Microseismicity along Xiaojiang Fault Zone (China) and the
Characterization of Interseismic Fault Behavior
Abstract
The Xiaojiang Fault (XJF) Zone locates in the southeastern of Tibetan
Plateau and defines the boundary between the South China and
Sichuan-Yunnan blocks. Historical large earthquakes were hosted on the
XJF, though its seismic hazard in the near future is under debate. In
this study, we utilize portable broad-band seismic network to unravel
the microseismic activities along XJF, and to further investigate the
fault structures and their properties. Adopting PALM, a newly developed
earthquake detection algorithm, we obtained ~13,000
relocated events. The micro-seismicity reveals widespread off-fault
structures showing conjugate geometry, while the major faults present
low seismicity. The fault branches conjugate to the main-fault present
intensive microseismicity, which hosts repeating events and presents
high b-value. Regional GPS stations reflect slips are mostly
concentrated along the XJF, while the slip rate on off-fault branches
correlates with seismic activities on these structures. Combining with
other recent seismological and magnetotellurics evidences, we suggest a
low strength on these off-fault structures, which may partially release
tectonic stress loading and serve as a barrier for future big
earthquakes. On the XJF, the microseismic events are clustered on the
fault junctions with low b-value. A special set of clusters between 25°N
to 25.5°N show an along-strike variation of depth from 10 to 25-km,
imaging the boundary between creeping and locked fault portions. We
revisit the seismic hazard problem of XJF, and conclude that XJF is at
the late stage of inter-seismic period.