Influence of crustal fracturing on the thermal springs and earthquake swarms distribution in the north-east part of the Baikal rift system (Russia)

Abstract

The Baikal rift system faults, having developed in the recent rift formation period, are characterized by hydrothermal and seismic activity. Especially in the northeastern part, the level of fracturing affects the localization of thermal outlets and the distribution of earthquake swarms. The specific features of the hydrothermal outputs and seismicity interposition, depending on the fracture heterogeneity and water saturation of the lithosphere layers, have not been previously evaluated. The results of the statistical analysis of the hydrothermal data, presented herein, show that most of the springs are distributed in areas of increased fault density. Multiple less hot hydrotherms are associated with zones of maximum density in the inter-block space. The spatio-temporal analysis of seismicity showed that migrations of weak and moderate seismic activity propagate from earthquake swarms through these zones. Swarms initiate the deformation front by propagating in the quasiplastic layer of the upper mantle at a speed of tens of kilometers per year, which can increase the aqueous fluid pore pressure in the lower earth’s crust, facilitate the movement of the fluid upwards along the section, and cause a process of successive stress relaxation in zones of high fracturing and concentration of hydrothermal springs. Earthquake swarms occur in areas of about average fracture density, associated with deep faults framing consolidated blocks of the earth’s crust. The hydrotherms with high or average temperature, and with probable deep source chemical composition components are related with such zones.

Methodical approach to isolation of seismic activity migration episodes of the northeastern Baikal rift system (Russia)

“…5, a) and is characterized by strong seismic events (M=5). The trend of seismic energy directional propagation from a cluster of Amut swarm main seismic event has been isolated in a previous study (Novopashina and Kuz'mina, 2019). The 22year northeast-southwest propagation of seismic process over a distance of 110 kilometers along the Barguzin fault zone corresponds to a velocity of about 5 km/yr.…”

“…The spatial distribution of earthquake foci in the migration chains depends on magnitude of the earth's crust fracture. In the previous study (Novopashina and Kuz'mina, 2019) zones of LgEsum extensionwere characterized as areas of intensive fracturing and diffuse heat flow, limited by deep faults with hydrothermal activity. Strong seismic events and swarms, observed at the edges of the migration sequences are, as a rule, connected with deep faults separating the fractured space between consolidated blocks of grater lithosphere elastic layer thickness (Mordvinova et al, 2016).…”

“…Migra-tions characterized by such rate, were previously recorded in Central Asia and the Cis Baikal (Sherman, 2013;Gorbunova and Sherman, 2012;Levina and Ruzhich, 2015;Novopashina and Sankov, 2018). The results of detailed studies of earthquake sequences in the northeast part of the BRS with a description of lithosphere properties, where sequences occur, are presented in Novopashina and Kuz'mina (2019). The migration rate directly depends on the relative velocity of plate interaction in the region.…”

“…The location of the projection zones I, II, III in the northeast part of the Baikal rift: а -relief and active faults (Lunina, 2016), bmap of the epicentral field. 1 -contour of the BRS, 2 -active faults of the BRS, general branches of BRS NE-part, 4 -projection center points, 5 -swarms of earthquakes (Solonenko and Solonenko, 1987;Melnikova et al, 2007) with their numbers in circles (1 -Amut 1979-1981, 2 -Kitchera (Kichera) 1999, 3 -Angarakan 1979-1983, 6 -zones of seismic data projection with their numbers (Roman numerals in squares), 7 -directions of seismic activity migration front, 8 -thermal springs of different temperature (Lysak, 2002), 9 -the BRS depressions with their numbers in the squares (1 -Baikal, 2 -Kictherа, 3 -Upper Angarа, 4 -Muyakan, 5 -Amut, 6 -Barguzin), 10 -contour lines of crust's fracture density for a pallet 0.37°x0.37° from (Novopashina and Kuz'mina, 2019). The sidebar Figure 3, a, presents azimuths rose charts of 5-degree projection areas I, II, III, respectively.…”

“…Three areas of study ( Fig. 1) are defined as detailing zones in places where seismic energy distribution were previously recorded (Novopashina and Sankov, 2018;Novopashina and Kuz'mina, 2019). In order to assess the stationarity of the seismic regime for each projection area, spatiotemporal diagrams of the released seismic energy, plotted for two different periods of seismic activation, were compared.…”