On Friday night, San Ramon was shaken by a series of earthquakes, marking notable geological activity in the region. The U.S. Geological Survey reported at least six earthquakes, each registering above a magnitude of 2.5.
Details of the Earthquake Swarm
The seismic activity began at 7:41 p.m. with an initial quake measuring 2.5. Just minutes later, at 7:49 p.m., two simultaneous tremors occurred, registering magnitudes of 2.9 and 3.6 respectively. A stronger quake, measuring 4.0, struck at 7:46 p.m., making it the most powerful quake that evening.
Subsequent Earthquakes
- First quake: 2.5 at 7:41 p.m.
- Second quake: 3.6 and 2.9 at 7:49 p.m.
- Fourth quake: 4.0 at 7:46 p.m.
- Fifth quake: 3.1 shortly after.
- Sixth quake: 2.9 within minutes.
The epicenters of these quakes were located east of the 680 Freeway and south of San Ramon. This region has recently experienced a significant increase in seismic activity.
Local Reactions
Residents expressed surprise and unease during the event. Krishna, a local, described the tremors as “really, really very loud” while she was on the top floor of a building. Another resident, Anabelle, described her car shaking back and forth, expressing some fear over the event.
Sarah, who also felt the tremors, compared the sensation to having too much to drink, despite being sober. Video footage captured during the earthquake swarm showed chandeliers swaying, highlighting the intensity of the events.
Recent Seismic Activity
This earthquake swarm is part of a broader pattern of seismic activity, with reports indicating a considerable frequency of smaller quakes throughout the preceding week. In fact, December has already recorded more than twice the number of earthquakes than the previous month.
The heightened seismic activity seen in San Ramon has not been observed for roughly a decade. The last significant spike occurred in November, where nearly two dozen quakes registered above a magnitude of 2. Additionally, the only comparable incident in the past 50 years occurred during a two-month period in 2015.
Understanding Earthquake Swarms
Earthquake swarms are characterized by a series of small quakes occurring in a short time in the same area. Experts clarify that such swarms do not necessarily predict larger quakes. According to a 2019 USGS report, swarms may indicate various geological processes, including:
- Slow movement along fault lines.
- Magma activity pushing against the Earth’s crust.
- Fluid interactions with geological faults.
Despite the rattling experience, residents are reminded that earthquake swarms typically have no correlation to imminent dangers.
