STRONG and FELT EARTHQUAKES of the TURKMEN-KHORASAN MOUNTAINS in 2017

Abstract

In 2017, the strongest earthquakes over the past two decades occurred in the central and southeastern Kopetdag – on April 5 with KR=14.3, MwGCMT=6.0 and on May 13 with KR=13.4, MwGCMT=5.7. The April 5 earthquake was also the strongest during the entire seismic history of a zone with a radius of 45 km from the epicenter. Both events were felt in the settlements of Iran, Turkmenistan, Afghanistan and other countries. The maximum shaking intensity was recorded in the nearest settlements of Iran – I=6 in the city of Torbet Jam during the earthquake on April 5 and I=7 in the city of Bojnurd during the event on May 13. For the earthquake of April 5, located in the contact zone of the southeastern Kopetdag with Binalud mountains, an isoseist map is constructed, on the basis of which the northwestern orientation of the isoseists are determined, coinciding with the strike of the nearest faults, of the aftershock cloud and of one of the nodal planes of the focal mechanism. At the same time, a southwest dip of the aftershock cloud is found, which does not correspond to the northeast dip of the nodal plane chosen as the active one. This discrepancy apparently indicates the complex structure of the fault zone, with areas of dip in different directions or with two parallel faults, which planes are dipping to the northeast and southwest. For the earthquake of May 13, 2017 in the central Kopetdag, which was preceded by a three-month seismic calm, the calm zone boundaries are defined, the spatial and temporal features of the aftershock process are studied. According to the determined equation of macroseismic effect propagation, the intensity at the epicenter of the May 13, 2017 earthquake is obtained – I0=7–8. This estimate is confirmed by the 7-point shaking intensity in Bojnurd (=24 km).