ISLETON – Another earthquake hit Sacramento County on Monday in the same area that was hit by a larger quake one week ago.
Thequake hit less than a mile northwest of Isleton in the Sacramento-San Joaquin Delta and was called an aftershock to last week’s quake. Although smaller than the earthquake on Wednesday, the people in Isleton said they still felt the shaking.
“It is scary because I have been having nightmares that I am in an earthquake,” said Myriam Carbajal, who works at Dejacks Country Store in Isleton.
The shaking was more intense last Wednesday, but at around 7:45 a.m. Monday, Carbajal felt the movement again.
“I didn’t think it was an earthquake,” said Carbajal. “I thought we were over it.”
The aftershock was first recorded as a 4.0 magnitude earthquake and then downgraded to a 2.9 magnitude quake, followed by a 2.5 quake an hour later.
“The sediments have a tendency to intensify the seismic waves to make them look bigger. It actually makes the earthquake look bigger,” said Robert Degroot with the U.S. Geological Survey.
Degroot said aftershocks are common and the earthquakes have been hitting soft soils near the Midland fault which is beneath the western edge of the Central Valley.
“When they hit soft soils, they tend to slow down and then they get bigger, which results in higher shaking levels,” Degroot told CBS13.
That is what happened during the Loma Prieta earthquake 34 years ago when a freeway about 60 miles from Santa Cruz collapsed.
“This is where people come in and do retrofitting,” Degroot said.
Building better structures on soft soils to withstand shaking has been a priority since that destructive earthquake. The recent shaking on soft soils near Isleton is a reminder to be prepared.
“It could happen again,” said Carbajal.
It is not just the concern of earthquakes that is top of mind for people in Isleton, the city manager is also worried about how the wastewater treatment plants will withstand the wet weather this winter.
In March 2023, primary treated sewage from Isleton’s wastewater plant spilled into the surrounding Mokelumne, San Joaquin and Sacramento Rivers.
“If the rains come, we could be back to the same situation we were in March,” said the city manager of Isleton, Chuck Bergson.
Bergson said multiple manholes and pipes broke in the sewage collection system during last winter’s storms.
“We are a small town and we are not a bank, and extending that kind of funds is kind of tough,” said Bergson.
Since March, Bergson said almost weekly he has repeatedly been asking the state for a quarter of a million dollars to help repair the 50-year-old treatment plant and avoid another sewage seepage.
In March 2023, the plant spilled about 3 million gallons of sewage, and Bergson said the pools already have more water than typical during this time of year.
There is a long-term plan to completely replace the sewage treatment plant system that will not start construction until likely 2025, but in the interim, Bergson said repairs need to be made to survive the winter months.
“Last year, we just got too much, and this year, we are in the same situation,” said Bergson.
The sewage treatment plants and levees have not experienced any damage from the earthquakes, but experts warn that the bigger concern is if a larger earthquake were to hit during flood season when there are high water levels and even more saturated soils.
The City of Isleton is looking to stay prepared for shakers and patch up its sewage plants before the winter season.
Bergson is hopeful to receive the money from the Office of Emergency Services and FEMA within the next two to three weeks so that the treatment plant will be able to withstand the wet season.