NGDIR News Section-- The November 12, 2017 M 7.3 earthquake near the Iran-Iraq border in northwest Iran (220 km northeast of Baghdad, Iraq) occurred as the result of oblique-thrust faulting at mid-crustal depth (~25 km). Preliminary focal mechanism solutions for the event indicate rupture occurred on a fault dipping shallowly to the east-northeast, or on a fault dipping steeply to the southwest. At the location of this earthquake, the Arabia plate is moving towards the north with respect to Eurasia at a rate of about 26 mm/yr. The two plates converge along a northwest-striking plate boundary in the general vicinity of this earthquake, driving the uplift of the Zagros mountains in Iran. The location of the event and the shallow, northeast-dipping plane of the focal mechanism solution are consistent with rupture of a plate boundary related structure in this region.
While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Oblique-thrust-faulting events of the size of the November 12th, 2017 earthquake are typically about 65x25 km (length x width).
Over the preceding century, the region within 250 km of the hypocenter of the November 12, 2017 earthquake has experienced 4 other M6+ earthquakes. The most recent of these was a M 6.1 earthquake about 100 km to the south of the November 2017 event in January 1967. In the late 1950s and early 1960s, a cluster of M 6.0-6.7 earthquakes occurred along the plate boundary about 200 km to the southeast of today's earthquake. In November 2013, a pair of M 5.6 and M 5.8 earthquakes occurred about 60 km south of the November 2017 event. They are not known to have caused significant damage or fatalities. A M 7.4 earthquake in June 1990, 400 km to the northeast of the November 12, 2017 event, caused between 40,000-50,000 fatalities, more than 60,000 injuries, and left more than 600,000 homeless in the in the Rasht-Qazvin-Zanjan area of Iran.