  8. INITIAL RESULTS • Catherine Holden: non linear inversion using the neighbourhood algorithm vr = 2.15 km/s, tr = ?? s  NOTE THE GOOD DATA FITTING !!!

  9. INITIAL RESULTS • Jiri Zahradnik: iterative moment-tensor deconvolution, combined with forward modeling vr = 2.6 km/s, tr = 1.0 s  NOTE THE GOOD DATA FITTING !!!

  10. THE SOLUTION • … and here comes the long awaited answer …. • vr = 2.7 km/s and tr = 0.8, using an isosceles triangle as SVF; • max. displacement ~ 2.5m, about 15 km north-west of the hypocenter • the rupture expanded primarily in the NW-direction

  11. CONCLUSIONS ► Can we conclude anything from this exercise yet?? ► First of all: work is needed to make this solutions agree -- consistent definition which stations to use and how to perform the data preparation, to eliminate any bias coming from there -- differences due to Green’s function calculations ?? -- differences due to inversion approach (linear vs. non-linear, parameterization, smoothing, misfit function, etc) ?? ► Next step: quantitative comparison of inverted slip models: -- cross-correlation analysis with respect to input model -- slip values at selected points -- overall slip distribution -- ….

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