APPLICATION OF SEISMIC FIRST ARRIVAL VELOCITY OF TOMOGRAPHY IMAGING TO LAOSHAN UPLIFT OF THE SOUTH YELLOW SEA BASIN

The Laoshan Uplift is located in the middle of the South Yellow Sea Basin. There is large difference of impedance between the Cenozoic and the Mesozoic-Paleozoic. It is, therefore, inferred that there should be a high-speed shield layer at the bottom of the Cenozoic, and the Meso-Paleozoic has experienced complicated tectonic deformation, and resulted in a low signal/noise ratio and poor seismic images. Therefore, it is difficult to acquire the accurate velocity of the Meso-Paleozoic through conventional picking up of stacking velocity in seismic processing, that has brought great difficulties to the velocity modeling of the prestack time migration and prestack depth migration. Qingdao Institute of Marine Geology (QIMG) has collected great amount of seismic data of large-capacity source and long cable from the Laoshan Uplift of the South Yellow Sea Basin, obtained the first-arrival wave from Meso-Paleozoic strata. This paper applies the first arrival wave tomography to inverse the Meso-Paleozoic velocity in the high-speed shield layer, mainly through picking up the first arrival-time and building up a velocity model by continuous iterative inversion, finally get the result velocity model. The result shows that velocity changes severely in lateral direction beneath the high-speed shield layer. The low-velocity layer may indicate clastic rocks with a velocity ranging 3 500-4 000 m/s, and the high-velocity layer indicate carbonate rocks with a higher velocity within the range of 5 100-5 500 m/s.