Key Takeaways
- A series of at least nine earthquakes struck southeast of San Ramon, California, with the largest having a preliminary magnitude of 4.0.
- The earthquakes occurred at depths of between 2.9 and 5.8 kilometers, with the closer to the surface an earthquake occurs, the more ground shaking and potential damage it will cause.
- The area has been hit by nearly 150 earthquakes in the past month, with the U.S. Geological Survey (USGS) attributing the frequent seismic activity to the complex geometry of the Calaveras Fault and other faults in the region.
- The USGS believes that the cracks in the faults allow fluids to infiltrate, leading to multiple small earthquakes occurring in quick succession.
Introduction to the Earthquakes
A wave of earthquakes struck southeast of San Ramon, California, on Friday evening, with the largest having a preliminary magnitude of 4.0. According to the U.S. Geological Survey (USGS), the 4.0-magnitude temblor occurred at 7:56 p.m., three miles southeast of the city, at a depth of 6.2 miles. This was not an isolated incident, as several other earthquakes were reported in the same area, ranging in magnitude from 2.1 to 3.8. The quakes were measured at depths of between 2.9 and 5.8 kilometers, which is relatively close to the surface.
Earthquake Details and Frequencies
The earthquakes occurred in quick succession, with the first reported at 7:41 p.m. and the last at 8:15 p.m. The magnitudes of the earthquakes varied, with the largest being the 4.0-magnitude quake at 7:56 p.m. Other notable earthquakes in the series included a 3.8-magnitude quake at 7:49 p.m. and a 3.1-magnitude quake at 7:57 p.m. The frequency and magnitude of the earthquakes are a cause for concern, as the area has been hit by nearly 150 earthquakes in the past month. This high level of seismic activity is unusual and has raised questions about the underlying causes.
Geological Explanation
According to Sarah Minson, a geophysicist at the USGS, the frequent earthquakes in the area can be attributed to the complex geometry of the Calaveras Fault and other faults in the region. The Calaveras Fault ends near San Ramon, and there is another thrust force coming in from Mt. Diablo, as well as other faults to the east, such as the Castro Green Valley Fault. This complex geometry creates a "cracked, messed up, geometrically very strange area" that allows fluids to infiltrate the faults, leading to multiple small earthquakes. The USGS believes that this is the primary cause of the frequent seismic activity in the area.
Impact on Local Residents
The earthquakes have had a significant impact on local residents, who are concerned about the frequency and magnitude of the quakes. ABC7 News spoke with several people at the City Center shopping mall, who reported feeling the earthquakes as they were doing their holiday shopping. One resident, Michala, described the experience as "just kind of weird" and noted that the earthquakes seemed to be coming from San Ramon. Another resident, Becky Zylberman, expressed concern about the frequency of the earthquakes, stating that "the first one was – and it’s just kind of weird they’re all coming out of San Ramon." The earthquakes have caused concern and disruption to daily life, with many residents wondering what is causing the frequent seismic activity.
Conclusion and Future Implications
The series of earthquakes that struck southeast of San Ramon, California, is a cause for concern, and the USGS is continuing to monitor the situation. The frequent seismic activity in the area is unusual and may be related to the complex geometry of the Calaveras Fault and other faults in the region. As the area continues to experience earthquakes, it is essential to stay informed and take necessary precautions to ensure safety. The USGS will continue to gather information and provide updates on the situation, and residents are advised to stay vigilant and prepared for any future earthquakes.
