Whose fault is it? Is it always Fair to Blame the San Andreas?

Before I go much further, I want to stress how serious earthquakes are. It's not really a laughing matter if you live as I do in earthquake country. Millions of people have died from earthquakes in the last century or two, and they are still recovering bodies in Venezuela from the quake last June (6,500 dead so far with tens of thousands still missing).

San Francisco after the 1906 earthquake

Still, it is important to be reminded about the threat that we in California live under. Quakes happen regularly in this state, and sometimes they are catastrophic. It's best to know the threat and to be ready for the day when the BIG ONES hit.

And we all know who to blame when that day comes, right? It's the San Andreas's fault...

Well, let's see if that is true...how well do we know our most famous fault?

Trace of the San Andreas fault on the San Francisco Peninsula. San Andreas Lake is in the foreground.

The fault was discovered and named in 1895 by Andrew Lawson, a professor at UC Berkeley. He was mapping the geology of part of the San Francisco Peninsula, and he named what he thought to be a minor fault after the nearby San Andreas Lake. In 1906 the catastrophic San Francisco earthquake struck and it was immediately apparent that the fault was far more important, as the surface rupture extended more than 200 miles. Subsequent mapping revealed a total length of some 600 miles.

Source: US Geological Survey

The fault is a transform plate boundary, dividing the Pacific and North American plates. The two plates are moving northwest, but the Pacific Plate is moving faster, causing relative motion that is right lateral.

Tectonic plates of the world. Source: US Geological Survey

Right lateral means that the side opposite the fault from the observer has moved to the observer's right, as seen below in a curb offset by lateral motion on the Calaveras fault in Hollister, California. The Calaveras parallels the San Andreas in Central California, and is considered part of the same system of plate motions.

Curb in Hollister, CA offset by right lateral motion on the Calaveras fault.

This seems an odd thing to point out, but the fault is segmented, and that's a good thing. It means that sections of the fault behave independently, with some portions moving via occasional earthquakes, while others move more or less continuously (fault creep, as pictured above). This segmentation means that stress can't build up along the entire length of the fault so that possible earthquakes have an upper limit of magnitude (magnitude 8 instead of 9 or 9.5; the difference is NOT trivial).

The fault began forming about 29 million years ago, and has moved more than 200 miles (during countless earthquakes of 15-20 feet per earthquake). This is best illustrated by the Pinnacles Volcano (in Pinnacles National Park in the Coast Ranges south of Hollister), which formed 22 million years ago, and was split by the fault and shifted 195 miles (the other half is in the Palmdale region).

Lots of people talk about the San Andreas fault, but relatively few people have actually seen it (or didn't recognize it when they did). What does the San Andreas look like? As it turns out, it's not always readily visible. Erosion tends to quickly erase evidence of fault motions, but they are preserved in many places if you know where to look. One of the most famous localities is Wallace Creek at Carrizo Plains National Monument west of Bakersfield. At that spot the San Andreas has offset the creek by 400 feet during perhaps two dozen earthquakes over the last 4,000-5,000 years (below).

Wallace Creek in Carrizo Plains National Monument

If the offset isn't clear from the ground view, check this aerial photograph of the same spot...

The fault is much easier to see where it is creeping continuously. The fault crosses Highway 25 near Pinnacles National Park, and I've documenting the changes there over the last quarter-century. The photo below shows the cracks in the highway as of October 2026.

San Andreas fault crosses Highway 25 north of Pinnacles National Park

The best way to see the fault is from above. I was lucky a few years ago to have a flight take me over Cajon Pass in Southern California where the San Andreas crosses the San Gabriel Mountains at Lone Pine Canyon (below). Lone Pine Canyon is visible briefly from Interstate 15 as you drive north.

People say things about the San Andreas fault. They're always finding fault, so to speak. Are these things true? Let's see...

• California will fall into the sea
• The San Andreas Fault causes all California earthquakes
• California has more earthquakes, and bigger earthquakes than anywhere else
• We are waiting for the “BIG ONE”

Let's check them out.

California will fall into the sea

Well, that is TRUE in a manner of speaking. To be sure, it doesn't happen Hollywood-style with Los Angeles or San Francisco sinking beneath the waves in a catastrophic quake complete with falling buildings and giant tsunamis. 

Attribution: Unknown. These things show up after many disasters, and it's a nuisance.

But sections of California have been slowly submerged over millions of years, especially in the Borderlands off the coast of Southern California. And Baja California is moving north along the San Andreas, eventually to become an island, heading ultimately to the Aleutian Trench off of Alaska.

So, for this one we must place the blame on the San Andreas...but we can blame Hollywood too, for incredible exaggeration on such matters

The San Andreas Fault causes all California earthquakes:

This one is easily dismissed as untrue. Just take a look at any site showing the locations of earthquake epicenters. The SCEDC site is especially good, Look below to see a week's worth of earthquakes in California and Nevada: it is immediately clear that earthquakes happen all over the region, and that dozens of other fault zones produce earthquakes.

Lots of blame to spread around for the earthquakes in California, not just the San Andreas!

Source: https://scedc.caltech.edu/recent/index.html

California has more earthquakes, and bigger earthquakes than anywhere else:

Let's roll the numbers. I'm not including the magnitude 9 quake of 1700, as it was most likely far too the north of California. Here they are:

• Number of (near) magnitude 8 quakes: 3 (1857, 1872 and 1906)
• Number of magnitude 7 quakes: 12-15
• Number of magnitude 6 quakes: 140+

As to whether these are the biggest in the world, it's not even close. Check out the list of the 10 largest quakes (actually 17 when including honorable mentions) in recorded history from the USGS:

Except for the bit of the Cascadia Subduction Zone in the far north part of the state, California simply doesn't have the conditions that can allow the incredible stresses required to produce magnitude 9 quakes.

We need to have a quick word about the nature of the magnitude scale. It is exponential, not linear. When calculating the energy of earthquakes, an increase of one magnitude represents an increase of about 32x the energy. Put another way, a magnitude 9 quake represents the energy release of 32 magnitude 8 quakes, and over a thousand magnitude 7 quakes (32x32).

Put another way, the Great Tohoku quake of 2011 in Japan at magnitude 9.1 released more energy in one event than all the recorded earthquakes in California's history!

So, no blame for the San Andreas when it hasn't done what it is blamed for!

We are waiting for the “BIG ONE”

The Big One. The one no one wants to think about. The Big Show.

The problem is, and you won't like it, that the statement needs to be refined a bit.

We are waiting for the Big Ones!

As noted previously, the San Andreas fault is segmented, and different parts have different seismic histories. There was the 1906 event in San Francisco, and the 1857 in Southern California. There is a segment in the Coachella Valley that has been lock up and building stresses for some 300 years. And there are other major faults capable of mayhem. The 1872 quake in Lone Pine wasn't on the San Andreas fault, and neither were many other magnitude 7 events.

Seismologists cannot predict individual quakes with any kind of reliability, but they deal quite well with probability. Working groups have produced maps that reflect the possibility of major quakes on any number of California fault lines and have produced probability maps like that above. It is a bit dated (2008), but there have already been 3 or 4 magnitude 6.7 and greater quakes, showing that the long-term predictions are valid. The quakes are going to happen. We just don't know precisely when.

So, no blame on the San Andreas, at least not yet this century! 

This one is subject to change...

This blog post was written to coincide with the Great California Shakeout to be held on Thursday Oct. 15 at 10:15 am. 

I will also be presenting a public lecture as part of Modesto Junior College's MAPS Speaker series on Friday night, October 16 is Sierra Hall, Room 132 on our west campus at 7:30 pm. I'll be speaking about, of all things, the San Andreas fault!

Why did the Road Cross the San Andreas Fault? 24 Years of Geologic Change (a new Update)

2002

I've been leading geology field studies trips to lots of places in the American West for 38 years and started to take digital pictures in 2001. I sometimes struggle to find new things to photograph when I visit a place for the 38th time, but in some cases, it is not a problem. There are geologic changes that happen on a yearly basis, and with twenty-four years of photos (minus two due to Covid), the changes become obvious. This is a continuing update from a post in 2013, and I'll probably continue updating for the foreseeable future.

2004

Highway 25 in the California Coast Ranges connects the town of Hollister with the access road to Pinnacles National Park (formerly Pinnacles National Monument). Along the way the highway crosses the San Andreas fault in a section where the fault creeps an inch or so each year (36°35'54.27"N, 121°11'40.19"W). Most years we've stopped to have a look at the effect the movement has on the pavement. In 2002 and 2004, the damage was obvious.

2008

By 2008 someone had patched the road, and no fault motion was evident.

2009

Little damage was evident in 2009 either. But by 2010 cracks had begun to appear as the fault stressed the pavement.

2010

The fact that the fault creeps in this region is a good thing. It means that stress is not building along the fault surface but instead is being released gradually. The sections of the fault to the north and south of the creeping section are locked by friction and are building up the ominous stress that will eventually produce quakes with magnitudes in the range of 7.5 to 8.0. The quakes are coming and we need to be as prepared as possible.

2012

By 2012, the road had been completely repaved, and  yet the shearing was already evident.

2013

It became even more pronounced by 2013 and in 2014. Just by chance, the person working as a scale was the same individual as in 2004.

2014

In 2015 the fractures were moderately larger. They'll need to start thinking of road repairs before long.

2015

In 2016 Laura once again provided scale, as she did in 2014 and 2004.

2016

Here in 2017, long-time trip volunteer Mary provides scale. The cracks in the road are just a bit larger, but they didn't look appreciably different than the previous year except for a twist (pun intended).

2017

On Dec. 2, 2018, the break to my eye seems more continuous. It's now been six years since the road was completely repaved.

2018

That year the paint was deformed (twisted) but not split (below).

2017

The offset paint strip reminds me of illustrations of elastic rebound theory, the idea that stress builds up on a fault line over time. In that model, the land on either side of the fault is distorted over time until the frictional resistance is overcome and the rock snaps back to its original shape. That won't be happening with the paint. Last year in 2017 I said "if they don't repair the road (as they often do; see above), it will probably show a clear break by next year." Here's what transpired:

First, a close-up on 2017's center stripe...

2017

And here's how it looked on Sunday, Dec. 2, 2018:

2018

As predicted, the break in the paint is complete...

In 2019 (those last few halcyon days before Covid) long-time volunteer Paul provided scale (he has been assisting MJC with field trips for 25 years!). The crack continues to grow, and I wouldn't have been surprised if it was patched by next year.

 The paint on the center strip is split even more.

November 2019

And then Covid happened and for a few years we were not able to conduct our field studies classes. In 2022 we made a return visit with our students and here is the then-current condition of the highway. It didn't appear that any repairs have been conducted yet. Our host is once again Laura, who was with us back in 2004 and subsequent years!

November 2022

Fault creep is not a constant. I didn't see a whole lot of change over the last three years, although I didn't get as many close-up shots. Here's a closer look with Paul, our other long-time volunteer. What do you see that is different?

November 2022

In 2023 the road continued to become more deformed, and the passing traffic produced an audible thump as it passed over the fault. Our host since 2004, Laura, was not able to join us, so her husband Ryan stood in her place.

Oct. 28, 2023

And then it was 2024, October 12 to be specific. Once again our guide is Laura, who has assisted on these trips since at least 2004. The crack continues with minor changes, and it may be overdue for another repaving job.

October 12, 2024

They may not have repaved the highway, but they did in fact repaint the center line, which obscures about two inches of right lateral offset.

That brings us to 2025 (October 11). Our long-time volunteers weren't on the trip this year, so River and Makayla jumped in to provide scale. 

Oct. 11, 2025

Oct. 22, 2025

The road hasn't been repaved since 2012, and the crack is continuing to slip and fracture. The pavement at the road median has fragmented, and completely repainted which hides the offset a bit.

Oct. 10, 2026

It's now 2026 and the road continues to buckle. Tsing and Jo provide scale this year. I'm mildly surprised that the road maintenance crews haven't fixed this section yet.

These little changes that happen at a rate visible in human lifetimes add up to huge changes when multiplied by thousands or millions of years. The nearby eroded volcano of Pinnacles National Park has been displaced 195 miles (315 kilometers) in the last 20 million years or so by movement along the San Andreas.

How will it look next year?

Geotripper Rates Hollywood Movie Geologists (AND, see "Tremors" at the State Theatre on May 20!)

One of my earliest blog posts (in 2008) was a list of my favorite depictions of geologists in movies. I've revisited it once or twice. It came to mind as we prepare to offer a showing of "Tremors" as a geology field studies fundraiser at the State Theatre in Modesto on May 20th at 7 pm. If you would like to attend or donate to our field studies fund, please check out the first comment!

What are the best depictions of geologists in movies? I have the definitive list below! I listed my number one choice, but the others are in random order.

As will be seen from my list, my taste in movies runs towards action-adventure as opposed to the "sophisticated" cinema ("There will be Blood" with Daniel Day-Lewis would otherwise take the top spot). But frankly, no movie with a geologist can exist without action and adventure...

Despite having grown up in southern California, and having lived through the 1971 Sylmar quake, I have never taken a picture of the Hollywood sign, so I offer a photo of a favorite Hollywood set, especially in the old westerns: the cliffs of Red Rock Canyon State Park on Highway 14 in the Mojave Desert. The rocks are Miocene continental floodplain sediments lifted up by fault motions on the Garlock and El Paso fault systems. Dr. Grant should be scaring that little kid with a velociraptor claw any moment now!

My favorite geologists in the movies:

And the winner is: Finn Carter as seismology graduate student Rhonda LeBeck!

1) Tremors (1990): Finn Carter as seismology student Rhonda LeBeck.

Speaking from an entirely gender-biased point of view, Finn wins my vote as the finest portrayal of a geologist in a Hollywood movie. Intelligent and creative, and cute, too. And finding strange underground worm things using a seismometer. The backdrop of the Eastern Sierra Nevada and Alabama Hills was an extra-special plus.

2) San Andreas (2015): Rock (Dwayne Johnson) as a character of some sort, and Paul Giamatti as a paunchy bearded hero geology professor named Hayes. I reviewed the movie in this post from 2015. I was struck that the "hero" of the movie saved around four people, while the "B"-plot geologist saved maybe millions of lives. The movie was also notable for showing a fellow geologist who was Asian (but he died in the movie, of course). 

The real hero of "San Andreas"

3) Volcano (1997): Laurie Latham as Rachel, Anne Heche as Dr. Amy Barnes (honorable mention)

Rachel didn't get much credit for being the first Hollywood geologist to get sucked into a volcano, but she displayed many of the traits of the real geologist: self-effacing, nervous in front of cameras, and yet a good and perceptive researcher. Of course, she wasn't a leading character. The actual 'star' of the film, Anne Heche gets honorable mention for looking at a topographic map on-screen, but then using a basketball to confirm that a street does in fact slope downhill the wrong way.

The smarter of the two geologists in "Volcano" (other than getting sucked into the lava)

4) Dante's Peak (1997): Pierce Brosnan (!) as Dr. Harry Dalton, Charles Hallahan as Paul Dreyfus, Grant Heslov as Greg and others

James Bond as volcanologist?? Well, I dunno...too clean-cut, too shaven, too cultured. Now, the rest of his team, though, they were more like the people I see and work with on a regular basis. Coffee addicts, intense, and lovers of volcanoes. Some of the portrayals of geological processes were done pretty well, except for that really fast-moving Hollywood lava, and driving a truck through said flow without dying from the radiant heat. And that acid lake that killed grandma. And that overly steep giant Hollywood volcano in Idaho (!). I really liked the bridge that got washed out at the end of the movie, though.

Well done, special effects people! Seems like they should have let the van go first, though.

5) King Kong (1976): Rene Auberjonois as Bagley

In his pre-"Deep Space Nine" days, Rene played a geologist who thought that the mysterious uncharted island was hiding a lot of oil. When shown to be wrong, he did what many geologists are known to do...he got drunk.

I think he would have been drunk even if it was oil.

6) Erin Brokovich (2000): Julia Roberts in the title role

The first scene of the movie had Julia Roberts saying "I love geology". I melted on the spot and was hers from that point on. Though she was actually a legal clerk and not a geologist, she was shown researching groundwater chemistry, taking samples of poisoned water, pulling dead rotting animals from wells, and running away from security guards after trespassing on company property. All in a day's work for any field geologist, I should think.

This is why I'm a geologist, not a biologist.

7) Raiders of the Lost Ark (1981): Harrison Ford as Indiana Jones

O.K., so he was really an archaeologist, but he dug in the earth a lot, and the character was said to be based on Roy Chapman Andrews, an adventuring paleontologist who explored the Mongolian deserts in search of ancient life in the 1920's. His expeditions found the now renowned Flaming Cliffs which contained fossils of protoceratops, oviraptor, and that most famous of movie dinosaurs, velociraptor. His party also discovered the nests of some dinosaurs, containing egg clutches in concentric circles, and some very rare Cretaceous mammals. They were chased by bandits and assaulted by horrible dust storms. And what geologist doesn't dream of dramatic adventures in the field? Also, in the third movie there were earthquakes, and the ground opened up and swallowed people!

8) Jurassic Park (1993) and Jurassic Park III (2001): Sam Neill as Dr. Alan Grant.

His character was ok, but I was most impressed by the office trailer for the paleontology dig in Montana; messy, dusty, newspaper clippings on the wall, lunch mixed with research; a true geology office! The third movie in the series mostly had people getting eaten, but as usual, the dinosaurs looked pretty cool.

This looks suspiciously like my own laboratory...

9) The Lost World: Jurassic Park 2 (1997):

Come to think of it, there weren't many paleontologists in this movie, except the guy in cowboy hat with the long beard who looked a lot like Robert Bakker. I think he got eaten by a velociraptor...(Update: I completely forgot that Julianne Moore was most certainly a paleontologist in the movie).

10) The Core (2003):

I don't really remember much about the geologists, but I loved the "element" they used to drill into the mantle and core in only two or three days; it was called "Unobtainium" (which was also in the plot for "Avatar"). And that giant mantle amethyst geode was pretty cool, even if the crystals killed some of the crew members.

11) Bringing Up Baby (1938): Cary Grant as Dr. David Huxley.

Handsome guy, looking for a dinosaur bone with beautiful Katherine Hepburn at her best, a pesky dog and a pair of leopards. What more could you ask?

12) Eight Below (2006): Bruce Greenwood as Dr. David McClaren.

A geologist willing to ride a dogsled for a week, face down avalanches, blizzards, crevasses, frostbite, a broken leg, and a fall into freezing cold water, all so he could find a meteorite in Antarctica. How he knew to look for that particular meteorite on a rocky mountainside as opposed to the surface of a glacier, I don't know. And they left those poor dogs behind....

13) 2012 (2009): Chiwetel Ejiofor as Adrian Helmsley.

2012 was notable for having an African-American as the lead geologist in an otherwise ridiculous movie. He provided the moral center for the hard decisions being made about the future of humanity. I give my students an assignment on finding geologists in movies, and this role comes up more than any other. Woody Harrelson, while not a geologist character, wins honorable mention for best geology-related death in a movie, as he is incinerated by the eruption of the Yellowstone Caldera.

If I'm 95 and sick, I want to go this way too.

While researching for this post, I came across an excellent review of geologists in movies in Earth Magazine which actually analyzes whether geologists were women or minorities, whether they were evil or not, and whether they survived to the end of the movie. I highly recommend it! 

Which movies did I miss? Please contribute to the comments!