Complex rupture process of the 2014 Thailand Mw 6.2 earthquake on the conjugate fault system of the Phayao fault zone

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Authors

Tira Tadapansawut, Yagi Yuji, Ryo Okuwaki , Shinji Yamashita, Kousuke Shimizu 

Abstract

The earthquake with a moment magnitude 6.2 that occurred in northern Thailand on 5 May 2014 is the largest recorded in Thailand by modern seismographs; the source is located in the multi-segmented complex fault system of the Phayao fault zone in the northern Thai province of Chiang Rai. This geological setting is appropriate environment for investigating a compound rupture process associated with a geometrically complex fault system in a magnitude-6-class earthquake. To understand in detail the rupture process of the 2014 Thailand earthquake, we elaborate the flexible finite-fault inversion method, used it to invert the globally-observed teleseismic P waveforms, and resolved for the spatiotemporal distribution of both the slip and the fault geometry. The complex rupture process consists of two distinct coseismic slip episodes that evolved along two discontinuous fault planes; these planes coincide with the lineations of the aftershock distribution. The first episode originated at the hypocenter and the rupture propagated south along the north-northeast to south-southwest fault plane. The second episode was triggered at around 5 km north from the epicenter and the rupture propagated along the east-northeast to west-southwest fault plane and terminated at the west end of the source area at 4.5 s hypocentral time. The fault system derived from our finite-fault model suggests geometric complexities including bends. The derived spatiotemporal orientation of the principal stress axis shows different lineations within the two rupture areas and heterogeneity at their edges. This geological setting may have caused the perturbation of the rupture propagation and the triggering of the distinct rupture episodes. Our source model of the 2014 Thailand earthquake suggests that even in the case of small-scale earthquakes, the rupture evolution can be complex when the underlying fault geometry is multiplex.

DOI

https://doi.org/10.31223/X56P7T

Subjects

Earth Sciences, Geology, Geophysics and Seismology, Physical Sciences and Mathematics

Keywords

2014 Thailand earthquake, Conjugate fault, Complex fault geometry

Dates

Published: 2021-07-22 16:51

Last Updated: 2021-07-22 23:51

License

CC BY Attribution 4.0 International

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Conflict of interest statement:
None

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