GEOMETRY AND KINEMATICS OF INTRAPLATE STRIKE-SLIP FAULTS IN GAOSHITI-MOXI AREA, SICHUAN BASIN, SW CHINA

Sichuan Basin is one of the largest oil and gas bearing basins in China. Gaoshiti–Moxi area is located in the south of Central Si-chuan Basin. The 3D seismic data of this area is merged pre-stack time migration data of recent years with a coverage area of 6600 km², bin size of 20 m×20 m, and deep dominant frequency of 28 Hz, which meet the require-ments of fine fault characterization.

1. Geometry characteristics

According to the difference in combination pattern of faults on section, three main structural styles are identified in the study area: steep and erect, flower structure, "Y" and reversed "Y" type faults. Steep and erect faults are the most common in strike-slip faults of the study area. The majority of them are transtensional faults, nearly vertical on section with a dip angle of more than 80°. The strike-slip faults in Gaoshiti–Moxi area mainly take on negative flower structure and half-flower structure composed of a series of concave-up normal faults distributed in the Sinian– Permian strata. "Y" and reversed "Y" types are two kinds of fault styles relatively rich in the study area, and appear as small grabens composed of two normal faults with opposite inclination.

There are three groups of strike-slip faults in the Cambrian in near EW, NW and NE strike respectively. They are in linear distribution. The near EW-trending faults are mainly distributed in Moxi–Longnüsi area in the north, with extension of 110 km along. The whole fault is composed of multiple sec-ondary faults, which are commonly overlap and divergent from west to east. The NE-trending faults are mainly distributed in the southwest of the study area, with poor continuity.

2. Kinematic characteristics

According to the cutting of fault and fold by strike-slip faults and the en-echelon arrangement of secondary faults in the main fault, it is inferred that the strike-slip faults in near EW and NW strikes in Gaoshiti–Moxi area are dextral transtensional strike-slip faults, while those in NE strike are sinistral transtensional strike-slip faults.

The horizontal and vertical displacements of the Paleozoic strike-slip faults in the study area were counted, in which the horizontal displacement was used to analyze the strike-slip strength, and the vertical throw was used to identify the faulting strength. The strike-slip strength of near EW trending faults is the strongest, with the maximum horizontal displacement of 550 m, while the strike-slip strength of the NE trending fault is the weakest. The activity of the Cambrian faults is stronger than the Permian faults.