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Toward automated directivity estimates in earthquake moment tensor inversion

Huang, Hsin-Hua and Aso, Naofumi and Tsai, Victor C. (2017) Toward automated directivity estimates in earthquake moment tensor inversion. Geophysical Journal International, 211 (2). pp. 1062-1076. ISSN 0956-540X. doi:10.1093/gji/ggx354.

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Rapid estimates of earthquake rupture properties are useful for both scientific characterization of earthquakes and emergency response to earthquake hazards. Rupture directivity is a particularly important property to constrain since seismic waves radiated in the direction of rupture can be greatly amplified, and even moderate magnitude earthquakes can sometimes cause serious damage. Knowing the directivity of earthquakes is important for ground shaking prediction and hazard mitigation, and is also useful for discriminating which nodal plane corresponds to the actual fault plane particularly when the event lacks aftershocks or outcropped fault traces. Here, we propose a 3-D multiple-time-window directivity inversion method through direct waveform fitting, with source time functions stretched for each station according to a given directivity. By grid searching for the directivity vector in 3-D space, this method determines not only horizontal but vertical directivity components, provides uncertainty estimates, and has the potential to be automated in real time. Synthetic tests show that the method is stable with respect to noise, picking errors, and site amplification, and is less sensitive to station coverage than other methods. Horizontal directivity can be properly recovered with a minimum azimuthal station coverage of 180°, whereas vertical directivity requires better coverage to resolve. We apply the new method to the M_w 6.0 Nantou, Taiwan earthquake, M_w 7.0 Kumamoto, Japan earthquake, and M_w 4.7 San Jacinto fault trifurcation (SJFT) earthquake in southern California. For the Nantou earthquake, we corroborate previous findings that the earthquake occurred on a shallow east-dipping fault plane rather than a west-dipping one. For the Kumamoto and SJFT earthquakes, the directivity results show good agreement with previous studies and demonstrate that the method captures the general rupture characteristics of large earthquakes involving multiple fault ruptures and applies to earthquakes with magnitudes as small as M_w 4.7.

Item Type:Article
Related URLs:
URLURL TypeDescription
Huang, Hsin-Hua0000-0002-1115-2427
Aso, Naofumi0000-0001-6255-7494
Tsai, Victor C.0000-0003-1809-6672
Additional Information:© 2017 The Authors. Published by Oxford University Press on behalf of The Royal Astronomical Society. Accepted 2017 August 18. Received 2017 July 13; in original form 2017 April 20. Published: 19 August 2017. We thank Zachary Ross, Lingling Ye, and Zhongwen Zhan for helpful discussion. We also thank Carl Tape and an anonymous reviewer for their constructive comments. The seismic data used in this study were obtained from the Broadband Array in Taiwan for Seismology (IESAS 1996), National Research Institute for Earth Science and Disaster Resilience (F-net), and Southern California Earthquake Data Center (SCEDC 2013). This work was partially supported by National Science Foundation grant EAR-1453263 and Ministry of Science and Technology grant 105-2116-M-001-026-MY2. Naofumi Aso was a Japan Society for the Promotion of Science (JSPS) Overseas Research Fellow (2015-146).
Group:Seismological Laboratory
Funding AgencyGrant Number
Ministry of Science and Technology (Taipei)105-2116-M-001-026-MY2
Japan Society for the Promotion of Science (JSPS)2015-146
Subject Keywords:Earthquake ground motions; Earthquake source observations; Wave propagation
Issue or Number:2
Record Number:CaltechAUTHORS:20171026-083324515
Persistent URL:
Official Citation:Hsin-Hua Huang, Naofumi Aso, Victor C. Tsai; Toward automated directivity estimates in earthquake moment tensor inversion, Geophysical Journal International, Volume 211, Issue 2, 1 November 2017, Pages 1062–1076,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:82693
Deposited By: Tony Diaz
Deposited On:26 Oct 2017 16:04
Last Modified:15 Nov 2021 19:52

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