Part 4: Earthquakes

Ajouté : 2026-05-09

[00:00:00]all right welcome to part four earthquakes now if you live in California earthquakes are just part of your life and for California natives you don't really think twice about earthquakes like oh there was an earthquake today um my daughter her first earthquake it was a small one and she happened to be with me when it happened and we kind of looked at each other and I started to laugh so she started to laugh so to her just like me we think earthquakes are fun now obviously they can be catastrophic and we'll talk about that uh but it's not something that we really stress about which makes me laugh because people who live in Hurricane prone areas think we're crazy because we're so complacent with earthquakes but it works in Reverse as well I think the people who live in Hurricane areas are crazy and tornado Tornado Alley don't even get me started on that one all right so what happens with with an earthquake so the movement has to start somewhere and it's typically where we see the maximum move movement along the fault plane so when there's an earthquake on the San Andreas fault the entire length of the fault doesn't move it's a small segment of it that moves where the movement begins is beneath the surface and that movement where begins is referred to as the focus the focus is not at the surface it's where we have our maximum displacement that's where the mo movement begins and that's what sends the vibration through the ground that we refer to as an earthquake the epicenter is the point on the ground directly above the focus and so if you have a tilted fault plane like we see with normal faults and a wee bit on the San Andreas fault the epicenter may not line up with where the ground breaks on the surface and then the epicenter will always be at depth every now and then a newscaster will talk about an epicenter being located 2 miles deep beneath the surface I'm like no no no no the epicenter is at the surface the focus is what's beneath the epicenter just a pet peeve about newscasters talking about earthquakes and getting it wrong so how do we measure the intensity those vibrations that move through the ground those waves of of motion that go through the ground there's the mer scale and this is what for decades scientists wanted us to use because the mer scale it's on a oh I forget if it's a 1 to 10 or well not being able to remember shows how much the M scale meant to me as I was supposed to learn it when I was younger um and it measures the damage and actually the physical movement because a vibration moving through the ground doesn't mean that the ground everywhere in California moves 10 feet it's just there's a vibration that moves through it um we never use it we always use the RoR scale um and the problem with the RoR scale it's not really a good measurement for damage and what we can expect to occur and it's measuring something other than movement and damage it's measuring the waves that move to the ground those seismic waves if you were to measure them on a RoR scale it um sorry on a seismometer it would move that little needle back and forth and so it's a logarithmic scale and for those of you who've forgotten your math logarithmic scale every time you move up in a number it's 10 times the amplitude so the motion the vibration that moves through the ground is 10 times more intense as you go from a one to a two and then that means as you go from a two to a three that's 10 times more intense but a three is a hundred times more intense than a one a four is a thousand times more intense than a one well that doesn't mean there's a thousand times more damage that doesn't mean that the thousand times more things get moved it just simply that vibration moving through the ground moves the the seismometer that's why scientists don't want us to use it but we're so used to using it over the decades if I said there was a three in Fullerton you'd go H if I said there was a six or a seven in Fullerton you'd go oh wow what kind of damage were there we've been exposed to earthquakes often enough that we know what to associate with them so often it's referred to as the modified scale where it's like yeah this is what the intensity was of the vibration but we're also talking about the damage that took place so we've used it often enough where that has become our de facto measurement for everybody in the public because if I told you there was a m scale 4 earthquake you guys would give me a Blank Stare if I said there was a RoR scale 7even in Los Angeles we all would have felt it and we all know there would have been damage in Los Angeles as well in California the San Andreas Vault moves north south actually kind of Trends from the southeast to the Northwest and we have a lot of faults that parallel the San Andreas fault itself and most of our recent earthquakes in the past few decades have been on these parallel faults to it and all those parallel faults in Southern California with some weird ones kind of thrown with the exception of a couple weird ones thrown in show that right lateral movement um we have the Garlock fault which runs at a right angle to the San Andreas fault so it it creates its own little special tension up in that area uh you'll notice that we've had a few in the six and the Seven uh the North Bridge earthquake in 94 created a lot of damage in that area the other recent ones in the last decade or so like in wi year and a little bit in Long Beach they've created only minor damage my sister's house uh had some plates that fell off the wall when the Woody earthquake happened a few years ago um I'm old enough to remember all of these earthquakes and U what they felt like but I was in coastal Orange County so there was no damage down here I just would go out and watch the chandelier shake to figure out what was going on with each one of those so should we be worried about earthquakes in California well yeah I mean we have all sorts of construction techniques when we bought our house uh we were refus to even look at homes that were built after 19 or before 1974 because the land not the Landers Quake um the Quake that happened in 71 really changed a lot of the construction techniques in California so we wanted something that was later so it could withstand a larger earthquake you know all of my bookcases are bolted to the wall uh I make sure I don't have anything hanging above the bed that would fall on my head if there was an earthquake in the middle of the night um nothing fragile or Irreplaceable is in a position where if I shook where it's being stored that it would fall and break so I take earthquake seriously and you all should too I have an earthquake kit um that's got emergency supplies but am I worried about everybody calls it the big one on the San Andreas fall let's take a worst case scenario that there's a 7.5 on the San Andreas fault at its closest point out here in San berino yeah the people in San berino are going to see Heavy damage and I really feel bad for them because that's going to be horrific however we're far enough away in South Orange County that the intensity of that earthquake won't be devastating yes you'll have stuff knocked over bookcases that aren't bolted down stuff will fall out of cupboards um but you're not going to die I'm not going to worry about that uh um I'd be more worried about the Newport Englewood fault that runs through here if it had a six we'd see far more damage in Orange County so a smaller Quake on a closer fault for us would be more devastating than a big Quake on the San Andreas Vault uh again this is something where you guys should take seriously and have I have a weak supply of food I'm not going to tell you where I live cuz it's for me and my kid and my wife um but we've got supplies if something happens now in South Orange County we have an extra added bonus and that's water and transportation because if there's an accident on the five freeway on a Friday how long does it take to get home how much does that affect traffic in South Orange County because there's really not a lot of other ways North and South through South Orange County so it creates horrible traffic bottlenecks imagine if a freeway overpass collapse on the five or worse even worse would be the the El Toro y that would be devastating so you're not going to be able to go anywhere well we also have the problem with water supplies most of our water comes through a pipeline that goes through Irvine and then is distributed to the local water districts that pipeline is a clay pipeline it was built a long time ago but clay does not like to bend and so there's the potential to lose water in South Orange County after an earthquake so you can't go anywhere and you're not going to have water that's why you need to have an earthquake kit at home uh we uh I know bottled water waste a lot of plastic but we don't use that much of it but I always keep at least a case or two of bottled water in the garage and then slowly but surely I rotate out some of those bottles of water and then buy another case and you know we consume those bottles of water but not every single day and so that way the water is still relatively fresh and I've got a lot but I don't have to do anything exotic like buying water that has a 10-year shelf life uh but we still have a water supply in case of an earthquake that 2014 that was the woodier Quake or the laab Quake sorry this was the one that damaged uh my sister's kitchen and of course the the travesty of the losses that occurred in liquor stores that always scares me I'm trying to picture what the hell you would do if you're in a liquor store when this is happening watermains broke she was without water for a week and a half two weeks and this was a minor 5.1 quake and she didn't have any water now it didn't affect the transportation link so she could get where she wanted to go but it still was very inconvenient for a period of time if we look at worldwide how common are these earthquakes well this is just from when I recorded this on November 2nd I looked at what the worldwide 2.5 earthquakes were in the last 24 hours and so you get an idea of how common they are now most of these are at plate boundaries you have some unusual ones thrown in here I honestly don't know what's going on in Texas but this is a hot spot up and through here this is the plate subsiding underneath under here but for the most part we'll notice that they are associated with the plate boundaries and in California if we look at the last week There's earthquakes every day let's face it most of them are ones and twos that unless you're in a solid structure right on top of it more than likely you're not going to feel it but if somebody says I'm predicting a c a um magnitude 4 earthquake in the next week just kind of laugh and like sure I bet there's going to be one I agree with you there will be one but it's just they're so frequent and even at that this four wasn't didn't do any damage this four in Mexico didn't do any damage either now the rdge crest earthquake in 2019 that was our last really big one it was far enough away where the damage was limited to that area in the interior and we're looking at both the vertical displacement of about uh 12 feet and then a horizontal displacement I believe it's around it varied but it I think at most it was around 15 to 18 feet of horizontal displacement notice it's right lateral yay right lateral movement and here we can see Google Earth kind of before and after kind of ampli if Ying it if you look at just the bottom it doesn't really move but if you look at the top you'll notice that it's got that right lateral shift of everything from the earthquake um and then the earthquakes afterwards all right so what happens damage wise now that that vibration it gets transferred into structures well let's face it a lot of structures aren't really designed to handle vibrations and movement and so in the case of the Northridge Earthquake in 1994 we learned a lot about some structures we learned a lot about parking structures that they needed to have more flexibility or strength to withstand a significant earthquake so Northridge Earthquake wiped out um quite a few parking structures um the San Francisco earthquake even though we had almost 30 ft of horizontal displacement it was a big Quake I mean it was a 7.8 uh most of the damage was from fires in the city of s Francisco a lot of the wooden wooden structures survived the earthquake but they did not survive the fires so the Silmar earthquake that was the one I couldn't remember the name of earlier in 1971 this was our first big earthquake in Southern California once we'd had that post-war ba uh boom in population so this is when prior to World War II and in the the most the largest previous earthquake we hadn't been suburbanized like we are now with tracks and tracks homes all over the place so by 1971 we started to see it so the silar Quake this was important cuz we had to change a lot of our design codes for buildings including like Hospital structures this building was brand new hadn't opened yet but because they build it super rigid it didn't Flex at all and so the vibration got transfered into this bottom floor and the whole upper structure these upper four floors just kind of shifted so the bottom floor is a skew like this and also it had this weird funky I'm sure there's a name for it um if you're taking architecture at Saddleback please feel free to fill me in on the name of this but it was a modular unit and so this was one solid structure and then at the end of that solid structure was the stairwell and um some of the HVAC and elevators but it was in this different structure here this is the roof this fell from up here it basically one solid structure just just kind of leaned over and fell because it couldn't handle the vibrations and then the same thing happened on another end of it so um and 1971 isn't that old these are historical ambulances they were about to have their grand opening so it's this hospital was destroyed and nobody was in it the timing was fortuitous that nobody died because it hadn't opened yet so here we can see this is why we had to change construction techniques this building shifted about 12 to 18 in on its foundation so you can see that how it's kind of stretched down here so now we have rules as far as attaching homes to their Foundation which the rest of the country thinks is really strange that we have to bolt our homes down and that's so they don't do this now we make fun of the rest of the country that has hurricanes and tornadoes because they have to attach their roofs to their house and we keep thinking what's going to happen to your roof here in California well a tornado will rip it off there but they don't have have to worry about this and also we changed construction rules for uh fireplaces this was a brick structure that went all the way up here and then it collapsed and fell so we see a huge decline in Brick fireplaces post 1971 rules that is a little Junior geographer with his grandmother touring some friends houses that lived in the area and yes that's me taking an early interest in geomorphology this was across the street uh the garage collapsed here we see kind of the outer structure failing and California's already had kind of a heavy 2x4 construction with the framing for houses now post 74 you have these 2x4s but you also have a sheet of plywood that's used on top of it that makes it even stronger and that plywood has to meet certain shearing standards the nails and screws you use in house Construction have to meet certain sharing standards so there's all these rules for construction that came about after the 1971 Quake so if you're going to buy a home get when that's built 74 75 1974 1975 or later San Francisco in 89 we learned about um the freeway construction that just having all this metal in the cement the rebar isn't enough because if that you shake the cement it cracks and so there's nothing to hold the rebar in place and so the rebar doesn't can't um hold up the structure and so now we have our all sorts of rules of either wrapping the cement in metal so you'll see some freeway freeway pylons that are wrapped in metal or the rebar itself before you pour the cement around it has all of this additional rebar that runs across it to kind of hold it in place if you ever travel to other parts of the United States look at their pylons that hold up Bridges and overpasses they're significantly smaller than what we have in California well they don't get earthquakes and we do so we have to over engineer our structures to withstand the shaking places that don't have that design rules when they have an earthquake we see tens of thousands die as opposed to a few dozen like we get in California so these earthquake rules really really help minimize the loss of life well what do you do with older buildings well these brick facades they're they don't stay on during earthquakes and so you'll see these metal plates here these are actually attached to a long metal bar that goes into the building and then this plate on the edge and the idea is that you're bolting this outer surface to the inner structure so here's a floor here here's a floor here there's a small attic space and then this is the roof and this is all attached to it now why you don't see it here because this is a new facade on top of the older bricks and so that attachment points are underneath the bricks there so you can't see them in San Francisco these have a a weird kind of star shape to them but this face here is bolted to the structure and there's obviously a staircase in this area because you can see the little slope that we have in it and here goes across the top and that's all keeping it place there's some other structures they have a a transparent fiberglass that's sprayed on the outside of it um but i' I'm still would never be comfortable living in a brick structure in California well what do you do with other buildings that are kind of more modern they don't have the brick facades this is the Costa Mesa City Hall which was built in the 1960s I believe um and so what they did is they put a metal exoskeleton around the outside of the structure to hold it in place and so these white lines these are actually metal structure around the outside of this inner building and it's holding the entire building in place I thought this was a really creative way to not have to build an entire new building is you just build a structure all the way around it to hold it in place now sometimes you'll hear about liquefaction well soil May behave strangely if you shake it as well especially if you got a moist soil or a high water table that soil will settle and if you've got large structures on it they will settle with the soil if you're really really bored take a bucket of sand and gravel and then fill it with water so it's just below the surface of the sand and gravel and then shake the bucket you'll see that wow look the sand and gravel settles yes it does um but that's liquefaction Japan had it happen really bad at the coob earthquake in 1995 where we saw a lot of structures there Japan and and United and California lead the world in earthquake construction techniques so every time something like this happens we study it and figure out how to not let it happen again as far as damage to the structures so we learned about Suburbia in 1995 how how to build better houses in 1995 we learned about how to prevent liquefaction damage um but it's always after the fact well when we talk about Coastal processes um we'll also talk about one of the things that can happen when you have a major earthquake near the coast so the 2004 tsunami which was one of the biggest natural disasters of the past 100 years as far as loss of lives and the scale of what happened with it we'll talk more about that later that was a massive event just because you have an earthquake doesn't mean you're going to have a tsunami but it's one of the potential causes for a tsunami you Just sh shaking the water isn't enough you have to displace it so you have to have something that in the earthquake you cause a landslide or some tectonic movement of the surface in order to get a tsunami but again we'll talk about that more later when we talk about um the the 2004 and then the 2011 tsunamis all right so that begs the big question of all of this about earthquakes can you predict an earthquake if somebody tells you that somehow or another there's going to be an earthquake in the next year no we don't know these are too inconsistent we can show areas that haven't moved in a while have the potential to move but is it going to happen tomorrow or is it going to happen in 50 years there's really there's no way to tell but what about earthquake weather when it's been hot and then it rains or maybe it's the other way around when it's rain and then it's hot or then it's gets really really dry different people have different definitions of earthquake weather uh no there there is no such thing U the variations in weather do not make it down into the deeper parts of the Earth's surface and so even a kilometer below the surface it's going to not know what the weather's like at the surface and so it's not going to affect the stresses in the subsurface that create the earthquake so no there is no such things as earthquake prediction all right everyone hope you enjoyed earthquakes and volcanoes