It's become an almost regular event. For three weeks in a row, a swarm of small quakes has rattled parts of Ventura and Los Angeles Counties.
Last Sunday’s quake had a magnitude 3.9. On March 9, it was a 4.1. And, on March 2 it was a 3.9. All three quakes were accompanied by a string of smaller temblors
So, what’s the story behind the seismic activity? A seismologist thinks a fault in the Malibu area may be the source of the activity.
The epicenters of the quakes have been occurring in the same general area, about eight miles south of Thousand Oaks, or about six miles northwest of Malibu.
"They're on the Malibu Coast Fault. As far as any fault that's close by, and would project down to that depth, it's probably the Malibu Coast Fault," said Ralph Archuleta, a seismologist who’s spent decades doing earthquake-related research at UC Santa Barbara.
"The Malibu Coast Fault sort of runs parallel to the coast of Malibu. But, right in that area (where the epicenters have been occurring) is where it turns, and then starts going in a more southerly direction, and then goes out into the channel...sort of like a bend in the fault is where these things are occurring," said the seismologist.
Archuleta added that the fault doesn’t have a history of major earthquakes but is capable of having one. "It's not very active. I don't recall any major earthquake like a magnitude 6 or greater having occurred on that fault. But, it's capable of producing a 6, a 6.5 quake."
The flurry of quakes in the region raises questions about what they mean. While they could be a precursor of something bigger, Archuleta said it’s statistically unlikely.
"If you have an earthquake, you have a 5% chance that there will be another earthquake at least one magnitude unit larger within 24 hours or 48 hours. It's like one in 20," said Archuleta.
Archuleta thinks the quakes are more likely a sign of pressure in a bend in the Malibu Coast Fault. "This is a place where there's a bend in the fault, maybe it's under a little bit more stress and so it's releasing some of that stress right now," said Archuleta.
"If you have an earthquake, you have a 5% chance that there will be another earthquake at least one magnitude unit larger within 24 hours or 48 hours. It's like one in 20,"Seismologist Ralph Archuleta
"As a seismologist, any time you start to see a cluster of earthquakes, you start to think, is this going to be a hypocenter for a larger earthquake? But, a lot of times they just die off. Nothing happens."
Researchers feel the recent quakes emphasize the need to be prepared for the potential for a major quake, and not just where the recent temblors have been focused. The Tri-Counties has several faults, including a series in the Santa Barbara Channel.
For instance, there’s one that stretches from downtown Ventura to the Santa Barbara and Goleta areas. It's known as the Ventura-Pitas Fault. Researchers have said it has the potential to generate a magnitude 7 quake.
The recent string of temblors between the Thousand Oaks and Malibu areas didn’t cause any injuries or significant damage. But, they may be providing an important wake-up call for the region to be prepared for when something much larger will occur.
