Coulomb stress changes caused by repeated normal faulting earthquakes during the 1997 Umbria‐Marche (central Italy) seismic sequence

Abstract

We investigate fault interaction through elastic stress transfer among a sequence of moderate‐magnitude main shocks (5 < Mw < 6) which ruptured distinct normal fault segments during a seismic sequence in the Umbria‐Marche region (central Apennines). We also model the spatial pattern of aftershocks and their faulting mechanisms through Coulomb stress changes. We compute stress perturbations caused by earthquake dislocations in a homogeneous half‐space. Our modeling results show that seven out of eight main shocks of the sequence occur in areas of enhanced Coulomb stress, implying that elastic stress transfer may have promoted the occurrence of these moderate‐magnitude events. Our modeling results show that stress changes caused by normal faulting events reactivated and inverted the slip of a secondary N‐S trending strike‐slip fault inherited from compressional tectonics in its shallowest part (1–3 km). Of the 1517 available aftershocks, 82% are located in areas of positive stress changes for optimally oriented planes (OOPs) for Coulomb failure. However, only 45% of the 322 available fault plane solutions computed from polarity data is consistent with corresponding focal mechanisms associated with the OOPs. The comparison does not improve if we compute the optimally oriented planes for Coulomb failure by fixing the strike orientation of OOPs using information derived from structural geology. Our interpretation of these modeling results is that elastic stress transfer alone cannot jointly explain the aftershock spatial distribution and their focal mechanisms.

Forecasting seismicity rates in western Turkey as inferred from earthquake catalog and stressing history

“…Nostro et al (2005) showed that this approach provides similar results with the isotropic poroelastic model (Beeler et al 2000;Cocco and Rice 2002). According to this model, the pore pressure changes depend on the volumetric stress changes such that DP = -BDr kk /3.…”

Fluid flow and seismicity pattern: Evidence from the 1997 Umbria‐Marche (central Italy) seismic sequence

“…Five out of six earthquakes occurred in areas of enhanced Coulomb stress by previous main shocks [Cocco et al, 2000;Nostro et al, 2005] showing evidences that the spatial pattern of seismicity is consistent with elastic stress interaction. However, the temporal evolution of seismicity shows a peculiar pattern: seismicity migrated and activated the southernmost main fault plane before the occurrence of its impending mainshock .…”

“…[6] Several features make the study of this sequence particularly interesting: (1) earthquakes were located with the double-difference and cross-correlation technique and the resulting errors are of the order of tens of meters [Chiaraluce et al, 2003]; (2) seismicity migrated toward the SE-direction progressively activating the main fault planes before the occurrence of their impending mainshocks ; (3) other [Nostro et al, 2005], but it cannot explain the presence of seismicity in the hanging wall of the main faults [Miller et al, 2004] as well as the temporal migration of seismic events; (4) there are evidence of the presence of fluids in this area [Chiodini et al, 2000]. All these factors motivate our study.…”

Strong Aftershock Study Based on Coulomb Stress Triggering—A Case Study on the 2016 Ecuador Mw 7.8 Earthquake

“…Coulomb stress triggering of moderate-to-large earthquakes has been observed in the US [4,[11][12][13], in Europe [14][15][16], on the Sunda Trench [17][18][19], and in Japan [20][21][22][23][24][25]. However, in South America and Ecuador, the stress triggering theory has yet to be extensively studied [26][27][28].…”