Static stress changes induced by the 1924 Pasinler (M=6.8) and 1983 Horasan-Narman (M=6.8) earthquakes, Northeastern Turkey

Abstract

The 1924 Pasinler & 1983 Horasan-Narman earthquakes which struck the Erzurum region occurred on the NE-SW-trending Horasan fault zone about 60 km east of Erzurum basin. The inversion of teleseismic seismograms, the aftershock pattern and the surface faulting of the 30 October 1983 (M-s, = 6.8) Horasan-Narman earthquake indicate that it had dominantly left-lateral motion. One moderately sized aftershock occurred 8 h after the main event and two others a year later on the NE extension of the fault zone. The aftershock distribution dominantly overlapped with the Horasan fault zone, and the aftershocks also migrated from south-west to north-east within the year following the mainshock, The results obtained from modelling of static stress changes caused by the 1983 earthquake are consistent with the spatial distribution of aftershocks. Macroseismic observations of the 1924 earthquake (M-s, = 6.8) indicated that this event occurred on the SW extension of the Horasan fault zone. Static stress modelling of the 1924 earthquake, by using the same input parameters of the 1983 event, has shown that its occurrence increased the stress in the region of the 1983 rupture zone. The static stress changes caused both by the 1924 and the 1983 earthquakes has increased the failure stress at the NE and SW extensions of the Horasan fault zone and in Narman area, Furthermore, the stress has decreased in the vicinity of the Erzurum fault zone, east of the city of Erzurum, the largest city in eastern Turkey, and in the populated Sarikamis area, This might delay the occurrence of a future probable damaging earthquake in these areas.