Natural Time Analysis of Seismicity in California: The epicenter of an impending mainshock

Upon employing the analysis in a new time domain, termed natural time, it has been recently demonstrated that a remarkable change of seismicity emerges before major mainshocks in California. What constitutes this change is that the fluctuations of the order parameter of seismicity exhibit a clearly detectable minimum. This is identified by using a natural time window sliding event by event through the time series of the earthquakes in a wide area and comprising a number of events that would occur on the average within a few months or so. Here, we suggest a method to estimate the epicentral area of an impending mainshock by an additional study of this minimum using an area window sliding through the wide area. We find that when this area window surrounds (or is adjacent to) the future epicentral area, the minimum of the order parameter fluctuations in this area appears at a date very close to the one at which the minimum is observed in the wide area. The method is applied here to major earthquakes that occurred in California during the recent decades including the largest one, i.e., the 1992 Landers earthquake.