Abstract
The paper presents the results of analysis of tectonics, modern relief morphology, active faults, and types of Cenozoic deformations in the epicentral area of the Ilin-Tas (Ms = 6.9) earthquake, one of the strongest events registered at the boundary of the Eurasian and North American lithospheric plates in northeast Russia. Geological, tectonic, and geophysical characteristics of the Yana-Indigirka segment of the Chersky seismotectonic zone are studied. The methods of investigation were elaborated at the Institute of the Earth’s Physics, RAS (Moscow), and were adapted to conducting seismotectonic work on the territory of northeast Russia. The results of instrumental observations are summarized, and manifestations of strong seismic events are discussed. Description is given of the structural–tectonic setting in which the Andrei-Tas seismic maximum developed. It originated under the effect of the Kolyma-Omolon terrane (indentor) which “intruded” into the Chersky seismotectonic zone on the side of the North American plate, thus leading to the formation of major seismoactive structures in the frontal Ilin-Tas folded zone. The indentor moved in NE-SW direction, which is consistent with the orientation of the major axis of isoseism ellipses (azimuth 50–85°) constructed from observation of macroseismic effects of the Uyandina (Ms = 5.6), Andrei-Tas (Ms = 6.1), and Ilin-Tas (Ms = 6.9) earthquakes.
Highlights
The beginning of the twenty-first century was marked by growing seismic activity in northeastern Yakutia
The epicentral zone of the earthquake was located within the seismic maximum of the Andrei-Tas block where, along with numerous weak shakes, strong quakes (Ms=5.2–6.1) have been detected earlier
Summary of the results of instrumental observations obtained by workers of the Geophysical Survey of the Siberian Branch, Russian Academy of Sciences, and the Michigan State University (USA) as well as joint studies of strong earthquake manifestations and interpretation of the available geological–structural (Parfenov et al 2001; Imaev et al 1990, 2000) and morphotectonic data permitted making a structural dynamic analysis of the epicentral zone of the Ilin-Tas earthquake and refining the dynamics of major seismotectonic processes occurring on the northeastern side of the Yana-Indigirka segment of the Chersky seismotectonic zone
Summary
The beginning of the twenty-first century was marked by growing seismic activity in northeastern Yakutia. The epicentral zone of the earthquake was located within the seismic maximum of the Andrei-Tas block (northeastern side of the Yana-Indigirka segment of the Chersky seismotectonic zone) where, along with numerous weak shakes, strong quakes (Ms=5.2–6.1) have been detected earlier. Summary of the results of instrumental observations obtained by workers of the Geophysical Survey of the Siberian Branch, Russian Academy of Sciences, and the Michigan State University (USA) as well as joint studies of strong earthquake manifestations and interpretation of the available geological–structural (Parfenov et al 2001; Imaev et al 1990, 2000) and morphotectonic data permitted making a structural dynamic analysis of the epicentral zone of the Ilin-Tas earthquake and refining the dynamics of major seismotectonic processes occurring on the northeastern side of the Yana-Indigirka segment of the Chersky seismotectonic zone. – refining the kinematics of motions on the northeastern side of the Yana-Indigirka segment and working out a regional structural dynamic model of major seismogenerating zones
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