Trenching, active faults in Kamchatka, Russia: paleoseismological and tectonic implications

The Kamchatka Peninsula is characterized by a central depression associated with active volcanism, aligned along a NNE-SSW direction. From the east, the depression is bordered by a system of NE-SW-striking faults, which separate it from the East Kamchatka Ranges. Field work was carried out in order to define the geometric and kinematic features, and paleoseismic activity of the Kumroch Fault, which is the east limit of the northern part of the depression. The strike and geometry of the fault scarps from aerial photos suggest a dip to the west, with a predominant normal kinematics. The lateral offsets of river terraces and stream channels suggest a component of dextral shear associated with the extensional motions. Trenching across a subsidiary minor fault permits to define its activity in relation to the dated dissected tephra layers. We distinguish at least five main faulting events which took place ~10.5, 6, 4.5 and, by a closely spaced two-event succession, in the interval of 3.2–3.3 Ka BP. The collected data suggest that the eastern part of the Central Kamchatka depression associates with a major active transtensional dextral fault, repeatedly active in the Holocene. Volcanic activity within the depression shows a certain correlation with the fault activity.