Wednesday, a 4.1 earthquake shook California 2 miles northeast of Yorba Linda and 5 miles east-northeast of Placentia. The United States Geological Survey reports that the quake began at 1:31 pm and could be felt from Seal Beach to San Clemente.
The event seems to have had no serious effects on the area, as the Orange County Fire Authority reports in the following tweet: "OFCA has had no damage reports as a result of the 4.1 mag earthquake in Yorba Linda. We are in normal operations."
Following the Yorba Linda quake, another one hit Brawley which registered as a 2.6. However, this is just the latest in a series of tremors to impact Brawley.
Brawley, California, a small town with 25,000 citizens located southeast of Los Angeles, was the target of a cluster of earthquakes this past Sunday.
While earthquakes are not unusual in Los Angeles, what stood out in this case was their frequency. After the initial earthquake, which was recorded with a magnitude of 3.9, about 300 aftershocks followed. They were mostly tremors, but the event was punctuated with both a magnitude 5.5 and a magnitude 5.3 quake. Earthquake clusters such as this have been known to last as long as two weeks.
U.S. Geological Survey geophysicist Robert Graves revealed that "The type of activity that we're seeing could possibly continue for several hours or even days,"
Since the cluster hit Brawley, scientists have been observing it, curious if a larger fault could be triggered as a result. One such fault is the Imperial Fault, the source of a magnitude 7.0 earthquake that occurred in 1940.
Jeanne Hardebeck, research seismologist for the U.S. Geological Survey states that "We don't have any reason to believe that the [earthquake] storm is going to trigger on the Imperial Fault, but there is a minute possibility that it could."
The mayor of Brawley, George Nava, admitted that "It's not uncommon for us to have earthquakes out here," but added that "this frequency and at this magnitude [is] fairly unusual."
And the fact that the aftershocks keep coming are a little alarming," he continued.
While we know that the quake cluster was caused by the movement of hot fluid in the Earth's crust, we don't know what triggers them.
"They seem to light up and turn off for reasons we don't understand," said USGS seismologist Susan Hough.
Hardebeck repeated the sentiment, stating: "We understand them even less than we understand normal earthquakes."