California rocked by multiple earthquakes in less than 12 hours

California Shaken by Series of Earthquakes in Rapid Succession

California was rattled by a series of seismic events, experiencing three earthquakes within a 12-hour period. The recent earthquake activity has prompted discussions about earthquake preparedness in the region. The tremors, detected by the US Geological Survey (USGS), included a 2.8 magnitude quake in Monterey County and two others near San Francisco, raising awareness but causing no reported damage.

Recent Seismic Activity

The latest earthquake, registering a magnitude 2.8, struck Monterey County at 4:16 PM ET. Prior to this, two tremors were recorded near San Francisco:

• Magnitude 2.8: Near Dublin, at approximately 7:58 PM ET on Tuesday.
• Magnitude 2.9: Close to Orinda, about six hours after the Dublin quake.

According to assessments from Michigan Tech University, earthquakes below magnitude 2.5 are generally not felt. Earthquakes ranging from 2.5 to 5.4 are often perceptible and may cause minor damage, though none has been reported from these recent California events.

San Andreas Fault Concerns

The Monterey County earthquake originated from the San Andreas Fault, a major geological feature extending 800 miles across California. Experts have voiced concerns about the fault being overdue for a significant seismic event, sometimes referred to as the “Big One.”

Potential Impact of a Major Earthquake

Projections from the Great California Shakeout suggest that a magnitude 8 or greater earthquake on the San Andreas Fault could impact over 39 million people along the West Coast.

Details of Recent Earthquakes

Wednesday’s Monterey quake occurred at a shallow depth of 21 miles, with no immediate reports of ground shaking. In contrast, the two earthquakes near San Francisco were felt by nearly 2,000 individuals, as reported through the USGS’s “Felt Report” system.

Calaveras Fault

The San Francisco area earthquakes occurred along the Calaveras Fault, a significant branch of the larger San Andreas Fault system, known for moderate to large earthquakes in the past.

Historical Context: Major San Andreas Earthquakes

The San Andreas Fault has been the source of two major historical earthquakes:

• 1857 Fort Tejon Earthquake: Magnitude 7.9, causing ground fissures and damage across a wide area, including Los Angeles. Despite the severity, it resulted in relatively few casualties.
• 1906 San Francisco Earthquake: Also magnitude 7.9, this catastrophic event led to widespread destruction and an estimated 3,000 fatalities, leveling much of San Francisco.

Expert Perspectives on Future Earthquakes

Angie Lux, a project scientist at the Berkeley Seismology Lab, indicated a high probability of a substantial earthquake in the coming decades. Dr. Sue Hough, a scientist with the USGS Earthquake Hazards Program, noted ongoing research and differing opinions regarding precursory signs of major earthquakes, with some studies suggesting increased activity beforehand, while others indicate no such warning.

California Earthquake Statistics

As of this year, California has experienced a high frequency of seismic activity, including:

• Over 10,000 earthquakes up to magnitude 4.6.
• 104 earthquakes between magnitude 3 and 4.
• 637 earthquakes between magnitude 2 and 3.

Understanding Earthquake Mechanics

The majority of earthquakes are a result of tectonic plate movement. These massive plates, forming the Earth’s surface, are constantly shifting. Friction along their boundaries can cause stress to accumulate. When this stress surpasses the frictional force, the plates suddenly slip, releasing energy in seismic waves that cause ground shaking.