Pattern of strong earthquakes

Abstract

The idea that one earthquake is associated with the occurrence of another earthquake is not new. In this study, we focus our attention on the relationships between the occurrence of a relatively strong earthquake in a certain seismogenic region and the occurrence of an earthquake of similar magnitude in a distant region. The complete catalog of seismic activity between 1904–2016 documents the subsequent events and over the years reveals a global, seismic activity pattern, (GSAP). This pattern is evident when an earthquake of magnitude M is followed within a relatively short period of weeks by an earthquake of a similar magnitude, and where the two events are located on latitudes of practically the same absolute value. Roughly 90% of all earthquakes of magnitude 6.5 and above follow the GSAP within a time window of less than a year. In addition, this high GSAP rate remains constant even after shuffling the dates of the earthquakes, several times. This is also evident in the current model of the tectonic plates and the frequency-magnitude relationships associated with each seismogenic zone. Subsequently, the observed seismic activity pattern is probably a statistical product and does not appear to relate to a physical causative process. At the same time, the significance of the GSAP, leads us to consider that the GSAP can be harnessed for statistical earthquake forecasting. This idea was, grounded and evaluated using synthetic earthquake catalogues where the success rates of forecasting an earthquake in catalog B followed the occurrence of an earthquake in catalog A. Additionally, the success rate of forecasting events in catalog B, according to the GSAP definitions are demonstrated to be statistically lower than the probabilities of a random occurrence in a similar magnitude earthquake which appears in ISC catalog B. These results were compared to actual cases. Arbitrarily selected pairs of seismogenic zones that are located on the same latitudes clearly demonstrate that the success rate of forecasting the earthquake occurrences that adhere to the GSAP are always higher than mere guesswork and therefor may be considered to offer a potential operational earthquake forecasting tool.