Particularities of Vertical Displacements Along the Delta Fault During the 1862 Tsagan Earthquake on Lake Baikal

Based on the ground penetrating radar, geological and morphostructural data, the particularities of single-event vertical displacements in Holocene sediments of various competencies along the land and underwater segments of the Delta fault activated on January 12, 1862 during the M ~ 7.5 Tsagan earthquake (southeastern side of the Baikal rift.). It is shown that the slip determined from the scarp morphology and the position of the main rupture in the section reflects the total displacement value, which is the sum of the brittle and plastic deformational components. The presence of water-saturated poorly consolidated sediments in the geological section increases the contribution of the plastic component. In this case, the width of the rupture zone increases. Despite the fact that the northeastern segment of the Delta Fault was submerged in the water of Proval Bay, the largest seismotectonic displacements occurred between the villages of Kudara and Sherashevo and on the outskirts of the village Dubinino in the land southwestern part of the structure, where the total displacement was 9,59 and 9,28 m, respectively. No such depths were recorded in Proval Bay after the earthquake. Along the Delta Fault under water, seismotectonic displacements were relatively small with a rather significant contribution of the plastic component from 26 to 53 %. This slip was a trigger for the seismic- gravity subsidence of the bay and sediment compaction, which continues to this day, judging by its almost unchanged depth since 1862 and the proximity of numerous seismic events, including the last Мs = 5.4 09.12.2020 earthquake happened on December 9, 2020 and strongly felt in Irkutsk.