The Imperial Valley has seen dozens if not hundreds of these sort of swarms over the century we have recorded. A swarm is a group of quakes (dozens to thousands) where there are many quakes close in size and no obvious mainshock. Often the size will grow like we've seen here going from M3s to M4s.

The Brawley swarm is continuing and getting a bit bigger. It began with a M3.5 at 4:14 pm. After 4 M3s, it gave us a M4.4 at 7:22. Then a couple more larger events M4.0 and M4.5. There is no sign of a drop off in number of events, so we shouldn't be surprised if we see at least a few more M3s.

So 2 areas with swarms ongoing in Southern California. A classic Brawley seismic zone swarm today in the Imperial Valley fault. Largest so far is M4.1. These continue until they stop so we will likely see more M3s tonight and may get bigger.

We have an exciting event coming up to bring music and science together- a collaboration between Colburn School and Caltech. April 25. In The Name of a Warming Earth' - Dr. Lucy Jones localnewspasadena.com/2026/in-the-...

My last anniversary is the happiest one of the week. Georg Philipp Telemann was born 345 years ago and we are celebrating with an all-Telemann concert by Los Angeles Baroque

The third anniversary of the week. 100 years ago today, LADWP began impounding water at the San Fransquito Dam in northern LA County. Exactly 2 years later on 3/12/1928, the dam failed suddenly and catastrophically, releasing 47million cubic meters of water, killing 430+ people.

Another anniversary. 15 years ago today, the M9.1 Tohoku earthquake and tsunami swept through northeaster Honshu, sweeping away whole towns and killing almost 18,000 people. Five years later, this town of Otsuchi was still struggling with what to allow to be rebuilt.

The 1933 Long Beach earthquake occurred 93 years ago today, beginning near Huntington Beach and rupturing north for 15 miles to just north of Long Beach. It cause strong shaking through much of the Los Angeles region. with the worst damage in Long Beach and Compton.

#EQHistory: 1971 M6.6 San Fernando. The event killed 65. In the aftermath Caltech seismologist Clarence Allen went to Sacramento with a message: geologists know where active faults are and we can prevent building on them. His testimony helped the passage of the Alquist-Priolo Act. buff.ly/Yzs6NPt

Tonight's M4.9 north of Indio is the largest quake in SoCal since the M5.2 near Julian last April.

A M4.9 quake occurred this evening north of Indio. It is east of the San Andreas fault, far enough away to not change the likelihood of a quake on the San Andreas. It's located very near the minor EW-striking Blue Cut fault earthquake.usgs.gov/earthquakes/...

I’m releasing a few new episodes of my podcast to discuss the science around wildfires podcasts.apple.com/us/podcast/g...

Again, Kyle and Judith provide a great summary of the science around this earthquake

Sometimes, music is the only tool I have for coping with the world. youtu.be/2Xj0KSgD24k?...

I love xkcd

This was a fun interview. It ended up being quite a retrospective on how seismology has changed over the 4 decades I have been in Pasadena. making-l-a.simplecast.com/episodes/luc...

In the last 24 hours, we have seen several M3s in 3 locations. The events near Ontario are at the western end of the Fontana trend. The Lytle Creek events are near the San Andreas & the Rialto events are where the Fontana trend intersects the San Andreas. Last week's M4.3 was at the Rialto location

The New York - Philadelphia - Wilmington urban corridor has felt small earthquakes roughly every 2-3 years. Moderately damaging earthquakes strike somewhere in the urban corridor roughly twice a century. So infrequent but not weird

On the M4.3 on the Fontana trend

Looks like a small swarm in the Fontana trend. This M4.2 had a few foreshcoks including a M3.0. The Fontana trend is a NE-striking lineation of earthquakes under the sediments of the San Bernardino Vslley. We believe it is one of the left-lateral striking faults that are south of the San Gabriels.

The 7/29/2025 M8.8 looks like a repeat of an earthquake in 1952

In addition to many M7+ earthquakes, this boundary has also hosted half a dozen M8+ earthquakes. Red circles mark the epicenter above the site where fault rupture began, and yellow shows the area on the megathrust fault that ruptured.

Even very small quakes can be felt if you are nearby (and a shallow quake is closer to people on the surface). But there is not much to be said about an M2.7 except that it happened earthquake.usgs.gov/earthquakes/...

Most births in Iceland are in the summer. www.youtube.com/shorts/oRw8d...

This study uses "overdue" to mean that time time since the last quake is longer than the average time between earthquakes. But that doesn't mean the next quake is more likely in the near future. The length of intervals between events is very variable even at one location.

This does not mean the big earthquake is more likely. Whatever is making for long intervals is happening now.

It is so cool to see actual fault offset, but I am also struck by how small the shaking is. This is the ultimate "near-field" site, but the shaking is not enough to topple any of the tall vases.

#FieldPhotoFriday Back from the beach and up into the mountains, sometimes the field techs need to go even higher! Atop an antenna at the peak of a mountain near Lake Arrowhead to be exact! Climbing can be a regular part of the job, they do what it takes to keep the data flowing!

I've partnered with OcTech, Caltech's choral octet, to create Courage To Care: a concert & discussion to process climate angst in a time of historic fires. If you're in SoCal, come build community with us! Sunday, April 27th, 7:30 PM Dabney Lounge on the Caltech campus Tickets: No tickets - free!

Interesting to look at the detailed relocations of the aftershocks to the M5.2. It looks like they are not on the main strand of the Elsinore fault.

Earthquake Early Warning requires estimating the magnitude from the first few seconds on just a few stations. It is always very rough but lets us get out something quickly. There is a lot of variation between locations. The final magnitude averages 100+ stations and is always more accurate

When my grandson's preschool teacher (in Orange County) told the children to Drop and Cover as the Julian quake happened, my grandson yelled out "And hold on!". I'm so proud

Today's M5.2 is the largest quake near the Elsinore fault since I came to California in 1983. But there were quite a few M4s along the way. A junior sibling to the San Andreas, the Elsinore is long enough to have given us some bigger events

I was proud to be a federal scientist at the USGS for 33 years. "Earth science in the public service" meant I could focus on creating and explaining science for public officials and providing public education, not just educating students at one university. theconversation.com/us-earthquak...

#AirTalk with Larry Mantle celebrates 40 years on air, with leading voices joining to help listeners better understand the many facets of L.A.—from science to politics to history. Hear from guests, including seismologist @drlucyjones.bsky.social in this special episode: laist.com/shows/airtal...

After the fires, the only person I wanted to talk to was @drlucyjones.bsky.social. I was so thrilled to be able to sit down with her for this interview for Dwell. Our conversation about LA's future was, at times, painfully honest — but ultimately very hopeful

This is an excellent post, summarizing the scientific data from the Myanmar earthquake. The long fault and close proximity to major cities indicate a high level of damage and we should expect the death toll to rise. But the ongoing civil war near Mandalay suggests we may never know.

This could be devastating. This is strike-slip mechanism on a plate boundary, much like the 1906 quake on the San Andreas. The rupture length is at least 300km. The capital, Yangon, is near the fault, but I can’t yet see if the fault ruptured towards Yangon or away from it

The Malibu quakes: There have now been 12 M≥3.0 quakes in approximately the same location north of Malibu since February 2024. In comparison, the previous 25 years had 7 M≥3s in the same location. A couple are clear aftershocks (within a few hours of a larger event), but the others are spread out

Wow! I'm honored that KUSC wanted to include me as a woman making history - in music! I've only got one composition to my name so this is very special. www.kusc.org/articles/wom...

A clickbait headline. The answer is no.

I was out on a walk during the M4.1 quake. Not much to say about it. Run-of-the-mill for earthquake country. The most interesting thing is that it is the 3rd M4 at essentially the same location over the last 13 months.

A M3.9 in North Hollywood. Too small to definitively assign to any fault, but the closest is the Hollywood fault. Yawn. Nothing much to say about an earthquake in earthquake country. I am in Boston and am heading back to sleep.

It's essentially impossible to definitively assign a small quake (with fault area ~100m) at 8 km depth to a fault we map at the surface. But these look like they could be on the San Andreas itself which is relatively rare. The focal mechanisms align with the fault orientation

I'm astonished at how many people have said they remember seeing me on TV after this quake - because I was 15 years old & living with my uncle's family in Taiwan. The news said "LA destroyed by earthquake" and it was 4 days before I could get a phone call to my parents in LA and learn they were fine

The California Earthquake Authority gives $3000 grants for seismically retrofitting your home. Registration is open now. See if you qualify at www.californiaresidentialmitigationprogram.com/our-seismic-...

“After a wildfire, the hazard to the public is not over,” said Jeremy Lancaster, California’s state geologist. …The two major hazards after a wildfire are flash flooding and post-fire debris flows.” www.nytimes.com/2025/01/16/c...

Misinformation is a secondary hazard in every disaster.