Quake swarm in San Ramon

In the past 24 hours there have been 23 small quakes in the San Ramon area on the Pleasanton fault, with magnitudes ranging from 0.8 to 3.0, and hypocenter depths around 8 km.

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Immediately friends began contacting me asking what this means. There’s good news and bad news.

The good news is that the San Andreas fault complex (including the Hayward, Calaveras, Pleasanton faults , etc) does produce periodic clusters of quakes like this, without the clusters necessarily meaning a larger quake in imminent.

The bad news is that such clusters also remind us that the stress in the rocks of the Bay Area is continually growing and shifting. So, in the long run, clusters like this are indications that the “Big One” is going to happen. So are the smaller, less-clustered quakes we get elsewhere on a daily basis. A cluster like this probably means that the tension beneath the surface is realigning, shifting in some new way. Such shifts are not necessarily good—one area gets less stress, another area gets more stress. And maybe that new additional stress is just the straw on the proverbial camel’s back needed to trigger a quake.

A problem is that we cannot tell how such shifts affect other faults. The Pleasanton fault is not thought to be a major player in earthquake hazards in the Bay Area—though there’s always the possibility it could surprise us. The shifting of stress could, however, put more stress on known culprits such as the Calaveras and Hayward faults.

The upshot of this San Ramon cluster is: Don’t Panic. It will probably just go away. But the upshot is also this: Prepare Now. Because this cluster is a reminder that the “Big One” is coming…


Another #GeologyFAIL

So today there was a minor 3.3 quake on the San Andreas near the epicenter of the 1906 quake. That sparked this odd headline from the San Francisco Chronicle:

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Mill Valley? When I read the headline I was flummoxed, thinking that some strange new fault had burst forth; normally that area sits between the San Andreas and the Hayward, and it would be downright weird to have an epicenter there.

But the quake was hardly close to Mill Valley. In fact, as you can see, it was much closer to SF. Closer to Sausalito. Closer to Daly City. It’s as if the reporter looked at the USGS epicenter map and picked a nearby city at random.

We can do better in science journalism than this. I’m not even going to ask what the “National Geological Service” mentioned in this article is supposed to be (the private company in Colorado or the USGS?) But it might also be important to mention that since today’s quake occurred in nearly the same place as the 1906 epicenter, it’s a bit worrisome. Not that we need to hunker down tonight, but every quake is a foreshock to some future quake, and every quake is an aftershock to some past gigantic quake that reminds us what we face…


What’s Scientifically Wrong With the San Andreas Movie

Screen Shot 2015-05-28 at 10.09.30 PMAs an earth scientist and a science educator, I cringed when I saw, many months ago, a trailer for the new film San Andreas. The movie opens tomorrow, and judging by the pre-release media, the movie is replete with scientific errors.

Movies can shape the perceptions of students. Bad movies can create misperceptions in students which are very, very hard for science educators to counter. Geology has been particular hard hit by Hollywood with a string of awful, scientifically-abominable movies such as The Core, Volcano, Dante’s Peak, The Day After Tomorrow. These films often took a kernel of truth–yes, fresh water surges from melting Greenland may change North Atlantic circulation patterns and decrease temperature, as is the case for Day After–and blow it up into a ridiculous fantasy. Such distortions of science are completely unnecessary, too, because the story of the plain facts is amazing enough and doesn’t need embellishments to be entertaining.

When the real San Andreas fault goes, it’s going to kill a lot of people, separate a lot of loved ones, cause waves of grief and suffering. Just the plain story would make a fine movie. So what Hollywood has instead done is decide that viewers are fools who can only be entertained by tripe gussied up with explosions. In service of this distortion, Hollywood has created a monstrosity. I expect that years from now I will have students ask question based on the San Andreas movie–just as I do for The Core, The Day After Tomorrow, and so on.

What’s wrong with the San Andreas movie? Let me count the ways:

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Error: The trailer shows this crack in the earth, suggesting that the San Andreas fault has opened up the ground maybe 20 meters across.

Fact: Faults do not open up the ground in this way, with a gaping hole leading down to nothingness. Though they may distort the surface, rarely is there a gap of more than few inches created even by the largest quakes. In fact, we know what the San Andreas fault does to the ground in big quakes, because after 1906 a photographer named Grove Karl Gilbert recorded images such as this:


There’s not really any “gap” here, despite the high magnitude of the quake. So I’m sure that after this movie comes out, future students will now expect several meter gaps from large quakes and want to know what was wrong with 1906.

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Error: The quake affects both LA and San Francisco.

Fact: The San Andreas is not one continuous crack, but rather a system where stress builds up and then is released, usually in discrete, limited sections. Though both Los Angeles and  the San Francisco Bay Area have many quakes every day, these quakes are not connected in any direct way.

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Error: A lot of structural damage occurs in the movie.

Fact: In 1906, most of the non-earthquake resistant buildings in SF came through the quake just fine. With today’s earthquake retrofitting and increased engineering knowledge, even fewer structures (as a proportion) would be damaged by a large quake. So the trailer seems to show utter devastation, skyscrapers falling on their sides. Nonsense. The worst that is likely to happen to skyscrapers is that they will be so damaged as to become uninhabitable; total collapse is very unlikely.

In 1906, the fire did far more damage to SF than the quake itself. This still from the trailer seems to show numerous fires, so in that respect it follows what might happen. But skyscrapers falling out of the sky? That’s dramatic–but wrong.

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Error: Hollywood is probably going to call this a 9 or 10 on the Richter scale, when we in fact would use the moment magnitude scale (Mw).

Fact: The San Andreas simply can’t produce quakes of that size. There are fault zones that can produce such monsters–the Cascadia fault zone off Oregon and Washington, for example. But such quakes involve subduction zones, where an oceanic plate pushes underneath a continent. That violent process involves tremendous friction and pressure and yields the biggest, deepest quakes we know.

That’s not what’s happening with the San Andreas. The San Andreas involves two continental plates grinding past each other, and produces relatively shallow quakes (the average depth being just 15 km).

The dynamics for the San Andreas are such that when enough stress builds for a ~Mw 8 quake, that’s about all the rocks can take and they break. So we can certainly get Mw 8s. But Mw 9s are extremely unlikely, simply because the rocks themselves cannot hold this kind of energy.

So when the San Andreas eventually goes–as it must–it will be bad. But not this bad.

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Error: A giant tsunami approaches San Francisco. Its height appears to exceed the roadway of the Golden Gate Bridge, which is 67 m, so we can judge the tsunami to be over 100 m high.

Fact: There are two major problems with this. One, tsunamis tend to be far smaller than this, often no more than a meter or two. The image of a giant, horizon-occulding wave is a myth created by Hollywood because it looks more dramatic. (Google for videos of Indonesia in 2004 to see just how dramatic and deadly the reality of a 1 m tsunami can be.)

Second, the San Andreas is very unlikely to produce tsunamis at all. What we need to create a big tsunami is a subduction zone quake where one side gets lifted up or dropped down several meters. Essentially the entire column of ocean water is moved all at once. That energy then spreads out in either direction perpendicular to the fault and where it intersects with land, surges on land in what often looks like a temporary elevation of sea level.

There’s not really any way for the San Andreas to move the ground in a way that would raise or lower the ocean column. In fact, the waters where the San Andreas cuts past San Francisco are only a few hundred feet deep, so even if it did lift up, it wouldn’t move that much water and thus wouldn’t create a big tsunami.

Maybe Hollywood is implying part of the continental shelf breaks loose and surges into the Pacific; that could conceivably happen (and we worry about similar situations in the Canary Islands). But if that happened, it would seem that the tsunami would go the other way, toward Hawaii and Japan.

In summary, the new movie San Andreas is likely to do a serious disservice toward the public understanding of science. And the effects of this movie will likely last a long time, influencing many students and hurting their chances of understanding a key phenomenon of our active world.

Sadly, these distortions are unnecessary. Nature is violent and dramatic enough to stand on its own, without Hollywood embellishment. Perhaps some day there will be an honest science movie, but that is not this day.

Earthquakes & the Paranoid Fringe


Two things recently happened: on 21 May, a 4.1 Mw quake struck Napa, considerably north and to east of the epicenter of the much larger Napa quake of last August.

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And yesterday, a 4.8 Mw (originally reported as much higher) quake struck some distance from Las Vegas.

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Now, normally geologists will tell you that there is no connection between such events. Four-pointers are pretty common, with worldwide occurrences usually over ten thousand per year.

Scientists know quakes happen all the time; that two happened a day apart was just coincidence. However, a relative of mine alerted me to a page on the website “Dutchsinse” that reported alarming connections between recent earthquakes. I looked into this further. The article, titled “West Coast, East Coast, Southern US Earthquakes Strike the Craton Edge–Plate Pressure Obvious,” appeared on the website of “Dutchsinse,” which describes itself as a page about “Earth Changes news, weather modification, earthquakes, volcanoes, and space anomalies.”

Yep, you read that right–weather modification. And sure enough, all over this page are references to HAARP (High Frequency Active Auroral Research Program), a staple of the fringe who think that The X-Files was a documentary showcasing the ways in which the secretive government is out to get you.

In reality, HAARP uses an Alaskan-based facility to conduct research into the ionosphere. To the conspiratorially-minded, however, the HAARP facility is how the government controls the weather, disables airplanes, and controls minds. Some even claim that President Obama used HAARP to create Hurricane Sandy, which struck just before his re-election. (Skeptic magazine has a nice takedown here.)

To these conspiracy theorists, HAARP has also been used to create earthquakes. And now the pieces fall into place–this site is implying the two quakes in Napa and Nevada are related because they were created by the government. That’s so bad it is, as physicists are fond of saying, not even wrong.

This site is a dark corner of the Internet. And it snared at least one unsuspecting person, my relative, who pointed out with alarm this seemingly-legitimate article. Many other dark corners exist, and each person needs to guard him or herself with a hefty dose of skepticism before venturing out into the raw, crazy world this country has become.

New Maps of Bay Area Seafloor

The USGS has released a great set of maps of the seafloor along the California coast, including this one of the Golden Gate entrance to the Bay:

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The high resolution images on the USGS site give a very detailed, beautiful view of the amazingly complex features in and around San Francisco Bay. While many people mistakenly imagine the Bay to be flat and featureless, there are gigantic ripples and numerous high points such as Shag Rock that, in the 19th century, were so close to the surface that they endangered shipping, and were subsequently blown up.

Other maps include Tomales Point, Drakes Bay, Pacifica, and Half Moon Bay.

Meh Quake Gets Headlines

Earthquake off coast shakes Northern California

This morning we were greeted with this headline about an overnight California quake. At  first glance, the reporting made it seem like something important or unusual. Let’s take a closer look and put this in context.

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This quake (top left of the picture) occurred a bit west of the Mendocino Triple Junction, the spot where the San Andreas fault ends. This tectonically-active area is where the Pacific Plate, the North American Plate, and the Juan de Fuca Plate all angrily merge together. It’s an inflamed spot on the skin of our violent planet, and no surprise that it should generate quakes.

Today’s quake–a Mw 5.1 –is nothing but a mild sneeze of the Earth. The unofficial geologic designation for quakes of this size is “meh.” There have been far bigger ones near the Mendocino Triple Junction. With a depth of just 24 km, this quake was felt at the surface, but wasn’t really anything approaching a big quake.

Of course, the Napa Quake last August also did not qualify as a “big quake,” though it did significant damage to areas in Napa and Vallejo. That really has more to say about the weakness of the soil in those places, and the vulnerability of our infrastructure, than about the size of the quake.

Perhaps the reason for the headline is that journalists are still a big trigger-happy in reporting because of the damage in Napa. At the same time, they tack the geologic context of this being no big deal.

It’s important to have the perspective that far, far larger quakes loom in our future, and if those quakes are more proximal to population centers, the damage will be significant. That’s the kind of headline we should be seeing from the media.

A Good, Scientific Ruling: Marin Cannot Ban Smart Meters

A bit off-geology, but science related:

A recent article in the Marin Independent Journal, “New ruling denies Marin jurisdictions power to ban smart meters,” reported a promising ruling by the California Public Utilities Commission.

Simply put, the county of Marin and the cities of Fairfax and Ross may not opt out of installation of Smart Meters, though Fairfax had tried to decree a three year moratorium. The reason for such a moratorium was citizen concerns about “health and discrimination against people sensitive to electromagnetic frequencies.”

Sensitivity to EMR? Medical science does not recognize such a thing. Beginning physics students can calculate how a distance of just a few meters drops powerful EMR fields down to background, making a “disturbance in the force” large enough to affect someone implausible. The fact that some people self-report symptoms of headaches and nausea from EMR exposure does not go very far as evidence. For one, without the proper measurement tools, they have no idea how much EMR they are bathed in. Two, there are many other medical reasons for such symptoms. Three, there is no plausible medical mechanism for Smart Meter EMR making people respond this way.

Believing that some people are “sensitive to electromagnetic frequencies” is a superstition of the Left. Like fear of cell phones or GMOs giving one cancer, the Left sometimes also engages in the same manner of science denial and the Right so frequently does in regards to evolution and climate change. Irrational fears and magical thinking abound among all people, and skeptics should call these irrationalities out whenever they are found.

But what’s the danger in just allowing those who are worried about EMR from opting out? The danger is governmental recognition of a problem which is not a problem, of a danger which is not a danger. In an ideal world, government actions would be guided by science and reason. When a city such as Fairfax tries to opt out of Smart Meters, this bolsters and encourages those whose irrational fears about EMR have overtaken their knowledge about EMR. If Fairfax does it, so may other cities. Soon dozens of cities are opting out of Smart Meters–without a shred of science behind the decision. Such irresponsible law-making enables irrationality. Instead of acquiescing to citizen demands to ban Smart Meters, our elected officials have the responsibility to educate this worried segment of the public why their worries are unfounded.

Imagine if a segment of concerned parents came before a city council wanting to express concern about vaccines and autism–a link which has zero scientific basis. Instead of correcting the misconceptions of these parents, the city council stokes their irrational fears by offering to ban vaccines within city limits. Everyone would call that irresponsible, and the same logic applies to city councils declaring moratoriums on EMR-producing devices.

There are real health hazards out there. For California, the top 3 leading causes of death are heart disease, stroke, and Alzheimer’s. EMR exposure ain’t on the list. It’s easy to understand why someone would become flustered by EMR exposure, because it’s invisible and seems seems scary. But what’s really scary is a cheeseburger. Diet is what’s killing people, not EMR.

Daly City landslides


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daly city landslides at Mussel Rock

The Mussel Rock area is where the San Andreas fault comes out to sea on the SF Peninsula, and right at this spot there is an interesting view of 1950s ticky-tacky houses perched right along the edge. These homeowners have a great view of the Pacific ocean–for now.

The 1906 earthquake caused a huge landslide at Mussel Rock, and the debris covers the fault trace so that now it is quite obscured. In times past, conceivably, the San Andreas was brilliantly exposed in steep cliffs, such as we find just a mile north at Fort Funston, but it will take a long time for erosion to recreate such a dramatic cliffside presentation of the San Andreas.

In the meantime, we can look at the precarious position of these homes and wonder what the builders were thinking.

The Famous Carnelians of Marin County


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Every semester I get questions from students at College of Marin about where they can find carnelians. They may have sifted through the chert pebbles at Rodeo Beach, in the Marin Headlands, in hope of spotting one of the elusive orange gems, but in most cases they’ve come up empty-handed. But they’ve heard there are carnelians out there, and they ask if I can tell them how to find them. I’m afraid the answer is yes–and no.


Carnelian is the name given to the reddish variety of chalcedony, which is itself a variety of the mineral quartz, which is formed of SiO2. It makes sense that we should find it among the vast cherts of the Marin Headlands, for these cherts are primarily composed of SiO2, and it is not a stretch of the imagination to see how liberated SiO2 becomes recrystallized into new forms.

Chalcedony is cryptocrystalline quartz, meaning that the minerals exist but are vanishingly small. In thin section chalcedony often presents as parallel fibers, but this structure is so small that in hand sample it appears dull and waxy. The transparency of quartz is present, however, and if small amounts of iron contaminants are incorporated as the crystal grows, it will take on a pleasant orangish-reddish hue. This is carnelian.

Carnelians have been used in jewelry for millennia, and many examples were found in the treasures of King Tut. One particular use for carnelians was in signet rings–used to press a symbol into hot wax, in an archaic kind of signature–because wax does not stick to carnelian.

One of the mysteries about the carnelians found at Rodeo Beach is their source. Rodeo Beach meets the Pacific at the mouth of the long valley that forms the merger of Gerbode and Rodeo valleys. Perhaps somewhere up there is an exposure of carnelian-rich rock?


Geologists and rock hounds have thoroughly tramped these hills in vain looking for this source rock. If we find carnelians at the beach, surely they must come from somewhere higher. It turns out that someone knows exactly where the carnelians come from.

My Top Secret Source™ revealed to me that years ago, following an exceptionally violent storm surge, the sand at Rodeo Beach was so throughly removed that the passage between Rodeo Lagoon and the Pacific Ocean opened up. This is near the edge of the parking lot, where one now walks down the steep embankment toward the sand. And there, deep under what is normally covered by the chert pebbles of Rodeo Beach, was an outcrop rich in carnelians. Yet just as swiftly as it appeared, the sand once covered the carnelian source rock. From the description of my Top Secret Source™, I think the outcrop is in the center of this picture:


It must be that every few decades, a storm is violent enough to expose and erode the carnelian source rock, liberating a burst of carnelians to mix with the countless chert pebbles at Rodeo Beach. Over the millennia, this led to a surplus of carnelians at Rodeo–a surplus which, when humans descended upon the beach and began actively hunting for them, disappeared so thoroughly that now only the tiniest carnelian fragments, some no bigger than a grain of dust, can be easily found.

So when my students ask how they can find big carnelians, the answer is you usually can’t. But that condition might change immediately after a vigorous storm, which tends to churn up much sand and reveal hidden gems. Or if the storm is exceptional, the source rock itself might make a brief appearance. For most of the time, though, you’ll just have to appreciate what Rodeo Beach has in abundance: beautiful chert fragments honed by nature’s own rock polisher.


What this blog is about

I am lucky enough to teach geology in one of the most geologically fascinating places on the planet. My students at College of Marin already know the greatness the Bay Area’s geology, where we can in the course of a single day stand on the San Andreas fault, touch serpentinite crumbling out of cliffs in view of the Golden Gate Bridge, see active landslides undermining million dollar homes, and put our boots right on the one of the most dangerous faults in the world, the Hayward fault. Visiting these places, and understanding what they mean, is what this blog is all about. This blog is a way for me to share with a wider audience my love of the geology of the Bay Area.

This blog will focus on the geology of Marin County, but will touch upon the surrounding areas too. And since California is the state with so many other amazing places–Yosemite, the Gold Country, Owen’s Valley, Death Valley, Mt. Shasta, the Klamaths–you can bet that places far outside Marin County will make an appearance from time to time.

If you have any questions, please contact me at geology.prof (at) yahoo.com.