Interoccurrence times and seismic hazard for upper-crustal volcanic chain earthquakes in El Salvador: are they Poissonian distributed?

Abstract

We study the statistical properties of time intervals between successive earthquakes for a given magnitude in the El Salvador volcanic chain, namely hereafter the interoccurrence times employing both the cumulative Poisson and the Weibull probability distributions. The dataset comprises magnitudes between M 4.0 and 6.93 within the years 1528–2018. We suggest that ITs pose the Weibull distribution for all events and that the Poisson distribution co-exists for ITs longer than the Weibull mean. Based on the probabilities distribution fit, we compute for engineering purposes ground motion and elastic response spectra for 5% damping employing time-dependent and independent seismic hazard models at San Salvador city, observing covariance of less than 7% amongst the models. The disaggregation analysis suggests that a magnitude 6.3 contributes most to the hazard and coincides with the magnitude bin of 6.25–6.50, which has the maximum conditional probability in the time-dependent model.