Spatiotemporal Patterns of the 2 April 2024 Hualien Earthquake Sequence and Finite-Fault Solutions of Significant Aftershocks

ABSTRACT The 2024 Mw 7.4 Hualien earthquake displayed a complex rupture process and an intricate aftershock (AF) sequence. In this study, we present a comprehensive analysis of the earthquake sequence, including finite-fault solutions for significant AFs. Using data from a dense temporary seismic network combined with automated phase-picking and earthquake location algorithms, we delineate the spatiotemporal evolution of the earthquake sequence. Using the Density-Based Spatial Clustering of Applications with Noise clustering algorithm, we group the seismicity into distinct clusters and identify two primary AF clusters. The first cluster is concentrated around the mainshock asperity, predominantly to the north, consistent with the northward rupture directivity observed in the mainshock. The second cluster, interpreted as a triggered swarm, began on 22 April and is localized within a confined shallow area to the south. The HypoDD catalog reveals a spatial pattern largely associated with significant AFs (ML>5.8), for which distributions are used to determine the corresponding fault planes based on moment tensor solutions. The results exhibit a clear spatial segmentation: whereas AFs to the north predominantly rupture on steeply east-dipping fault planes, those to the south, including the swarm events, rupture along a shallowly west-dipping plane. Finally, we revisit and assess prior investigations into the mainshock kinematics, drawing on insights from the spatiotemporal evolution of the AF sequence and the asperity distribution associated with significant AFs.