December 27, 2023, Akitkan Earthquake (mb = 5.4) in the Zone of the Marginal Suture of the Siberian Platform (Northern Baikal Region)

We consider the December 27, 2023, earthquake (mb = 5.4) that occurred on the margin of the Siberian Platform, on the northwestern slopes of the Akitkan Ridge. The earthquake epicenter is spatially associated with a structural suture (deep thrust fault) separating the Siberian Platform and the Baikal fold belt. The seismic event was followed by hardly any aftershocks. Its maximum shaking intensity was IV (MSK-64); it was observed at distances up to 180 km. The December 27, 2023, Akitkan earthquake is localized in a previously aseismic region, far from active areas of the Baikal Rift. It suggests a new look at seismic activity of fault structures bordering the Siberian Platform. The focal mechanism, determined from P-wave first-motion polarities at regional stations, demonstrates normal fault movements on inclined fault planes with a submeridional strike, which agrees with the orientation of the structural suture. This does not contradict seismogeological data indicating that an inversion of tectonic movements can be observed in some segments of the deep thrust fault zones. The December 27, 2023, Akitkan earthquake confirms modern seismic activity of the Akitkan seismic source zone and the fundamental possibility of relatively strong seismic events being generated by marginal structures of the Siberian Platform.