In the "News" section of the Russian Science Foundation (RNF) website, a press release describing the electromagnetic research conducted by the staff of Research Station of the Russian Academy of Sciences in Bishkek city (RS RAS) at various sites of the Issyk-Ata fault (Kyrgyzstan) under the RSF project № 22-27-00567 was published.
Scientists in Kyrgyzstan have identified seismically dangerous areas of the active Issyk-Ata fault
Source: RSF Press office
Translation: RS RAS
Geophysicists have developed a geoelectric model that makes it possible to find areas in lithospheric faults where earthquakes are likely to occur. For this purpose, the authors studied the electrical properties of the earth's crust in the zone of 150-kilometer-long Issyk-Ata fault in Kyrgyzstan. The results of the study, supported by an RSF grant, were published in the scientific journal “Geophysics”.
The RS RAS staff have conducted profile electromagnetic soundings on different sections of the Issyk-Ata fault and determined the electrical characteristics of cross sections of the fault along its strike. This approach allowed them to assess the heterogeneous geoelectric structure of the fault zone volume, i.e., to understand how the fault behaves at depth.
Crustal faults are especially common in mountainous regions. In Kyrgyzstan, one of the largest and most active one is the Issyk-Ata fault, which is more than 150 kilometers long. This fault belongs to the system of marginal faults of the Northern Tien Shan and divides the low foothills of the Kyrgyz Range from the flat part of the Chui Depression. The central segment of the Issyk-Ata fault is located in the southern suburbs of Bishkek city. The movements and interaction of lithospheric blocks lying in the fault zone create tectonic stresses here. Where the accumulated stresses reach a critical level exceeding the strength of the rock mass, a sharp displacement of rocks along the fault occurs. Eventually, the accumulated energy is discharged in the form of a strong earthquake. In order to assess where earthquakes can be expected in the near future, scientists are trying to identify potentially dangerous locations on faults in the Earth's crust where such critical stresses can accumulate.
To investigate the geoelectric structure of the fault in its upper part up to depths of 50-100 meters, the authors used the electrotomography method using “Skala-48” multielectrode measuring station. The authors placed electric cables along the mountain sections and send probing pulses of electric current into the ground. Then current pulses that passed through the earth's crust were recorded using measuring electrodes. The probing current propagates in the earth's crust taking into account its electrical properties, and therefore the current pulses registered at the measuring points have different characteristics (shape, amplitude) than those initially sent into the ground. These changes depend on electrical resistance of the earth's crust in a particular area. The obtained data formed the basis for construction of geoelectric model of the earth's crust of different fault sections.
By conducting measurements at the same location for several days, the authors were able to assess how electrical resistivity changes over time. As a result of such monitoring in different segments of the Issyk-Ata fault, the scientists identified which blocks of the fault zone are most active in geoelectric terms. The scientists obtained high values of these parameters for the southern part of Bek-Too2 profile, located 5 kilometers southeast of Bishkek city and found that one of the most seismically dangerous segments of the Issyk-Ata fault is located here.
"Now all our attention has been given to the Issyk-Ata fault. We plan to expand the study and build a geoelectric model of entire marginal faults system on the border of Northern Tien Shan. We would also like to supplement our study with satellite geodetic observations. This will allow us to obtain experimental data on crustal surface movement in the region under study and compare them with the results of electromagnetic observations," says the head of the project supported by the RSF grant, Director for RS RAS Dr. Anatoly Rybin.
