Scholarlink

<p>Off-fault seismicity, occurring away from primary fault traces, plays a crucial role in crustal deformation and seismic hazard assessment but remains poorly resolved in structurally complex regions. The central southwestern boundary of the Sichuan-Yunnan Block is an area of high seismicity, where numerous moderate earthquakes (e.g., the 2013 <i>M</i><sub>S</sub> 5.5 Eryuan, 2016 <i>M</i><sub>S</sub> 5.0 Yunlong, and 2017 <i>M</i><sub>S</sub> 5.1 Yangbi earthquakes) have occurred away from major mapped faults, highlighting the need to characterize off-fault deformation. In this study, using a dense array of 200 seismometers deployed between January and May 2021, we precisely relocated 13,005 events and determined 432 focal mechanisms, revealing widespread off-fault seismicity across the study area and contrasting seismicity patterns on either side of the Weixi-Qiaohou-Weishan Fault (WQWF). The clustered off-fault seismicity west of the WQWF aligns with recent <i>M</i>⩾5 earthquakes. The 2013 Eryuan and 2017 Yangbi earthquakes occurred on a normal fault and an intersecting strike-slip fault, respectively, and the transition from normal to strike-slip faulting during the 2013 Eryuan aftershock sequence indicates dynamic fault interactions. The 2016 Yunlong earthquake ruptured a geometrically complex fault zone with along-strike variations. In contrast, seismicity east of the WQWF is diffusely distributed, reflecting highly fragmented crustal structures and a complex fault system. Despite these structural differences, focal mechanisms on both sides of the WQWF are consistent with the regional NNW–SSE compressional stress regime. Moreover, the temporally migrating earthquake swarms, persistent activity, and depth concentration of off-fault earthquakes imply a significant role of hydrothermal activity and crustal rheology, supported by low-resistivity anomalies from magnetotelluric observations and low-velocity anomalies from seismic tomography. These results enhance our understanding of off-fault earthquake mechanisms, fault interactions, and regional stress evolution, with implications for seismic hazard assessment in northwestern Yunnan and other tectonically complex regions.</p>

错误：搜索内容不能为空，请输入英文关键词
错误：关键词超出字数限制，请精简
高级检索

Abundant off-fault seismicity along the central southwestern boundary of the Sichuan-Yunnan Block

  • 期刊论文

  • 发表日期：

    2026年7月20日

查看全文
  • Xianwei Zeng,
  • Chunquan Yu,
  • Rao Gu,
  • Gongheng Zhang,
  • Qiang Yao,
  • Qianfeng Zhang

摘要

Off-fault seismicity, occurring away from primary fault traces, plays a crucial role in crustal deformation and seismic hazard assessment but remains poorly resolved in structurally complex regions. The central southwestern boundary of the Sichuan-Yunnan Block is an area of high seismicity, where numerous moderate earthquakes (e.g., the 2013 MS 5.5 Eryuan, 2016 MS 5.0 Yunlong, and 2017 MS 5.1 Yangbi earthquakes) have occurred away from major mapped faults, highlighting the need to characterize off-fault deformation. In this study, using a dense array of 200 seismometers deployed between January and May 2021, we precisely relocated 13,005 events and determined 432 focal mechanisms, revealing widespread off-fault seismicity across the study area and contrasting seismicity patterns on either side of the Weixi-Qiaohou-Weishan Fault (WQWF). The clustered off-fault seismicity west of the WQWF aligns with recent M⩾5 earthquakes. The 2013 Eryuan and 2017 Yangbi earthquakes occurred on a normal fault and an intersecting strike-slip fault, respectively, and the transition from normal to strike-slip faulting during the 2013 Eryuan aftershock sequence indicates dynamic fault interactions. The 2016 Yunlong earthquake ruptured a geometrically complex fault zone with along-strike variations. In contrast, seismicity east of the WQWF is diffusely distributed, reflecting highly fragmented crustal structures and a complex fault system. Despite these structural differences, focal mechanisms on both sides of the WQWF are consistent with the regional NNW–SSE compressional stress regime. Moreover, the temporally migrating earthquake swarms, persistent activity, and depth concentration of off-fault earthquakes imply a significant role of hydrothermal activity and crustal rheology, supported by low-resistivity anomalies from magnetotelluric observations and low-velocity anomalies from seismic tomography. These results enhance our understanding of off-fault earthquake mechanisms, fault interactions, and regional stress evolution, with implications for seismic hazard assessment in northwestern Yunnan and other tectonically complex regions.