Stress relations in three recent seismic series in the Murcia region, southeastern Spain

Abstract

In this work we study the relation between the seismicity belonging to three recent seismic series in the Murcia region, southeastern Spain, with the coseismic stress changes due to their largest shocks. The first series occurred in 1999 near the town of Mula, with a mainshock magnitude of Mw = 5.1; the second series occurred in 2002, in the region of Bullas 35 km SW from the 1999 series, with events of magnitudes Mw ≤ 5.0. The last one occurred three years later (2005), 5 km SE from the 2002 series with magnitudes of events Mw ≤ 4.8. For the analysis, we relocated the seismicity of each series, next we computed the coseismic stress change produced by its main events and a foreshock and finally tested the possible stress relations inside and among the series based on the Coulomb Failure Stress changes. Our results show that the Mula 1999 main earthquake, associated in different publications to the Crevillente fault, was positively influenced for triggering by the foreshock. We also find that the 1999 series aftershocks were jointly influenced for triggering by both the foreshock and the mainshock events. From a comparative analysis of P wave arrivals, the series seems to be associated to different neighbouring seismogenic zones belonging to the Crevillente system. For the Bullas 2002 and the Bullas–La Paca series, we found that it is unlikely that any of them have been triggered by the previous Mula 1999 event, but it appears that the main event in 2002 had an important influence on the triggering of its aftershock activity and the promotion of the mainshock and aftershock seismicity in the zone of the 2005 series. Summing the effects of the last two main events, it may have been produced different zones of high stress increase on the aftershock area of the 2002 and 2005 series. Finally, the seismicity of the two latest series could be associated to different neighbouring seismogenic zones.