Seismotectonic deformations and stress fields in the fault zone of the 2003 Chuya earthquake, Ms = 7.5, Gorny Altai

The seismotectonic deformations related to the Chuya earthquake September 27, 2003 in the Gorny Altai (M_s = 7.5) are studied in detail. These deformations developed as advanced systems of R-and R’-shears, gash fractures, and compression structural features in loose sediments. In bedrocks, the older shear zones were reactivated, the previously existing fractures were renewed and propagated further, and new faults and crush zones were formed. The system of seismic dislocations is a fault zone no less than 4 km wide that extends in the northwestern direction. As follows from the structural elements that reveal a systematic mutual orientation, the internal structure of this zone is typical of a right-lateral strike-slip fault. The initial stress field that led to the development of the entire assemblage of seismotectonic deformations related to the Chuya earthquake corresponds to the strike-slip type with the NNW, almost meridional direction of compression axis (σ₁) and the ENE, almost latitudinal direction of the tension axis (σ₃). The local variations of the stress state were expressed in an insignificant shift of σ₁ to the northwest or northeast, in the short-term change of relative stress values with retention of their spatial orientation, and in the increasing inclination of σ₁ in front of the previously existing fault. The comparison of the internal structure of the seismotectonic fault zone with a tectonophysical model of faulting in large continental systems with a right-lateral offset indicates that the distribution of the advanced faults corresponds to the late stage of faulting, when the main fault is still not formed completely, but its particular segments are already developed distinctly. It is shown that at high rates of displacement the structural features in markedly different rocks develop according to the general laws of solids’ deformation even near the day surface.