By Ginette King

January 2026  

You jolt upright in the darkness to the sound of clinking rattles and a sense of alarm as your bed shakes, your heart beating rapidly as the low rumble and movement subsides. Then silence. An earthquake. How big? Where was it? A quick online search for “USGS latest quakes” reveals the answer: A very local quake, practically right on Bennett Valley Road! Only 2.4 in magnitude, with the epicenter almost under your house. Nearly 30-minutes later, another one. Then another. And a few days later, another. What is this madness? Most of us are familiar with a small quake then a bigger one (foreshock, main shock). Or vice versa (main shock, aftershock). But small tremor after tremor? It’s a swarm.

Typically swarms include a series of low-magnitude earthquakes in a localized area that persist from days to months in duration, without a much larger accompanying quake. What does a swarm mean? It’s unclear. The evidence shows they don’t seem to indicate a larger quake is coming. But they are a great reminder for us to prepare. Our swarm started on December 12 with quakes ranging from imperceptibly small up to 4.0 (as of this writing), including days in between with no seismic events of notice.

The San Ramon Valley in Contra Costa County, meanwhile, continues its own much more abundant swarm of 150+ small quakes during the last two months; a recurrence of swarms in the same area as recently as 2015, 2017, and 2021.

What’s happening in the East Bay in some ways mirror our situation in Bennett Valley. Both the Calaveras fault near San Ramon and the Hayward fault near us are right-lateral strike-slip fault zones capable of producing sizeable quakes in the 6.5-7.0 range. Both are also related to other significant fault lines. The Calaveras fault is an eastern branch of the San Andreas fault system. In 2016 the Hayward fault was acknowledged to extend north into what we call the Rodgers Creek fault in Bennett Valley and downtown Santa Rosa..

Interestingly, both the Rodgers Creek fault and the Maacama fault are considered extensions of the Hayward fault subsystem, which is itself deemed to be an extension of the San Andreas fault.

Our recent local quake cluster, however, is not necessarily a direct result of the Rodgers Creek fault, despite its close proximity. It could be a byproduct of the Bennett Valley geography as we sit with the Rodgers Creek fault on the Western side and the Maacama fault system on the Eastern side. The tension between two (or more) faults creates an area called a pull-apart basin.

I spoke with Sonoma State University Geology Professor and Department Chair Matty Mookerjee recently who explained that pull-apart basins, areas between two close-proximity faults moving in roughly opposite directions, slowly sink as the bookending faults move and shift, creating a depressed area that water naturally runs into and can fill with sediment over millennia.

Faults, like fissures on the surface of an iced-over lake, fracture and splinter making complex patterns with one ending as another veers off to form a new line. Scientists grant each fault line a unique name as they are discovered, but the relationship of each fault, how the energy flows between them, is not a perfect science; sometimes discovering a new fault only as a result of a sizeable earthquake that behaved surprisingly or a study yielding earth dislodgement indicating a now-quiet fault line.

Energy flows along the path of least resistance. But exactly how that energy flows from one to another is not always evident. For example, there is a noticeable jog in the fault line as the Hayward fault crosses the bay and continues northward. If a quake begins on the Hayward fault in the East Bay and heads north, will it continue directly up and across that offset and up to the Rodgers Creek fault or splinter off to another nearby fault? According to the USGS, the likelihood of a quake happening to both lines is less likely than to just one line at a time. But you can watch a scenario video of if they both happened at the same time here (see Santa Rosa (looking south) perspective by scrolling down on the page).  

It's Not Just Earthquake Magnitude

Why do some tremors feel so much worse than others, even those of the same magnitude? A few key variables make the difference.

Soil Type: Bedrock is remarkably stable – hence how the Parthenon in Athens, Greece has withstood devastating quakes much better than the city below it. In contrast, areas consisting of loose sediment, sand, or manmade rubble “fill” like the Marina District in San Francisco, an amplification can occur. When amplification happens, it increases both the duration of the shaking (think a bowl of Jello continuing to shake after being moved) and the magnification of the movement itself as the energy from below increases surface movement.

As you likely know, Santa Rosa experienced greater death and damage per capita from the 1906 quake than San Francisco did. Why was this? Unfortunately, due to our geology, significant parts of the Santa Rosa region (near the intersection of highways 12 and 101, for example) are susceptible to this kind of amplification effect. To witness a sobering simulation of that quake, watch this YouTube video (looking south from just above the 12/101 interchange). Dark areas show stronger intensity.

Liquefication is a worst-case example of amplification, when the ground behaves like water (from being water-logged, for example) and cannot support the weight of structures above it.

Your Location: Your hyper-specific location is another factor. If you are standing in a high-rise on the 40th floor you will have a different experience of a quake than that same exact quake if you’re on the ground floor. It feels different if you are driving vs. walking, sitting vs. standing, asleep vs. awake, inside vs. outside (the sounds, concerns of building debris falling on you, for example). I personally felt the Loma Prieta 1989 quake all the way down in San Luis Obispo, but seemingly only because I was sitting perfectly still with my feet on a concrete floor (and it was a shallow quake whose shockwaves traveled further).

Depth: How deep a section of a fault lies directly impacts how far the energy has to travel through to reach the surface. It takes more energy to move deeper quakes because of the weight of rock and land resting atop it. Therefore, we usually don’t experience deeper quakes of a given magnitude to feel as strong as a shallower quake.

Duration: Larger earthquakes have a close (but imperfect) relationship to the duration of the event. The bigger the magnitude, the more energy is being released and the longer it takes to dispel the force of it. This, in turn, increases the likelihood of damage. What a building can withstand for 20 seconds can vastly differ against the same forces for 200 seconds.

In addition to these factors, some quakes come on gradually with a rolling motion that can make you feel queasy. Others jolt so hard they feel violent and abrupt. Experts don’t have a conclusion yet as to the difference, what each means and why on the same fault we can get both kinds. Until we can peer through the earth to visibly see all of the fault lines and natural structures below and directly measure the tension within each, it’s too complex to definitively conclude. New fault lines are being discovered. New understandings of the forces of nature continue to be revealed.

Don’t Be Scared, Be Prepared

So how do we truly get ready for the earth moving beneath us at any time? As the fires reinforced in our consciousness, having a “go bag” ready, along with a supply of food and water is smart. Know how to turn off the gas to your property (pro tip: Keep the wrench right there at the main gas line). Have an emergency plan for your family. Secure heavy/tall furniture to walls. Secure your home to its foundation with the right bolts. Know which sturdy table you’ll get under in each room. Keep shoes by your bed so you won’t step on sharp objects in the dark. Keep a battery-powered radio handy.

One “be prepared” tip I hadn’t thought of until I saw it mentioned in an academic report was that of earthquake-induced landslides. Obviously, it crosses our mind in wet winters, but seismic events are relevant, too.

Note areas of landslide on your property that show evidence of loosening or steep spots vulnerable to giving way during a seismic event and reinforce them, if possible. The USGS provides an interactive map showing areas of greater slide risk here.

We are fortunate to live in this beautiful Bennett Valley area. Putting up with some tremors and the risk of a bigger quake is something we live with every day. It’s a part of the rich ecosystem and landscape, like the soaring hawks, the thick clay topsoil, the speedy Western fence lizards, and the wind blowing through the grand oak trees. Everything living system works together. Even if Mother Earth needs to stretch and shake sometimes, I wouldn’t change a thing.