2. Geological setting
The ECSSB was developed on the broad continental shelf of the southeast
Eurasian continental segment; to its west is the Zhemin upwarping folded
zone, and it is separated from the Okinawa Trough, Ryukyu island arc,
and Ryukyu Trench by the Diaoyu Island upwarping folded zone in the
east. The north is bordered by a ray from the Yangtze River to Jizhou
Island, and the north is bordered by a ray from the Guangdong to Taiwan
provinces. The basin is approximately 1,400 km long from north to south
and 250–300 km wide from east to west, with a total area of
approximately 26.7 × 104 km2.
Influenced by the subduction of the Philippine plate to the Eurasia
plate during the Eocene to Oligocene period, the ECSSB is in a state of
back-arc spreading. Simultaneously, seismic data showed apparent
extension fracture activity near the NE direction, which resulted in the
formation of a structural framework with nearly east-west zoning and a
nearly north-south block in the plane. In addition, the ECSSB can be
divided into three secondary building units:
western
geotectogene, central uplift belt, and eastern geotectogene from west to
east. Among them, the eastern geotectogene can be classified into
Diaobei Sag, Xihu Sag, and Fujiang Sag from south to north (Zhu et al.,
2012; Ju et al., 2016; Chen et al., 2017; Hao et al., 2018; Zhu et al.,
2019; Su et al., 2020) (Fig. 1).