Features of Regional Variations of the Spontaneous Field

Abstract

According to the classification principle of field sources, the geoelectric field E is composed of the spontaneous field ESP and telluric field ET. The ESP originates from the physical and chemical actions of underground media. Its change and stability have usually obvious characteristics of local sites. The ET originates from the space current system and tidal forces, and shows the nature of broad areas in diurnal variation waveforms and spectral characteristics. In respect of the microscopic mechanism of their formations, the ESP and ET can have partly same processes of mechanisms. In 2008-2013, in the vicinity of the north-south seismic zone in China mainland, the data of representative 13 geoelectric field observatories suggest that the ESP of most sites do not exhibit clear annual variation waveforms, and their stabilities depend on regions, sites, orientation, tectonic activities and other factors. In these areas, the variation of ESP showed some common phenomena like relatively steady rises and falls, rapid jumps, sudden jumps and so forth. In the vicinity of major fault and local areas, the trend turning points of big variations often show the features of temporal synchronization and quasi-synchronization. The data stability may be similar at the same period of time, while its variation forms are usually irrelevant for site factors. During the more steady phase of the ESP, the preferred orientation α of crack water seepage calculated by the application of spectral features of tidal geoelectric field tends to be in a relatively stable state; during extreme fluctuations of the ESP, the α often experiences significant changes. The α calculated on a daily basis according to the spectral characteristics of the tidal geoelectric field may reveal the daily variation information of fissures, crack water seepage, principal compressive stress of the site, which thus can help analyze the process of microscopic mechanism of macro changes of the ESP and ET.

Source modelling and stress transfer scenarios of the October 30, 2020 Samos earthquake: seismotectonic implications

“…On April 2, 1996 a moderate (M w 5.3) earthquake occurred very near to the fault with quasipure normal, E-W-striking focal mechanism (Kiratzi and Louvari, 2003; Figure 1b). The microseismic investigation of Tan et al (2014) revealed a cluster offshore of the central northern coast with a spatial distribution that depicts a N-dipping fault. This fault is also the candidate fault of the 2020 mainshock.…”