Source of the 1902 Shamakhi Earthquake on the Background of Attenuation Field Inhomogeneities and Seismicity of the Western Caspian Region

Abstract

The article studies the characteristics of seismic coda wave attenuation in the vicinity of the source of the 1902 Shamakhi earthquake and in adjacent zones of the Western Caspian region. The relationship between the features of seismic processes and spatial inhomogeneities of the attenuation field is considered. The attenuation field is represented by zones (blocks) with a high Q-factor and close to isometric in plan view, and by the linear zones of strong attenuation (weakened zones, which coincide with faults). Sources of the strongest earthquakes are confined to the zones of maximum attenuation contrast. It was revealed that the structure of the attenuation field agrees with the structure of the S-wave velocity field: low-velocity anomalies correspond to low-Q zones. Unidimensionally extended volumes of intense localized seismicity, located in weakened zones, are considered. In one of these volumes, in the focal zone of the 1902 Shamakhi earthquake, manifestations of active deep degassing processes were observed: mud volcano eruptions and earthquake swarms with upward-moving sources during a series have been recorded. It is noted that the most remarkable seismic events, and, above all, the major 1902 Shamakhi earthquake, correlate with the minima of the Earth’s rotation speed.