Local earthquakes as a component of seismic hazard of Chernivtsi region

Abstract

The localization of epicenters and the intensity of local earthquakes in the Chernivtsi region were studied. It has been established that low-energy earthquakes can create a local dangerous level of shaking in its north-eastern part. The seismic danger of the territory of Chernivtsi region is usually identified with the manifestations of earthquakes in the epicentral zone of the Vrancea Mountains. In this, the most seismically active part of the Carpathians, deep-focus earthquakes with stable localization of foci occur. The Vrancea seismic body can be considered as a zone that is in a constant mode of preparation for a strong earthquake, while the earth's crust above the strip of deep-focus hypocenters is practically seismic. The highest, so far registered, intensity of earthquakes in the Chernivtsi region earthquakes of the Vrancea zone is 7, the predicted maximum is estimated at 8 points on the MSK-64 scale. At the same time, the danger of local earthquakes was considered insignificant, and the study of the peculiarities and intensity of their manifestation was of little relevance. The aim of the study is to analyze the location of epicenters and assess the intensity of local tectonic earthquakes in the Chernivtsi region. Components of seismic hazard of any area are the manifestations of local earthquakes and the impact of seismic shocks, the epicenters of which are outside it. Chernivtsi region is not characterized by high local seismic activity, but so far, several local earthquakes with an intensity in the epicenter of 4-5 points have been registered in its territory. A rather strong earthquake was felt in Chernivtsi on May 10, 1950 at 2 o'clock. 10 min (Greenwich). The duration of his three jolts, which took place in the vertical direction, did not exceed 2-3 seconds. During the earthquake, doors opened, dishes rang in closets, and window glass shattered in some rooms. The intensity of the earthquake GV Brusentsov scored 5 points. The most notable seismic event, the shocks of which were felt in the northwest of Chernivtsi region, was the earthquake that occurred on January 20, 1903 at 3 o'clock. 4 min (Greenwich). Intensity in the epicenter, located near the village. Dobrovlyany (Ternopil region), rated 6 points on the MSK scale. At this intensity, the magnitude of the earthquake, the focus of which was at a depth of 10-15 km, was about 4.5. In the territories of Kelmenetsky and, especially, Sokyryansky districts, earthquakes are felt, the epicenters of which are located in the south of Khmelnytsky and Vinnytsia regions. Several earthquakes were registered in the same area, which were felt in the city of Novodnistrovsk with an intensity of 3-4 points. Their occurrence is associated with disturbance of geodynamic balance in the near-surface part of the earth's crust, caused by filling the bowl of the Dniester reservoir. The epicenters of the earthquakes were located 15-20 km east of the Dniester HPP dam. The magnitude in the case of the strongest shocks was 3.5-3.8, their intensity near the epicenter - 5 points. The estimated depth of the hearth was 5 km. An important feature of these energetically weak earthquakes was the small (2-5 km) depth of the focus. Under such conditions, at magnitudes of 2.8–3.8, a high (5.5–7.3 points) level of shaking was observed in the epicenter, but the intensity decreased rapidly with increasing epicentral distance. Evidence of the possibility of a seismic event of considerable intensity in the northeast of Chernivtsi region may be the presence of paleoseismic dislocations in this area. In particular, such a geological and geomorphological complex located on the Dniester canyon near the village. Mosquitoes, described in the work of B. Ridush and Y. Kalush. The reason for the formation of the Komariv paleoseismic dislocation may be the manifestation of a local tectonic earthquake. The territory of Chernivtsi region is not characterized by high seismic activity. The intensity of local energetically weak (with M≤4.5) earthquakes did not exceed 5-6 points of the MSK scale. When the hypocenters were found at shallow depths within the earth's crust, a marked level of shaking was observed in the epicenters, which rapidly decreased with increasing epicentral distance. The epicenters of the earthquakes were located along the lines of tectonic faults of the south-western edge of the Eastern European platform and the Pre-Carpathian marginal depression. The danger for the regional center of Chernivtsi in 5-6 points can be created by the intensification of Chernivtsi or Storozhynets tectonic faults, the last of which was marked by an earthquake in 1950. More intense (5-7) points may be local manifestations of earthquakes in the south-eastern part of the region, in particular, near the city of Novodnistrovsk. The seismic activity of tectonic processes within the mountainous, north-western part of the region needs to be studied.