Swarm of earthquakes rattle San Ramon; experts say tremors are reminder to be quake ready

SAN RAMON, Calif. (KGO) -- In the last month, there have been nearly 150 earthquakes along a fault in San Ramon, including the 3.1 tremor that hit Tuesday morning.

"I felt shaking I was sleeping upstairs," said Roger Greninger of San Ramon. "It shoot pretty good and then we heard the creaking too - where the house creaks."

He and his wife felt the earthquake just before 6 a.m. Their old dog "Scruffy" did not.

Greninger says the 3.1 magnitude quake in San Ramon literally hits close to home.

"We were at the epicenter just about a block and half from our home," said Roger Greninger.

Francine Greninger isn't so worried about the swarm of earthquakes that have hit San Ramon.

"In 1964 when I was 11, I lived in anchorage with my family. We experienced the largest earthquake in north America which I believe as a 9.2 in anchorage at that time," said Francine Greninger.

But others say they're a bit anxious.

"We're definitely nervous. She's has a little anxiety about it," said Danny Laurente. "We definitely felt the shaking, the jolts."

Scientists describe the noticeable earthquake activity in the area.

"Somewhere in the area of 150 earthquakes have happened in this area since early November," said Robert de Groot with the USGS.

The Berkeley Seismology Lab says there have been 24 small earthquakes in San Ramon in the past week.

"The only place there has been a swarm has been in San Ramon," said Richard Allen, Director of the UC Berkeley Seismology Lab.

Earthquake experts say a "swarm" is when we have multiple small magnitude earthquakes over a period of time.

"It's pretty scary when people feel earthquakes on a regular basis like this," said Allen. "They are small magnitude but they come with a strong jolt which people are feeling in San Ramon."

Allen explains why the quakes have been happening.

"We all know there are multiple faults running through the Bay Area -- the San Andreas Fault, the Hayward Fault, the Calaveras Fault and several other faults," said Allen. "This swarm activity happened at the northern end of the Calaveras Fault, where we see the fault kind of terminating and becoming a series of smaller faults and dipping at various angles."

There have also been other small earthquake all across the Bay Area over the past few months.

"There have been small earthquakes in the Bay Area. We've had two earthquakes at this point along the Hayward Fault in different locations. Again, (they were) small magnitude earthquakes and then on Sunday, we had an earthquake in the Napa area as well," said Allen.

UGSU says every day there are about 50 earthquakes that happen throughout the state of California but they're so small that you and I can't feel them.

Some wonder if the recent swarm of quakes in San Ramon might be a precursor of the big one.

Experts say that's not necessarily the case.

There have been swarms of earthquakes before. No major magnitude quake following them.

"There have been other swarms in the area as recent as 2015. There was something like 644 earthquakes," said de Groot. "None of these events resulted in a bigger earthquake - something we consider to be damaging. There's really about a 5% chance that this would lead to something bigger."

"We had more than 10 swarms like this over the course of the last few decades. This flares from time to time," said Allen.

But, scientists say it's the "Big One" could happen anytime so, they say it's best to be prepared.

"We live in the Bay Area. We know this is earthquake country, so we all have to be ready for a (large magnitude) earthquake at any time," said Allen.

"We definitely have our (earthquake) preparedness kits ready," said Laura Laurente of San Ramon.