PALEOSTRESS ESTIMATION BY FAULT KINEMATIC ANALYSIS BASED ON 3D SEISMIC DATA

The project goal is to use seismic data as an input to develop the technique of paleostress field reconstruction. This technique is based on the study of structural maps of seismic horizons with the following identification of the net-slip vectors on the fault surfaces. The proposed technique allows for the following results to be obtained: (1) orientation of the fault surfaces (dip, strike) and net-slip vectors (rake, magnitude) and (2) local stress field (orientation of the main axes of the stress field and shape of the stress ellipsoid). The technique was tested at two study areas with different tectonic stress regimes: Archinsk (West Siberia) and Kuyumba (Siberia).

Available seismic data of the Archinsk area is related to the lower part of sedimentary succession represented by Lower and Middle Jurassic shales and sandstones. In Mesozoic, the N-NW trend of the compression axis was dominant. During formation of the unconformity that separate Paleozoic carbonates and Mesozoic clastic rocks, normal displacements were significant. After that, shallow to moderate dipping of the main compression and tension axes points to predominance of strike-slip tectonics showing that during Mesozoic period there were several stages of fault activity. The results are basically in agreement with available paleoreconstruction models for this area.

The main study object of the Kuyumba area is the Meso- and Neoproterozoic sedimentary succession, in which, fault tectonics and paleostress field are poorly explored. Our study has shown that kinematic characteristics of faults and parameters of the stress field have changed toward the top of succession. Three stages of formation of the faults are revealed: (1) partial inversion of ancient normal faults; (2) the most intensive compression with prevalence of thrust and strike-slip faults at N-NE orientation of the main compression; (3) strike-slip faulting at the W-NW orientation of the main compression. The second and third stages are correlated with the tectonic events, which were taking place during the late Neoproterozoic evolution of the active southwest margin of the Siberian platform.