Active faulting in the south of Central Kamchatka

Abstract

The paper describes general pattern of active faulting in the area of the southern termination of the Central Kamchatka Depression, where the Central Kamchatka structures give place to those of South Kamchatka. The authors discuss what fault can be termed «active» and describe the methods used in active fault studies including trenching. A case study of one of active faults considered representative demonstrates application of these methods. Ground penetrating radar profiling was used as a complementary method. Paleoseismological interpretation of the faulted young sedimentary sequence, and radiocarbon and tephrochronological dating of both deformed and intact layers suggest that the most recent event on the fault occurred between 8.4 and 10 Ka years ago. The total dip-slip offset reached ~1.4 m, and the surface rupture may have extended to 8 to 15-16 km. Estimation of MW of the event-related earthquake yields 6.5. We suggest that all the active faults in the area are most likely moving by impulses and are thus seismogenerating structures. Main active faults in the region are arranged en echelon in an array of NW-SE strike. Normal kinematics of the faults together with stepping sense indicate overall right-lateral movement along the array, likely accompanied with some array-normal extension. It is suggested that the array may be the southern ocean-directed extension of the East Kamchatka fault zone. If so, there may exist a structurally isolated block of eastern Central Kamchatka, which moves oceanward relative to West and South Kamchatka. The need for further studies of active faulting in this relatively densely populated area of Kamchatka focused at the documenting of all the seismogenerating structures and assessment of fault-related seismic hazard is emphasized.