Estimating the Epicenter of an Impending Strong Earthquake by Combining the Seismicity Order Parameter Variability Analysis with Earthquake Networks and Nowcasting: Application in the Eastern Mediterranean

Abstract

The variance κ1 of the natural time analysis of earthquake catalogs was proposed in 2005 as an order parameter for seismicity, whose fluctuations proved, in 2011, to be minimized a few months before the strongest mainshock when studying the earthquakes in a given area. After the introduction of earthquake networks based on similar activity patterns, in 2012, the study of their higher order cores revealed, in 2019, the selection of appropriate areas in which the precursory minima βmin of the fluctuations β of the seismicity order parameter κ1 could be observed up to six months before all strong earthquakes above a certain threshold. The eastern Mediterranean region was studied in 2019, where all earthquakes of magnitude M≥7.1 were found to be preceded by βmin without any false alarm. Combining these results with the method of nowcasting earthquakes, introduced in 2016, for seismic risk estimation, here, we show that the epicenter of an impending strong earthquake can be estimated. This is achieved by employing—at the time of observing the βmin—nowcasting earthquakes in a square lattice grid in the study area and by averaging, self-consistently, the results obtained for the earthquake potential score. This is understood in the following context: The minimum βmin is ascertained to almost coincide with the onset of Seismic Electric Signals activity, which is accompanied by the development of long range correlations between earthquake magnitudes in the area that is a candidate for a mainshock.

Estimating the Epicenter of a Future Strong Earthquake in Southern California, Mexico, and Central America by Means of Natural Time Analysis and Earthquake Nowcasting

“…In this figure, we observe that the fit using the Weibull distribution provides a fair approximation with root mean square of residuals [ 102 ] equal to 0.0177. This property of the Weibull distribution is in accordance with the results found by Pasari and Sharma [ 79 ] for Himalayan EQs as well as with those later found in Reference [ 19 ] for Eastern Mediterranean.…”

“…To estimate the seismic risk, EN uses an EQ catalog to calculate from the number of ‘small’ EQs, defined as those with magnitude but above a threshold , i.e., , the level of hazard for ‘large’ EQs. As mentioned in the Introduction, the EQ catalogs adopted [ 11 , 12 , 19 , 77 , 78 , 79 , 80 , 98 ] are global seismic catalogs such as the Advanced National Seismic System Composite Catalog or the NEIC PDE catalog and for the completeness threshold of the EQ catalog is usually selected [ 11 ]. Along these lines, the magnitude threshold has been considered [ 12 , 78 ] for applications in areas such as Greece, Japan, and India that lie outside the United States.…”

“…In Section 3 of Reference [ 19 ], it has been shown that the 〈EPS〉 mean value where the summation is made over all the lattice points , estimated numerically in an 〈EPS〉 map drawn with self-consistency radius R and covering an area A of average radius may take the form where is related to [ 19 ] the fractal dimension [ 103 ] of EQ epicenters.…”

“…Recently, our group has combined [ 19 ] NTA and EN together with the properties of the earthquake networks based on similar activity patterns (ENBOSAP) [ 20 , 21 ] for a similar purpose in the Eastern Mediterranean region where seismicity is much less intense than in the region N W of our present interest. We see that when strong EQs are frequent, as is the present case, we can simplify the approach of Reference [ 19 ] just by using NTA and EN.…”

“…Especially for seismicity, the study of this order parameter by means of its variability [ 56 ] revealed [ 9 , 21 , 57 , 58 , 59 , 60 , 61 , 62 , 63 ] the presence of characteristic minima before the occurrence of strong EQs. Interestingly, the precursory Seismic Electric Signals (SES) activities [ 64 , 65 ], which are a series of low frequency electric signals ( 1 Hz) observed before strong EQs [ 64 , 65 , 66 , 67 , 68 , 69 , 70 ] have been shown to appear [ 19 , 71 , 72 ] almost simultaneously with the variability minima.…”