SinoProbe deep seismic reflection profiling across the Sichuan basin

Sichuan basin lied in northwestern Yangtze block,is the late Mesozoic-Cenozoic foreland basin. Distribution of Marginal orogen around the basin margin is a prominent landscape feature. The basin affected by the marginal mountain thrusting toward the basin, was involved in numbers of times and multi-boundary structure deformation. So the Sichuan basin provides an ideal area for studying the basin-range coupling and tectonic superposition and complex relationship of multi-border.In order to obtain the deep fine structure, CAGS completed 200km long deep reflection profile across the Sichuan basin in 2009, with funding from project “SINOPROBE-02” and the China NSF (40830316). The profile lines in the gentle tectonic zone from the central Sichuan basin to the northwestern basin, extends northward the Longmen mountain foreland belt and stops southward the Huaying mountain. Three kinds of explosive-source of 4-6kg,40kg and 100kg are used for high resolution data. Data acquisition focused on experiments of 40kg and 100kg charge. Acquisition parameters are given in Table 1.Based on analysis of raw data and test of the method and parameters,we determined suitable processing methods and flow, and received preliminary section. The section shows structure of the crust and upper mantle cover in the basin and two distinct interfaces appear at 6s and 13.8s (TWT).1)In the upper crust from 0s to 6s,sets of nearly level continuous strong reflection waves appear,which are typical reflection characteristics of sedimentary strata.The sedimentary strata thicken to the northwest at the front of the Longmen Mountain,and gradually thin to the southeast.2) Reflection characteristics of the lower crust between 6s and 13.8s are different from that of the sedimentary strata. Nearly level strong reflection characteristics in the west and the arc-shaped reflection characteristics in the east, indicated that tectonic deformation are more intense under eastern than western Sichuan.3) Moho reflection characteristics in the western and eastern basin are different.The section showed the west of basin is mainly characteristic of nearly level Moho reflections at 13.8 s.Moho deepen before the fault zone of Huaying Mountain and occur dislocation. Lower crust and Moho reflection feature of the basin reveals that the Sichuan basin is not the same rigid block, the craton basement of the Sichuan basin was composed of east and west part,and rigidity of the western are stronger than eastern.The subduction and old collision structure were buried under Huaying Mountain fault.Table 1 data acquisition parameters