Home – Home – Jornals – Russian Geology and Geophysics 2025 number 8

The distribution of more than three dozen strongest intraplate crustal earthquakes (with M_w ≥ 6.9) recorded in Central Asia (20°-55° N, 55°-120° E) for the years 1973-2022, including the level of their aftershock activity and background seismicity in the field of velocity heterogeneities of the medium, is considered. The analysis of background and aftershock seismicity with m_b(isc) ≥ 4.5 (according to International Seismological Center isc.ac.uk) was analyzed at the sites of 3° × 3° focal areas. The total scalar seismic moment of the background seismicity and aftershock sequence was calculated within the sites. The background seismicity was estimated for the 50-year time period before and after the main earthquake and its aftershocks. The duration of the aftershocks series is limited to one year. Against the background of the generalized seismotomographic model of Asia (at a depth of ~50 km), crustal foci of 24 strong earthquakes mainly tend to the zones of sign change of P -wave velocity anomalies, three earthquakes are recorded in the low velocity zones and 4 in the high velocity zones. The largest values of the total scalar seismic moments released during the implementation of background seismicity are located within the negative P- wave velocities anomalies, as well as along the boundaries of anomaly sign change. When scalar seismic moments are released during aftershock and background activity, as well as the main event, the prevailing values remain within E+27. Increased values (E+28) are typical for zones of anomalies sign change and areas of positive P -wave velocity anomalies. Low values of total scalar seismic moments of background and aftershock events are observed in the focal zone of six sites (3° × 3°). It is supposed that exactly the limiting magnitude for 100-years (1901-2022) was realized in these zones, and the release of accumulated stresses could be carried out exactly due to the strongest earthquakes.