HIGH RESOLUTION VELOCITY STRUCTURE OF THE NORTH CHINA CRATON BASEMENT BY BLASTING SEISMIC WAVE—RESULTS FROM DAFENG–BAOTOU REFRACTION PROFILE

Abstract

Due to the high density of observation points and shots, we obtained the 21-shot seismic data with high signal-to-noise ratio along the 1334 km long Dafeng-Baotou profile. On the basis of the analysis of the Pg wave phase characteristics, we processed the data by the inversion method and constructed the fine structure of the basement, revealing the discrepancy of basement structure in different tectonic blocks. The basement depth of Northern Jiangsu basin is 4.5∼9.0 km and that of Jiangsu-Shandong uplift is 1.5∼2.0 km. Strong fluctuations of the burial depth and velocity structure may be considered as the seismologic manifestation of the collision and extrusion between North China and the Yangtze plate. The basement of Western Shandong uplift area shows the feature of shallow burial depth, high speed and stable structure, while the Pg wave characteristics in the North China basin are lagged travel time, low apparent velocity, basement depth from 7.0 km to 10.0 km, and the local fluctuations in the velocity structure and basement interface. Lots of phenomena above reveal that this area is a large-scale basement depression zone with thick Cenozoic sediment. Moreover, in different tectonic units of the basin, the tectonic pattern of local basement patch and coexistence of depression and uplift shows obvious tectonic characteristics, such as remarkable Cenozoic sedimentary activities, significant velocity and thickness changes and the unstable structure. Taihang mountain piedmont fault and Liaolan fault are significant seismologic features. On both sides of these two faults, the velocity structure shows intensive lateral heterogeneity, and the basement interfaces collapse as cliff. This study reveals that the Taihang mountain piedmont fault is an important tectonic zone in North China. Its complexity is not only reflected in different landforms and strata on its two sides, but also reflected in the significant differences among the basement depth, velocity structure, the crust and even the mantle lithospheric structures. To the east of Taihang mountain, the important symbol is large scale crustal and lithospheric thinning, which result in the obvious differences and strong lateral heterogeneity of the basement structure, the crust and even the lithosphere structures between the western and eastern North China Craton destruction