Abstract
The Mw 7.6 Olyutorskii earthquake of April 20, 2006, struck the southern edge of the Koryak Highland, in a region of great complexity at the junction of the North American, Eurasian, and Pacific plates. This seismic event was notable for several remarkable features. Firstly, it had an unexpectedly large magnitude, leading to a reassessment of the seismic hazard in the Northern Kamchatka region. Secondly, the GCMT focal mechanism solution showed two nodal planes corresponding to nearly thrusting displacements on a 40–51° dip** rupture plane. However, geological field studies conducted in the epicentral area allow to map at the surface three primary segments of a 120 km long rupture zone. The central segment showed predominant right-lateral strike-slip displacements, while the NE and SW segments exhibited mostly thrusts steeply dip** SE with smaller strike-slip components. Thirdly, aftershocks were recorded in an area extending over 200 km southwestward from the surface ruptures mapped in the field, with an intense activity observed in a vast area 75 km to the NW from the surface ruptures. Fourthly, although the ruptures found during fieldwork were dip** to the SE, most aftershocks occurred NW of them, with their depth decreasing in the NW direction. SAR interferometry resolved this apparent discrepancy between seismological and field-geology data, indicating that the primary displacements occurred northwest from the central and southwest segments of the ruptures at the earth's surface. We present in our study a new rupture model based on SAR, GPS, and field geology data. The model consists of a major blind thrust extending NW and three rear subvertical ruptures that reached the earth's surface and were mapped during the field survey. Additionally, models of the main Mw 6.6 aftershocks that occurred on April 29, 2006, and May 22, 2006, are presented. Our new model reconciles all collected data, with a direction of movements on the major thrust agreeing with the rotation of the previously suggested Beringia microplate around a pole situated in the North of the Chukotka peninsula.
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Acknowledgements
We express our gratitude to the European Space Agency (ESA) for providing SAR images obtained from ERS and ENVISAT satellite. We also acknowledge the Japan Aerospace Exploration Agency (JAXA) for their contribution of ALOS-1 images under the scientific project ER2A2N075. Seismology data used in this study were obtained from the USGS and GCMT catalogues, and we thank them for providing access to their data. Our special thanks go to F. Polltz for sharing his Static-1D code.
Funding
The work of the Russian authors was supported by the Russian Science Foundation Grant #23-17-00064 “Getting new data on the development of volcanic and seismic processes in the Kuril-Kamchatka subduction zone by enhancement the methods of analysis and complex geodynamic interpretation of the results of satellite and ground-based observations”.
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All authors contributed to the study conception and design. SAR data processing and analysis were performed by ET, seismology data were analyzed by VS. State of inverse problem was performed by VM and MD. All authors commented on the manuscript, read and approved its final version.
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Mikhailov, V.O., Timoshkina, E.P., Diament, M. et al. Enigma of the Olyutorskii Earthquake Resolved by SAR Interferometry. Pure Appl. Geophys. 180, 3423–3433 (2023). https://doi.org/10.1007/s00024-023-03351-6
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DOI: https://doi.org/10.1007/s00024-023-03351-6