A global search inversion for earthquake kinematic rupture history: Application to the 2000 western Tottori, Japan earthquake

Abstract

[1] We present a two-stage nonlinear technique to invert strong motions records and geodetic data to retrieve the rupture history of an earthquake on a finite fault. To account for the actual rupture complexity, the fault parameters are spatially variable peak slip velocity, slip direction, rupture time and risetime. The unknown parameters are given at the nodes of the subfaults, whereas the parameters within a subfault are allowed to vary through a bilinear interpolation of the nodal values. The forward modeling is performed with a discrete wave number technique, whose Green's functions include the complete response of the vertically varying Earth structure. During the first stage, an algorithm based on the heat-bath simulated annealing generates an ensemble of models that efficiently sample the good data-fitting regions of parameter space. In the second stage (appraisal), the algorithm performs a statistical analysis of the model ensemble and computes a weighted mean model and its standard deviation. This technique, rather than simply looking at the best model, extracts the most stable features of the earthquake rupture that are consistent with the data and gives an estimate of the variability of each model parameter. We present some synthetic tests to show the effectiveness of the method and its robustness to uncertainty of the adopted crustal model. Finally, we apply this inverse technique to the well recorded 2000 western Tottori, Japan, earthquake (Mw 6.6); we confirm that the rupture process is characterized by large slip (3-4 m) at very shallow depths but, differently from previous studies, we imaged a new slip patch (2-2.5 m) located deeper, between 14 and 18 km depth.Citation: Piatanesi, A., A. Cirella, P. Spudich, and M. Cocco (2007), A global search inversion for earthquake kinematic rupture history: Application to the 2000 western Tottori, Japan earthquake,

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“…Section 4 is dedicated to a series of synthetic case studies where we infer slip amplitudes, rupture velocity, and rise time. For this, we use the source-receiver geometry of the Tottori 2000 earthquake, for which various different rupture scenarios have been reported in the literature [e.g., Iwata and Sekiguchi, 2002;Semmane et al, 2005;Piatanesi et al, 2007;Monelli et al, 2009]. We analyze one scenario exclusively based on 3-C data and compare the results to a second scenario including 6-C data at only half as many stations.…”

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“…The model parameters are allowed to vary within each subpatch through bilinear interpolation of the nodal values. They adopt a single window approach and the source-time function is represented by a regularized Yoffe function (Tinti et al, 2005) with time to peak slip velocity equal to 0.225 s. Their joint inversion of strong motion and static displacement records is performed using a two-stage nonlinear technique (Piatanesi et al, 2007). During the first stage a heat-bath simulated-annealing algorithm constructs the ensemble of models that efficiently sample the good data-fitting regions.…”

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“…This discrepancy is likely to be related to the inferred location of the Tottori hypocentre within an area of a small amount of final slip (e.g. Semmane, 2005;Piatanesi et al, 2007). Taking the corresponding rise times into account, this may explain a weak detectability by means of TR for the hypocentral parameters of the Tottori event.…”