“Not another earthquake!” I am sure that this is the thought that most Japanese citizens would jump to if they heard that one of the absolute largest earthquakes ever recorded occurred earlier this year right on the Japanese sea border. The magnitude 8.3 earthquake rattled the earth below the Sea of Okhotsk, an area enclosed by the Russian, Chinese, and Japanese borders.
Luckily, this earthquake occurred deep below the surface, where even large motions do not cause significant effects on the surface, just as we cannot feel the shifting of tectonic plates. This earthquake was a ‘deep earthquake,’ which occur between 400 to 720 kilometers below the earth’s surface.
Unlike ‘shallow-focus’ earthquakes, which occur in depths less than 70 kilometers, such as the one that shook the Tohoku region in 2011, the frequency and magnitude of deep earthquakes is longer and smaller.
This deep earthquake, however, poses a new enigma to scientists. At a depth of an estimated 609 kilometers, it measured an 8.3 on the Richter magnitude scale. The 2013 earthquake created a new record for being the largest deep earthquake in documented history. It was 30 percent larger than the 1994 deep earthquake detected under Bolivia, an earthquake that previously was the largest deep earthquake.
Under immense pressure exerted by the miles of earth above, these earthquakes typically occur over a long period of time because quick shifts between tectonic surfaces are inhibited by the vast weight and pressure. Researchers constructed models to estimate the velocity and rupture duration of the Bolivian earthquake, which was calculated to be between one to two kilometers per hour, with about a 40 second rupture duration.
Seismologists worldwide are captured by this recent phenomenon. In particular, a group of seismologists are University of California at Santa Cruz has been studying the 2013 earthquake. In their recent publication, they create a model to describe the occurrences within the event. Using a model that takes into consideration the available potential energy, the static stress drop, and the rigidity of the location, they reason that the velocity of the earthquake was an approximate four kilometers per hour.