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Multichannel seismic data on the continental shelf have been used to image the rift-related shallow structural units of the Pearl River Mouth Basin across the northwestern margin of the South China Sea. The Hainan Uplift, Zhu 3 Depression and Shenhu-Ansha Uplift zones are bounded by normal faults or listric-normal faults, which suggest lithospheric extension on the continental shelf. Graben structures 10-15 km wide are imaged on the Wanshan Uplift and Northern Fault Terrace from the reflection data. The thinned continental crust and anomaly rift-related crust in the depression zone and the transitional crust indicated by the wide-angle OBS velocity model dominate the crustal structure of the continental shelf in the continental margin of the South China Sea. The different total crustal stretching factors in different shallow structural units suggest that non-uniform horizontal stretching controls the crustal thinning. The total crustal stretching factor is ca. 1.4-1.6 at the coast area, ca. 1.67-1.8 in the rift-depression zone and ca. 1.7-1.75 in the transitional crustal domain. Pure-shear crustal thinning controls the crustal extension in the rift-depression zone. The high heat flow anomaly in the vicinity of the seismic lines and anomaly rift-depression velocity structure suggest that the crustal thinning on the continental shelf of the South China Sea can be produced by lateral mantle flow within the hotter regional lithospheric background. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Cenozoic tectonic evolution of the South China Sea is reflected in diverse tectonic processes including continental rifting, seafloor spreading, subduction, terrane collision and strike–slip fault movement. A continent–ocean transition zone in the northern South China Sea caused by the lithospheric extension when the continent underwent break-up, rifting and later seafloor spreading, is clearly imaged in the multi-channel seismic data presented in this study. The morphological units of the continent–ocean transition zone are the rift-depression, the volcanic zone and tilted fault blocks. The volcanic zone represents a highest extension zone within the continent–ocean transition zone and is mainly distributed in the southern slope uplift zone along the northern passive margin of the South China Sea. The large listric-normal faults bounding the Dongsha Rise and Baiyun Sag are evidenced in the seismic image. The passive margin in the northern South China Sea underwent the wide-rift to narrow-rift process in the transition zone as inferred from the relation between the surface heat flow and initial rifted crustal thickness. The continent–ocean transition zone in the continental margin of the South China Sea is consistent with high heat flow zone (average 90 mW.m − 2 ) observed in the previous heat flow measurements and at ODP Site 1148, and is manifested in a sharp change of the P-wave velocity. The rifted margin of the South China Sea is a non-typical magma poor passive margin or an intermediary form between the Iberian-type non-volcanic and the Greenland-type volcanic margin compared to the world's typical passive margins. [ABSTRACT FROM AUTHOR]

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 onshore-offshore 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. [ABSTRACT FROM AUTHOR]