Swarm Of Earthquakes Strike California: Scientists Watching San Andreas Fault

HOLLISTER, CA — An earthquake swarm that struck central California this week has scientists keeping an eye on the well-known San Andreas Fault.

According to data supplied by the U.S. Geological Survey in Menlo Park, an earthquake swarm struck the area near Ridgemark — just south of Hollister — Sunday night into Monday morning, when 18 earthquakes of varying intensities struck within a 24-hour period.

It's been a common occurrence lately.

On Tuesday afternoon, a magnitude 4.2 quake struck the area at 2:38 p.m.

That night, another temblor hit, when a 3.0 quake was reported, south-southeast of Ridgemark, at 10:14 p.m., according to the USGS. The quake was felt as far away as Atascadero to the south.

The area lies directly over the San Andreas Fault.

The Oct. 17, 1989 Loma Prieta earthquake is the most recent major earthquake associated with the San Andreas Fault. The 7.9 magnitude 1906 San Francisco earthquake was the largest earthquake ever recorded on the fault, according to the USGS.

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According to the Weather Channel, scientists at the USGS are not overly concerned about the most recent swarm of quakes and say it is unlikely to be a sign the "big one" is on the way.

The USGS website describes an earthquake swarm that occurred in Brawley, California, in 2012:

An M5.5 earthquake occurred at 1:57PM PDT on August 26th, 2012, and was preceded by nearly 200 events ranging M1.4-5.3. The snapshot below is the swarm as of the morning of August 28.

To give you an idea of some of the recent Ridgemark activity, here's a recent rundown of earthquakes reported in California, according to the USGS, with magnitude, location, date, UTC time of the quake, and depth. UTC 24-hour time time is seven hours ahead of Pacific Standard Time:

1. 3.0 - 2km WSW of San Juan Bautista, California

   2016-07-20 07:08:04 (UTC)

   5.6 km
2. 3.0 - 14km SSE of Ridgemark, California

   2016-07-20 05:14:04 (UTC)

   3.2 km
3. 2.9 - 14km SSE of Ridgemark, California

   2016-07-19 21:48:15 (UTC)

   5.6 km
4. 4.1 - 13km NE of Chualar, California

   2016-07-19 21:39:20 (UTC)

   2.1 km
5. 4.2 - 13km SSE of Ridgemark, California

   2016-07-19 21:38:38 (UTC)

Image of 1989 Loma Prieta earthquake damage via CIR Online/Flickr