P-wave velocity structure of the Sulu orogenic belt in the Yellow Sea, East China: Evidence from wide-angle ocean-bottom seismograph data

The Sulu orogenic belt, formed by the collision between Sino-Korean and South China blocks, has important geological implications due to its unique tectonic setting. To understand the deep crustal structure of the extension of the Sulu orogenic belt in the Yellow Sea, we presented a 220-km long active-source ocean-bottom seismometer wide-angle reflection/refraction profile across the Yellow Sea. The obtained P-wave velocity structure exhibits significant horizontal and vertical variations. The middle and upper crustal regions of the north beneath the survey line exhibit a higher velocity and larger thickness than those of the south, whereas the opposite is the case with the lower crust. The lower crustal high-velocity zone in the Northern Depression of the South Yellow Sea Basin is a manifestation of the mantle material upwelling and accretion to the lower crust. Magmatic intrusions occurred along the faults and formed a high-velocity zone in the middle and upper crusts. Due to undulating Moho interface and varying crustal velocities, the Qingdao-Rongcheng fault is identified as a fault in the Sulu orogenic belt without the significance of tectonic zoning. This study shows that the Sino-Korean Block, Sulu orogenic belt and South China Block are bounded by the Jimo-Muping faults (an extension to the sea), Qianliyan fault and deep fault of the South Yellow Sea. Furthermore, the Sulu orogenic belt may have been formed by the northward subduction of the South China Block beneath the Sino-Korean Block during the Indosinian orogeny to the east of the Shandong Peninsula.