It is already well known that the "when, where and how strong" earthquake prediction problem cannot be solved by only analyzing the database from former earthquakes. A possible solution to this problem is proposed herein based on the analysis of the physicochemical processes as participants in earthquake preparation and on the characteristic rate of reflection of these processes on the Earth's surface. The proposed procedure includes monitoring of correlation of electromagnetic fields variations with tidal waves. This solution provides a way of selecting a complex of reliable earthquake precursors using the Inverse Problem Method for earthquakes which will occur in the region around the monitoring point (radial distance ≈ 700 km) in the next seven-day period [1].

In this paper we present an approach for forecasting the imminent regional seismic activity by using geomagnetic data and Earth tide data. The time periods of seismic activity are the time periods around the Sun-Moon extreme of the diurnal average value of the tide vector module. For analyzing the geomagnetic data behaviour we use diurnal standard deviation of geomagnetic vector components F (North, East, Down) for calculating the time variance GeomagSignal. The Sun storm influence is avoided by using data for daily A-indexes (published by NOAA). The precursor signal for forecasting the incoming regional seismic activity is a simple function of the present and previous day GeomagSignal and A-indexes values. The reliability of the geomagnetic "when, regional" precursor is demonstrated by using statistical analysis of day difference between the times of "predicted" and occurred earthquakes. The base of the analysis is a natural hypothesis that the "predicted" earthquake is the one whose surface energy density in the monitoring point is bigger than the energy densities of all occurred earthquakes in the same period and region. The reliability of the approach was tested using the INTERMAGNET stations data located in Bulgaria, Panagurishte, PAG (in the time of EU IRSES BlackSeaHazNet (2011-2014) project. The steps of program for solving the "when, where and how" earthquake prediction problem are shortly described. S. Cht. Mavrodiev et al. 103