Characteristics of the crustal structure and hypocentral tectonics in the epicentral area of Nan’ao earthquake (M7.5), the northeastern South China Sea

Abstract

1918 Nan'ao earthquake (M7.5) occurred in the northeast coastal areas of Guangdong Province. With the seismogeological survey of the epicentral area and history materials analyses, the earthquake epicenter was estimated to locate in the intersection part of the Binhai fault zone (Littoral) and Huanggangshui fault, which strikes NEE and NW, respectively. The activities of the NEE-striking thrust fault and NW-striking extensional fault that were attributed to 1918 Nan'ao earthquake occurred in the Dongshan Island of the epicentral area; they reflected the focal stress field with compression in NW-SE direction and extension in NE-SW direction. The isoseismal contour of seismic intensity X shows a shape of 'X' composed of two mutually overlapping ellipses with two axes striking NEE and NW, respectively, and such shape implies that the occurrence of this earthquake is controlled by a pair of conjugate seismotectonic faults constituted by the NEE-striking Binhai fault zone and the NW-striking Huanggangshui fault. The Binhai fault zone is a dominant seismogenic structure, and the NW-striking Huanggangshui fault is the subdominant one. The onshoreoffshore deep seismic profile that crossed the epicentral area and was perpendicular to the strike of the Binhai fault zone was obtained. According to the analyses of the seismic data, the Binhai fault zone is defined as a low velocity zone with SE dip-slip in the crustal structure section. The Binhai fault zone is a boundary fault between the South China subplate and South China Sea subplate. The crust structure on the northwest side of Binhai fault zone is a normal continental crust with a thickness of 30 km, and the one on the southeast side of the fault zone is a thinning continental crust with a thickness of 25-28 km. The Binhai fault zone is an important seismogenic fault and also is an earthquake-controlling fault. The intersection part between the Binhai fault zone and the low velocity zone of upper crust is advantageous to stress concentration and strain energy accumulation, and presents the deep dynamic conditions for the earthquake's pregnancy and occurrence.

A Multimodel Framework for Quantifying Flow and Advective Transport Controlled by Earthquake-Induced Canister Failures in a Reference Case for Radioactive Waste Geological Disposal

“…Based on the assumption and the study of Shimazaki (1986) [33], the maximum magnitude for the diffuse seismicity was specified as 6.5. This maximum magnitude of 6.5 is consistent with the observed seismic data within this region after eliminating events related to the Binhai fault [34]. Additionally, the seismicity rate of diffuse seismicity is derived based on the truncated exponential model [35].…”

Stretching characteristics and its dynamic significance of the northern continental margin of South China Sea

“…Yao et al [8,9] proposed that the crustal structure changes obviously from South China to shelf area when he researched on the 3D crustal structure on the northern continental margin of the South China Sea, he believed that crustal thickness of Chaoshan area is about 30 km. Xu et al [10] proposed that the crust in north of the offshore fault zone is in normal thickness and thinned to the south of the offshore fault zone. He suggested that the crustal thickness of South China is about 35 km through speed structure calculation.…”

Seismic imaging of a mid-crustal low-velocity layer beneath the northern coast of the South China Sea and its tectonic implications

“…Through numerical simulation, Li et al, (2019) argues that LVLs could determine the width of the hyper-extended crust in the northern margin of the South China Sea (SCS). The LVLs may also be responsible for the present-day seismicity and historical earthquakes by providing an unstable crustal structure (Zou, 1998;Xu et al, 2006). Yet, due to limited coverage of the former 2D active source J o u r n a l P r e -p r o o f seismic experiments (Figure 1), the distribution of the LVLs in the northern coast of the SCS is not clear.…”