SEISMICITY OF CHUKOTKA, NORTHEASTERN RUSSIA

Abstract

The seismicity of Chukotka forms the central part of a Trans-Bering seismic belt that extends from the Koryak highlands through the Seward Peninsula to central Alaska. The seismicity of the Chukotka section has been recorded teleseismically (1928 to present), using a temporary network (1964-1966), a multiinstrument single station (1966-1982), and a regional network (1980-1993). Three seismic zones are identified within the Chukotka section of the Trans-Bering seismic belt: the Kolyuchin Gulf-Eastern Chukotka zone, a western extension of the rift system of Seward Peninsula, Alaska; the Koryak-Provideniya-Seward zone, representing the transpressional southern boundary of the Trans-Bering seismic belt; and the Anadyr-Amguema-Chukchi Sea zone, a weak, transtensional zone of seismicity forming the northern edge of the Trans-Bering seismic belt. The rest of Chukotka is relatively aseismic; the seismicity reported from the Polyarnyi area is anthropogenic. The Kolyuchin Gulf-Eastern Chukotka zone is a highly active transtensional zone (earthquakes to magnitude 7) with three northeast-striking segments of seismicity that are presumed to be transform faults offsetting rift segments. The Koryak-Provideniya-Seward zone is characterized by thrusting in its southern end, which changes to transform motion in the Gulf of Anadyr, and connects with the east-west-striking rift systems in Chukotka and the Seward Peninsula. The seismicity and focal mechanisms are consistent with the existence of an independent Bering Sea block rotating clockwise with respect to North America about a pole in western Chukotka. The Trans-Bering seismic belt forms the northern border of the Bering Sea block.