Geomorphological Indicators of Strike-Slip Displacements on Urup Island (Great Kuril Ridge)

Urup Island is located in the southern part of the Great Kuril Ridge. The island is characterized by contrast relief with a significant depth of vertical dissection that has been greatly influenced by the latest tectonic processes. According to geological data, this island is currently located in a strike-slip stress field. The axis of the maximum compression is oriented in the southeastern direction. This can be explained by the subduction interaction of the Pacific and Sea of Okhotsk lithospheric plates at an acute angle of about 55°. Visual and automated interpretation of space images and digital terrain models and analysis of the erosional pattern allowed us to identify geomorphological signs of strike-slip displacements. These include the echeloned arrangement of lineaments as separation fractures in right-lateral strike-slip zone in the area of the Rybnaya River and on the Skvoznyakovy isthmus, where dislocations of unidentified kinematics were previously revealed. Zones with an asymmetric erosion pattern, which are naturally oriented in the northeast direction, were considered. Within these zones, small tributaries are located on one side of a watercourse of the highest order as separation megafractures. The 1989 earthquake occurred in the setting of latitudinal horizontal tension. In the area of the earthquake epicenter, the linear lowering of relief with a feathery pattern of watercourses was recorded. We interpreted this as a morphostructure of tension. The similar assumed strike-slip zones, which strike generally along the azimuth of 130°–140°, were recorded on the Pacific coast of the island. The orientation of these zones, as well as the kinematics of the proposed strike-slip faults identified from geomorphological data, are consistent with the general conceptions about the stress–strain state of the Southern Kuriles and with the reconstructed main normal stress axes of the Kastrikum Peninsula on the basis of fracture measurements. All these facts point to the possibility of the proposed structural-geomorphological interpretation of the Urup area. In general, our new data on the configuration and kinematics of the proposed active strike-slip faults and morphostructures of tension add to the existing conceptions about the latest deformations of the study area.