Full length ArticleThe February 1, 2011 Mw 4.7 earthquake: Evidence of local extension in western Transbaikalia (Eastern Siberia)

- The rare earthquake (Mw = 4.7) in western Transbaikalia is considered.
- Earthquake source is controlled by the Zagan metamorphic core complex structure.
- Evidence of local extension revealed for western Transbaikalia.

We consider the rare February 1, 2011 earthquake Mw 4.7 that occurred in the low active region of western Transbaikalia, Russia. Its epicenter relates to the Zagan metamorphic core complex (MCC). From geological data, MCCs are characterized by signs of regional extension. We calculated earthquake source parameters (hypocentral depth, moment magnitude, scalar seismic moment and focal mechanism) from the data on amplitude spectra of surface waves and the first body-wave arrivals recorded on regional stations. The results obtained show that the focus of this event was formed in the conjunction zone between the low-angle dipping zone of plastic flow (detachment) included in the structure of the Zagan MCC and the listric fault related to the adjacent basin. A normal fault focal mechanism proves the processes of horizontal extension near the MCC, with one nodal plane being low-angle dipping (dip 35°) that agrees with the dip of the detachment zone. As long as this zone is characterized by high rates of tectonic deformation, we suppose that normal-fault displacement in the earthquake origin is carried out along the low-angle dipping rupture plane. Taking into account that in the territory of western Transbaikalia, compression and strike-slip regimes of seismotectonic deformations dominate, we suppose that the extension in the focus of the earthquake under study has a local character, and is caused by the structure of the Zagan MCC.

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