By David Jacobson, Temblor and Manuel Berberian, Ph.D.
This morning, ten M=4.0+ earthquakes struck the Iran-Iraq border. The largest of these, a M=5.5 near the Iraqi city of Mandali, was also widely felt in Baghdad. Because the area around the epicenter is sparsely-populated, there are no reports of major damage, though five people were injured. However, some more minor damage has been seen close to the epicenter (see below). These earthquakes come less than two months after a M=7.3 quake struck less than 150 km to the north. That earthquake killed over 500 and destroyed numerous buildings.
Based on the USGS focal mechanism, this morning’s earthquakes were compressional in nature. This compression is due to the collision of the Arabian and Eurasian plates at a rate of approximately 24 mm/yr. This collision is also responsible for the formation of the Zagros Mountains, which extend through both Iran and Iraq. Today’s quake struck along the southern edge of the Zagros Mountains.
At this stage, it is not clear whether these earthquakes are remote aftershocks of the M=7.3 in November, or isolated events. Nonetheless, that have brought further shaking to the border region. This area was last strongly shaking when a M=6.1 earthquake in 1967 hit the area.
From the Global Earthquake Activity Rate (GEAR) model, which is available in Temblor, we can see if these earthquakes should be considered surprising or not. This model uses global strain rates and the last 40 years of seismicity to forecast what the likely earthquake magnitude is in your lifetime anywhere on earth. In the figure below, one can see that around this morning’s earthquake, a M=5.5+ is likely in your lifetime. Therefore, these quakes, while a reminder of the region’s seismic hazard, should not be considered surprising.