I’m still waiting for a set up for I’m sorry for your loess. It’s been years now, decades even, the funny guy equivalent of geologic time. Just my luck when I die they’ll bury me in Wisconsin and the gravedigger will complain about the crumbly rock and I’ll just lay there mute and stiff and unfunny.
Category Archives: Geology
Quake
(Posted to Facebook on July 6, 2019)
Yesterday’s earthquake was 7.1 near Trona and the intensity drops with the distance from the epicenter. And drops quickly. It was probably a high 6 in Ridgecrest. Had Ridgecrest experienced the full 7.1 it would have been damaged as Trona apparently is, “looking like a tornado went through the town” according to an eyewitness. Down here in LA it probably felt like a high four on the Richter scale if you lived on soil or sand, a lot less if your house is built on bedrock (we only felt the big one in our pad high atop Mt. Waverly, none of the fore or aftershocks). Quakes also feel considerably stronger if you live on the upper floors in multi-story buildings. But no one down here in LA felt anything like that 7.1 they experienced 160 miles north of us in Trona (which is still out of touch with the outside world, apparently) or 120 miles north of us in Ridgecrest.
So yes, the earthquake was stronger than the Northridge quake at the epicenter, but everyone in LA was much closer to that epicenter. Hence stuff fell down in Los Angeles in 1994, even big stuff like freeway overpasses. Probably little if anything fell down with the city limits this time.
Still, it was fun yesterday watching visiting New Yorkers freak out on social media with tales of terror and jerky videos of sloshing hotel pools. Oh the humanity.
“So for us on the east coast, how does an earthquake in the desert feel different from an earthquake in the mountains?”
The earthquake coverage over the weekend by CNN and MSNBC was appallingly bad. Utterly unscientific tabloid style journalism. Local coverage in LA was vastly superior. The networks could at least try to have geologists on call. Trump isn’t alone in being anti-science, apparently.
I never metamorphic I didn’t like or if you can’t say something gneiss say nothing at all.
Beautiful little piece of reddish rock, layered, I picked up along the side of the road west of the Salton Sea under the assumption it was chunk of petrified wood. Closer examination at home showed that it is more likely a fossilized and mineralized square inch of beach, or perhaps grains of sand laid down in the bed of a slow moving stream, or in an inlet of the long gone sea. Buried and compressed it hardened into sandstone and then was folded into the earth, under millions of tons or rock, and heated by the mantle below (or perhaps the energy displaced by the slow movement of the fault beneath our feet), which transformed the component sediments into something still layered but harder and more crystalline. Gneiss. Not sure where the red came from. Perhaps this was once one of the red sandstones one sees everywhere in the West, littered with dinosaur bones. There was iron everywhere once, it seems to have turned all the sediments red. Perhaps there was more oxygen in the atmosphere then, enough to turn a tree into a torch at the slam of a baseball bat, enough to oxidize all the traces of iron in the sand into a brilliant red. Perhaps. That’s the theory, anyway. Of course, most of California didn’t even exist when that famous red sandstone was laid down. California was still deep down in the mantle, or moving inexorably eastward as ocean floor before slamming into North America. No dinosaurs ever trod the sands that solidified into this stone.
Now I find this little rock here, in the sand, no metamorphic outcroppings let alone mountains for miles. So water dropped it here. Who knows how much weather that took? How many torrential rains and flash floods were required to drop this little rock here at my feet on these archaic flats? It sat there, glittering in the waning sun, surrounded by the sand verbena that clustered in vast herds across the ancient sea floor. They shivered in the dry wind, as if cold, though the temperature was near ninety and the rock was warm to the touch, as if right out of the oven. I picked it up and rolled it about in my hand, thinking of ancient worlds.
A rock on my desk
Damn, thought I found this nifty chunk of basalt out near Anza Borrego. It’s got a flat bottom (no jokes) and it is yet another rock I have on my desk for allegedly utilitarian purposes. This one, I told my wife, would make a great paperweight. But I just like rocks. I stood there in the ninety degree heat just west of the Salton Sea Basin, flowers in a zillion colors in every direction, fixated on the rock in my hand. I love basalt. I pictured it forming far below my feet, rising, cooling, a tiny bit of the earth’s mantle cooled and frozen into hard, simple stone. I was hoping it was a billion years old. I always hope basalt is a billion years old. It wasn’t. The basalt in the area was a mere hundred million years or so. Still, it does make a good paper weight, even if it’s a relative infant, mantle wise. There is something fundamental about basalt, a strength, a simple plainness, an assurance that our planet is solid and very real in the vast emptiness of the universe.
But a few minutes ago, eyes drifting from the TV where the LA Kings were being humiliated by yet another Canadian team, I started looking closely at my paper weight again. The lighter, granitic smears bothered me. Why were they there? And I hadn’t paid much attention to the bits of white on the surface. With the Kings collapsing in their own zone again, I grabbed a magnifying glass. It’s not a very good one, but through it I studied those white bits. Damn–structure. I screwed up my eyes and squeezed every bit of nearsighted vision I had remaining. Sure enough, there it was-a cylinder, ringed, tapering. Perhaps some sort of gastropod shell, some kind of pointy shelled snail maybe an inch long. I look carefully over the rock and see similar structure in some other bits. Shells. This is limestone. A very dark limestone. I took it into the kitchen and let water run over it. Wet, it’s nearly black. I found an article online about black limestone, and how to tell it from basalt. Basalt typically contains some larger non-basalt crystals. I pored over the surface of the rock again with the magnifying glass looking for crystals. Nothing. Just little hints of fossils. Bits of living things. This rock is made of organically produced structures that once contained soft bodied, skeletonless creatures, invertebrates. Organisms that needed the shelter of a shell they made themselves. Animals trying not to be eaten.
It dawned on me that I was holding in my hand the end result of the evolution of predators, of meat eaters, because before predation there was no need for shells. Everybody ate algae. There was need for shells or hard body parts or beaks or teeth. But I was holding those long deceased animals’ shells. A half billion years of protection against murder reduced to its basic minerals and a few whole bits and congealed together on the floor of the ocean after the animals shed or died in them, then pressed down by the weight of millions of years of sediments above, then hardened into rock, into this limestone. It’s like holding a handful of millions of untold histories.
The black color? I suppose it’s black the way some shales are black, shales of hardened darkened mud. I really don’t know. Basalt would have been so simple. Formed deep beneath us under the tectonic plates we stand on, and stretched out into ocean floors, then lifted up as the plates crunch into each other, pushed upward into mountains and then broken down again by water and wind and earthquakes, carried along by floods too many to count and left in the dirt at my feet between bunches of violet sand verbena and a few wild poppies. A simple story, basalt. Now I have instead a compacted chunk of the story of life, and I stare at the damn thing and feel hollow.
Liquefaction in the Heart of Screenland
Oh (he says to a seismically hypersensitive friend), you work in Culver City…. That explains how you felt an earthquake (technically a microquake) that measured 2.8 on the Richter scale. I try to notice nothing below 4.0, but then I am jaded. But Culver City is built on the Los Angeles River floodplain. In fact, the Ballona Creek that trickles unnoticed though the neighborhood was an alternate channel for the L.A. river in its carefree, unchanneled days. And the soil there must be many feet deep, sediments that go who knows how far back, and are more sandy than clay, given the source (the Santa Monica Mountains). What this means for your nerves is that sandy alluvial soils are prone to liquefaction, and amplify the slightest of earthquakes, so that something beneath of dignity of an Angeleno sitting on bedrock, as in my neighborhood, is noticed by highly sensitive types in Culver City. Were it a more manly earthquake, something, say, in the vicinity of an 8 plus, the earth beneath you would be as water and you’d never be heard from again, and Amoeba could at last have what remains of your record collection.
Here’s a link to a convenient map of the Culver City liquifaction zones. They’re in teal. This map is available on Culver City’s official website, though I doubt they tell anyone, since there’s more teal than is tasteful. Teal is best in small quantities. It’s a pungent off-blue and a little goes a long way, like a rank cheese. Also it makes Culver City look so screwed. Like beyond screwed. Like doomed. Which it’s not, really. It’s that damn teal. Pastels would have been much better.
Incidentally, Culver City is the Heart of Screenland.
Road cut
(Found this in the drafts, it must be a decade old at least.)
The drive to Lake Hughes via San Francisquito Canyon Road took a helluva long time but was gorgeous and great sight seeing with amazing roadcuts…man, the fault has done some terrible things to those rock layers. Some were busted into fragments and frozen in place and solidified. All this incredible, slow motion tectonic violence, immense layers of rock ground to particles, destroyed. Who knows what they were, islands, maybe, they think California is the result of islands, small little land masses all smooshed together at the edge of the North American craton. A zillion faults run through everything, Los Angeles shakes, makes us all nervous, things fall over and break. Oh well.
Solimar
(Found buried in the drafts, I think it’s from 2015.)
Unfortunate news, this fire…when the rains come this portends mudslides in the burn area and a blocked 101. I suspect the people living on the strand there are feeling a little nervous, considering that stretch’s history. La Conchita is only a couple miles up the 101 and has had three major slides in the last 20 years. The center of gravity on those very loose ocean-facing slopes is completely different soaked than it is dry, and when saturation reaches critical mass acres of earth will slump almost silently downward till it reaches a point where a new and correct center of gravity is reached. Back in 2004 or 2005 ten people were killed in La Conchita, buried alive. There was no warning. Suddenly the hillside slid down, and acres of top soil– with vegetation eerily in place–remained intact, just in a new place. It’s a tiny place, La Conchita, just a village, and we drove round its few blocks after the first slide in 1995 just to get a close up view of a of the power of mud on the move. On the street that had borne the brunt of it the fronts of houses were intact but the insides had been forced through the front windows by sodden earth, one of the eeriest things I’ve ever seen. Fortunately the homes in Solimar Beach are the ocean side of the freeway, not as threatened as La Conchita which is tucked between the 101 and the bluffs on a little sliver of a plain that must have seemed heavenly–there was a banana farm there, so unique was the microclimate–till the earth came down on top of it. It seems heavenly again, too, and now that the bluffs have done their sliding perhaps they are safe again. Not so Solimar. All that ground is still up there overhead, and when the rains come from the southwest they can open on those hills like the biblical flood. California has amazingly dynamic geology, so much movement, some inexorably slow and some instantaneously sudden, and you’ll find yourself staring at a boulder the size of a house sitting in an open field and have no idea how it ever got there.
Earthquakes in the grand scheme of things
“Scientists Fear the BIG ONE is Coming as FOUR Major Earthquakes Strike in 48 Hours” exclaimed The Express in proper tabloid fashion. Japan is rocked by four quakes in two days, each over 6 on the Richter scale. Not a terrible quake, a 6.0 or so, but a rocker and scary enough. There were even a couple deaths. Japan handles temblors like this well. They are used to them. Of course seismologists worry that they might be foreshocks announcing a real monster of a quake, though Japan is used to those too. Alas, there is nothing unusual at all about earthquake clusters like the four The Express is screaming about, especially in Japan, where four tectonic plates–the vast North American, Eurasian, and Pacific plates, and the smaller Philippine plate–grind against each other with slow violence. The northern half of Japan is mostly part of the North American plate, the Southern half is the Eurasian plate, and the Pacific plate is forcing itself beneath the Eurasian plate (a process called subduction) at a rate of about three and a half inches a year. Sometimes the subduction process gets stuck for a few years and then, after enough pressure builds up, it moves forward with a jolt. Sometimes it’s a little jolt. Sometimes it’s a 6 point jolt. And sometimes it’s a jolt so big everything shakes to pieces and the sea comes roaring back in a tsunami. That’s Japan. We have earthquakes in California as well, of course, but no one is subducting anybody. Rather our plates are slowly grinding past one another, so that the shaking, even at its worse, cannot get to the same level as Japan is prone to. In Alaska, though, where the Pacific plate is being subducted by the North American plate, you can have earthquakes of astonishing violence, like the one that leveled Anchorage in 1964.
The Express story hinted that the quakes in Japan could set off quakes in, say, California. As if somehow earthquakes were all interconnected. And while earthquakes on the same (or on linked) fault lines can be related theoretically, ones thousands of miles away can’t possibly be, because there would not be enough energy released from an initial quake to go through thousands of miles of solid rock from Japan to California. And the fact that there are four major quakes in 48 hours in a general region–say across East Asia–is just chance, as there are hundreds of quakes 6+ every year and sometimes a few of them happen within a couple day stretch.
Remember that earthquakes, in the grand tectonic plate scheme of things, are extremely minor events, just little quivers, nothing. While to us they can be terrifying, devastating, even catastrophic, in geologic terms they are just everyday things. After all, every great mountain range in the world is the result of literally millions of earthquakes. When you think how few large earthquakes you have lived through living in, say, Los Angeles, you get an idea of the time scale in building mountains, and how we can play no role at all in that process whatsoever. Nothing alive can. Mountains rise and erode as if life never existed at all. Because in the grand scheme of things life means next to nothing, really. Life is just a process for making coal or limestone.
Earthquake
(2014)
3-dimensional view of major Southern California faults. Vertical faults like the San Andreas are pencil thin lines, those at an angle to the surface are broad brush strokes. (Taken from the highly recommended site earthquakecountry.org.)
That Puente Hills fault that caused the quake out in Brea yesterday (in 2014) is the one that terrifies geologists. They used to think the Elysian Park fault was the killer–our house sits right atop that one–but it now appears to be dormant. But in the last ten thousand years the Puente Hills fault has snapped in a huge way four times, and each of those quakes was a 7 plus on the Richter scale. That would be ten times at least as powerful as the 1994 Northridge quake. Furthermore, the Northridge fault directed its energy away from downtown (with explains how places as far away as Fillmore were leveled) but the Puente Hills fault would direct its energy towards downtown. I suppose that is how people in downtown last night felt the shaking of a quake centered in Brea so strongly (and why we scarcely noticed while we were out in Tujunga). The Puente Hills fault stretches from roughly Brea to Beverly Hills, and it has three active areas–Brea, Whittier (remember the Whittier Narrows quake in 1987?) and here. And I mean right here…downtown Los Angeles is square in the middle of it, and the zone’s width goes from just below USC to about where I am in Silver Lake. In fact, being that I am typing this while literally astride the Elysian Park fault, our place is just outside the Puente Hills fault zone, not that we wouldn’t shake like hell anyway. We wouldn’t shake as bad as people on the nearby flatlands, their homes built as they are on layers of sediments, but we’ll be shook up something awful. I dread the thought of it. It won’t be boring, anyway. (There was another shaker on the Puente Hills Fault in January 2015 that got everyone’s attention just a few blocks from us but that we literally did not feel at all. Not even the cat noticed.)
The Puente Hills fault is a thrust fault. Everyone knows how the San Andreas fault (which cuts through the Antelope Valley down into the Coachella Valley fairly distant from us) is between two plates that slide past one another. Every once in a while the plates get stuck and then snap apart. The movement is horizontal. West of the fault goes north, east goes south. But a thrust fault is vertical movement, that is the fault zone is thrust upward. As the tectonic plates move, pressures build up in the rock beneath us. Stress fractures appear, which we call faults. Those pressures reach a point where something has to give and when they do, you get an earthquake along one of those stress fractures. Most of the times these quakes are imperceptible to anything but a seismograph machine. Sometimes they are strong enough to wake the cat. Sometimes they are strong enough to set off a flurry of chatter on Facebook. And sometimes they are bigger than that. In a really big quake along the Puente Hills fault zone, the ground will suddenly lurch up a meter or two, meaning that the part of town from USC up through downtown will be instantly elevated above the area south of it. Think of it this way: all the north south streets–Alameda, Hope, Flower, Figueroa, Hoover, Vermont, etc.–would suddenly be unusable, because at some point past Exposition Boulevard there would be a three or even six foot drop straight down. Not gradual, not sloping, but straight down. You will need a ladder to proceed down the sidewalk. That is what huge quakes on thrust faults do.
No one knows when this will happen. It will happen. There is no way it will not happen. But it could be before I finish this post, or it could be in a couple thousand years. Every city on the West Coast from Anchorage (trashed in 1964) to San Diego (my first earthquake memory) faces the prospect of a disastrous earthquake. That is the geologic reality of living on the Pacific Rim. It’s scary as hell if you think about it much, so I don’t think about it much. We try to be a little prepared, though. Just in case. Ya never know.
I wasn’t going to post this. Like maybe it’s too creepy. But maybe people should know. A lot of you do already. But it’s amazing how many residents of this area have no idea what might happen if we roll seismic snake eyes.
Now I need a drink.
And you will too, after seeing this Visualization of a Puente Hills Earthquake. It is in real time, and the color key represents the degree of shaking. Blue is the least violent, green more so, yellow even more and on into the red. You notice that the more intense shaking–the greener, yellower and even red colors, are in the flatlands between downtown and the Palos Verdes Peninsula. The sediments of the basin there are up to six miles deep, laid down mostly when the land was ocean bottom and compressed into the easily crumbled rock that you see in some roadcuts. But the meandering Los Angeles River has over thousands and thousands of years left deep, sandy soils that once made for terrific farmland and now are really prone to intense liquefaction when the ground shakes. There was intense damage in this area after the Northridge quake, probably all of which was caused by liquefaction. The ground under overpasses on the Santa Monica Freeway lost its solidity and the poor things just toppled. That’s an impressive sight, and immense concrete bridge in pieces on the ground. That was the destructive power of liquefaction. And that epicenter was much further away than this hypothetical Puente Hills quake would be. The damage from a 7 magnitude quake in the Downtown area would be exponentially greater. A lot more overpasses would topple. A lot of houses will be red tagged. What a mess.
Probably be some great yard sales, though.
Anchorage, 1964. You’ll be happy to know that no matter how nasty a quake the San Andreas has in store for Southern California, this sort of thing will not happen. The Anchorage quake was one vast tectonic plate (the Pacific) suddenly shoving itself beneath another (the North American plate). Subduction they call it, a slow process that every once in a while gets stuck. When subduction unsticks you get scenes like this. The North American plate side of 4th Street here wound up 38 feet above the Pacific plate side, making parking difficult. This cannot happen on the San Andreas, which is where the same two plates just slide past each other, one heading north, once south. Occasionally things get stuck and then, after some time, unstuck. It was the unstuck that leveled San Francisco in 1906. And it will be a similar unsticking that will someday level Palmdale and Palm Springs, shaking the rest of us something awful. However, there would be no displacement like that in Anchorage–the San Andreas unsticking would be a sudden horizontal movement, not vertical. If that makes you feel any better.
Brick's Science 