Daily-Seasonal Variation in the Number of Remotely Observed, Pulsed, ULF Electromagnetic Earthquakes and the Spatial Distribution of Their Generation Zones on the Earth’s Surface

Abstract

Based on data from long-term observations at two geophysical observatories, Borok and College, distantly spaced in latitude and longitude, the results of remote observation of pulsed electromagnetic, ultralow-frequency (ULF) signals detected from distant earthquakes are analyzed withinminutes of the seismic event. The daily and seasonal dependences of the frequency of occurrence of precursors in observatories and the nature of the spatial distribution of their generation zones on the Earth’s surface are studied. Two maxima are distinguished in the daily distribution of the recurrence frequency: in the evening and morning hours of local time. In the seasonal course, there is a maximum in the spring and an increase in the winter months. In the spatial distribution, there is an uneven location of sources around the globe: they are grouped into separate zones and cells that reflect separate regions on the map with manifestations of seismoelectromagnetic activity. Examples are given to illustrate the appearance of precursors. It is noted that the dynamic spectra of signals from earthquakes occurring in different regions of the Earth’s surface were similar. They were repeated at different magnitudes and focus depths and were observed in one time interval allocated relative to the moment of the earthquake. The results of the analysis indicated the universality of the processes of the generation of impulsive precursors preceding an earthquake, as well as the fundamental possibility of a short-term warning (of a few minutes) of an approaching earthquake.