Doublet earthquake

Seismologists sometimes refer to a pair of similarly sized earthquake shocks that occur relatively closely spaced in time and location as an earthquake "doublet." This is distinct from the normal pattern of earthquake aftershocks. Aftershocks gradually diminish in magnitude and generally come from the same origin as a mainshock, whereas doublet earthquakes originate from a place other than the original earthquake. The first earthquake can be some considerable distance and time away from the second. The magnitude of the second quake may be slightly larger than the first. This type of earthquake occurs once or twice every year but are far rarer than more typical earthquakes. In earthquake prone regions officials do not plan on doublet earthquakes occurring since they are a rare occurrence. However, when they do occur, they have a high disaster potential.

A relatively recent doublet earthquake occurred late in 2006 and early in 2007 in the Kuril Islands of Japan, which had not had a large-scale earthquake since 1915. The first earthquake occurred on November 15 and had a magnitude of 8.3. Shortly after this, seismic activity began in the Pacific plate where the second earthquake occurred on January 13, which had a magnitude of 8.1. There was only 1 reported injury from the first earthquake and no reported injuries from the second earthquake since they both originated in the ocean. However, each earthquake caused a tsunami and the earthquake on November 15 created a tsunami that reached the coast of California, causing $500,000- $1,000,000 in damage. There may also be examples of triplet earthquakes, such as the 2010 Mindanao earthquakes.

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