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The 2005 Ilan earthquake doublet and seismic crisis in northeastern Taiwan: evidence for dyke intrusion associated with on-land propagation of the Okinawa Trough

Lai, Kuang-Yin and Chen, Yue-Gau and Wu, Yih-Min and Avouac, Jean-Philippe and Kuo, Yu-Ting and Wang, Yu and Chang, Chien-Hsin and Lin, Kuan-Chuan (2009) The 2005 Ilan earthquake doublet and seismic crisis in northeastern Taiwan: evidence for dyke intrusion associated with on-land propagation of the Okinawa Trough. Geophysical Journal International, 179 (2). pp. 678-686. ISSN 0956-540X. doi:10.1111/j.1365-246X.2009.04307.x.

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Northern Taiwan underwent mountain building in the early stage of the Taiwan orogeny but is currently subjected to post-collisional crustal extension. It may be related to gravitational collapse or to the rifting of the Okinawa Trough, which lies offshore northeastern Taiwan. The Ilan Plain, northeastern Taiwan, which is bounded by the normal fault systems and filled up with thick Pliocene–Pleistocene sedimentary sequences, formed under such an extension environment. Over there on 2005 March 5 two earthquakes with about the same magnitude (M_L = 5.9) occurred within 68 s and produced intense aftershocks activity according to the records of Central Weather Bureau Seismic Network of Taiwan. We relocated the earthquake sequence by the three-dimension earthquake location algorithm with the newly published 3-D Vp and Vp/Vs velocity model, and determined the first-polarity focal mechanisms of the earthquake doublet. One major cluster of aftershocks which trends E–W and dips steeply to the south can be identified and picked up as a potential fault plane. The focal mechanisms of the two main shocks are both classified as normal type by first-polarity but strike-slip by centroid moment tensor inversion; however two methods both yield consistent E–W strike. Static coseismic deformation was additionally determined from Global Positioning System (GPS) daily solutions at a set of continuous GPS stations and from strong-motion seismographs. These data show NW–SE extension at high angle to the fault plane, which cannot be explained from a simple strike-slip double-couple mechanism. On the other hand, the small vertical displacements and steep fault plane cannot be explained from a simple normal event as well. We present from elastic dislocation modelling that the geodetic data are best explained by significant component of tensile source with centimetre-scale of opening on a 15-km-long fault extending from 1 to 13 km depth. We therefore interpret the crisis as the result of dyke intrusion at the very tip of the Okinawa Trough, which is reasonably driven by backarc spreading.

Item Type:Article
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URLURL TypeDescription
Chen, Yue-Gau0000-0002-8693-583X
Avouac, Jean-Philippe0000-0002-3060-8442
Wang, Yu0000-0003-3589-9274
Additional Information:© 2009 The Authors. Journal compilation © 2009 RAS. Accepted 2009 June 23. Received 2009 June 17; in original form 2008 December 30. We are grateful to editor, Prof Xiaofei Chen, and three anonymous reviewers for their kind helps and constructive comments. This research is financially supported by the Central Weather Bureau and the National Science Council of the Republic of China under grant nos. NSC 96-2116-M-002-001 and NSC 96-2745-M-002-001.
Group:Caltech Tectonics Observatory, Seismological Laboratory
Funding AgencyGrant Number
Central Weather BureauUNSPECIFIED
National Science Council of the Republic of ChinaNSC 96-2116-M-002-001
National Science Council of the Republic of ChinaNSC 96-2745-M-002-001
Subject Keywords:Seismicity and tectonics; Backarc basin processes; Dynamics: seismotectonics; Neotectonics; Kinematics of crustal and mantle deformation; Crustal structure
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Other Numbering System NameOther Numbering System ID
Caltech Tectonics Observatory101
Issue or Number:2
Record Number:CaltechAUTHORS:20091029-112404757
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:16520
Deposited By: Tony Diaz
Deposited On:02 Nov 2009 19:41
Last Modified:08 Nov 2021 23:27

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