Long-term stress modelling: Implications for large earthquake forecastingSuleyman Sami Nalbant Earthquakes occur when stress level on a fault reaches the yielding stress. Inability to know neither absolute stress levels nor yielding stresses on a fault is a major obstacle for seismologists to forecast future earthquakes. The technique of mapping Coulomb stress changes due to earthquakes inherently assumes an arbitrary zero stress level as a starting point in time. How far one should go back in time before the effect of this assumption disappears is unknown at present. In practice, this is actually limited with availability of historical seismic catalogs, rupture parameters and details of heterogeneous secular loading. Fortunately a section of the Sunda megathrust located along the west coast of Sumatra goes beyond these limitations over a time period longer than a seismic cycle. We have calculated Coulomb stress changes both coseismic and secular and scaled them with the coupling constants on the megathrust since 1797. We note that the rupture area of the 2005 M=8.6 Nias earthquake, slipped between 5 and 15 metres, has been correlated with high stress levels ranging from 18 to 48 bars before the occurrence of the earthquake. This is consistent with a model in which the rupture area of a future earthquake is controlled with correlated high pre-stressed areas on the fault plane. |
