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Moving from 1-D to 3-D velocity model: automated waveform-based earthquake moment tensor inversion in the Los Angeles region

Wang, Xin and Zhan, Zhongwen (2020) Moving from 1-D to 3-D velocity model: automated waveform-based earthquake moment tensor inversion in the Los Angeles region. Geophysical Journal International, 220 (1). pp. 218-234. ISSN 0956-540X. doi:10.1093/gji/ggz435.

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Earthquake focal mechanisms put primary control on the distribution of ground motion, and also bear on the stress state of the crust. Most routine focal mechanism catalogues still use 1-D velocity models in inversions, which may introduce large uncertainties in regions with strong lateral velocity heterogeneities. In this study, we develop an automated waveform-based inversion approach to determine the moment tensors of small-to-medium-sized earthquakes using 3-D velocity models. We apply our approach in the Los Angeles region to produce a new moment tensor catalogue with a completeness of M_L ≥ 3.5. The inversions using the Southern California Earthquake Center Community Velocity Model (3D CVM-S4.26) significantly reduces the moment tensor uncertainties, mainly owing to the accuracy of the 3-D velocity model in predicting both the phases and the amplitudes of the observed seismograms. By comparing the full moment tensor solutions obtained using 1-D and 3-D velocity models, we show that the percentages of non-double-couple components decrease dramatically with the usage of 3-D velocity model, suggesting that large fractions of non-double-couple components from 1-D inversions are artifacts caused by unmodelled 3-D velocity structures. The new catalogue also features more accurate focal depths and moment magnitudes. Our highly accurate, efficient and automatic inversion approach can be expanded in other regions, and can be easily implemented in near real-time system.

Item Type:Article
Related URLs:
URLURL TypeDescription
Wang, Xin0000-0002-6180-0058
Zhan, Zhongwen0000-0002-5586-2607
Additional Information:© 2019 The Author(s). Published by Oxford University Press on behalf of The Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2019 October 2. Received 2019 September 23; in original form 2019 June 14. Published: 07 October 2019. This research is supported by SCEC 2019 award 19011 and Air Force research grant 18C0058. We have used waveforms and parametric data from the Caltech/USGS Southern California Seismic Network (SCSN) (doi: 10.7914/SN/CI) stored at the Southern California Earthquake Data Center (SCEDC, doi:10.7909/C3WD3xH1). The generalized Cut-and-Paste 3-D (gCAP3D) code is downloaded from We thank Robert Graves for providing the 3-D finite-difference code and useful discussions, and Voon Hui Lai for her help in setting up the initial 3-D finite-difference simulations. We thank Egill Hauksson and Jennifer Andrews for useful discussions about the SCEDC catalogue. We are also grateful to Editor Sidao Ni and two anonymous reviewers for suggestions that greatly improved the manuscript. Sac 2000 and GMT (Wessel et al.2013) were used for basic data processing and figure development.
Group:Seismological Laboratory
Funding AgencyGrant Number
Southern California Earthquake Center (SCEC)19011
Air Force Office of Scientific Research (AFOSR)18C0058
Subject Keywords:North America; Waveform inversion; Earthquake source observations; Wave propagation
Issue or Number:1
Record Number:CaltechAUTHORS:20200130-152735699
Persistent URL:
Official Citation:Xin Wang, Zhongwen Zhan, Moving from 1-D to 3-D velocity model: automated waveform-based earthquake moment tensor inversion in the Los Angeles region, Geophysical Journal International, Volume 220, Issue 1, January 2020, Pages 218–234,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101014
Deposited By: Tony Diaz
Deposited On:30 Jan 2020 23:39
Last Modified:16 Nov 2021 17:58

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