On the Devastating Earthquake at the Iran–Iraq Border

Abstract

The process of the lead up and development of a catastrophic seismic event that affected the Earth’s crust and the upper mantle, which led to a change in the natural environment in the western part of the Zagros folded mountain belt, is analyzed. The macroseismic effect, the focal mechanism, the aftershock sequence, the seismotectonic position of the epicentral area, and other parameters characterizing the features of the zone of this catastrophic earthquake with magnitude М = 7.4 that occurred near the Iran–Iraq border on November 12, 2017, are described. In one settlement (Iraq, the city of Dzharband khan), a macroseismic effect corresponding to 9-points according to the Modified Mercalli Intensity scale is recorded. An area of about 150 × 100 km2 underwent impacts of 7–8 points, tremors with the intensity of 5–6 points covered an extensive area of about 800 × 700 km2, and 4- to 5-point impacts were observed all over western Iran and eastern Iraq and appeared in major cities such as Tehran, Baghdad, Kirkuk, Ahvad, and Pasht. In the period from November 12, 2017, until January 21, 2018, more than 50 aftershocks with magnitude mb = 4.2–5.6 were registered in the epicenter zone of the earthquake according to data from the Federal Research Center Geophysical Survey of the Russian Academy of Sciences (RAS). Their epicentral area extended in the near-meridional direction along the Iraq–Iran border, primarily to the south from the epicenter of the main shock. Its length reached about 210 km and width was about 60 km. The position of the epicentral field of the aftershocks makes it possible to associate the earthquake focus of November 12, 2017, with the Khanaqin fault zone of the meridional strike and dextral strike-slip kinematics. The fault crosses Zagros diagonally near the Iran–Iraq border. Given that the size of the earthquake focus is established by the distribution of epicenters of the aftershocks, it covered the Khanaqin fault zone almost over its entire length. Sufficient attention is paid to the identified prognostic effects. The data of observations from geophysical observatories reflecting the processes of earthquake lead up and development are presented. Before the earthquake of November 12, 2017, the information and measuring systems of the North Caucasus geophysical observatory of Schmidt Institute of Physics of the Earth, RAS, had recorded gravitomagnetic disturbances of the ultralow frequency range. These prognostic effects appeared a few hours before the main shock. The conditions of the origination and development of seismogravity and gravitomagnetic disturbances are specified. In light of the presented material, it becomes clear that the experimental study of a separate class of fundamental gravitomagnetism problems identified in recent years is a defining problem of geophysics today. The gravitomagnetic disturbances in the lithosphere and other geospheres of the Earth recorded at large distances from the focal area can be considered a source of information on the time of appearance of the main high-magnitude shock. To use these effects for a real prediction of the expected magnitude and location and time of the pending earthquake, it is apparently necessary to develop a monitoring network at the observatory equipped with specialized measuring systems that can detect weak gravitomagnetic and seismogravity signals in the high-interference signaling environment on the Earth.