9 ms·

When, not if: how do San Franciscans live with the threat of the next quake?

81 points by yread 13y ago

_stephan 13y ago
If you don't buy earthquake insurance, can you count on state or federal disaster relief programs to pay for reconstruction? [Edit] Or to rephrase the question, do disaster relief programs create a moral hazard that should be countered by making earthquake insurance in high-risk areas mandatory (with possible subsidies by the state)?
- blaze33 13y ago
  The wikipedia page of the 1906 earthquake[1] is quite instructive: > Capt. Leonard D. Wildman of the U.S. Army Signal Corps reported that he "was stopped by a fireman who told me that people in that neighborhood were firing their houses…they were told that they would not get their insurance on buildings damaged by the earthquake unless they were damaged by fire". [1] http://en.wikipedia.org/wiki/1906_San_Francisco_earthquake#Subsequent_fires http://en.wikipedia.org/wiki/1906_San_Francisco_earthquake#S...
  - ekianjo 13y ago
    Well in 1906 the US were not really the welfare States they have become (turning point after the 1960s).
  - Spooky23 13y ago
    The issue wasn't that simple. The Army marched in and pretty much went rogue -- they came in and started blowing up buildings to create firebreaks and caused more fires in the process. The city was also particularly vulnerable to destruction from fire. Lots of unstable landfill, the water used for fire fighting was in underground cisterns that were damaged, and key firefighting personnel were killed. There's a recent book "San Francisco is Burning" that is a really good account.
- biesnecker 13y ago
  It's hard to imagine private insurance companies being able to actually pay out their obligations in the event of a massive earthquake in any metropolitan American city. Federal (and to a smaller degree, state) governments will almost certainly put up most of the money for recovery and rebuilding.
  - endersshadow 13y ago
    It's time for you to learn about reinsurance: https://en.wikipedia.org/wiki/Reinsurance https://en.wikipedia.org/wiki/Reinsurance
    - elpool2 13y ago
      I wonder how much damage it would take to bankrupt even the reinsurers. Would a hurricane Katrina sized disaster hitting every city from SF to Vancouver do it?
- mathattack 13y ago
  There is most definitely a moral hazard. Look at parts of Florida that have to be rebuilt year over year at the federal government's expense.
danieltillett 13y ago
I always thought it was the classic human response to disaster planning - a large river in North Africa.
- panacea 13y ago
  The human response to disaster planning is offloaded to a committee who's responsible for disaster mitigation. Call it a government. Residents living on the banks of that large river in North Africa built a fucking awesome risk mitigation strategy for said government. Eternal life under a stacked pyramid of stones.
facepalm 13y ago
I wonder, could it make sense to build houses in risky areas more like ships?
- danieltillett 13y ago
  What is required to make a building survive a big quake has been known for some time - the real question is has it been done on the building you are in when the next big quake hits.
  - Tyrannosaurs 13y ago
    A friend who lives in Tokyo relatively frequently experiences fairly large quakes - everything shakes, the buildings wobble, you pick the stuff up off the floor and get on with what you were doing. Sure for a really big quake it would be more significant but the engineering there is really impressive.
    - brazzy 13y ago
      Your friend may be exaggerating; I lived in Tokyo for a year and experienced a grand total of two earthquakes that were barely noticeable.
      - Tyrannosaurs 13y ago
        We may be interpreting "relatively" differently.... He's lived there quite a while and has experienced several which have woken him up.
  - dredmorbius 13y ago
    And more specifically (concerning regional resilience): how much of the existing housing stock is built to standards which will survive a likely quake? San Francisco's last slate-cleaning came in 1906, though parts of the city were constructed far more recently. The 1989 earthquake (nearly 100 km distant and comparatively mild (6.9, as opposed to an 8 or 9 mag such as the 1906 quake) still caused significant structural damage throughout San Francisco, though major damage was limited to a few neighborhoods and specific buildings -- more major damage was concentrated largely to the south, closer to the epicenter. Most of Tokyo was destroyed during WWII, and has been rebuilt since. Japan also experiences frequent powerful earthquakes (several M8+ quakes are noted by the USGS: http://earthquake.usgs.gov/earthquakes/world/historical_country.php#japan http://earthquake.usgs.gov/earthquakes/world/historical_coun...), effectively requiring more robust building standards. Though my understanding is that there's a great deal of collaboration between Japanese and Californian engineers on this work.
jfb 13y ago
"Whistling past the graveyard". There's good stuff in John McPhee's Assembling California [1] about the '89 Loma Prieta earthquake, and about earthquakes in general. [1] http://www.nytimes.com/books/98/07/05/specials/mcphee-california.html http://www.nytimes.com/books/98/07/05/specials/mcphee-califo...
chrisfarms 13y ago
"Between now and 2038, there’s a 99.7% chance of a 6.7-or-larger earthquake striking somewhere in California" I can't see that date without thinking a 32bit timestamp prevented them from calculating over a larger range. :)
- ekianjo 13y ago
  6-7 is not THAT bad. Most modern buildings should be able to handle this relatively fine. In Japan usually nothing recent falls apart until after 7. Anyway, in terms of casualties, it all depends where the epicenter exactly is, and at what time of the day or night the earthquake strikes.
  - mikeg8 13y ago
    But the average age of a house in japan is not even close to the average age of many San Francisco homes...
    - ZirconCode 13y ago
      That is mostly because of war, and not due to natural disasters.
      - mikeg8 13y ago
        This has some truth but not the whole picture. I recently listened to a fascinating Podcast from Freakenomics Radio called, "Are Japanese homes disposable?" where they discussed a huge cultural difference regarding how the Japanese view their homes. When they purchase a home, they usually tear it down and build a new one from scratch. Once a home is built, the Japanese invest almost zero money/effort into maintenance. The average half-life of a home there is 38 years compared to over 100 in the US (not just SF). Growth in their construction industry is rapid despite almost stagnant economic growth. Anyway, it was just super interesting and definitely worth a listen to, especially because "earthquake fear" is an overstated factor in their housing production.
cordite 13y ago
The same story applies to Utah Valley, we are 60 years overdue
- marknadal 13y ago
  One of the biggest reasons I have avoided moving to SF is because of earthquake liquefaction dangers. I however just recently moved out to Provo Utah from LA temporarily - I didn't know this was a hotbed as well. How would you compare the threat levels here to SF? Comparable? Or severely less than SF?
  - dalek2point3 13y ago
    You might fins some help here: http://geomaps.wr.usgs.gov/sfgeo/liquefaction/susceptibility.html http://geomaps.wr.usgs.gov/sfgeo/liquefaction/susceptibility...
  - matrix 13y ago
    The risk is lower, but still high. The last estimate was a 16.5% chance of a magnitude 7.0 earthquake in 100 years[1]. I expect the probability will be revised to be higher in the seismic hazard assessments due to be released this year. 7.0 doesn't sound big, but keep in mind, the epicenter would be quite close to the surface and likely to be right in the middle of a highly populated area on the Wasatch Front (Salt Lake City, Cottonwood Heights, etc). Also, many buildings in the vulnerable areas pre-date construction codes that take seismic risk into account. For example, it wasn't until the late 70's that they started reinforcing masonry construction. [1] http://www.livescience.com/28782-utah-bigger-earthquakes-wasatch-fault.html http://www.livescience.com/28782-utah-bigger-earthquakes-was...
- cossatot 13y ago
  The Wasatch fault zone does pose a significant seismic hazard but earthquakes on the WFZ are not nearly as regular as on the San Andreas. On this page [1] (second picture, left side) is a figure showing the instances of known earthquakes along the fault through time; you can see that they're quite irregular, both in space and time. An updated compilation of this data [2, gated] has better accounting of the uncertainties and a fuller record, especially on the older end. In any case, it's clear that some of the fault zone seems to be 'overdue' but other segments, including the Weber and Provo segments, have had moderate earthquakes within the past ~500 years, which is a bit shorter than the median recurrence interval. The SLC segment on the other hand may have enough accumulated stress to cause a pretty significant earthquake. Note that it's really not clear to what extent faults rupture periodically; there are researchers who argue that the likelihood of an event is basically independent of the time since the last event (basically a Poisson distribution), those who argue for fairly regular events, and everything in between. It probably varies a lot from fault to fault and is more regular on big plate boundary faults like the San Andreas than on smaller (or slower-moving) intraplate faults like the Wasatch Fault. The real danger, both here and for the San Andreas system, is that an earthquake will break through the segment boundaries and cause a much, much larger earthquake. It's not been demonstrated that this is has happened on the Wasatch fault (there is one instance about 6000 years ago where this is possible within the data uncertainty) but this has happened in California in the 1906 S.F. and 1857 Fort Tejon earthquakes. Although this might not cause more displacement of the fault in any one location, it creates such a bigger swath of destruction that there are more opportunities for associated disasters (fires, floods from dams breaking, etc.) and make response much more difficult. It's also a bit outside my expertise but I think that for a long rupture, there is enough constructive interference of surface waves from the earthquake that ground shaking is much greater than is predicted from displacement at any point on the fault. [1]: http://michaelhaskinseportfolio.weebly.com/earthquake-hazards-along-the-wasatch-fault.html http://michaelhaskinseportfolio.weebly.com/earthquake-hazard... [2]: http://www.bssaonline.org/content/98/6/2918.short http://www.bssaonline.org/content/98/6/2918.short
jofer 13y ago
What's interesting is that everyone's very aware of the seismic hazard along the San Andreas, but many people aren't aware of the much larger (but much less frequent) hazard in the Seattle/Portland area. The San Andreas is a strike-slip system. It's not capable of generating very large (magnitude 8 or greater) earthquakes. The Cascadia subduction zone has had magnitude 9 earthquakes in the past. The last one was on Jan. 26th, 1700. (Thank Japan for having excellent historical records of earthquakes and tsunamis. We know a large earthquake occurred around 300 years ago in the area, and thanks to Japan's record of the tsunami it caused, we can make a solid link to the exact date.) We don't know the statistical hazard as well due to the small sample size, but when the next large Cascadia earthquake occurs the damage will be absolutely catastrophic. It's not just the direct earthquake damage, but also the tsunami hazard. You need vertical offset to cause a tsunami. A strike-slip system like the San Andreas is very unlikely to cause a tsunami. The permanent offset is dominantly horizontal, so the only way to generate a tsunami is through secondary effects such as landslides. (Also, most of the length of the San Andreas is onshore.) Subduction zones are thrust systems. One plate moves up, and the other moves down. Earthquakes there are likely to produce permanent vertical deformation at the surface. Furthermore, certain types of subduction zones are more prone to generating large tsunamis. A deep earthquake is unlikely to cause much deformation at the seafloor, and therefore doesn't generate as large of a tsunami. However, the shallower the rupture penetrates, the larger the deformation at the seafloor is, and therefore the larger the tsunami is. Certain types of subduction zones are more prone to having large earthquakes that rupture all the way up to the seafloor. (The amount of sediment on top of the incoming oceanic plate is thought to play a large role in this, among other things. The recent Tonankai earthquake in northern Japan turned a lot of what we thought we knew about this on its head, though.) The Cascadia subduction zone is one of the end-member types that's likely to have both large earthquakes and large tsunamis. We know it has in the past, and it's likely to in the future. It's unusual in that most of the deformation along the fault occurs through periodic creep ("slow-slip events") that doesn't cause an earthquake. (Actually, as we're finding out, it's not that unusual around the world, but it was first observed and is best documented in Cascadia.) However, while this creep does relieve a significant portion of the accumulated elastic strain, it doesn't relieve all of it. The plate boundary fault is still accumulating elastic strain that will eventually be released in a large earthquake. At any rate, just something to think about. The seismic hazard in the Bay Area can be reduced through proper engineering solutions. (Though SOMA is going to be in very rough shape for the reasons this article mentions. Lesson for next time: Don't bulldoze all the rubble into a pile and then build on top of it!) For Cascadia, though, you can't engineer your way around a magnitude 9 earthquake and tsunami. You do the best you can, and try to avoid putting critical infrastructure near the coast.
discardorama 13y ago
Don't look at it as an "earthquake", look at it as a buying opportunity! ;-D
- aylons 13y ago
  Actually, if most buildings get destroyed without insurance, prices will rise as offer shrinks. Unless you're trying to buy terrains for construction.
raldi 13y ago
The problem is that earthquake insurance is so expensive and so high-deductible that a risk analysis only concludes it's worth getting if you live in an especially risky neighborhood, or have an especially at-risk house. So only the riskiest buildings get it. So the average customer of the insurer skews ever closer towards the extremely at-risk end of the spectrum. So the insurance companies have to raise the rates and deductibles. And then you go back to step one, and the vicious cycle gets even more extreme.
- thaumasiotes 13y ago
  > So only the riskiest buildings get it. > So the average customer of the insurer skews ever closer towards the extremely at-risk end of the spectrum. > So the insurance companies have to raise the rates and deductibles. This chain of "logic" only makes any sense if you assume that the insurance companies have to offer all their customers the same rates and deductibles. If the building owners can figure out that they're facing an elevated risk, why can't the insurance companies?
  - raldi 13y ago
    They're mandated by California law to insure anyone who wants it.
    - thaumasiotes 13y ago
      That doesn't address anything I said. My parent comment already presupposed that they're able to change their rates. Are they really required to insure anyone who wants it, all on exactly the same terms? If so, maybe the problem isn't that earthquake insurance is just a natural death spiral?
      - raldi 13y ago
        > all on exactly the same terms It's not that simple, but it is that heavily-regulated: http://law.onecle.com/california/insurance/10089.html http://law.onecle.com/california/insurance/10089.html
steven2012 13y ago
Actual former SF resident here. I'll tell you exactly why I would live in SF, it's because it's one of the most beautiful cities in the world, and I also choose not to live my life in fear. Yes, there's a threat of earthquakes. Yes, I'm sure there is going to be an earthquake at some point, possibly even large. I experienced a tiny earthquake in SF a few years ago and it scared the shit out of me, because my entire apartment was shaking. But there are threats everywhere. Would I buy a house (if I can afford one, that is) in a liquefaction area? No. But there are plenty of areas of SF that don't have imminent liquefaction risk. And the chance of actually dying is quite low. There are plenty of things to worry about, but earthquake would be on the bottom quartile for me. And compared to the benefits of living in SF, it isn't even a big concern.
hspain 13y ago
Californians especially are woefully unprepared for disaster. I started a local company (http://expresssurvival.com http://expresssurvival.com) selling survival kits and emergency gear to try to help the community get prepared and realize the importance of having those supplies when that next earthquake hits. Most of us understand that its not a matter of if, but when we will need those emergency supplies, but as someone pointed out earlier, we are "whistling past the graveyard."
hindsightbias 13y ago
It's up to the landlords. Soft-Story retrofits are the law now. http://www.sfgsa.org/index.aspx?page=6048 http://www.sfgsa.org/index.aspx?page=6048 "On the anniversary of the 1906 San Francisco Earthquake, Mayor Ed Lee signed into law the Mandatory Soft Story Retrofit Ordinance. This legislation requires the evaluation and retrofit for “multi-unit soft-story buildings,” defined as: Wood-frame structures, containing five or more residential units, having two or more stories over a "soft" or "weak" story, and permitted for construction prior to January 1, 1978."
cylinder 13y ago
I can't believe only 10% of SF homeowners have earthquake insurance. Unfortunately, I'm sure there will be a taxpayer funded bailout of all these people once their homes are damaged/destroyed in the next big one. So, why bother?
sssbc 13y ago
So lets disrupt a bit: 1. Identify companies with liquidity, significant exposure to earthquake damage (down to the liquification zone offices) 2. short their stock 3. Wait for the 99.7% chance of earthquake by 2038 (more math to follow) 4. profit! Warren Buffet might be interested, since he's taken up betting against idiots. YC application, here I come!

81 points by yread 13y ago

If you don't buy earthquake insurance, can you count on state or federal disaster relief programs to pay for reconstruction? [Edit] Or to rephrase the question, do disaster relief programs create a moral hazard that should be countered by making earthquake insurance in high-risk areas mandatory (with possible subsidies by the state)?

blaze33 13y ago
The wikipedia page of the 1906 earthquake[1] is quite instructive: > Capt. Leonard D. Wildman of the U.S. Army Signal Corps reported that he "was stopped by a fireman who told me that people in that neighborhood were firing their houses…they were told that they would not get their insurance on buildings damaged by the earthquake unless they were damaged by fire". [1] http://en.wikipedia.org/wiki/1906_San_Francisco_earthquake#Subsequent_fires http://en.wikipedia.org/wiki/1906_San_Francisco_earthquake#S...
- ekianjo 13y ago
  Well in 1906 the US were not really the welfare States they have become (turning point after the 1960s).
- Spooky23 13y ago
  The issue wasn't that simple. The Army marched in and pretty much went rogue -- they came in and started blowing up buildings to create firebreaks and caused more fires in the process. The city was also particularly vulnerable to destruction from fire. Lots of unstable landfill, the water used for fire fighting was in underground cisterns that were damaged, and key firefighting personnel were killed. There's a recent book "San Francisco is Burning" that is a really good account.
biesnecker 13y ago
It's hard to imagine private insurance companies being able to actually pay out their obligations in the event of a massive earthquake in any metropolitan American city. Federal (and to a smaller degree, state) governments will almost certainly put up most of the money for recovery and rebuilding.
- endersshadow 13y ago
  It's time for you to learn about reinsurance: https://en.wikipedia.org/wiki/Reinsurance https://en.wikipedia.org/wiki/Reinsurance
  - elpool2 13y ago
    I wonder how much damage it would take to bankrupt even the reinsurers. Would a hurricane Katrina sized disaster hitting every city from SF to Vancouver do it?
mathattack 13y ago
There is most definitely a moral hazard. Look at parts of Florida that have to be rebuilt year over year at the federal government's expense.

danieltillett 13y ago

I always thought it was the classic human response to disaster planning - a large river in North Africa.

panacea 13y ago
The human response to disaster planning is offloaded to a committee who's responsible for disaster mitigation. Call it a government. Residents living on the banks of that large river in North Africa built a fucking awesome risk mitigation strategy for said government. Eternal life under a stacked pyramid of stones.

facepalm 13y ago

I wonder, could it make sense to build houses in risky areas more like ships?

danieltillett 13y ago
What is required to make a building survive a big quake has been known for some time - the real question is has it been done on the building you are in when the next big quake hits.
- Tyrannosaurs 13y ago
  A friend who lives in Tokyo relatively frequently experiences fairly large quakes - everything shakes, the buildings wobble, you pick the stuff up off the floor and get on with what you were doing. Sure for a really big quake it would be more significant but the engineering there is really impressive.
  - brazzy 13y ago
    Your friend may be exaggerating; I lived in Tokyo for a year and experienced a grand total of two earthquakes that were barely noticeable.
    - Tyrannosaurs 13y ago
      We may be interpreting "relatively" differently.... He's lived there quite a while and has experienced several which have woken him up.
- dredmorbius 13y ago
  And more specifically (concerning regional resilience): how much of the existing housing stock is built to standards which will survive a likely quake? San Francisco's last slate-cleaning came in 1906, though parts of the city were constructed far more recently. The 1989 earthquake (nearly 100 km distant and comparatively mild (6.9, as opposed to an 8 or 9 mag such as the 1906 quake) still caused significant structural damage throughout San Francisco, though major damage was limited to a few neighborhoods and specific buildings -- more major damage was concentrated largely to the south, closer to the epicenter. Most of Tokyo was destroyed during WWII, and has been rebuilt since. Japan also experiences frequent powerful earthquakes (several M8+ quakes are noted by the USGS: http://earthquake.usgs.gov/earthquakes/world/historical_country.php#japan http://earthquake.usgs.gov/earthquakes/world/historical_coun...), effectively requiring more robust building standards. Though my understanding is that there's a great deal of collaboration between Japanese and Californian engineers on this work.

jfb 13y ago

"Whistling past the graveyard". There's good stuff in John McPhee's Assembling California [1] about the '89 Loma Prieta earthquake, and about earthquakes in general. [1] http://www.nytimes.com/books/98/07/05/specials/mcphee-california.html http://www.nytimes.com/books/98/07/05/specials/mcphee-califo...

chrisfarms 13y ago

"Between now and 2038, there’s a 99.7% chance of a 6.7-or-larger earthquake striking somewhere in California" I can't see that date without thinking a 32bit timestamp prevented them from calculating over a larger range. :)

ekianjo 13y ago
6-7 is not THAT bad. Most modern buildings should be able to handle this relatively fine. In Japan usually nothing recent falls apart until after 7. Anyway, in terms of casualties, it all depends where the epicenter exactly is, and at what time of the day or night the earthquake strikes.
- mikeg8 13y ago
  But the average age of a house in japan is not even close to the average age of many San Francisco homes...
  - ZirconCode 13y ago
    That is mostly because of war, and not due to natural disasters.
    - mikeg8 13y ago
      This has some truth but not the whole picture. I recently listened to a fascinating Podcast from Freakenomics Radio called, "Are Japanese homes disposable?" where they discussed a huge cultural difference regarding how the Japanese view their homes. When they purchase a home, they usually tear it down and build a new one from scratch. Once a home is built, the Japanese invest almost zero money/effort into maintenance. The average half-life of a home there is 38 years compared to over 100 in the US (not just SF). Growth in their construction industry is rapid despite almost stagnant economic growth. Anyway, it was just super interesting and definitely worth a listen to, especially because "earthquake fear" is an overstated factor in their housing production.

cordite 13y ago

The same story applies to Utah Valley, we are 60 years overdue

marknadal 13y ago
One of the biggest reasons I have avoided moving to SF is because of earthquake liquefaction dangers. I however just recently moved out to Provo Utah from LA temporarily - I didn't know this was a hotbed as well. How would you compare the threat levels here to SF? Comparable? Or severely less than SF?
- dalek2point3 13y ago
  You might fins some help here: http://geomaps.wr.usgs.gov/sfgeo/liquefaction/susceptibility.html http://geomaps.wr.usgs.gov/sfgeo/liquefaction/susceptibility...
- matrix 13y ago
  The risk is lower, but still high. The last estimate was a 16.5% chance of a magnitude 7.0 earthquake in 100 years[1]. I expect the probability will be revised to be higher in the seismic hazard assessments due to be released this year. 7.0 doesn't sound big, but keep in mind, the epicenter would be quite close to the surface and likely to be right in the middle of a highly populated area on the Wasatch Front (Salt Lake City, Cottonwood Heights, etc). Also, many buildings in the vulnerable areas pre-date construction codes that take seismic risk into account. For example, it wasn't until the late 70's that they started reinforcing masonry construction. [1] http://www.livescience.com/28782-utah-bigger-earthquakes-wasatch-fault.html http://www.livescience.com/28782-utah-bigger-earthquakes-was...
cossatot 13y ago
The Wasatch fault zone does pose a significant seismic hazard but earthquakes on the WFZ are not nearly as regular as on the San Andreas. On this page [1] (second picture, left side) is a figure showing the instances of known earthquakes along the fault through time; you can see that they're quite irregular, both in space and time. An updated compilation of this data [2, gated] has better accounting of the uncertainties and a fuller record, especially on the older end. In any case, it's clear that some of the fault zone seems to be 'overdue' but other segments, including the Weber and Provo segments, have had moderate earthquakes within the past ~500 years, which is a bit shorter than the median recurrence interval. The SLC segment on the other hand may have enough accumulated stress to cause a pretty significant earthquake. Note that it's really not clear to what extent faults rupture periodically; there are researchers who argue that the likelihood of an event is basically independent of the time since the last event (basically a Poisson distribution), those who argue for fairly regular events, and everything in between. It probably varies a lot from fault to fault and is more regular on big plate boundary faults like the San Andreas than on smaller (or slower-moving) intraplate faults like the Wasatch Fault. The real danger, both here and for the San Andreas system, is that an earthquake will break through the segment boundaries and cause a much, much larger earthquake. It's not been demonstrated that this is has happened on the Wasatch fault (there is one instance about 6000 years ago where this is possible within the data uncertainty) but this has happened in California in the 1906 S.F. and 1857 Fort Tejon earthquakes. Although this might not cause more displacement of the fault in any one location, it creates such a bigger swath of destruction that there are more opportunities for associated disasters (fires, floods from dams breaking, etc.) and make response much more difficult. It's also a bit outside my expertise but I think that for a long rupture, there is enough constructive interference of surface waves from the earthquake that ground shaking is much greater than is predicted from displacement at any point on the fault. [1]: http://michaelhaskinseportfolio.weebly.com/earthquake-hazards-along-the-wasatch-fault.html http://michaelhaskinseportfolio.weebly.com/earthquake-hazard... [2]: http://www.bssaonline.org/content/98/6/2918.short http://www.bssaonline.org/content/98/6/2918.short

jofer 13y ago

What's interesting is that everyone's very aware of the seismic hazard along the San Andreas, but many people aren't aware of the much larger (but much less frequent) hazard in the Seattle/Portland area. The San Andreas is a strike-slip system. It's not capable of generating very large (magnitude 8 or greater) earthquakes. The Cascadia subduction zone has had magnitude 9 earthquakes in the past. The last one was on Jan. 26th, 1700. (Thank Japan for having excellent historical records of earthquakes and tsunamis. We know a large earthquake occurred around 300 years ago in the area, and thanks to Japan's record of the tsunami it caused, we can make a solid link to the exact date.) We don't know the statistical hazard as well due to the small sample size, but when the next large Cascadia earthquake occurs the damage will be absolutely catastrophic. It's not just the direct earthquake damage, but also the tsunami hazard. You need vertical offset to cause a tsunami. A strike-slip system like the San Andreas is very unlikely to cause a tsunami. The permanent offset is dominantly horizontal, so the only way to generate a tsunami is through secondary effects such as landslides. (Also, most of the length of the San Andreas is onshore.) Subduction zones are thrust systems. One plate moves up, and the other moves down. Earthquakes there are likely to produce permanent vertical deformation at the surface. Furthermore, certain types of subduction zones are more prone to generating large tsunamis. A deep earthquake is unlikely to cause much deformation at the seafloor, and therefore doesn't generate as large of a tsunami. However, the shallower the rupture penetrates, the larger the deformation at the seafloor is, and therefore the larger the tsunami is. Certain types of subduction zones are more prone to having large earthquakes that rupture all the way up to the seafloor. (The amount of sediment on top of the incoming oceanic plate is thought to play a large role in this, among other things. The recent Tonankai earthquake in northern Japan turned a lot of what we thought we knew about this on its head, though.) The Cascadia subduction zone is one of the end-member types that's likely to have both large earthquakes and large tsunamis. We know it has in the past, and it's likely to in the future. It's unusual in that most of the deformation along the fault occurs through periodic creep ("slow-slip events") that doesn't cause an earthquake. (Actually, as we're finding out, it's not that unusual around the world, but it was first observed and is best documented in Cascadia.) However, while this creep does relieve a significant portion of the accumulated elastic strain, it doesn't relieve all of it. The plate boundary fault is still accumulating elastic strain that will eventually be released in a large earthquake. At any rate, just something to think about. The seismic hazard in the Bay Area can be reduced through proper engineering solutions. (Though SOMA is going to be in very rough shape for the reasons this article mentions. Lesson for next time: Don't bulldoze all the rubble into a pile and then build on top of it!) For Cascadia, though, you can't engineer your way around a magnitude 9 earthquake and tsunami. You do the best you can, and try to avoid putting critical infrastructure near the coast.

discardorama 13y ago

Don't look at it as an "earthquake", look at it as a buying opportunity! ;-D

aylons 13y ago
Actually, if most buildings get destroyed without insurance, prices will rise as offer shrinks. Unless you're trying to buy terrains for construction.

raldi 13y ago

The problem is that earthquake insurance is so expensive and so high-deductible that a risk analysis only concludes it's worth getting if you live in an especially risky neighborhood, or have an especially at-risk house. So only the riskiest buildings get it. So the average customer of the insurer skews ever closer towards the extremely at-risk end of the spectrum. So the insurance companies have to raise the rates and deductibles. And then you go back to step one, and the vicious cycle gets even more extreme.

thaumasiotes 13y ago
> So only the riskiest buildings get it. > So the average customer of the insurer skews ever closer towards the extremely at-risk end of the spectrum. > So the insurance companies have to raise the rates and deductibles. This chain of "logic" only makes any sense if you assume that the insurance companies have to offer all their customers the same rates and deductibles. If the building owners can figure out that they're facing an elevated risk, why can't the insurance companies?
- raldi 13y ago
  They're mandated by California law to insure anyone who wants it.
  - thaumasiotes 13y ago
    That doesn't address anything I said. My parent comment already presupposed that they're able to change their rates. Are they really required to insure anyone who wants it, all on exactly the same terms? If so, maybe the problem isn't that earthquake insurance is just a natural death spiral?
    - raldi 13y ago
      > all on exactly the same terms It's not that simple, but it is that heavily-regulated: http://law.onecle.com/california/insurance/10089.html http://law.onecle.com/california/insurance/10089.html

steven2012 13y ago

Actual former SF resident here. I'll tell you exactly why I would live in SF, it's because it's one of the most beautiful cities in the world, and I also choose not to live my life in fear. Yes, there's a threat of earthquakes. Yes, I'm sure there is going to be an earthquake at some point, possibly even large. I experienced a tiny earthquake in SF a few years ago and it scared the shit out of me, because my entire apartment was shaking. But there are threats everywhere. Would I buy a house (if I can afford one, that is) in a liquefaction area? No. But there are plenty of areas of SF that don't have imminent liquefaction risk. And the chance of actually dying is quite low. There are plenty of things to worry about, but earthquake would be on the bottom quartile for me. And compared to the benefits of living in SF, it isn't even a big concern.

hspain 13y ago

Californians especially are woefully unprepared for disaster. I started a local company (http://expresssurvival.com http://expresssurvival.com) selling survival kits and emergency gear to try to help the community get prepared and realize the importance of having those supplies when that next earthquake hits. Most of us understand that its not a matter of if, but when we will need those emergency supplies, but as someone pointed out earlier, we are "whistling past the graveyard."

hindsightbias 13y ago

It's up to the landlords. Soft-Story retrofits are the law now. http://www.sfgsa.org/index.aspx?page=6048 http://www.sfgsa.org/index.aspx?page=6048 "On the anniversary of the 1906 San Francisco Earthquake, Mayor Ed Lee signed into law the Mandatory Soft Story Retrofit Ordinance. This legislation requires the evaluation and retrofit for “multi-unit soft-story buildings,” defined as: Wood-frame structures, containing five or more residential units, having two or more stories over a "soft" or "weak" story, and permitted for construction prior to January 1, 1978."

cylinder 13y ago

I can't believe only 10% of SF homeowners have earthquake insurance. Unfortunately, I'm sure there will be a taxpayer funded bailout of all these people once their homes are damaged/destroyed in the next big one. So, why bother?

sssbc 13y ago

So lets disrupt a bit: 1. Identify companies with liquidity, significant exposure to earthquake damage (down to the liquification zone offices) 2. short their stock 3. Wait for the 99.7% chance of earthquake by 2038 (more math to follow) 4. profit! Warren Buffet might be interested, since he's taken up betting against idiots. YC application, here I come!