Seismological features of the littoral fault zone in the Pearl River Estuary

The data collected from an onshore-offshore seismic experiment off the Pearl River Estuary in 2010 reveal existence of the Littoral Fault Zone (LFZ) located about 12 km south of Dan'gan Island, which is about 20 km wide and mainly dips southeast at a high angle. The deposit thickness in the LFZ increases rapidly, which causes the travel time of seismic phase Pg of permanent stations lag obviously at the corresponding position of LFZ. By seismic phase analysis and travel time fitting, a P-wave velocity model is constructed on the both sides and within LFZ from shallow to deep. The modeling results show that the sedimentary layer in the LFZ has a velocity of 1. 8 similar to 3. 5 km/s, and the upper crust has a velocity of 5. 2 similar to 6. 1 km/s, and the lower crust has a velocity of 6. 3 similar to 6. 6 km/s. The Moho depth of the LFZ changes abruptly from 29 km on the landside to 27 km on the seaside. The different seismic velocity structures on the opposite sides of the LFZ certifies that this fault is the boundary between the normal continental crust of South China and the thinned continental crust of the South China Sea. The low velocity layer (LVL, 5. 5 similar to 5. 9 km/s) on the top of lower crust exists in South China and the onshore-offshore transitional area with about 3 km thickness, which is thinning seaward gradually to pinch-out. The LVL is a weak zone in the crust, which links the NEE-striking LFZ and NW-striking fault zone to form the seismogenic structure of the Pearl River Estuary area