Kim, YoungHee and Liu, Qinya and Tromp, Jeroen (2011) Adjoint centroid-moment tensor inversions. Geophysical Journal International, 186 (1). pp. 264-278. ISSN 0956-540X http://resolver.caltech.edu/CaltechAUTHORS:20110808-121421143
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We determine centroid-moment tensor (CMT) solutions by minimizing waveform differences between observed and simulated seismograms based on an adjoint method. Synthetic seismograms and Fréchet derivatives are calculated based on a spectral-element method. The non-linear adjoint CMT inversion algorithm requires three simulations for each iteration: one ‘forward’ simulation to obtain synthetics for the current source parameters, one ‘adjoint’ simulation which involves injecting time-reversed differences between observed and simulated seismograms as simultaneous virtual sources at each of the receivers, and an extra forward simulation to compute the step length in the conjugate-gradient direction. Whereas the vertical component of the adjoint wavefield reflects the radiation pattern near the centroid location, the components of the adjoint strain tensor capture the elements of the moment tensor. We use the method to determine adjoint CMT solutions for two representative southern California earthquakes using recent 3-D crustal model CVM-6.2. The adjoint CMT solutions are in good agreement with classical Hessian-based CMT solutions involving 3-D Green's functions. In general, adjoint CMT inversions require fewer numerical simulations than traditional Hessian-based inversions. This faster convergence holds promise for multiple moment-tensor and kinematic rupture inversions in 3-D earth models.
|Additional Information:||© 2011 The Authors. Geophysical Journal International © 2011 RAS. Accepted 2011 March 28. Received 2011 February 26; in original form 2011 January 6. Article first published online: 5 May 2011. The numerical simulations for the time-reversal images of the source were performed on the Caltech Division of Geological & Planetary Sciences Dell cluster. SEM simulations for the moment-tensor inversions are accomplished on the tightly coupled system (TCS) component of the Scinet Consortium. SciNet is funded by the Canada Foundation for Innovation (CFI) and by the Province of Ontario as well as the University of Toronto, Faculties of Arts and Science, Engineering and Medicine. Data and synthetic seismogram processing is accomplished based on the Seismic Analysis Code (SAC, Goldstein & Snoke 2003). All plots are made with the Generic Mapping Tool (GMT) (Wessel & Smith 1991). The open source spectral-element software package SPECFEM3D used for this paper is freely available for download via the Computational Infrastructure for Geodynamics (geodynamics.org). QL is supported by the Discovery Grants of the Natural Sciences and Engineering Research Council of Canada (NSERC) and the University of Toronto Startup Fund. JT acknowledges support by the National Science Foundation under grant EAR-0711177. The authors thank Carl Tape for providing updated 3-D southern California model CVMH6.2. Finally, we thank Editor Wolfgang Friederich, Yann Capdeville and an anonymous reviewer for helpful comments which improved the manuscript.|
|Subject Keywords:||Inverse theory; Earthquake dynamics; Earthquake source observations; Computational seismology; Theoretical seismology|
|Official Citation:||Kim, Y., Liu, Q. and Tromp, J. (2011), Adjoint centroid-moment tensor inversions. Geophysical Journal International, 186: 264–278. doi: 10.1111/j.1365-246X.2011.05027.x|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||08 Aug 2011 20:34|
|Last Modified:||08 Aug 2011 20:34|
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