Complex Electromagnetic Monitoring of Geodynamic Processes in the Northern Tien Shan (Bishkek Geodynamic Test Area)

Abstract

At the Bishkek geodynamic test area in the Northern Tien Shan, complex electromagnetic monitoring was conducted, including a wide frequency range by magnetotelluric sounding in various modifications and induction sounding with a controlled impulse source (method of sounding in the far zone, SFZ). The geoelectrical sections of the lithosphere were constructed for the study area. Based on the geophysical monitoring data and the profile MT monitoring data on the Baitik depression, the main faults belonging to the Northern Tien Shan fault system were detected: Shamsi-Tyundyuk (Predkirgizsky), Baitik, Chonkurchak, and Issyk-Ata. From the geoelectrical data, we obtained new information that is independent of other geophysical methods used for studying the deep structure of the Earth-the hidden fault structures and the geoelectrical segmentation of the study area were revealed. The latter reflects the main elements of the block structure of the junction zone of the Chuya basin and the Kirghiz ridge. This information needs to be taken into account when constructing a comprehensive model showing the geological, geophysical and geodynamical features of the development of the Tien Shan, a vivid example of an intracontinental orogen. The MTS, FS and SFZ data from the Ak-Suu and Chon-Kurchak electromagnetic monitoring stations were interpreted. Based on the representative array of experimental electromagnetic data, we analyzed the effective depths of field penetration, which are most sensitive to changes in the electromagnetic parameters of the medium for the stationary and routine observation sites with respect to the clusters of seismic events. This paper discusses the development of the azimuth MT monitoring technique and the analysis of the time series of electromagnetic parameters, which were used for determining the contribution of each component of the impedance tensor to the informativeness of the monitoring studies. The data from the 2004-2016 KNET Catalogue of the Research Station of RAS were analyzed in order to investigate the relationship between the space-time seismicity distribution and the electrical conductivity variations that correspond to the features of the seismicity pattern at depth. Examples discussed are the time-frequency series of MT monitoring in 2007 and 2016 at the Ak-Suu and Chon-Kurchak stations that identified anomalous electromagnetic parameters corresponding to the fluid redistribution model for the pore-cracked medium: syn-phase decreasing and increasing values of the parameter by the orthogonal azimuths. Thus, a phenomenological model has been tested. It relates the change in the stress-strain state of the medium with the redistribution of fluids between the systems of fractures, which causes variations in the active and reactive components of the electrical resistance.

The Role of Field Training in STEM Education: Theoretical and Practical Limitations of Scalability

“…They will be based on the principle of unity of technologies of scientific expedition support [19]. As such, the Research Station of the Russian Academy of Sciences at the Bishkek Geodynamic polygon is suitable for these conditions [33][34][35]. The network of field test sites will include regional field scientific and educational centers.…”

Analysis of the features of the spatio-temporal distribution of geoelectric inhomogeneities in the Earth’s crust and seismic events

“…1), and in the study of the seismicity distribution therein (Fig. 2) [1][2][3][4][5]. However, the confinement of earthquake sources to geophysical inhomogeneities of the Earth's crust, including fault structures, is still controversial.…”

“…The structure of the absorption field correlates with the tectonic structure of the area, in particular, the weakened zones correspond to the fault zones [7]. Analysis of the position of the hypocenters of seismic events and the distribution of velocity inhomogeneities in the earth's crust allows us to conclude that earthquakes are confined to high-gradient zones of geoelectric models [2][3][4][5]. Very often, these structures flatten out and have the form of listric faults (lateral compression structures) characteristic of areas of intracontinental compression.…”

On the dynamics of the electromagnetic parameters of the Northern Tien Shan lithosphere

“…The time interval for recording the MT-field ranges from several hours to several days, which determines the depth of soundings. At present, on the territory of the BGPG, a sufficiently large experience has been accumulated in conducting monitoring magnetotelluric (MT) observations in order to study the geodynamic processes occurring deep in the Earth in connection with the preparation of seismic events [4][5][6][7][8]. Reliable geoelectric models of the seismically active junction zone of the Kyrgyz ridge and the Chuy basin have been built on the basis of the performed electromagnetic methods, and interesting practical results of experimental electromagnetic research [9,10], focused on monitoring geodynamic processes in seismically active regions, have been obtained.…”

“…different electrical conductivity in different directions. This factor makes it possible, under favorable conditions, to use the method of azimuthal magnetotelluric monitoring [4,5] to determine the predominant direction of fractured zones and changes in their intensities at different depths.…”