Temporal Distribution of the Aftershocks after the February 14th, 2023, Mw 5.4 Romania

Abstract

We apply statistical analysis to study the temporal pattern of earthquake occurrence in the aftershock sequence of the 2023 Romania M_W 5.4 earthquake. The temporal clustering of aftershocks is a dominant non-random element of the seismicity, so that, when the clusters are removed, the remaining activity can be modelled as a Poisson process (as first approximation). The maximum likelihood method was used for estimating the parameters (K, c and p) in the modified Omori formula for the aftershock sequence. The goodness of fit between the aftershock occurrence and different statistical models has then been tested using a transformation from the time scale t to a frequency-linearized time scale τ. It is assumed that on this time axis the aftershocks are distributed in time as a standard stationary Poisson process if the choice of the parameters K, c and p is correct. We further used the Akaike Information Criterion as a measure for selecting the best among competing models. The aftershock sequence of the February 14th, 2023, M_W  5.4 Romania earthquake is best modelled by the combination of one ordinary and one secondary sequence.