The large earthquake of 27 August 2008 in Lake Baikal and its precursors

It is known that changes in geochemical fields may be due to the formation and development of earthquake foci. Hydrogeochemical fields at observation sites can be disturbed by underground shocks of sufficient energy, which occur at specific epicentral distances. Our study aimed to reveal these relationships by analysing the concentrations of helium and radon in groundwaters of Southern Pribaikalie, the area around Lake Baikal in Russia. Water samples were taken daily at 10 a.m. from artesian well No. 3 in Zeleny Mys, Irkutsk region. After water sparging, radon concentrations were measured by beta-detection Camera-01 and INGEM-1 (magnetic discharge indicator of helium) to determine helium concentrations. We analysed the concentration values in connection with 22 seismic events that occurred from 2010 to 2016 at the hydrogeochemical observation site (energy classes K of 10.4–14.5; epicentral distances of 40–750 km; conditional energy of K’>6). Based on the radon and helium concentration diagrams, specific regularities were established in the concentration variations before the earthquakes. Generally, concentration variations (increasing/decreasing) in excess of 1.5–2.0 standard deviations preceded earthquakes. This article presents the study results and discusses variations in the radon and helium concentrations, which are due to the seismic process and can be considered as a short-term precursor of earthquakes.

Section: поиск предвестников землетрясенийunclassified

The study of dissolved helium and radon concentrations in groundwaters of Southern Pribaikalie in connection with seismic processes

Semenov

Lopatin

Чечельницкий

2020

“…В частности, естественно предполагать увеличение газовой и флюидной проницаемости областей земной коры, в которых происходит этот процесс [Alekseev et al, 2001]. В связи с этим нередки случаи предсейсмических вариаций концентраций растворенных гелия и радона в подземных водах [Ulomov, Mavashev, 1967;Mavlyanov et al, 1979], в том числе в водах Байкальской рифтовой зоны [Semenov, 2010;Semenov, Smekalin, 2011;Semenov et al, 2014Semenov et al, , 2016, которые рассматривались в качестве предвестников возникновения землетрясений.…”

Section: предвестники землетрясенийunclassified

Model of Tectonic Earthquake Preparation and Occurrence and Its Precursors in Conditions of Crustal Stretching

Semenov¹,

Kashkovskii²,

Lopatin³

2018

In connection with changes in the stress-strain state of the Earth's crust, various physical and mechanical processes, including destruction, take place in the rocks and are accompanied by tectonic earthquakes. Different models have been proposed to describe earthquake preparation and occurrence, depending on the mechanisms and the rates of geodynamic processes. One of the models considers crustal stretching that is characteristic of formation of rift structures. The model uses the data on rock samples that are stretched until destruction in a special laboratory installation. Based on the laboratory modeling, it is established that the samples are destroyed in stages that are interpreted as stages of preparation and occurrence of an earthquake source. The preparation stage of underground tremors is generally manifested by a variety of temporal (long-, medium-and short-term) precursors. The main shortcoming of micro-modeling is that, considering small sizes of the investigated samples, it is impossible to reveal a link between the plastic extension of rocks (taking place in the earthquake hypocenter) and the rock rupture. Plasticity is the ability of certain rocks to change shape and size irreversibly, while the rock continuity is maintained, in response to applied external forces. In order to take into account the effect of plastic deformation of rocks on earthquake preparation and occurrence, we propose not to refer to the diagrams showing stretching of the rock samples, but use a typical diagram of metal stretching, which can be obtained when testing a metal rod for breakage (Fig. 1). The diagram of metal stretching as a function of the relative elongation (to some degree of approximation and taking into account the coefficient of plasticity) can be considered as a model of preparation and occurrence of an earthquake source in case of rifting. The energy released in the period immediately preceding the earthquake contributes to the emergence of its precursors. This article discusses various earthquake precursors with reference to the energy model of tectonic earthquake preparation and occurrence in conditions of crustal stretching.

“…Так, изучение влияния сейсмического процесса на режим подземных вод было начато по гидрогеодинамическим параметрам и широкому спектру гидрогеохимических характеристик [Kissin et al, 1982;Pinneker et al, 1985;Shabynin et al, 1988;Shabynin, 2004]. В настоящее время эту связь пытаются проследить по единичным характеристикам, таким как гелий [Semenov, Smekalin, 2011], радон [Lopatin, 2015;Semin-sky, Tugarina, 2013;Seminsky K.Zh., Seminsky А.К., 2016] и изотопные отношения урана и стронция [Rasskazov et al, 2015].…”

Section: Introductionunclassified

Geological Factors and Physicochemical Processes of Groundwater Formation in the Tunka Depression

Pavlov¹,

Чудненко²,

Голубев³

et al. 2018

The article describes the complex hydrogeological conditions of the Baikal rift zone viewed as a large structural element and pioneers in distinguishing two independent hydraulic systems in the study area. Groundwater resources and compositions of groundwater in these two systems are generated in fundamentally different ways. In the deep sediment layers, groundwater generated due to sedimentation is at the stage of elision (exfiltration) water exchange. Active phase transition of clay minerals to hydromica causes an additional water release, and sedimentary water and regenerated groundwater infiltrate from the condensed clay strata to sandy horizons. This process is accompanied by decompaction, heaving sand, and high (extra-high) reservoir pressures. Nitrogen-rich water and carbonic thermal water associated with faults and fault nodes are widespread in the basement of the Tunka depression. The thermal water result from infiltration and, together with fresh water, represents a uniform hydraulic system. Its development is determined by the dynamics of infiltration water in the water-feeding area in the Tunka loaches. At different hypsometric levels of the hydrogeological section, nitrogen-rich water descends, while carbonic thermal water ascends, and these processes occur simultaneously. Our study is focused on the physicochemical processes of the interaction between groundwater and sedimentary and crystalline rocks. It shows that the ion-salt and gas compositions of not only nitrogen-rich thermal water, but also those of methane water and carbonic thermal water occur in the 'water-rock' system without involving any additional substance from external sources. Compared to other thermal water, the composition of carbonic water is formed in a more complex way: first, it goes through the stage of the nitrogen-rich thermal water while passing through the aluminosilicate rocks and only then interacts with the carbonate rocks and become carbonic. The formation of carbonic water is accompanied by intensive karst processes at depths, which are ceasing closer to the surface. As a result of degassing, an opposite process is activated: authigenic minerals and travertines are formed on the surface. Groundwater and its gas phase are involved in the formation of rocks with a negative temperature, which are abundant in the Tunka depression, as well as large positive forms of the relief. It is shown that the activity of groundwater is not limited to the role of a filler in the host rocks and an intermediary medium between different geospheres. Groundwater is an active agent that initiates, controls and implements many geological processes.