A Seismic Swarm Near Neshkan, Chukotka, Far Northeastern Russia

Felt earthquakes have been occurring almost daily near the village of Neshkan, Chukotka (67.05N, 173.02W), in far northeastern Russia, since December, 2002, shortly after the Denali earthquake in Alaska. The events occur in a region that has experienced several large events in the past, including four magnitude 7 events in the 1920s and magnitude 5-6 events in 1962, 1971, and 1996. As a result of this activity, a permanent seismic station was deployed at Neshkan in September, 2003, and two field stations were operated during the second half of that month. During the two week field deployment, over 150 events were recorded, the largest having a magnitude of 3. About twenty-five events were recorded well enough to locate; these form a linear trend from 1 km west of the village south-southwest over a distance of 20 km. In addition, a small pond drained near the village suggesting there has been some near surface deformation. We suggest these events are associated with a previously unknown fault which defines the eastern edge of the Kolyuchin basin. Analysis of the 1996 sequence suggests that that series may have ruptured the same fault as well. These events, in addition to relocations of small events in the central part of the peninsula, suggest that much of the recent seismic activity occurs on northeast striking faults and that their significance has previously been underrated. Earthquakes continue (through June, 2004) to be recorded at the Neshkan station, some with S - P times which indicate that many of the events are occurring within a few kilometers of the village; 600 events were recorded in December, 2003, alone. Hot springs, signs of active faulting, and quaternary volcanics are found throughout eastern Chukotka, some in close proximity to Neshkan. Combined with similar evidence on Seward Peninsula, it is suggested that an extensional regime exists near Neshkan and this raises the possibility that the events are related to magma migration.