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.
The fault displacement (and therefore the tsunami height) at Tohoku was much larger than we had ever seen for that short a fault. So the planning was for a smaller event. We need to remember that the mean values are what's most likely to happen, not what will happen.
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 3/10/1933 Long Beach quake killed 120 people and brought home the dangers from unreinforced masonry buildings. It led to the first seismic provisions in the building code and the passage of the Field Act that ensured strong seismic safety measures for public schools.
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
Volcano's producers sent the script to Caltech to ask if they could use Caltech name. Caltech lawyers asked me and Kate Hutton for our opinions because the seismologists seemed based on us. Permission was denied. "Rachel" dies in the lava. "Amy" falls in love with the OES guy. Who's the worst fate?
"Normal" aftershock sequence in California is a wide range - 95% of sequences range over a factor of a thousand (from 1 of a particular size to 1000 of that size). So this sequence is higher than the mean but still completely normal
That was actually the Joshua Tree earthquake of April 1992. Just 10 km or so west of today's quake. He now has his own PhD and his own little boy
Well, in Joshua Tree, you are likely to be feeling more tonight. This is a moderately active aftershock sequence. But remember the number falls off rapidly with time, with the second day having half as many aftershocks as the first day.
Tonight's M4.9 north of Indio is the largest quake in SoCal since the M5.2 near Julian last April.
To those with long memories, this looks similar to the beginning of the 1992 Joshua Tree sequence. However, 1992 was west of this event and thus closer to the San Andreas.
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...
As a fellow not-"really"-geologist, how about lithified or perhaps metamorphosed fault gouge? When I was doing rock mechanics experiments on fault gouge almost 50 years ago, a real geologist gave me this specimen and said it was from an exhumed fault. Looks pretty similar.
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
(2 of 2) 3. The shallow depth suggests it is at the top part of the subduction zone that moved in the 2011 M9 3/11 disaster. By our standard definitions, this would be classified as aftershocks of 2011.
1. Earthquakes occur in sequences, so this is one sequence that happens to have a lot of both foreshocks and aftershocks. 2. The focal mechanism shows a thrust fault, suggesting this is on the subduction interface. ... (1 of 2)
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...
Only the Rialto events are aftershocks to the July 31 M4.3. The Lytle Creek events are near the San Andreas but not necessarily on it. We often see small events around the San Andreas but some analyses suggest they are on small faults not the main surface that will move in the big quakes.
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.
I’m seeing lots of questions about whether the rate of great earthquakes is changing or whether climate change affects earthquakes. The answer is no. The long term rate of these big events is about 1/decade. But the distribution is random. The last one was 2011 in Japan
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.
Not obviously. Quakes are many kms below the surface so surface impacts rarely make a difference. Water table depletion can reduce the pore pressures (pressure in the water at depth) and that can slightly reduce the risk (just like fracking-related injection increases the pressure causing quakes)
