Geophysical study of the epicentral area of the Katav-Ivanovsk earthquake (05.09.2018, M5.8)

Resarch subject. To investigate the epicentral area of the Katav-Ivanovsk earthquake (05.09.2018, M5.8), which has so far been the strongest seismic event in the Urals during the entire period of instrumental observations. The surface manifestation of the main earthquake shock, the development of the focal zone in time, as well as the deep structure and geodynamic characteristics of the area, were studied.

Materials and methods. The methods of seismic catalog analysis and remote and archive geophysical data study were applied. The nature of centurial variations in the level of magnetic field and the manifestation of fault tectonics was studied using audio magnetic-telluric sounding (AMTS). The speed of  modern vertical movements was assessed by monitoring the gravitational field. The temperature of water in the well at a depth of 100 m was monitored. The processing and re-interpretation of archival gravimetry and magnetometry data was aimed at identifying lineament systems and clarifying disruptive faults.

Results. It is shown that the earthquake occurred in the area of reduced fragmentation of the geological environment and was accompanied by a natural decrease and disappearance of the local  magnetic field anomaly of 300 nTl in 36 years. One year before the event, a prolonged increase in the 
number of weak earthquakes (R 500 km) was observed, followed by a slight levelling-off in the first half of 2018. Two months before the event, an increase in seismic activity was noted again followed by a slump one month before the even. In September, the main shock was registered, followed by a swarm of seismic events. Among the latter, there were 3 with a magnitude exceeding 4. At present, the seismic regime has stabilized at the long-term average level. An increase in the groundwater temperature at a rate of 0.02 °C per month is currently observed.

Conclusions. An increase in the deepground temperature contributed to the demagnetization of magnetic inhomogeneity, as well as to an increase in (in addition to tectonic stresses) temperature stresses in the earth’s crust, which jointly caused the seismic event.

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