It’s a typical query after an earthquake shakes the Bay Space and jolts folks’s consideration.
Does this imply a much bigger one is coming?
Typically. However not normally, consultants stated Monday, after a 4.3 magnitude quake centered in Berkeley awakened 1000’s of individuals throughout the Bay Space at 2:56 a.m. early Monday morning.
“There is a small chance that this is a foreshock to something larger,” stated Angie Lux, a seismologist on the Berkeley Seismology Laboratory. “But there is a less than 1%. It could happen but it is not really statistically significant.”
In response to the U.S. Geological Survey, the possibility of a smaller quake, with a magnitude 3, occurring in the identical space within the subsequent week is 16%. The probabilities of one other magnitude 4 are 2%. And a magnitude 5 or above? Lower than 1%.
Bigger earthquakes normally produce bigger aftershocks, she famous. When an aftershock is bigger than the primary quake, it turns into the primary quake, and the sooner quake is described as a foreshock.
That occurred in 2019 in the course of the Ridgecrest Earthquake, which occurred in close to the desert city of Ridgecrest in Kern County. On July 4 that yr, the primary principal shock, a 6.4 quake, hit at 10:33 am. It was adopted by greater than 1,400 aftershocks, lots of them small. However the subsequent day there was a 5.4 aftershock, and 4 hours later, the biggest quake, a 7.1 shook the agricultural space.
“A 4.3 earthquake like the one today is not a big earthquake,” Lux stated. “When there is a big quake, large aftershocks are expected because it has affected a large portion of the fault. This affected a smaller area, so there is less likelihood of it triggering a larger quake.”
Sarah Minson, a analysis geophysicist with the U.S. Geological Survey’s Earthquake Science Middle at Moffett Subject, famous that quakes 4.0 and above are comparatively uncommon.
Throughout the 56 years from 1967 to 2022, there have been 279 earthquakes in Bay Space counties that have been magnitude 4 or above, she famous. That’s about 5 per yr. A lot of these have occurred in rural areas, like northern Sonoma County close to the Geysers, or in unpopulated parts of the Diablo Vary.
“In most earthquakes, the largest aftershock is one unit lower than the main shock,” she stated. “So if you have a 4, the most likely aftershock is going to be a 3 or a 2 that you don’t even feel.”
Monday’s quake, the biggest within the Bay Space in almost three years, triggered no critical harm or accidents. It occurred alongside the Hayward-Rodgers Creek Fault. The final main quake there was in 1868. Traditionally, geologic research have proven a serious quake has occurred on the fault about each 140 to 170 years on common .
Monday’s occasion ought to encourage folks to bolt bookshelves to the wall, put putty beneath priceless vases and china, and put aside some provides in an emergency equipment, like 72 hours of water per particular person, Lux stated.
“Everybody wants to know when the next one is going to happen,” Lux stated. “We don’t know. But we know we live in earthquake country. Don’t get scared. Be prepared. One day it will happen.”
Initially Printed: September 22, 2025 at 2:14 PM PDT
