Earthquake Risk

[wabmester]

I live near the Cascadia Subduction Zone. We're about due for a magnitude 9.0 quake. Or maybe a cluster of 30 or so 8.0's instead.

We just closed the window on a short period of Episodic Tremor and Slip (ETS), a time at which megaquake risk apparently increases by a factor of 25-65.

I know we have a few geologists here, and at least one earthquake expert. A couple questions:

1) I've never experienced an M9 quake. Am I pushing my luck by living here?

2) Should I vacation in, say, Kansas during ETS activity?

 

[bssc]

2) Should I vacation in, say, Kansas during ETS activity?

You would be next door to Missouri, where four of the most severe earthquakes in North America, the New Madrid Sequence, occurred. Do you really want that? The safest place might be on a ship somewhere.

 

[wabmester]

The safest place might be on a ship somewhere.

Really? The last time this happened here on the west coast, Japan got hit with a 5m tsunami. A *lot* of water got displaced.

 

[haha]

I think I had better read up on this. Have a link?

Ha

 

[wabmester]

I've been obsessing reading for the last 20 minutes or so:

latest ETS report

risk assessment

I lost the link to a good paper that included a simulation of the effects in the region. I'll update if I find it.

Edit: here it is, a 30MB pdf:

link

 

[unclemick]

Hmmm - you are going to have to work on living a really long time - to make sure you don't miss the 'good' quake.

1943-1969 in the PacNW, I only managed two 'little' ones - one in kindergarten and one as a Junior at at the UW.

heh heh heh heh - go Dawgs. Don't let the reading keep you up late at night.

 

[wabmester]

I was here for Nisqually, an M6.8 similar to what SoCal gets every once in a while.

The last M9 was in 1700, and they expect them here every 300 years or so.

 

[scrinch]

The last time this happened here on the west coast, Japan got hit with a 5m tsunami. A *lot* of water got displaced.

While the recent Sumatra-related tsunami propagated across the Indian Ocean the surface water disturbance was detected by satellite radar. The surface displacement was about 1 meter, with a wavelength of (as I recall) several hundred kilometers. If you were floating out in the middle of the Indian Ocean when the wave passed by, you would never have had an inkling that anything was wrong. It is only in the shallows that the wave piles up to impressive proportions.

Personally I wouldn't hesitate living in the Pacific Northwest because of the earthquake risk (the weather, maybe). Just like in California, I would make sure that I live in a single story, wood frame house with modern shear protection in the walls. I wouldn't sleep below a window or a bookcase or anything heavy on the wall. If you're at the beach or harbor and you see all the water rushing offshore, head for the highest ground you can find, NOW. Others may feel differently, but I think that there are much greater risks to life and limb to worry about before earthquakes (like car crashes, heart attacks, cancer, etc).

 

[wabmester]

We're in a single-story wooden structure that should have above-average shear strength. But everything here is built on sandy loam, and we're on a medium bank by the shore.

Given that we were without power for a week due to a little wind, I figure we'll be cut off from civilization for months if we're hit by an M9. So, I'm trying to get a handle on ETS as a predictor. I might be able to use this as an excuse to get a bigger boat, if nothing else.

 

[kramer]

In a first world country, I think that earthquakes are more about property risk than life and limb risk (assuming you are not right on the coast, because the tsunami warning time on that fault is very low). But everyone should have several days or probably a week of supplies to tide them over in any emergency (to survive without any assistance, electricity, and communications).

I think even the San Fran Bay Area quake of 1989, one that the region was not really prepared for, only killed about 1 in 100000 or so, which is fewer people than die in car accidents here each month.

Also, it never hurts to know your neighbors and to have a plan in advance.

When I talk with people here in the Bay Area, I notice that they tend to pooh-pooh the idea of earthquake insurance because they implicitly assume the highly unlikely is impossible, which I think is a common logic error.

Kramer

 

[unclemick]

Hmmm- here's a really stupid question:

After living thirty years in hurricane alley - after one hits - the pissing contest is always between what was covered by flood versus wind damage - happens every time.

Sooo - if you get 'quaked' AND 'tsunamied' - does one insurance cover it all??

heh heh heh heh

 

[Shawn]

1) I've never experienced an M9 quake. Am I pushing my luck by living here?

2) Should I vacation in, say, Kansas during ETS activity?

Natural and other hazards are everywhere. While I don't know the relative odds, my guess is that you are more likely to be killed from a tornado in Kansas than from an earthquake in the Pacific Northwest. 40,000 people die from auto accidents each year in the United States. Personally, I don't fear for my life everytime I get in my car. This doesn't mean I'm not careful. I still wear my seatbelt and drive defensively. Likewise, people living in earthquake country should be cautious. For example, your house should be bolted to the foundation and you should have ample emergency supplies for several days.

As for a M9 earthquake along the Cascadia subduction zone, the jury is still out. The general scientific belief is that a large earthquake will occur sometime in the next few hundred years. I don't remember the official near-term probability (or estimated probability), but I believe it is around 5% (e.g., 5% chance that a large event will occur in the next 30-50 years). There is considerable speculation as to whether the entire subduction zone will rupture (~M9), or if it will rupture in smaller segments. Some people believe that aseismic creep or other nonseismic deformation is occurring, meaning that the stresses along the subduction zone are not increasing as rapidly as they normally would.

Also, it is important to note that even though a M9 earthquake is about 30 times larger than a M8 earthquake, this doesn't mean that the ground motions (amplitude of ground shaking) will be 30 times larger. It simply doesn't work that way for large earthquakes.

I live in the San Francisco Bay Area where the earthquake hazard is also large. However, I don't give it much thought (well, I do give it a lot of thought but for different reasons). Yes, there will be large earthquakes in the future but my overall risk is relatively low. My house is bolten to it's foundation; nothing large is going to fall on me when I'm asleep; and I have enough food and supplies to last several days. To each his own, but I don't have earthquake insurance.

 

[lazygood4nothinbum]

i remember when my friend had his house hardened against earthquakes. he showed me all the work behind the scenes. the tie-backs, the crisscross bracing. it was an impressive amount of work but to see that 5,000 sq ft, two-story house perched on the side of a mountain in the hollywood hills, well, i did my very best not to laugh.

as to the boat, it's not so much the size but how fast & far you can get. i've heard places like hawaii are good for boats because the ocean drops right offshore, so with warning, you can get to safe deep water pretty fast.

i was thinking of getting out of hurricaneville or at least to northern/central florida where the land would beat them up a bit before they hit. but according to the last few tornados it ain't so safe there either. i guess you can obsess about it, forget about it, or rent.

 

[wabmester]

Thanks for the feedback, Shawn. I was hoping you'd chime in. If I read it correctly, the risk paper I linked to above estimates a 1 in 500 chance of a megaquake during ETS if certain assumptions (wrt clustering) are true. That strikes me as high risk. Higher than, say, driving drunk, which I don't do.

 

[Nords]

If I read it correctly, the risk paper I linked to above estimates a 1 in 500 chance of a megaquake during ETS if certain assumptions (wrt clustering) are true. That strikes me as high risk.

I'd say that you're at a higher risk of developing a tic.

We've had a couple quakes out here, so surely we're done for a long time!

 

[scrinch]

For the record, I'm a geologist, I live in the SF Bay area, my house is bolted to its foundation, and I don't have earthquake insurance either. I'm more concerned about my family not getting killed by falling bricks or glass than paying for damage to the home. With the low absolute chance of occurrence and the high deductible, I'm willing to self-insure.

 

[Nords]

For the record, I'm a geologist, I live in the SF Bay area, my house is bolted to its foundation, and I don't have earthquake insurance either. I'm more concerned about my family not getting killed by falling bricks or glass than paying for damage to the home. With the low absolute chance of occurrence and the high deductible, I'm willing to self-insure.

Wouldn't earthquake insurance premiums be so high that you'd buy the house every 5-10 years anyway?

 

[Shawn]

Thanks for the feedback, Shawn. I was hoping you'd chime in. If I read it correctly, the risk paper I linked to above estimates a 1 in 500 chance of a megaquake during ETS if certain assumptions (wrt clustering) are true. That strikes me as high risk. Higher than, say, driving drunk, which I don't do.

I looked at the risk paper. It isn't really a paper, but a presentation given at the Seismological Society of America meeting in 2004. I do not know if their work has been published. The author's make fairly substantial assumptions to arrive at their conclusions. One assumption is the clustering hypothesis, which is based on fairly limited data. The other assumption is that episodic loading (stress build up) along a fault substantially increases the likelyhood of an earthquake. While these are reasonable claims, it does not mean that they are true. Some aspects of earthquake work are well founded, but other aspects are quite speculative. There is nothing wrong with speculation as it is one of the driving factors behind research, but speculation is very often wrong. Keep in mind that the paper states the odds to be somewhere between 1/500 and 1/200,000, a 400-times difference. This provides some indication as to how much the choice of assumptions can change the outcome. The authors are honest in that they discuss multiple possibilities. The 1/500 was their worse-case-scenario (actually it was a little worse than this).

 

[wabmester]

Wouldn't earthquake insurance premiums be so high that you'd buy the house every 5-10 years anyway?

The problem isn't that the premiums are too high. It's that the deductibles are so high that you're only covered in the case of catastrophic failure, which is both low probability *and* it will kill you if it happens.

OK, I'll load up on some more supplies, check to see how the house is attached to the foundation, and maybe set up a web cam so everybody can see what an M9 looks like when it happens.

Between this and bird flu, I'm thinking about becoming a full-bore survivalist.

 

[kramer]

In the San Francisco Bay Area earthquake insurance prices just dropped about 17%.

Kramer

 

[USK Coastie]

wab, think about a propane powered generator and tank (securly anchored ) for wind storms, earthquakes and the occasional snow storm.

 

[scrinch]

Wouldn't earthquake insurance premiums be so high that you'd buy the house every 5-10 years anyway?

I haven't gotten an earthquake insurance quote for a couple of years, but as I recall the premium was more like 1% of the full replacement cost of the house, with about a 10% deductible. I think a homeowner would be much better off spending that money to bolt down the house to the foundation and install any needed additional shear panels. You'd be investing your money in home improvements that would increase your chance of survivability rather than in insurance to pick up the fallen pieces afterward.

 

[cute fuzzy bunny]

An ex-girlfriend works at FEMA and looks to be in line to lead up the tsunami task force for the west coast...is that a great job or what? If we dont get one, she's done great! If we do, all plaintiffs will be washed out to sea!

Anyhow, she lives about 2 miles from the hayward fault, which is supposed to go and go big anytime now.

'Nuff said?

I think the short answer is that we might see a huge quake on the west coast.

Tsunami possibilities are certainly in existence. California has been struck by dozens of them over the past 150 years, with waves as high as 60'. Just 50 years ago a pretty nice sized 1720 foot wave hit just a few hundred miles north of you Wab.

But we might not.

As a point of reference, I live 150 feet from the ocean, nowhere near any active faults, although theres a volcano thats been dormant for some millions of years so close I could hit it with a rock.

I'm keeping and eye on that volcano.

Earthquake insurance is a crock. Unless your house is sitting on the fault line (in which case you might not get insurance at all or pay through the nose for it), your chances of having more than 10% of the home value in damage is about nil. As Scrinch says, spend the money making your house less susceptible to damage.

 

[WanderALot]

We live in SoCal and our earthquake insurance is around $400/year with a 15% deductible. Every year I go back and forth on whether it is worth it and then just end up renewing it. It seems like we heard a lot more about earthquakes about a decade back but that might be because of Northridge happening.

 

[cute fuzzy bunny]

Make an informed decision...have a structural engineer/earthquake report done to show what threats are in your area and what the weak points in your home might be, and get costs to do some upgrades.

Of course, like northridge, you might have some microfaults in your area that arent known about.

Off the top of my head, a $400 premium sounds pretty cheap so odds are you arent that close to a major threat. If your house was built in the last 15 years or so, it should have the latest building codes applied and not have any major weaknesses.

I never investigated it, but if the insurers offered a very cheap 50% deductible policy, I'd take one of those just to cover my ass a little bit. Never saw one that varied far from the mandated 10/15% levels though.