Another One! Earthquake Rattles Southern California

Southern California was struck by a magnitude 4.0 earthquake on Saturday morning.

Good morning Southern California! Did you feel the magnitude 3.9 quake about 3 miles southeast of Ontario at 10:34 am? The #ShakeAlert system was activated. See: https://t.co/owsXYYHedY @Cal_OES @CAGeoSurvey @USGS_Quakes @ListosCA pic.twitter.com/qQXM9spkAm

— USGS ShakeAlert (@USGS_ShakeAlert) September 7, 2024

Shaking was felt across Los Angeles, Orange County and Riverside Counties.

A magnitude 3.5 earthquake first struck near Ontario at 10:05 am local time followed by a 4.0 quake at 10:34 am local time.

No reports of injury or damage.

Welp! Turns out that little M3.5 was a foreshock, because we just felt a M3.9 earthquake here in northern Orange County. We also got a @MyShakeApp alert! Looks like we have a new maximum magnitude for this area of the Fontana Trend. #earthquake #Ontario pic.twitter.com/w9DbkGTH9K

— Brian Olson ️ (@mrbrianolson) September 7, 2024

Seismologist Dr. Lucy Jones weighed in on the latest quakes to strike Southern California.

Today we are having a small swarm in the Fontana Seismicity Lineation, a northeast-striking line of many small quakes. Today we have so far M3.9, M3.5 and many M1s and M2s. I’ve seen this tyoe of cluster in Fontana dozens of times in my decades watching SoCal quakes.

— Dr. Lucy Jones (@DrLucyJones) September 7, 2024

I was going to argue about the maximum magnitude comment, sure that I remembered bigger ones in the past. But I searched the catalog and the largest quake of the last 90 years is the same M3.9 in 1953 https://t.co/IkzsjRBj82

— Dr. Lucy Jones (@DrLucyJones) September 7, 2024

Although a magnitude 4.0 quake is considered relatively small for California, the number of temblors that have hit the region this year is troubling.

Two sizable earthquakes struck Southern California last month.

I felt this quake for a change. A M5.2 located at the southern end of the Central Valley. It is near the White Wolf fault that produced a M7.5 in 1952 but does not appear to be on that fault.

— Dr. Lucy Jones (@DrLucyJones) August 7, 2024

I missed feeling this quake – I was parking the car at a grocery store. This was a M4.4 in South Pasadena, essentially the same location as the M3.4 on June 02.

— Dr. Lucy Jones (@DrLucyJones) August 12, 2024