TITLE:
The Earthquake Occurred in the West of Kazakhstan, Buzachy Peninsula on April 25, 2023
AUTHORS:
Natalya Nikolaevna Mikhailova, Aidyn Serikovich Mukambayev, Alexander Yefimovich Velikanov, Assem Aidarkyzy Issagali
KEYWORDS:
Earthquake, Seismic Station, Hypocenter, Magnitude, Seismic Hazard
JOURNAL NAME:
Open Journal of Earthquake Research,
Vol.14 No.2,
March
28,
2025
ABSTRACT: Until recently, Western Kazakhstan was considered a non-seismic region of Kazakhstan, particularly in the southern and northern parts of the Caspian Sea. Earthquake catalogues of Kazakhstan had almost no data on earthquakes in this region, which is likely to be a consequence of the lack of systematic seismic observations in this area. During the Soviet and post-Soviet periods, no permanent seismic stations were installed in this region. However, the region has recently attracted increased scientific interest due to the presence of extensive oil and gas fields, the active development of which has been accompanied by the rapid urbanisation of the cities of Aktau and Atyrau. The seismic hazard assessment and the construction of general seismic zoning (GSZ) maps of the Republic of Kazakhstan, as well as detailed seismic zoning of individual administrative regions of Western Kazakhstan, require the availability of reliable data on seismic events occurred in the past. The identification of seismic generating zones in the GSZ-2017 map, currently in force in Kazakhstan, is mainly based on a set of geological, tectonic and geophysical data; however, there has been no confirmation of their connection with modern seismic activity. Over the past 15 years, the stations of the network of the National Nuclear Centre of the Republic of Kazakhstan, which are located approximately 1000 km away from the area of the earthquake under study, have recorded a number of earthquakes with magnitude mb = 3 - 4 in the areas of hydrocarbon deposits. The nature of these deposits was considered to be induced, associated with oil and gas production. A station closer to the study area was installed only in 2022 in the north of the Caspian Sea within the framework of the international project SNECCA [1]. It is located about 400 km away from the studied event area. The earthquake occurred on 25 April 2023, magnitude of mb = 4.6, is noteworthy as the first event of this nature to be instrumentally recorded by stations in Kazakhstan and by significant number of seismic stations of various networks in other states. It was felt in numerous settlements across Kazakhstan. A detailed analysis of this earthquake has confirmed the presence of natural seismic activity in the region that was previously considered as aseismic. In this paper, much attention is given to the determination of the instrumental characteristics of this earthquake. A large amount of available data from different processing Centers is involved, data from both individual three-component stations and seismic arrays are used in combination, and different processing methods are applied to locate the hypocentre. The position of the hypocentre in relation to the seismic generation zones identified on the existing General Seismic Zoning Maps (2016) was considered. The obtained data demonstrated the relevance of establishing seismic stations in the considered region for permanent monitoring of seismicity, including weak natural and anthropogenic events. Information about such events will serve to solve important tasks of seismic hazard assessment in Western Kazakhstan.