Identification of trends in the Tancítaro-Parícutin seismic swarm sequence through fractal characteristics of inter-event times

Abstract

Seismic swarms in a volcanic field can be indicators of the movements of volcanic activity and stagnant magma in the Earth’s crust. In the Tancítaro-Parícutin volcanic region, to the west of the Michoacán-Guanajuato volcanic field in Mexico, at least six seismic swarms have occurred in the last 25 years. However, greater precision is still required due to the distance between and non-permanence of the seismic stations. We used data from a broadband station of the Earth Sciences Research Institute (INICIT-UMSNH) and records from Mexican National Seismological Service (SSN), Center for Geosciences (UNAM) and Mexican National Center for Prevention of Disasters (CENAPRED) to relocate and obtain focal mechanisms for four selected seismic events. We applied the fractal methodology to analyze the inter-event times of the seismic swarm sequences. Two well-defined swarm sequences were identified, and, subsequently, the fractal behavior of the logarithm of inter-event times was analyzed by means of the Hurst and Holder exponent. Our goal was the identification of the different dynamical stages acting during the seismic swarm generation processes, that seem to be related to the stress transfer in different seismogenic faults. By means of the b-values and the temporal evolution of the Hurst exponent, at least five different stages can be distinguished during the Tancítaro-Parícutin seismic swarms. These stages appear to be determined by dynamic changes in the seismic sequence, also indicated by the focal mechanisms whose fits with faults that were apparently activated during the seismic swarm. The Tancítaro-Parícutin seismic swarm processes indeed show multi-fractal behavior, which may be related to different stages in the diffusion process.