Surface-rupturing paleoearthquakes in the Kurai Fault Zone (Gorny Altai, Russia): Trenching and geophysical evidence

Abstract

The Kurai Fault Zone (KFZ) is one of the most hazardous seismogenic structures in the Gorny Altai (Russia). The KFZ have generated five paleoearthquakes with Mw = 6.6–7.6 and ESI 2007 shaking intensities of VIII to XI. The ultimate event, presumably in the second half of the 18th century, was preceded by four paleoearthquakes approximately 1.3, 3.2, 5.8, and 6.3 ka ago. The morphology of fault scarps, trenching results, deformation features in Neogene sediments, as well as electric resistivity surveys, reveal reverse slip mechanisms. All earthquakes were sourced by south-dipping backthrusts with respect to the main north-dipping reverse and thrust faults along which the Kurai Range is stepping over the two basins. The backthrusting maintains the growth of forebergs in front of the Kurai Range. Narrow basins limited by reverse faults separate forebergs from the Chuya and Kurai basins. Joint interpretation of geological (including trenching) and geophysical (ERT and GPR) data reveals the resistivity structure of the area with seismogenic faults traceable to depths of 40–50 m. The KFZ model, with the reconstructed relationships between the intramontane basins and the flanking mountains, as well as the structural control of large earthquakes, makes good reference for other worldwide regions of current and past seismicity in compressional settings. Assessment of probable magnitudes and recurrence of earthquakes within the KFZ is of special importance in view of the future deployment of the gas pipeline from Russia to China.