Revisiting the 2010 Jiashian and 2016 Meinong Earthquakes in Taiwan: Geodetic Evidence for Shared Eastward-Dipping Ramp Fault

ABSTRACT Coseismic surface deformation from the 4 March 2010 Mw 6.3 Jiashian and the 5 February 2016 Mw 6.4 Meinong earthquakes in southern Taiwan was measured by Global Navigation Satellite System for both events and Interferometric Synthetic Aperture Radar for the 2016 event. Several coseismic slip models for both events have been published, with those models developed using different estimation strategies and based on constrained a priori model parameter ranges. Here, we use a common estimation strategy to revisit coseismic slip models of the two earthquakes based on the geodetic observations, without constraining model parameters a priori. We employ a graph-guided fused LASSO inversion within a two-step, integrated estimation approach to infer fault geometry parameters and image coseismic slip. Our coseismic model for the 2010 Jiashian earthquake aligns well with the focal mechanisms and published models. In contrast, we find that the geodetic data suggest that the slip surface of the 2016 Meinong earthquake is more northerly oriented and shallower, with a more thrust slip component, than what is indicated by the focal mechanisms or previous coseismic slip models. We argue that constraints placed on fault geometry, particularly fault depth, biased the previous coseismic slip models. The similarity in fault strikes of our final coseismic models, combined with the proximity of the inferred fault-slip regions, indicates that these two earthquakes likely occurred on a single-fault structure with increasing dip to the east, evocative of a midcrustal flat–ramp–flat fault structure.