Poster #082, Seismology

Weak Off-fault Structures Revealed by Microseismicity along Xiaojiang Fault Zone (China) and Their Implications for Seismic Hazard Assessment

Yijian ZHOU, Shiyong ZHOU, PKU Yue, Li Zhao, Zhousheng YANG, & Yuan YAO
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Poster Presentation

2020 SCEC Annual Meeting, Poster #082, SCEC Contribution #10522
The Xiaojiang Fault Zone (XJF) is located in the southeastern margin of the Tibetan Plateau, which defines the boundary between the South China and Sichuan-Yunnan blocks. Seismic hazard assessment of XJF is of great scientific and societal importance due to frequent occurrence of destructive earthquakes. In this study, we utilize broadband seismic records from densely deployed regional networks to unravel the spatial and temporal pattern of microseismicity, and use the catalog then infer fault structures around XJF. We developed a waveform-based automatic microseismicity detection and location algorithm (WAMDLA) and obtain a catalog of more than 13,000 well located microseismic events. The m...icroseismicity reveals widespread off-fault structures along XJF. Micro-seismicity near the main fault are only concentrated near its junction with off-fault structure. To investigate the difference in stress state and slip behavior between the main fault and off-fault structures, we further map the b-value and identify repeating earthquakes. These results show that the off-fault structures are characterized by high level of microseismicity and high b-value, and are able to generate repeaters. Because most micro-seismicity occurred on off-fault structures, the associated b-values is not necessarily related to the stress status of the main fault. To assess the magnitude potential, we take b-value of on fault clusters as a reference, and find that the relative b-value on XJF is lower than its northern counterparts, i.e. the Anninghe-Zemuhe Fault (AZF) and Xianshuihe Fault (XSHF). This agrees with the relative moment deficit values of these three faults estimated by geodetic method: M7.2, M7.4, and M7.6 for XSHF, AZH, and XJF, respectively. In time predictability, a recurrence interval of 300 year for M7 event is provided by paleoseismic studies. These evidences infer the XJF has a high potential for a M>7 earthquake in the near future.
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