Investigating Time Dependent Stress Changes Globally Following Large Earthquakes (M≥7)

Abstract

Triggered earthquakes can cause disproportionate damages depend on their magnitudes. In fact, there is a causal link between the spatial distribution of those events and the stress changes induced by the mainshock. Co-seismic stress loading is one of the key factors in determination of triggering mechanism. However, the time lags ranging hours to years and the stress diffusion over wider areas cannot be evaluated with the co-seismic process alone. In some cases, the stress interactions for long periods and larger areas can be attributed to post-seismic viscoelastic relaxations. In this study, M≥7 earthquakes from the Global Centroid Moment Tensor (GMCT) catalogue are modelled as dislocations to calculate shear stress changes on following earthquake nodal planes near enough to be triggered. The catalogue scanned for all other events (4.5<M<7) that occurred within ±2° from the centroid rupture planes. According to Omori law, which is one of the most reliable time predictable diagram of aftershock distributions, 10-year periods were used for the stress calculations. The events that had computed within ±0.01 to ±1 MPa stress change limits, considered as potential triggered events. The global co-seismic stress calculations show that 60.6% of the triggered events occurred in regions where the shear stress increased. The global stress change by incorporation viscous flow into co-seismic stress change were also tested. In this case, an increase in the rate of triggered events in both positive (15%) and negative (9%) shear stress areas were obtained. Despite the rate of triggered events has climbed significantly in both areas, only 2% of the changes have been computed globally. These rates are highly depending on fault mechanism across the plate boundaries. Thrust faults in the catalogue, for example, influence the stress distribution over broader regions and the dimension of fault ruptures. Therefore, thrust faults in the catalogue prevails the global statistics for both co-seismic and viscoelastic stress calculations. The results also demonstrate the significant effect of viscous flow, following large earthquakes, which cannot be neglected in stress interaction analysis.