Preliminary Investigation on the Seismotectonics of the Southeastern China Using Relocated Microseismicity

Monday, 15 December 2014
Ailan Zhu1, Xiwei Xu2, Ye Ren1, Dongjun Sun1 and Peng Wang1, (1)Earthquake Administration of Shanghai Municipality, Shanghai, China, (2)Institute of Geology, CEA, Beijing, China
The southeastern China in the mainland is characterized by moderate seismicity, which belongs to the southern China block. Few studies have been carried on to the seismotectonics for this region since most active faults are buried under the thick Quaternary sediments with low to moderately historical earthquake activity. However,many large earthquakes in the world that occurred at the unexpected tectonic regime without surface or known active faulting and large historic earthquake documentation alarm us that it should pay more attention to this region. In this paper, we investigate the buried active faults and the potential seismic hazard using the relocated background seismicity. The earthquakes occurred in the region from 106°E to 122°E and from 22°N to 35°N between 1990 and 2014 are relocated by using the doubble difference algorithm. In general, most earthqukes concentrate to the boundary regions of the southern China block, while distribute very scarcely in the central area. The relocated earthquakes mainly distribute to the depth between 0 and 15km in the west from 106°to 115°, while to 0-25km in the east from 115°to 122°,which indicates that the seismogenic zone may become deeper from west to the southeastern coast region. It is observed that many relocated clusters organized obviously to linear patterns, which may imply to the existence of the buried active faults that were not found ever before. The inferred buried faults mainly strike to northwest or northeast. The geometry parameters of the faults are obtained from the cross sectional profiles.In some regions, several seimic clusters align to a belt that may infer the existence of a large seismic zone, even stretching to more than 300km long, which may possess great potential seismic hazard we might not realize.