The Great San Francisco Earthquake(s)
On October 8th, 1865, the "Great San Francisco Earthquake" hit south of the city of San Francisco, magnitude 6.3.
On October 21st, 1868, the 'Great San Francisco Earthquake" hit near Haywards, east of the city, across the bay, magnitude 6.8.
On April 18th, 1906, the "Great San Francisco Earthquake" hit the Bay Area, magnitude 7.6.
The death tolls were unknown (but small), 30, and about 3,000, respectively.
Eighteen significant earthquakes happened after that (and five or so had happened between the first "great quakes") before February 9th, 1971, when the Sylmar earthquake (magnitude 6.7, death toll 65) occurred in the San Fernando Valley. So, about 25 major earthquakes happened in California, of varying degrees of significance with respect to property damage and loss of life, since the earliest influx of immigrants associated with the Gold Rush, which is how California got permanently and meaningfully populated by Europeans.
Right after the Sylmar earthquake, a law was passed that required that earthquake hazard be considered as part of the approval process for new development.
One hundred and six years of time during which a significant earthquake occurred about every four years, passed before the first meaningful response by the civilization living on top of these active faults. Civilization does, indeed, have its faults. As it were.
Will Seattle and Portland Suffer Cataclysmic Earthquakes Any Time Soon?
Meanwhile, to the north, in British Columbia, Washington State, Oregon and parts of northern California, earthquakes were not recognized as a problem. They hardly ever happened. Buildings, homes, bridges, gas-lines, and other infrastructure were deployed without consideration of earthquake hazard for decades.
However, the earthquake hazard in that region is probably much greater in some ways than the earthquake hazard around Los Angeles and San Francisco, which are regularly rocked by fault-line activity. Here, the great plates that make up our planet's surface do something different than they do in the southern California.
In southern California, the plates are mainly grinding past each other. Fragments of the plates separated by fault lines are squishing past each other like an eraser rubbing against paper. It is not a smooth process, but rather one in which pressure builds up and is released at numerous locations, with each of those release events resulting in some sort of earthquake.
To the north, the main interaction between the plates is the subduction of one plate beneath the other. The subducting (going under) plate moves steadily under the continent, with little fanfare other than slowly elevating that part of the continent, tilting of the land upward to the west and downward to the east (relatively speaking). Then, every now and then, there is an adjustment. The top plate drops all at once, causing a major change in elevation that results in coastal areas being suddenly under the sea, and also resulting in a major earthquake, perhaps magnitude 9.
(Remember, each whole number on the scale used to measure earthquakes is one order of magnitude, so a magnitude 9 earthquake is 100 times stronger than a magnitude 7 earthquake).
It appears that the nearly 700 mile long zone of subduction has suffered 19 "subduction zone earthquakes" over the last 10,000 years, with many more affecting a smaller length of this zone. So, long term, a major earthquake affecting an area hundreds of miles long and who knows how wide, and by major earthquake I mean as never seen before by living humans in the region, and hardly ever observed in recent times anywhere on the planet, affects an area larger than many countries.
Can earthquakes be predicted?
It is said that earthquakes can't be predicted, but from the point of view of regular humans (as opposed, say, to geologists or statisticians) they can be. Many people think weather can be predicted, right? Well, not really. We can make long term predictions of months or even years about overall changes in the climate, and we can predict what the weather will be like in several hours from now. But anything in between is largely guess work except in a few rare cases (the track of hurricanes can sometimes be predicted pretty well several days out, even before they exist, at least roughly).
Same with earthquakes. Sort of. The short term with earthquakes is, unfortunately very very short. We know when an earthquake starts that there will be an earthquake over the next several seconds or minutes. That is a little like predicting that it is going to be raining over the next little while when the first drops fall from the sky. You've heard of predicting earthquakes longer term, like over days. Every now and then someone observes something that seems to be associated with the geological processes that produce earthquakes, then there is an earthquake, and bingo, we've got a method of prediction. But so far every time this has happened, that method of prediction has been invalidated by reality, when it fails to predict subsequent quakes, or produces false positives.
(An interesting example of this happened just yesterday when a scientist -- but not a geologist -- happen to observe the presence of huge amounts of various gasses appearing along the coast of California, and thought this might be the indicator of an impending earthquake. This prediction was supported by a several years old research project that suggested that gas outflows might predict earthquakes. I'm pretty sure the gas outflow idea has not developed. And, it turns out that the scientist who observed the California gas was simply looking at a common meteorological phenomenon that involved normal human pollution combined with certain atmospheric conditions. Nothing to see here!)
However, long term, earthquakes can be "predicted" using the term "predicted" in modern vernacular parlance. What I mean by that is that the earthquake hazard for a given region can be estimated over longish periods of time with reasonable certainty. We can say, for example, that there is a 63% probability of there being one or more earthquakes of 6.7 magnitude or greater between the years of 2007 and 2036 in certain clearly defined parts of California around San Francisco. This is based on a combination of empirical observation of earthquake frequency and an understanding of how earthquakes happen. According to one study, there is about a one in three chance of a Cascadia subduction zone earthquake (magnitude 8 or 9 or so) over the next fifty years.
So, when planning development or putting together emergency systems, it is possible to know two things. One, what kinds of earthquakes are going to happen (in terms of location, overall range, and magnitude, etc.) and what is the chance of something like this happening.
How do we adapt to earthquakes?
From this emerges something rather counter-intuitive. It turns out that the magnitude of the largest likely quake is more important than the likelihood that it will happen during any medium length time period. It does not matter if a magnitude 9 earthquake is 10% or 1% likely to happen over the next 20 years when you are building a major interstate highway bridge or a skyscraper. What matters is that you build the thing to handle a magnitude 9 earthquake (or, I suppose, prepare yourselves for total destruction of the thing, and have a backup plan of some kind). Development in southern California has to deal with magnitude 7-point-something quakes during the lifespan of a major long-lived structure, while development in Washington and Oregon has to deal with magnitude 8 or 9 quakes during the lifespan of a major long-lived structure. The truth is, your highway bridge near San Francisco has a good chance of being shaken by a magnitude 7 quake, while a highway bridge near Seattle may well outlive its usefulness and be replaced or retrofitted before the once in 500 year trans-Cascadia 9+ quake hits. But you still have to build it to handle the quake because you don't want to be that guy. (Who didn't, and then everyone died, and it was your fault.)
There is an interesting historical pattern in the recognition of, and in addressing, earthquakes both in the US an around the world. That century plus time period between what should have been a clue that San Francisco was a quake zone and the first meaningful safety conscious zoning regulation happened initially because developers covered up the first few quakes. They pretended they didn't happen, downplayed, lied, etc. The 1906 quake was too big to really cover up, of course. Covering up switched to lobbying and lobbying kept regulations off the table for many more decades. Then several dozen suburbanites, voters, taxpayers, whatever got wiped out by a quake that really wasn't all that bad compared to some of the earlier ones, and a law got passed. So this part of the pattern is denial, followed by different kinds of denial, then some more denial.
Denial of what? Science, of course.
The second part of the historical pattern is science progressing. While most early and mid 20th century construction went along blind to earthquake hazard in southern California because people were being willfully stupid, earthquake unsafe construction proceeded in the northern regions because science had not yet figured it out. Then the denial vs. science thing happened, and is still going on. Decisions have been made at various levels of government in the Cascade subduction zone area that will doom people of the future (one year from now, one century from now, we can't say) to disaster.
A great new book on earthquakes: "Earthquake Time Bomb" by Robert Yeats
Do you find any of this interesting or important? Then you need to read Earthquake Time Bombs by Robert Yeats.
Yeats explains what earthquakes are. Then he discussed the development of earthquake science, and the politics, cultural response, and technological response to earthquakes, starting with the examples I gave above plus the Haiti earthquake. Then he goes around the world to most of the major earthquake zones and examines the same processes -- the geology, the geological science, the engineering and political responses, etc. -- in each area.
Yeats is an expert on this, and in fact, has been involved in what he refers to, I think correctly, as the "paradigm shift" in understanding earthquake hazard and risk. This is a shift that happens both within the science and the regulatory and social systems that necessarily address the hazards and risks. He also explains the difference between hazards and risks. Yeats is the go to guy when you want to find out about what to do about earthquakes.
How do we know about the 19 subduction zone earthquakes in the Pacific Northeast that happened over thousands of years? What went wrong at Fukushima, and how do the Japanese deal with earthquakes? What about that New Madrid fault in the middle of the US? What about the Rift Valleys of Africa (where I worked)? What are we doing to do next, what is undone, and how do we do it? These are all addressed in the book.
I came away from Yeats book feeling better about earthquakes. I already knew about the Cascadia quakes and a bunch of other stuff, having done research that required an understanding of tectonic processes myself (though this is not my area). What made me feel better is the simple fact that we can adapt to earthquake hazards by first understanding what they are locally, then applying the proper technology and other systems.
The problem is bad, of course, in regions where earthquake hazard is high, and pre-adaptation is not done for any of a number of reasons, including political or economic ones. Yeats contrasts Japan, the most earthquake ready country in the world, with Haiti, one of the least.
Geology is fun. Earthquakes are one place where the rubber hits the road in geology. This book is a great overview and an important analysis of earthquake hazard and risk worldwide. I highly recommend Earthquake Time Bombs by Robert Yeats.
We actually know the date and approximate time of the last major earthquake in Cascadia. Not from written records of people living in the area, of course (though the event apparently is part of their folklore), but from records of the tsunami it caused in Japan. The event occurred in January 1700, as confirmed by tree ring dating of forests that were submerged as a result (the last tree ring for many of those trees was the summer of 1699).
Of course most of the infrastructure was built before anyone knew there was an earthquake hazard, so people are seriously worried that an earthquake will take out most of Seattle west of I-5. They are already trying to replace the Alaskan Way Viaduct in downtown Seattle, but that project isn't going well--the excavator, AKA Big Bertha, keeps getting stuck.
Thank you for the book suggestion; I have sent a "free sample" to my Kindle reader. One subject I would like to know more about is how earth quakes effect fresh water seeps and springs.
It is a great book.
"They are already trying to replace the Alaskan Way Viaduct in downtown Seattle, but that project isn’t going well–the excavator, AKA Big Bertha, keeps getting stuck."
Not to worry: Much of Seattle will have to relocate anyhow in 80 years or so.
I am not from Seattle, so take this with a grain of salt:
However, it doesn't look to bad by 2100, as we would be at less than 3 feet inundation and 71% of the parcels affected are zoned industrial. Looks like about 16 residential parcels would be affected.
RickA: I am not from Seattle, so take this with a grain of salt:
"However, it doesn’t look to bad by 2100, as we would be at less than 3 feet inundation and 71% of the parcels affected are zoned industrial. Looks like about 16 residential parcels would be affected."
Thank you for the link. The writer's model is fine as far as what he modeled, but he left out a shit load of other factors. If the problem was *ONLY* sea level rise (in the Pacific Northwest), then Seattle would have a vastly smaller problem than most places on the planet. But Seattle is not at risk only by sea level rise.
Seattle is protected from storm surge about 80% of the time; the North Pacific High Pressure Zone protects against storm surge throughout the Puget Sound region during the summer because it deflects storms to the south (and recently, some times north, to Alaska). When the high pressure zone moves southward in the winter, the fetch of Puget Sound and the region can, and does, cause storm surge. The page you directed me to (thank you) did not account for the fact that in shallow waters such as in Puget sound, the northern channel, and Juan de Fuca Straight, the increased sea level amplifies storm surge by a factor of about 300:1 (the Pacific Institute published a survey on the subject about six years ago).
The problem is Seattle's fresh water supply, and it's support infrastructure: they cannot survive the increased storm surge incursion of salt water. Seattle is fortunate in that it has many islands in the way to dampen storm surge--- without sea level rise, the odds of storm surge flooding in Seattle are very rare.
Ignoring storm surge, roughly 10% of the human population in and around Seattle will have to relocate. Periodic salt water incursions means far more people will have to relocate. Washington, and Seattle, are expending wealth by adding new infrastructure (tunnels, roads, bridges) in areas that are at risk; that seems irresponsible to me. Far better they spend the funds on contraception, family planning, urban dismantling, and population reduction.
I'd like to amplify your statement: "(Remember, each whole number on the scale used to measure earthquakes is one order of magnitude, so a magnitude 9 earthquake is 100 times stronger than a magnitude 7 earthquake)." That's true for the seismic wave amplitude. But, paraphrasing Wikipedia (https://en.wikipedia.org/wiki/Richter_magnitude_scale): The energy release of an earthquake, which closely correlates to its destructive power, scales with the 3⁄2 power of the shaking amplitude. ... a difference in magnitude of 2.0 is equivalent to a factor of 1000 in the energy released.
RickA, generally, because of the overall geology, the west coast will have less land taken by the sea because of sea level rise than many other areas.
Of course, when a Cascadia subduction quake happens, that lowers the coastal areas considerably, aside from sea level, in coordination with a massive tsunami. According to the book.
"However, it doesn’t look to bad by 2100, as we would be at less than 3 feet inundation and 71% of the parcels affected are zoned industrial."
The ability of the human mind to justify irresponsibility is astounding.
Ricka: “However, it doesn’t look to bad by 2100, as we would be at less than 3 feet inundation and 71% of the parcels affected are zoned industrial.”
wheelism: The ability of the human mind to justify irresponsibility is astounding.
To be fair, RickA is correct that Seattle will not be damaged by sea level rise as a great many other places in the world such as the USA's east coast. At least he made the effort. (Wry grin)
@8: in his short time around RickA has demonstrated himself to be a world class dick and science denier on many topics. His output is prolific, if sickening.
At least I am polite - which is more than I can say for your comments.
Also - do you really think "Much of Seattle will have to relocate anyhow in 80 years or so."
Are you sure I am a science denier?
Or perhaps I merely have a different opinion than you.
Let me begin with that I am a member of the WA Tsunami Working Group. On average a major tsunami has struck the WA coast every 300 to 500 years. It has now been 316 since the last major tsunami has hit.
I live about 30 miles east of the Cascadia subduction zone at about 5 to 10 feet above sea level. If we have a fault rupture (probably a 9+ quake), I would have 15 to 30 minutes to reach a safe elevation for the coming tsunami (not going to happen).
Federal funding for tsunami programs has been dropping over the recent years, so less public education is being performed. A congressman from the Midwest stated that a tsunami would not effect his state, even though a large percentage of his state's grain exports go through NW ports.
Hopefully, Dr. Yeats book will open more eyes not only on the west coast but across the nation.
Rich, thanks for that comment, very motivating!
If you go to google earth and look at elevations in Seattle, you find that it is mainly the port that would be affected as well as the Green River valley running by Boeing Field. Downtown Seatlle is built on hills, and there is a narrow strip along the sound that is subject to innundation. Futher if you look at lake Washington again you find the land rises rapidly from the lake.
Drive around Seattle and you see hills. So yes you loose the port (which is on made ground) as well as other areas that have been filled in, but the original landscape has hills.
Further because the land was under ice 15k years ago there is still some rebound possible. Some studies suggest 10m since the ice receeded.
Isostatic rebound has mostly already happened. There is very little left.
Current subduction activity is pushing the coastal area up by 2mm/year.
I guess if there's a big earthquake every 500 years, that would mean a sudden drop of about 1m is on the cards.
It seems such earthquakes are tsunamogenic, so there could be 15-20m of tsunami on top of that to cope with, although the local lie of the land determines if it runs up higher:
It seems 500m is possible.....But I'm sure Rick's lack of concern is fully educated.
My comments were not directed at tsunamis, but sea level rise generally by 2100.
If you live by the coast and there is an earthquake, I would definitely head for higher ground immediately.
I wouldn't even wait for a tsunami warming - I would just assume one for every earthquake over about 6.0.
But Desertphile was indicating that the entire city of Seattle would be underwater by 2100 due to sea level rise and I was unconcerned by that scenario, given the data I linked to.
You are free to disagree.
Desertphile - I know that in 2015 a small quake (http://www.cbc.ca/news/canada/british-columbia/magnitude-4-8-earthquake…) off of Vancouver Island temporarily changed a hot spring there to a cold spring. And a 7.7 quake off of Haida Gwaii and Alaska in 2012 completely shut off a coastal hot spring there. As far as I know it is still cold and dry. So earthquakes definitely can affect underground water courses.
"Are you sure I am a science denier?"
Yes - reference any comment you made about climate change.