Role of fault structural heterogeneity in nucleation location of the Mw\u2009≥\u20097 Earthquakes in Iran

Abstract

The along-strike geometrical complexity of the strong (M\u2009≥\u20097) earthquake fault ruptures in Iran is investigated to get insight into the high potential locations for the future earthquakes. Since 1900, 12 large earthquakes have been occurred in Iran that were scattered in the north, east and west of the country and can be categorized into four major groups. Four out of 12 M\u2009≥\u20097 earthquakes took place near the fault intersection (e.g., the 1909, 1978, 1979 and 1981 earthquakes), two large earthquakes near the restraining step overs (e.g., the 1930 and 1990 earthquakes), two large earthquakes near the restraining bends (e.g., the 1929 and 1997 earthquakes) and four large earthquakes near the fault linkages (e.g., the 1957, 1962, 1968 and 2017 earthquakes). It is concluded that the restraining features (i.e., step overs or bends) as well as the fault intersections and fault linkages mostly act as barriers, which storage large strain and then may be the host of the large earthquakes. All the main shocks in the study area were located in the positive Coulomb stress change areas. We present the probable nucleation sites on the faults with structural complexities in Iran as the potential points for the future earthquakes. Large earthquakes often have foreshocks, seconds or hours, before the occurrence. In the case of the 1930, 1990, 1997 and 2017 earthquakes, some foreshocks were reported and recorded. We found that the foreshocks happened near the extensional features along the main shock fault rupture at the weakest portions in which the normal stress reduced. The subsequent stress adjustment attributed to the foreshock breakage, may facilitate the eventual sliding and propagation of the entire rupture during the large earthquakes. It is concluded that the occurrence of foreshocks on the extensional features of the faults with geometrical complexities may be regarded as the warning sign before the strong earthquakes.