CHANGES IN COULOMB STRESS DURING CASPIAN EARTHQUAKES IN 2023 WITH M=5.6

Abstract

The article analyzes two significant Caspian earthquakes that occurred on July 4, 2023 local time 00:01 and December 7, 2023 local time 08:15 with a local magnitude of M=5.6. For this purpose, the source mechanisms of these earthquakes were constructed, and two stress state coefficients were analyzed - Lode-Nadai and Coulomb stress. In 2023, as in previous years, the Caspian Sea water area is characterized by high seismicity. The highest density of hypocenters was observed at a depth of 42-68 km. The magnitude of the displacements in the source shows that fault-slip type movements predominate here. A total of 19 earthquakes were plotted and analyzed in the Caspian Sea in 2023. These earthquakes were associated with the zone of influence of the Agrakhan-Krasnovodsk, Turkmenbashi, Sangachal-Ogurchi, Shakhov-Azizbekov, Siyazan and Garabogaz-Safidrud faults. Based on these mechanisms, the Lode-Nadai coefficient was constructed and it was established that the sources of Caspian earthquakes are located in the extension zone. The solution of the moment tensor showed that the movement at the source of the July 4 earthquake arose under tension conditions. Movement in the source along both planes is shear. The length of the outbreak was 6.1 km, width – 4.53 km. The movement along the fault was 24 cm. In the source of the earthquake that occurred on December 7, 2023, according to the solution of the mechanism, movement in the source also occurred under tension conditions. The type of movement, along the first plane NP1 of a northwest strike and along the second plane NP2 of an east-southeast strike, is a strike-slip fault with fault elements. The moment magnitude was determined to be Mw=5.4. Seismic moment 1.56*10²⁴ dyn*sm. The depth of the source is 48 km. The length of the outbreak was 6.58 km, width – 5.49 km. The movement along the fault was 24 cm.