The town of San Ramon, in the East Bay, was the focus of this series of earthquakes. The area is located right above the Calaveras fracture, an active branch of the San Andreas fracture system.
The Calaveras fracture is likely to cause a 6.7 term earthquake, enough to affect millions of people in the San Francisco Bay area. The US GeologicalGS estimates a 72% chance of such a powerful earthquake occurring before 2043.
The series of earthquakes began on November 9, with a strong 3.8 richter. Since then, the earthquakes have occurred continuously and show no signs of stopping. The most recent earthquake, recorded on December 23, was strong at 2.7 degrees richter.
Although seismic events occurred in large numbers, that does not mean a major catastrophic is about to happen in the short term, said Sarah Minson, a research geophysicist at the USGS Seismology Center in Moffett Field, California.
Given the size and location of the earthquakes, there is currently no significant chance of a major event occurring over the major fractures, she explained.
A 6.7 term richter on the Calaveras fault will be classified as a major seismic event, which could cause serious damage in the densely populated areas of the East Bay.
For comparison, the 1989 Loma Prieta earthquake with a magnitude of 6.9 richter caused widespread devastation and was called a major earthquake at that time. The USGS is also currently using a 6.7 grade richter threshold to assess the long-term probability of a major earthquake in the San Francisco Bay area.
Little earthquakes, like any other small earthquake, are not a sign of a major upcoming earthquake, said Ms. Annemarie Baltay, a geophysicist at the USGS. However, we live in areas that are prone to earthquakes, so preparing for a major event is always necessary."
Baltay further explained that these small earthquakes are likely to appear due to fluid moving in the Earth's crust, a normal process. However, many system failures in the area can facilitate these micro-movements.
USGS data shows that similar earthquake clusters have occurred in the area in 1970, 1976, 2002, 2003, 2015 and 2018.
Such a phenomenon has happened many times before and since then there have been no major earthquakes, said Sarah Minson.
