Offshore California, Indonesia and Central America: Earthquakes 12-18 December 2012

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Earthquakes of at least M4.0 ine the week of 12-18 December 2012. Image credit: USGS

The week of 12-18 December 2012 was characterised by a number of significant, but not major earthquakes.

The United States Geological Survey’s real time earthquake map shows a total of 85 recorded tremors of at least magnitude 4 (≥M4.0) of which 25 were ≥M5.0 and three over M6.0.

The distribution of the tremors showed that, as expected, there was plenty of activity along the southern edge of the Eurasian plate where it is forced against the Indo-Australian plate.

The whole area of the western Pacific, both along this boundary and further north, also showed high levels of movement, including a cluster of tremors in the area of the M7.3 off Japan on 7 December, where 6 aftershocks of between M4.0 and M5.0 were recorded.

Largest Earthquakes: California, Papua New Guinea and Indonesia

The largest earthquake of the week, and one which generated particular interest, was the M6.3 which occurred off the Californian coast on 14 December. Most Californian earthquakes are associated with the San Andreas Fault zone, the major transform boundary between the North American and Pacific plates. This earthquake was the result of faulting within the plate rather than at plate boundaries and was not associated with the boundary itself. Although it was the largest earthquake recorded in (or off) California so far in 2012, it was not a typical Californian seismic event.

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