San Cayetano Fault? Earthquake swarms hit north-northwest of Santa Paula

August 22, 2012
Santa Paula News

Three small earthquakes near Santa Paula were reported early Sunday morning, just the latest in a series of swarms that also struck near the same area on Saturday and Wednesday, according to the U.S. Geological Survey.

The 12 recorded seismic events occurred at or in the vicinity of the San Cayetano Fault, which ranges north of Santa Paula. Most of the dozen small earthquakes - the largest was a 3.0 magnitude on the Richter scale - were mapped in an area near or at the intersection of San Cayetano and Mission Ridge-Arroyo Parida faults.

Sunday’s first earthquake was reported at 12:05 a.m. and registered a 2.0 on Richter scale. It was centered six miles north-northwest of Santa Paula and eight miles east of Ojai, and struck 7.5 miles deep, the agency reported.

One minute later at 12:06 a.m. another 2.0 magnitude quake struck six miles northwest of Santa Paula and six miles east-southeast of Ojai at a recorded depth of 12.1 miles. The final micro-earthquake in the morning hours of August 19 was recorded at 2:38 a.m. and registered a 1.5 magnitude, seven miles north-northwest of Santa Paula at a recorded depth of 6.3 miles.

On Saturday, August 18 six earthquakes struck the same area, with the largest earthquake registered a 3.0 magnitude and the others ranging between 1.7 and 2.7 magnitude. The micro-earthquakes - 1.7, 2.0 and 3.0 and two others registering at 2.7 - were recorded Saturday between 7:40 a.m. and 7:52 a.m., and according to the USGS were followed at 12.22 p.m. with the last event of the day, which registered 1.7 magnitude. All were recorded in the same general area of the others, five to six miles north-northwest of the city.

The swarms started Wednesday, August 15 with three events: the first one was a 1.6 magnitude recorded at 8:09 p.m., occurring six miles north-northwest from Santa Paula at a depth of 8.1 miles. The second shaker, a 1.3 magnitude event, was recorded at 8:18 p.m. at a depth of 7.4 miles, also six miles north-northwest of Santa Paula.

Wednesday’s third micro-earthquake was the largest, a 1.9 magnitude event that was recorded 8.4 miles below the Earth’s surface at 8:34 p.m. It was also mapped six miles north-northwest from Santa Paula.

The magnitude-3.0 earthquake was rated with an intensity level that meant it was likely “felt only by a few persons at rest, especially on upper floors of buildings,” according to the USGS website. Intensity is determined by a quake’s “effect on people, human structures, and the natural environment,” according to the website.

Sixteen people from as far as Oxnard reported they felt two of the larger events that registered 3.0 and 2.7 on the Richter scale. In years past, swarms of small earthquakes have been reported in the neighboring Fillmore area.

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