M4.8 Earthquake Strikes Near Santa Barbara: 29 May 2013

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California quake location – here’s where May 29 Santa Barbara earthquake struck. Image credit: USGS

Another California earthquake – magnitude 4.8 (M4.8) struck west of Santa Barbara, California, on 29 May at a depth of just 8km, but despite impact forecasts suggesting a 24% possibility of at least one fatality and a 30% change of economic loss, the area reports no damage.

Residents throughout the county felt the tremor, which was at its most intense in and around Santa Vista, where shaking registered as moderate to strong, and was followed by a number of smaller aftershocks.

Tectonic Setting of the 29 May Earthquake

The earthquake of 29 May had its epicentre off the Californian coast in the Ventura Basin, an area of complex reverse faults which is an important source of oil. The wider tectonic setting is one of continental movement, with the oblique motion of the Pacific plate against the North American plate giving rise to overall lateral movement along the boundary, characterised by the San Andreas fault zone.

Lying to the west of the main fault zone, the underlying geology of the Santa Barbara area consists of a mixture of sedimentary and other rocks which have been uplifted by the movement of the two plates. This continuing uplift (the USGS gives an average rate of 2-5 mm but also notes that a single earthquake event can cause an increase of up to 20 feet) has not only generated the Santa Ynes mountains which lie parallel to the shore, but is also the cause of extensive faulting within the Ventura Basin.

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