Lateral resolution analysis of deep crustal sounding: A case study on the data from ocean bottom seismometers in the northern South China Sea
深地震探测的分辨率分析——以南海北部OBS数据为例

Deep seismic sounding surveys in the past two decades show obvious crustal structure changes both across and along the northern margin of the South China Sea. In the surveys, some very closely spaced survey lines displayed remarkable differences in crustal structure. To find the reasons for the differences and to analyze the reliability of crustal structure, ocean bottom seismometer (OBS) data from the west and east sides of the Dongsha Islands were reprocessed and inverted with tomography technique. The routine processing and inversion procedures include clock correction, position correction, finite-difference ray-tracing-based tomography, checkerboard test and comparison of the inverted crustal model with initial models. As a key step, we analyzed the lateral velocity resolution and smoothed out the short wavelength velocity variation which maybe most probably artifacts in the final velocity models. Resolution test results show that the lateral resolution declines rapidly with depth. Within the depth range 0~8 km, the lateral resolution is 10 km; as to the depth of 8~17 km, the lateral resolution is 10~40 km; for the lowest part, 17~33 km, the lateral resolution is 40~80 km. With such a resolution check to a previous experiment, a previously inferred 6 km-wide deep fault zone that extends downward to the Moho interface in the coastal South China area is proved to be impossible to be imaged clearly.