Earthquake of April 5, 2017, MW = 6.0, in Northeast Iran: Focal Parameters, Aftershock Series, and Macroseismic Manifestations

Abstract

The article considers the earthquake of April 5, 2017 with M_{W GCMT} = 6.0 near the Turkmen–Iranian border, northeast of the Iranian village of Sefid Sang. During the entire seismic history of the region, this was the strongest seismic event within a 45 km radius of the epicenter. The earthquake caused widespread destruction in four villages; two people died and 100 were injured. The shaking was felt in population centers in Iran, Turkmenistan, and other countries. According to the compiled isoseist map, the northwestern orientation of isolines of equal intensity, coinciding with the strike of the nearest faults, and strong damping of the shaking intensity across tectonic structures were established. The macroseismic field equation has been established, which is close to the Blake–Shebalin equation with average world coefficients. According to both equations, the shaking intensity at the epicenter is estimated as I₀ = 8. The northwestern (southeastern) orientation of the aftershock cluster and their southeast migration were revealed, which made it possible to choose the nodal plane of the focal mechanism with a similar strike as the active one. The fault plane parameters, length L = 30 km and width W = 12 km, have been estimated for the area of the highest aftershock density. The law of the decrease in the number of aftershocks with time has been established, which indicates rapid decay of the aftershock process.