Shallow fault rupture of the Milun Fault in the 2018 M w 6.4 Hualien earthquake: A high-resolution approach from optical correlation of Pléiades satellite imagery

Yu Ting Kuo, Yu Wang, James Hollingsworth, Shao Yi Huang, Ray Y. Chuang, Chih Heng Lu, Yi Chun Hsu, Hsin Tung, Jiun Yee Yen, Chung Pai Chang

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Abstract

We use high-resolution Pléiades optical satellite imagery to study the distribution and magnitude of fault slip along the Milun fault surface rupture, which broke during the 2018 Hualien earthquake (M w 6.4) in eastern Taiwan. Correlation of pre- and postearthquake stereo Pléiades images reveals detailed 3D surface displacements along the 8-km-long Milun fault, with maximum ∼1 m left-lateral offsets across the fault. Along the northern section of the Milun fault, our correlation results indicate a localized deformation zone, with offset values slightly larger than the maximum offsets reported in the field (∼77 cm). To the south, the left-lateral offsets become increasingly distributed, producing arctangent shapes in displacement profiles crossing the fault. In places, the deformation zone reaches widths of 200 m and can be explained by a shallow east-dipping fault rupture extending from 2 to 3 km depth to 70–120 m below the surface. A very shallow coseismic rupture on the Milun fault is consistent with a shallow locking depth interpreted from previous geodetic analyses from the interseismic period. Despite a few highly discontinuous and irregular surface ruptures reported along the southern section of the fault, our results suggest the main fault slip (up to 1 m) stopped at very shallow depths below the surface, in which ∼60% of the deformation may be accommodated as off-fault deformation (OFD). In this upper ∼100 m of the crust, OFD may be promoted by a significant change in material strength, as the fault crosses from bedrock and/or consolidated sediments into weaker, water-rich, poorly consolidated alluvial sediments.

Original languageEnglish
Pages (from-to)97-107
Number of pages11
JournalSeismological Research Letters
Volume90
Issue number1
DOIs
StatePublished - 1 Feb 2019

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