Deep-learning-based construction of a high-resolution earthquake catalog for the 2023 Jishishan [Formula: see...

On 18 December 2023, a [Formula: see text] 6.2 earthquake struck Jishishan, Gansu Province, northwestern China. The resulting aftershock sequence provides an important opportunity to investigate the seismogenic structure and postseismic activity in the source region. In this study, we analyzed continuous waveform data recorded by 31 seismic stations within 250 km of the epicenter from 19 to 31 December 2023 to construct a high-resolution earthquake catalog. Seismic phases were automatically detected using the deep-learning phase picker PhaseNet, followed by phase association and preliminary location with the REAL algorithm. Absolute location were then refined using VELEST, and relative relocations were performed using HypoDD. The resulting catalog contains more than 3200 earthquakes, more than three times the number reported in the routine catalog of the China Earthquake Networks Center (CENC), substantially improving the completeness of the aftershock sequence. The relocated events are mainly concentrated at depths of 5-16 km within an aftershock zone approximately 18 km in length and 13 km in width, defining two major aftershock clusters. Fault-structure analysis indicates that the aftershocks exhibit a clear NW-SE alignment and are primarily concentrated between the northern and southern marginal faults of the Lajishan fault zone. These observations suggest that the mainshock likely ruptured a secondary or previously unmapped fault located between the two major mapped faults, whereas the subsequent sequence reflects a complex damage zone driven by stress redistribution. The high-resolution earthquake catalog presented here provides new constraints on the detailed structure of the aftershock sequence and contributes to a better understanding of the seismogenic setting of the region.