USGS is reporting many earthquakes in Iran, including a magnitude 5.1 and magnitude 4.1 seismic event which struck yesterday and the day before respectively. Overall, there have been 9 earthquakes over the country in the last few weeks, with many occurring since fighting between Iran and Israel escalated.
Iran is one of the most seismically active countries in the world, being crossed by several major faults that cover at least 90% of the country. As a result, earthquakes in Iran occur often and are destructive. The Iranian plateau is subject to most types of tectonic activity, including active folding, faulting and even volcanic eruptions. It is well known for its long history of disastrous earthquake activity. Since 1900, at least 126,000 fatalities have resulted from earthquakes in Iran.
In addition, the Iranian plate is bordered by the Indian plate to the southeast, the Eurasian plate to the north, and the Arabian plate to the south and west. The close proximity to these plate boundaries and constant movement among the plates makes it susceptible to frequent earthquakes.
Much of the earthquake activity is light to mild with significant lethal quakes occurring less often.
The earthquakes in the last 72 hours are notable though because they’ve been the strongest to strike in the country over the last 30 days and because they’ve struck away from plate boundaries in areas that usually don’t see significant earthquakes.
According to USGS, earthquakes with a magnitude of 2.0 or less are rarely felt or heard by people, but once they exceed 2.0 , more and more people can feel them. While damage is possible with magnitude 3.0 events or greater, significant damage and casualties usually don’t occur until the magnitude of a seismic event rises to a 5.5 or greater rated event.
It isn’t clear what is creating these seismic events; while sensors around the world can’t detect them, without accurate ground truth by scientists or other observers on the ground, it’s hard to say with a high degree of confidence what is responsible. They could be plate-boundary related or they can even be bombing attacks or bombing tests.
USGS says that a nuclear explosion can cause an earthquake and even an aftershock sequence. However, earthquakes induced by explosions have been much smaller than the explosion, and the aftershock sequence produces fewer and smaller aftershocks than a similar size earthquake. Not all explosions have caused earthquakes. The range of a possible earthquake triggered by an explosion is limited to a few tens of kilometers from the shot point.
USGS has done research to see what weapons can do to trigger earthquakes. The possibility of large Nevada Test Site nuclear explosions triggering damaging earthquakes in California was publicly raised in 1969. As a test of this possibility, the rate of earthquake occurrence in northern California (magnitude 3.5 and larger) and the known times of the six largest thermonuclear tests (1965-1969) were plotted and it was obvious that no peaks in the seismicity occur at the times of the explosions.
According to USGS, the largest underground thermonuclear tests conducted by the U.S. were detonated at the western end of the Aleutian Islands in Amchitka. The largest of these was a five megaton test that occurred on November 6, 1971 with an energy release equivalent to a magnitude 6.9 earthquake. While it was a powerful bomb which created its own shaking, it did not trigger any earthquakes in the seismically active Aleutian Islands.
