The Plot by Geologists Has Succeeded: You are Ready for the BIG ONE

Note: Please accept that this is tongue-in-cheek semi-parody, and is in no way meant to minimize the viral pandemic that is deeply affecting our society. Please take all appropriate measures to prevent the spread of the virus...

The long years of planning and the endless meetings in secret have finally borne fruit. The geologists have finally prepared American society for the BIG ONE (the BIG earthquake, the BIG volcanic eruption, the BIG hurricane). Straight-forward education didn't work, since no one read the reams of information put out by the hard-working geologists, so we finally had to use the arrival of the Covid-19 virus to make our point: disasters will happen and we have to be ready for them.

It's unfortunate that people had to panic and go running into stores to buy up huge amounts of materials basically unrelated to the virus: the bottled water, the paper towels, the non-perishable foods. But through the power of suggestion, we geologists managed to get people to buy just the kinds of things one would need in the aftermath of a major quake when help and assistance by emergency workers might be days or weeks away.

There is nothing that makes a geologist cringe more than a government official saying something along the lines of “It’s an unforeseen problem. … Came out of nowhere.”. That's almost never true. Every government official has all kinds of emergency planning materials available to them, and presidents have entire government bureaucracies designed to prepare for emergencies and disasters. Unless they disband them, as happened to the White House’s National Security Council Directorate for Global Health Security and Biodefense in 2018. Many people no longer remember the words of Bobby Jindal in 2009 in a response to a State-of-the-Union address, but geologists will always remember: he was complaining about “$140 million for something called volcano monitoring. Instead of monitoring volcanoes, what Congress should be monitoring is the eruption of spending in Washington, D.C.".

It has been interesting (and terrifying) to watch the response of people to the pandemic. Millions didn't take it seriously and continued life as normal. Some understood the warnings of the epidemiologists and started making preparations, buying reasonable amounts of cleaning supplies and disinfectants. It has been a slow-motion disaster that unfolded over several months. Volcanic disasters may be similar; eruptions have precursors that can last for months.

But earthquakes will come on suddenly and without warning. And unlike with the pandemic, the infrastructure of society will be severely compromised. It won't be stores with empty shelves...it will be stores in ruins. The electricity will go off, and with it the faucets and toilets won't have water. The hospitals won't be overwhelmed over a period of days or weeks, they be inundated all at once if they are functioning at all. It's in those kinds of moments that having water, food and emergency first aid supplies can be the difference between a good or bad outcome during a disaster.

There will be some important differences. Earthquakes and volcanic eruptions are regional, not national disasters. The infrastructure will be destroyed in some places, but will be functioning in others. Because of this, it won't take all that long for emergency workers to begin arriving from outlying areas where the damage isn't so bad.

There is one other really big difference when these geologic disasters strike: we won't be constrained by 'social distancing'. We'll be available to help each other out. Remember the words of Fred Rogers:

For me, as for all children, the world could have come to seem a scary place to live. But I felt secure with my parents, and they let me know that we were safely together whenever I showed concern about accounts of alarming events in the world. There was something else my mother did that I’ve always remembered: “Always look for the helpers,” she’d tell me. “There’s always someone who is trying to help.” I did, and I came to see that the world is full of doctors and nurses, police and firemen, volunteers, neighbors and friends who are ready to jump in to help when things go wrong. 

Strive to be one of the helpers in all that is to come.

For more on earthquake preparedness, especially in the Bay Area, check out:
https://pubs.usgs.gov/fs/2016/3020/fs20163020.pdf

Driving Through the Most Dangerous Plate Boundary in the World: Looking for the "Big One"

Tomales Bay just might be the most contradictory places in all of California. On the one hand, it is one of the most peaceful and serene places in the state, a largely undeveloped fifteen-mile long bay, protected from the worst of Pacific storms and waves by Inverness Ridge. On the other, it hides the trace of the San Andreas fault, and California's worst earthquake ripped through the bay in 1906.

We are just getting started on our journey across the most dangerous plate boundary in the world, but our journey is an exploration of a fossil convergent boundary, not an active one. But that doesn't mean it's not dangerous. A Mesozoic convergent boundary was present off of California for well over 100 million years, producing hundreds of thousands of magnitude nine earthquakes and tsunamis. Thousands of volcanoes would have erupted along the inland arc. But the subduction zone responsible for all the mayhem was replaced in late Cenozoic time by a transform boundary, the San Andreas fault system. The San Andreas has been responsible for plenty of mayhem itself, but the magnitude eight earthquakes that occur here are only one-thirtieth of the power of a nine.

It may seem like a large bay like Tomales would have been a major harbor and port along the California coast, but the waterway is mostly very shallow, and the mouth of the bay is subject to heavy wave activity and hidden shifting shoals. Getting in and out of the bay can be very hazardous (according to the state, in one year alone 13 boaters lost their lives there).

Once in the bay, the water is generally calm and is popular with small boaters, kayakers and fishing enthusiasts. A few small villages are present, including Olema, Inverness, Point Reyes Station and Marshall. Mostly the bay is undeveloped, and is a unique environment compared to the rest of the California coast. The calm water in the interior bay is the exception rather than the rule, and is an important natural habitat for a large number of species. A fair portion of the bay is protected as Tomales Bay State Park and much of the west shore is part of Point Reyes National Seashore. Several parcels along the eastern shore are part of the Golden Gate National Recreation Area.

Looking at Inverness Ridge from the east shore of Tomales Bay. Photo by Mrs. Geotripper.

Rocks within the San Andreas and related fault zones (the San Gregorio and Golden Gate faults in this instance) are highly sheared and ground up so they are easily eroded. Linear valleys will often form along fault zones, and such was the case here near Point Reyes. The valley extended from Bolinas Lagoon and Olema to the northern end of Tomales Bay, but when the last ice age ended around 12,000 years ago, sea level rose and flooded much of the stream floor. That was the origin of Tomales Bay. The rocks west of the fault, as noted in the last post, are composed of granitic and metamorphic rock related more to the Sierra Nevada and Mojave Desert than the North Coast. They have been carried north hundreds of miles by the lateral movement along the San Andreas fault.

Source: USGS (http://pubs.usgs.gov/of/2005/1127/)

The recurrence interval of massive earthquakes on the northern segment of the San Andreas fault is not exactly clear. Besides the well-known 7.8 magnitude tragedy in 1906, there is evidence of other major seismic events in 1522, 1686 and either 1748 or 1838, suggesting a return of giant quakes roughly every 125 years or so. Other studies have suggested longer intervals, and no one is suggesting that they occur at regular intervals. There is even some suggestion that major events are related to large seismic events (magnitude 8.5-9.0) on the Cascadia subduction zone off to the north. Long story short, the "Big One" in Northern California may happen tomorrow, or it could happen 300 years from now. And large quakes are possible on other faults in Northern California, especially the San Gregorio and Hayward fault zones. And the San Andreas fault in Southern California is on an entirely different rupture schedule. If you are going to live here on the west coast, the watchwords are "be prepared".

Bolinas Lagoon (and pinnipeds)

As we drive south from Bear Valley and the headquarters for Point Reyes National Seashore, we are following the trace of the San Andreas fault. In 1906, the fault rupture shifted the ground here as much as twenty feet, the largest such offsets recorded. After a few miles we reach the north end of Bolinas Bay.

The waves coming into Bolinas Bay tend to refract as they encounter Duxbury Point and swing around so they carry sand northwest. This has caused the formation of a sand spit that closes off Bolinas Lagoon, forming one of the nicer tourist beaches in the San Francisco Bay Area, Stinson Beach. Three different faults cross this sand bar, the San Andreas, the San Gregorio, and the Golden Gate. I wonder if this kind of information is reported on deeds of sale for the string of homes on the sand bar.

We continue our journey southward along the coast on Highway 1 as it winds its way along the cliffs beyond Stinson Beach. The road climbs quickly onto the rugged slopes of the peninsula called the Marin Headlands. We have crossed the San Andreas fault, and are now on the North American Plate. The rocks here are very different, as we have reached the "most dangerous plate boundary in the world" (past tense). We will explore further in the next post.

Stinson Beach, Bolinas Lagoon, and the Point Reyes Peninsula.

The BIG ONE is COMING! Well, yeah, but...

The San Andreas fault in the San Francisco Bay area. The two reservoirs are Crystal Springs and San Andreas, which gave California's most important fault its name. Photo by Geotripper.

It seems like there has been a bit of shaking going on in California over the last few weeks. There was the 6.9 quake off the coast of Eureka on March 9, a 4.4 magnitude tremor in the San Fernando Valley on the 17th, and now the 5.1 magnitude quake in La Habra. It's enough to make people paranoid about quakes in general, and the BIG ONE in particular. Are these precursors to the BIG ONE? Are they relieving some of the stress that will prevent the BIG ONE from being so bad? We love to talk about the BIG ONE, and if the media outlets have their way, we will worry and fret about it, enough so as to tune in to their stations for more scary updates (to keep those ratings afloat). I've rarely been impressed by media coverage of earthquakes, and this week has been no exception. I've heard through tweets that some media outlets trumpeted official statements warning of bigger quakes to come in 24 hours while conveniently forgetting to mention the "5% chance of" statement that preceded the word "bigger".

Of course, in some ways it's worse. We're not waiting for the BIG ONE in California. We are waiting for the BIG ONES. The San Andreas fault gets lots of attention, but there are numerous active fault zones in California, and the San Andreas itself behaves like four independent fault systems. There was the devastating earthquake near San Francisco in 1906 that garners much attention, but there was an equally large quake near Fort Tejon in Southern California in 1857, and the Salton Sea region was shaken around 350 years ago. These different segments of the San Andreas seem to move every century or so. A huge quake shook the eastern Sierra Nevada in 1872, killing a tenth of the population in the Owens Valley (28 people). Each of these quakes were in the range of magnitude 7.7-7.9, although some estimates range as high as magnitude 8. Add to this list the 1952 Tehachapi quake (7.3-7.6), the Landers quake of 1992 (7.3-7.5), the Hector quake of 1999 (7.1), the El Mayor quake of 2010 (7.2, just over the border in Baja), and the Cascadia Subduction Zone quake of 1700 that no doubt affected the northernmost part of the state. It was very likely a magnitude 9 event.

I should mention that I successfully predicted these quakes. We discussed earthquakes and the "art" of earthquake prediction in my classes two weeks ago. We pointed out that psychics predict earthquakes all the time, and that they are never wrong (how wrong can you be when you say "I see a major city being devastated by an earthquake this year" without specifying a day or location?). To prove the point, I predicted that a quake would happen in northern California within a few days, and that another would happen in the south state as well. I make this prediction every semester, and I am rarely wrong. All such predictions are crap, of course, and do no one any good.

No one can predict earthquakes, and anyone who says they can is lying or is deluded. But we can predict where they will happen, and we can determine the probability that they will take place within a certain time frame, usually 30 years. This is the nature of the maps that I am posting here from the U.S. Geological Survey, the Southern California Earthquake Center, and the California Geological Survey. Such maps are a most useful tool for educating the public about where the greatest seismic risks are located in the state (note how distressingly close they are to the most populated parts). There is a lot more to the tectonic framework of our state than just the San Andreas fault!

It is interesting to me that since these probability maps came out in 2007, we've already had a 6.9 quake in northern California, and if you count just over the border, we've had our predicted magnitude 7 quake in 2010. It is important to note that neither of these events had any particular effect on the stress levels that have built up on faults like the San Andreas, Hayward and San Jacinto. They are still just as likely to shake in the next 25 years or so. What do we take from this? The quakes are coming, and we need to be prepared for them (start here: http://www.data.scec.org/earthquake/preparedness.html). Everyone who lives in California should have emergency supplies of water and food. Even if you live outside the high risk parts of the state, you will still be affected, as the energy grid will be damaged and emergency services we take for granted will be headed into the areas where damage is the worst.

Do these kinds of disasters make you rethink the idea of living in California? You could move to Kansas and put up with tornadoes. You could go to Nebraska and enjoy the Polar Vortex. You could go to Louisiana or Florida and deal with oil spills and hurricanes. You could move to Oregon or Washington and deal with volcanic eruptions. There really is no place that is free of natural disasters, and the processes that cause them may sometimes have the benefit of producing beautiful scenery and interesting geological outcrops. I'll pick California every time.

In California, We Are Waiting for the BIG ONE! True or false? What everyone "knows" about earthquakes

Comic art by Zeo

We've reached the end of our seven question quiz on what everyone "knows" about California earthquakes, things which may be true or maybe aren't. These questions were the basis of a community lecture I gave a few weeks ago. The last two questions concerned the ability of psychics and animals to predict earthquakes, and yes, psychics are frauds when it comes to earthquake prediction, and we can't sense the world the way animals do, so basically, it is impossible to predict earthquakes in the kind of timely manner that will allow people to take cover or leave town. We just can't do that, not yet.

But there is still that nagging statement that you hear all the time in California. It's today's true-false question:

In California, we are waiting for the BIG ONE! True or False??

When I was on stage at the lecture, I made sure to say "the BIG ONE" in capital letters. How do you say something in capital letters? You do it in a deep baritone voice with your hand cupping the microphone; it's very dramatic.

So what is the answer? Well, actually the question is wrong and requires a bit of modification. Let's try it again, and in that deep baritone voice:

In California, we are waiting for the BIG ONES!

There, that's better. If we can't predict earthquakes, then how can this statement be possible? Doesn't it require the ability to predict earthquakes? Yes, it does. So the statement must be false. But it is not. The answer is TRUE!

Predicting earthquakes is not possible in the short term, as in hours or days, but a great deal can be said about the probability of earthquakes in a particular area over a period of decades. We can do this on the basis of the historical and prehistorical record of earthquakes along a particular fault zone, and by analysis of building stresses and tilting over a large region, as revealed by GPS stations and other related technology Check out the methodology of the 2007 Working Group on California Earthquake Probabilities in this USGS PDF file.

As can be found on the map above, numerous fault zones represent a threat to the state of California. The fault zones are of different lengths, and therefore some will produce smaller quakes, but several are capable of producing large shocks approaching magnitude 7, and maybe even larger. These include the San Jacinto fault, the Owens Valley fault, the Hayward and Calaveras faults, and others. Even more important is the fact that the San Andreas itself is not a single monolithic fault zone. It has segments that behave independently. This was shown in 1857 and 1906, when completely different sections of the fault gave way, producing shocks that approached magnitude 8.

The most recently published studies show that earthquakes of 6.7 magnitude or greater are a virtual certainty over the next 30 years. The chance for an even greater quake is ominous, exceeding 70% for a magnitude 7.0, and a lesser, but still significant chance of even larger events. In a way, one of these quakes has already occurred, even though it was just south of the state: the El Mayor-Cucapah quake this year in northern Baja California was a magnitude 7.2 event.

Another wild card is the possibility of a large quake along the Cascadia subduction zone in the northernmost part of the state. It was not included in the probabilities, but numerous magnitude 7 quakes have taken place in that region in recent decades.

The lesson to be drawn from these predictions is that damaging earthquakes have happened all over California, and they will continue to do so in the future. Some of these quakes will be major events, causing many deaths and massive damage over large areas. The probability forecasts have great value in the sense that they are a warning to residents across the the state to be prepared at all times for earthquakes. We cannot know the precise moment that a large earthquake will strike, but we do know where they will happen, and how big they can be.



The Redlands Earthquake Swarm: California Has Her Faults; Lots of Them!

A swarm of small and moderate earthquakes has been shaking things up in Southern California in and around the town of Redlands. The largest, on February 13, was magnitude 4.1, with five additional events between 3.1 and 3.6 in the days that followed. Well over a hundred smaller quakes have been detected as well. Swarms are interesting and exciting if you live on top of them, but they don't usually signify bigger things; the earth is shifting a bit, and that is often the end of it. On much rarer occasions, they may be a sign of an impending larger event, a foreshadowing disturbance of the earth similar to the cracks and pops a tree branch makes before it breaks (disclaimer: I am NOT making ANY kind of prediction; I don't have any access to data, nor do I have the background to do so, and seismologists know better than to try and make a short-term prediction of any quake). My message for the day is to remind people who live in earthquake country that they should ALWAYS be prepared for a large seismic event.

The view from Santa Rosa Peak in the Peninsular Ranges reveals the parallel valleys of the San Jacinto fault. The perspective is towards the west; the San Andreas fault is some twenty miles to the east of the peak

There is another opportunity here: a lot of people, when they hear of quakes in California, think San Andreas Fault. Many California residents who have lived here all their lives cannot think of the name of another fault in the state, but our landscape is literally crisscrossed by active faults (look at the map above; most of the brown lines are active faults). Most earthquakes in CA happen on faults other than the San Andreas, and this week's swarm is no exception. It appears to be taking place on one what is arguably the most active fault in the state, the San Jacinto fault.

The San Jacinto fault is certainly part of the San Andreas system. It splits off from the San Andreas at the east end of the San Gabriel Mountains, and runs roughly parallel to the San Andreas for 140 miles south into the Imperial Valley. It has the same type of motion, right lateral (features on the opposite side of the fault have been shifted to the observer's right). Since it began moving a few million years ago, something like 15 miles of lateral motion has taken place.

The San Andreas fault is justly famous for several devastating earthquakes, including the 1906 San Francisco event that killed 3,000 people, and the 1989 Loma Prieta quake (the World Series quake). It also produced a magnitude 8 event in southern California in 1857. But most of the time the fault is quiet (in a menacing way; it is storing up stress). Compare this with the history of the San Jacinto system (courtesy of Wikipedia):

1890 - Magnitude 6.5 that occurred in the "San Jacinto or Elsinore Fault region".

1892 - Another magnitude 6.5 occurred in the same region as the 1890 earthquake.

1899 San Jacinto Earthquake - Magnitude 6.4 earthquake destroys San Jacinto and Hemet.

1918 San Jacinto Earthquake - Magnitude 6.9 earthquake strikes the same area that was damaged by an earthquake 19 years earlier, with an epicenter roughly 10 mi NW of the previous earthquake.

1923 North San Jacinto Fault Earthquake - Magnitude 6.3 earthquake damaged the San Bernardino and Redlands area. Last time the fault, which runs under the I-215/I-10 interchange, ruptured in this area.

1937 Terwilliger Valley Earthquake - Magnitude 6.0

1942 Fish Creek Mountains Earthquake - Magnitude 6.3

1954 Arroyo Salada Earthquake - Magnitude 6.2

1968 Borrego Mountain Earthquake - Magnitude 6.5

1987 Superstition Hills Earthquake - Magnitude 6.6 (Note: some consider it to have occurred on a fault completely unrelated to the San Jacinto Fault Zone)

These quakes are considerably smaller than the 1906 event, by a factor of 32 or more (it takes the energy of 32 magnitude six quakes to equal the energy of a single magnitude 7 quake; a magnitude 8 quake is 32 times more powerful than a magnitude 7 quake and more than a thousand times more powerful than a six). But they clearly happen more often . The message is clear: to live in California, we must be prepared not just for the BIG, HUGE ONE, but also lots of lesser BIG ONES.