Earthquake potential of the Zhaotong and Lianfeng fault zones of the eastern Sichuan-Yunnan border region

The NE-trending Zhaotong and Lianfeng fault zones of the eastern Sichuan-Yunnan border region are poorly studied on earthquake issues. To know whether the two fault zones have seismic potential for strong and major earthquakes, we make a comprehensive study by integrating multidisciplinary data of active tectonics and regional dynamics, distribution of relocated small earthquakes and focal mechanism solutions, historical earthquake rupture-areas, GPS deformation field, modern seismicity and its parameter patterns, etc. Our study shows that the Zhaotong and Lianfeng fault zones are a part of the boundary separating the Sichuan-Yunnan block and the South China block, and also the margin between the active and deformed secondary faulted block of Daliangshan and the relatively stable South China block. Structurally, the fault zones appear as two parallel and southeastward thrusting fault zones with the currently right-lateral strike-slip faulting along with significant thrusting components. Along the Zhaotong fault zone the time without major earthquakes is proved to have been over 1700 years at least, and a seismic gap exists there. The GPS deformation patterns suggest that the Zhaotong and Lianfeng fault zones have locked in different degrees. Also, several areas of low b-values or high stress exist on the Zhaotong fault zone near Ludian and on the southern segment of the Lianfeng fault zone. A locked or highly stressed fault segment of the Zhaotong fault zone between Ludian and Yiliang has been identified from low b-values and lack of current small earthquakes, and the moment magnitude for a maximum potential event on this fault segment is estimated to be about M(w)7. 4. We therefore conclude that mid- to long-term seismic potential for strong or major earthquakes exists on the Zhaotong fault zone. But, the seismic potential of the Lianfeng fault zone still needs to be studied further.