M5.3 Earthquake Strikes Offshore Oregon, January 30 2013

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Location and tectonic setting of the M5.3 Oregon earthquake. Image credit: USGS

Location and tectonic setting of the M5.3 Oregon earthquake. Image credit: USGS

A magnitude 5.3 (M5.3) earthquake occurred 160 miles off the Oregon coast in the early hours of January 30, 2013. At the time of writing, local news media reported no damage from the tremor, which occurred at a depth of 6.4 miles, and no tsunami warning was issued.

Oregon Earthquake: The Tectonic Setting

The state of Oregon lies immediately east of the Cascadia subduction zone, where the Juan de Fuca Plate (which forms the last remnants of a much larger plate, the Farallon plate) is subducting beneath North America, breaking into smaller plates as it does so. This collision, which is occurring at a rate of between 25-39mm per year, is the mechanism which gives rise to the uplift of the Cascade mountain range.

The January 30 earthquake did not, however, occur along the subduction front itself but along a fracture a fracture zone towards the south. The Blanco fracture zone lies between two offset segments of ocean ridge, where new crust is being created. The dominant movement here is strike-slip (lateral) – one factor (along with tis relatively small magnitude) which explains the lack of a tsunami.

Earthquakes in Oregon

The M5.3 is a relatively minor earthquake, in terms of magnitude and of damage: the state’s largest and most damaging tremors have, in the past, tended to occur on land above the subducting edge of the Pacific plate. Within Oregon, the largest tremor listed by the USGS in its historic earthquakes list is an M6.8 in 1910; two other earthquakes of above M6.0 were recorded in 1993 and 2003, the latter also along the Blanco fracture zone.

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