第八届青年地学论坛

Two destructive earthquakes in 1600 and 1918, with magnitudes of 7.0 and 7.5, highlight that the offshore area of East Guangdong is one of the most seismically active regions in the rifted northern margin of the South China Sea (SCS). However, the location and extent of the main active faults in this area remain poorly constrained. Using newly acquired high-resolution multi-channel seismic (MCS) reflection data, we investigate the detailed offshore fault structure of East Guangdong. The interpreted data reveal the location, continuity and geometry of the NEE-strike Littoral Fault Zone (LFZ). The LFZ consists of a series of large basement faults which form a terraced sidewall fault zone and correspond to negative high gravity anomalies. It is distributed roughly parallel to the coastline at a distance about 30-60 km with a fault zone width of about 25-60 km. The fault zone was active during the Cenozoic, and recorded significant intraplate deformation during the continental rifting with fault displacement of kilometer level. As the significant basement changes and the low velocity characteristics derived from wide-angle seismic data, we propose the LFZ to be a lithospheric-scale fault zone separating the northern margin of the SCS from the South China Block. The listric faults in the LFZ control the formation and development of sedimentary basins or depressions. Many active faults were identified near the seafloor, which correspond well to the locations of the recent earthquakes. The NEE-trending LFZ intersected with the NW-trending active faults, resulting in a weak tectonic zone in the crust, which is probably the reason for frequent seismicity and strong earthquakes distribution in this area. Intense Cenozoic magmatism, Middle Miocene in age, was identified in the profile near the Nanpeng Islands. The widely developed fault structures provide pathways for the upward migration of magma. The NW-trending faults may have caused the fault zone to be dislocated and blocked the westward transport of magma.
 

Littoral Fault Zone,multi-channel seismic profile,East Guangdong offshore area,Northern South China Sea,offshore active faults