On seismic activation of the central part of the Aegean volcanic arc
Abstract
Relevance. The central part of the Aegean volcanic arc has a complex geological and tectonic structure. The extended Santorini-Amargos volcanic-tectonic lineament is prominent, home to the large, active, submarine volcanic edifices of Santorini-Columbo. This area was the source of the 1956 doublet earthquakes with magnitudes M=7.4 and M=7.1 that are the strongest in the Mediterranean Basin. The occurrence of anomalous seismic activity in this area reflects the complex interplay of volcanic-tectonic processes. The study of these processes is a pressing and extremely important scientific task. The aim of this work is to determine, using a comprehensive analysis of seismic data, whether this process is associated with geodynamic activation of the subduction zone of interaction between the African macroplate and the Hellenic mesoplate, or whether it represents a seismic reflection of deep magmatic activity in the Santorini-Columbo underwater volcanic structures. Methods. To achieve this aim, modern methodological approaches and algorithms for cluster analysis of seismic events were applied. Focal mechanisms of the events resolved, and wave pattern features were studied, as well as quantitative metrics of frequency characteristics, duration, and total moment of the tensor (MT) of focal radiation. The results of the comprehensive analysis lead to the conclusion that the entire anomalous process is volcanic in origin and reflects deep magmatic activity along the entire length of the Santorini-Amargosa submarine volcanictectonic lineament. The temporal dynamics of the anomalous process indicates that it reflects the simultaneous occurrence of a short-term pulsation of the magma chamber of the dormant Columbo submarine volcano and tremors of the entire extended submarine volcanic-tectonic lineament. Most likely, the detected activation is associated with an additional injection of magmatic material, in the form of fluids, from the upper mantle into the magma reservoir in the Columbo volcanic edifice area and its diffusion along the entire length of the submarine volcanic-tectonic lineament. A hypothesis is proposed that the additional injection of light fluids from the upper mantle into the magma reservoir feeding the Santorini-Amargosa tectonic lineament is caused by extreme elastic stresses in the focal region of a developing large tectonic earthquake.
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