Thursday, April 7 Japan’s northeastern coast was rocked by a 7.1 magnitude earthquake less than a month after being hit by a magnitude 9 earthquake and tsunami. William & Mary Geology Professor Chuck Bailey discusses the aftershock and a 6.5 earthquake in Mexico the happened on the same day.
How unusual is it to have high magnitude quakes so close together?
Typically, there are 10 to 20 magnitude 7 earthquakes per year, say one per month on average. Magnitude 6 quakes are more common, in any given year 120 to 150 might occur, which averages out a to a magnitude 6 quake, somewhere in the world, every few days. These quakes occurred within two hours of one another, which is somewhat unusual, but not particularly significant.
Could the Mexico and Japan quakes be related ?
It is very unlikely that these two earthquakes are related. They are many thousands of kilometers apart and the shortest path, between the quakes focal points, is through the deep Earth. The Veracruz quake was rather deep and likely related to subduction of the Cocos plate under Central America, the Japanese quake is another of the many aftershocks associated with the March 11th quake produced as the Pacific plate is subducted.
Japan, now Mexico. Quakes getting closer to U.S., could Memphis be next?
There is no reason to reach the conclusion that quakes are getting ever closer to the United States. In the past month over 250 earthquakes of magnitude 3 or larger have occurred in the United States, none have been large or damaging quakes, but seismicity is an ongoing process.
What do you think is most significant about these events?
The array of both foreshocks and aftershocks from the Japanese earthquake is impressive. A huge amount of energy was released by the magnitude 9 quake and the large displacement of the crust along the ruptured fault has further stressed the crust producing numerous aftershocks that, on their own, are significant earthquakes.