How big of an earthquake can california houses withstand?

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How big of an earthquake can california houses withstand?

Postby paulsiu » Wed Mar 16, 2011 12:12 pm

Anyone know how large of an earthquake can a California house built in the 90's withstand? I was looking through some of the building code, but I don't see a figure.

Paul
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Postby phositadc » Wed Mar 16, 2011 12:31 pm

I don't know the answer to your question, but given how badly my building in Los Angeles shook last year from a 7.3 that was pretty far away (several hundred miles if I recall correctly), I bet an 8.9 would do some serious, serious damage if it struck anywhere near a populated area.
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Postby sscritic » Wed Mar 16, 2011 12:34 pm

I lived in Northridge in 1994:

Best: single story
OK: two story
Worst: split level
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Postby thechoson » Wed Mar 16, 2011 12:55 pm

I tend to think of building "earthquake codes" like car safety.

Cars are mandated to be safe in certain situations- say a frontal crash at 40 mph, side crash at 30 mph. If you are in a modern car and get in a crash of that severity with a similar size car, you are going to be ok probably.

But if you are going 80 mph, or if a car hits you going that speed, or you get hit by a Hummer, those crash standards won't protect you, you are dead.

I would imagine that homes built in the 90s are designed to withstand the majority of earthquakes. But if a big one hits nearby, I doubt they can cost efficiently build housing strong enough to withstand that.

Look at the recent damage from the New Zealand quake (which everyone has forgotten about due to Japan). A lot of buildings built to California like codes were destroyed. And that was a 6.4 I believe, although very shallow.
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Re: How big of an earthquake can california houses withstand

Postby Valuethinker » Wed Mar 16, 2011 1:38 pm

paulsiu wrote:Anyone know how large of an earthquake can a California house built in the 90's withstand? I was looking through some of the building code, but I don't see a figure.

Paul


I don't know. However the omens are good. California houses are wood framed, and relatively low to the ground. Codes are, I think, pretty tough in CA. Houses will collapse, but the people will be alive under them and possibly not too seriously hurt.

it's commercial buildings, and violations of code, that are likely to cause the real casualties. Shopping malls and (god help us) schools collapsing. Office buildings.

My nightmare is of The Big One hitting during the school day. Then we'll find out how good CA's building inspectors and codes are.

In China over 8,000 children died in the last big one as a result of corrupt practices in schools' construction.
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Postby LynnC » Wed Mar 16, 2011 3:12 pm

chrikenn wrote:I don't know the answer to your question, but given how badly my building in Los Angeles shook last year from a 7.3 that was pretty far away (several hundred miles if I recall correctly), I bet an 8.9 would do some serious, serious damage if it struck anywhere near a populated area.


7.3 last year, really? Where?

I'm in SoCal and would have remembered that one. I have included the link for the strongest earthquakes in the US.

The strongest ones for me was the Whittier quake and the Northridge quake, both under 7.0.

LynnC

http://earthquake.usgs.gov/earthquakes/ ... orical.php
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Postby Random Musings » Wed Mar 16, 2011 3:15 pm

I wonder how many homes in California could withstand having Charlie Sheen reside in it for one year.

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Postby LynnC » Wed Mar 16, 2011 3:21 pm

The link above shows that earthquakes happen in many states, not just California. We should all be taking this time to revisit our "earthquake / disaster kits."

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Postby chaz » Wed Mar 16, 2011 4:47 pm

LynnC wrote:
chrikenn wrote:I don't know the answer to your question, but given how badly my building in Los Angeles shook last year from a 7.3 that was pretty far away (several hundred miles if I recall correctly), I bet an 8.9 would do some serious, serious damage if it struck anywhere near a populated area.


7.3 last year, really? Where?

I'm in SoCal and would have remembered that one. I have included the link for the strongest earthquakes in the US.

The strongest ones for me was the Whittier quake and the Northridge quake, both under 7.0.

LynnC

http://earthquake.usgs.gov/earthquakes/ ... orical.php


the Northridge quake did a lot of damage.
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Postby Manbaerpig » Wed Mar 16, 2011 4:58 pm

my 100 year old wood framed house will be on me like white on rice :)

but I think I have some chance of surving it, its a single story. termites have probably brought the weight down a bit :)
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Postby sscritic » Wed Mar 16, 2011 5:04 pm

chaz wrote:
LynnC wrote:
chrikenn wrote:I don't know the answer to your question, but given how badly my building in Los Angeles shook last year from a 7.3 that was pretty far away (several hundred miles if I recall correctly), I bet an 8.9 would do some serious, serious damage if it struck anywhere near a populated area.

7.3 last year, really? Where?

The strongest ones for me was the Whittier quake and the Northridge quake, both under 7.0.
http://earthquake.usgs.gov/earthquakes/ ... orical.php

the Northridge quake did a lot of damage.

The Northridge quake was a 6.7, which is why a 7.3 would be in the records.

Here is a list for Southern California:
http://www.data.scec.org/chrono_index/quakedex.html

If you look at the map, you will see very few above 7.5 magnitude (dark orange or red).
http://www.data.scec.org/clickmap.html

Northridge is the light orange dot just above and slightly to the left of the L is Los Angeles.
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Postby Manbaerpig » Wed Mar 16, 2011 5:19 pm

Not all Richter #'s are alike, obviously, in damage potential.

Depending on geography, how far the epicenter is down in the crust, and various factors regarding the S&P waves the resulting damage is highly variable.

Loma Prieta wasnt that big, for instance. It also dissovled the foundation of the hunters point area in SF nearly 60 miles away and collapsed the upper deck of the bay bridge.

Similarly Northridge brought down a ton of concrete split level apartment buildings right to the ground level.
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Postby bluemonday » Wed Mar 16, 2011 5:23 pm

Your probably in fairly good shape, but there are far too many variables to say with certainty. What type of soil do you have, clay, fill, are you on bedrock,etc.? What (known)fault lines are you near( there may be unknown ones that could affect you as well )? Where is the theoretical next big one, relative to your house, centered, what is it's depth, magnitude, duration,etc. Is your structure built to code minimums, or better? What is/was the code in your jurisdiction at the time of building? Is it a multi-story, with living quarters over a garage( higher risk of collapse )? Do you have un-reinforced "pony walls"( hopefully not)? -It's not as simple as asking when was the house built. Anything built after roughly 1957 had to have the house bolted to the foundation at a minimum, but there are lots of variations beyond that.
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Postby Easy Rhino » Wed Mar 16, 2011 5:35 pm

LynnC wrote:7.3 last year, really? Where?

the one on Easter near Mexicali?

Good shaking here in San Diego, but virtually no damage.
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Postby sscritic » Wed Mar 16, 2011 5:56 pm

Easy Rhino wrote:
LynnC wrote:7.3 last year, really? Where?

the one on Easter near Mexicali?

Good shaking here in San Diego, but virtually no damage.

Must be. It was a 7.2 (April 4, 2010)
http://earthquake.usgs.gov/earthquakes/ ... 607652.php
No damage was reported in Los Angeles or San Diego.
...
The quake was felt for about 40 seconds in Tijuana, Mexico, causing buildings to sway and knocking out power in parts of the city
http://www.huffingtonpost.com/2010/04/0 ... tml#s78478
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Postby stan1 » Wed Mar 16, 2011 7:11 pm

I live in California. My bigger worry is the New Madrid fault in Southern Missouri/surrounding areas which let loose an estimated magnitude 8.0 earthquake in 1811/12. There's two hundred years worth of masonry buildings and building codes that are not set up to handle earthquakes.

There may still be a lot of damage in California, but the codes will hopefully at least enable people to walk out of buildings after the quake instead of having to pull people out of the rubble after a building collapses.
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Postby i<3Investing » Wed Mar 16, 2011 7:48 pm

So I'm a structural engineer, so if this gets kind of technical that's why.

In California, buildings are designed for a Maximum Considered Earthquake. Basically they have been designed for the maximum force that the building code can consider feasible (I believe the maximum known earthquake from the San Andreas was a magnitude 8.0).

For most of the country the maximum earthquake has a 2% probability of exceedance in 50 years (2500 year return period).

I will say that wood single story residences are some of the strongest structures in existence. So much so that most of them are exempted from being reviewed by a structural engineer.

Also, an interesting side note is each magnitude increases the amount of energy released by 32. So the 9.0 that Japan just felt was roughly 1,000 times more energy than the Northridge quake.
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Postby Allan » Wed Mar 16, 2011 8:39 pm

i<3Investing wrote:So much so that most of them are exempted from being reviewed by a structural engineer.


I assume new homes are required to be engineered designed and certified in California.
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Postby LynnC » Wed Mar 16, 2011 8:48 pm

i<3Investing wrote:
I will say that wood single story residences are some of the strongest structures in existence. So much so that most of them are exempted from being reviewed by a structural engineer.



My dad was a contractor and always said to buy a single story, wood framed home for quality.

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Postby thechoson » Wed Mar 16, 2011 9:09 pm

LynnC wrote:
i<3Investing wrote:
I will say that wood single story residences are some of the strongest structures in existence. So much so that most of them are exempted from being reviewed by a structural engineer.



My dad was a contractor and always said to buy a single story, wood framed home for quality.

LynnC


Do they even build these in California anymore? All the new homes seem at least 2 stories now
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Postby thechoson » Wed Mar 16, 2011 9:11 pm

I live on the top floor of a 4 story apartment complex where the bottom floor is a parking garage. This is in the Bay Area.

I am in for a world of hurt if/when the big one hits.

Hopefully by them I'll have saved enough money to have bought a nice single story house.
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Postby zinnia » Wed Mar 16, 2011 9:12 pm

"the Diablo Canyon nuclear plant on the California coast, which sits less than a mile from an offshore fault line, does not include a ready response for an accident triggered by an earthquake. Though experts warned from the beginning that the plant would be vulnerable to an earthquake, asserting 25 years ago that it required an emergency plan as a condition of its license, the Nuclear Regulatory Commission fought against making such a provision mandatory as it allowed the facility to be built."
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Postby Shawn » Wed Mar 16, 2011 9:35 pm

Also, an interesting side note is each magnitude increases the amount of energy released by 32. So the 9.0 that Japan just felt was roughly 1,000 times more energy than the Northridge quake.

This is true.

However, it's important to note that the ground motions (shaking amplitude) for the 2011 M9.0 Japan earthquake (now being called the Tohoku earthquake) were not necessarily larger than the ground motions for the 1994 M6.7 Northridge event. The Japan earthquake had a higher magnitude primarily because the fault rupture occurred over a larger surface area. Specifically, approximately 100,000 km^2 of the fault failed, compared to only 300 km^2 for the Northridge event. The slip (distance one side of the fault moves relative to the other) was larger too, but that had a much smaller effect.

The point is that ground shaking tends to saturate for larger earthquakes (e.g., more than M 6 or 7). Larger earthquakes tend to be more damaging because the shaking occurs over a much broader geographical area due to the larger dimensions of the fault rupture. It is not that the shaking itself is that much stronger (although the shaking can last longer for the bigger events).

Some of the most important parameters that influence ground shaking are the underlying geology (e.g., deep sedimentary basins tend to trap and amplify seismic energy) and a phenomenon known as directivity. Directivity is the focusing of seismic energy in the direction of fault rupture (the earthquake or rupture starts at the epicenter and often, but not always, moves in one primary direction).

As counter intuitive as it sounds, it turns out that for larger earthquakes, the ground shaking is often poorly correlated with the distance from the epicenter. For example, the epicenter of the 1906 M7.8 San Francisco earthquake was 3 km off the coast of San Francisco along the San Andreas fault. Ignoring the fire, the earthquake would likely have been much more devastating to the city if the epicenter was 100-200 km to the northwest or southeast (this is the directivity effect).

Also, houses are relatively small structures and are most impacted by the higher frequency ground motions. Larger earthquakes (e.g., M7+) do not contain much more high frequency energy than smaller earthquakes (e.g., M 6-7). Larger earthquakes are much more likely to impact bigger structures (sky scrappers or long-span bridges).

There is a famous picture of an old shack that was a few feet from the fault in the 1954 M6.8 Dixie Valley earthquake in Nevada. The shack was relatively undamaged. Even if the earthquake was M 8 or 9, the shack probably would have survived. If a house can survive a M 6-7 earthquake, it probably can survive a larger event.

Image
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Postby DiscoBunny1979 » Wed Mar 16, 2011 9:36 pm

Just a tid bit of info for folks . . . from what I remember, most of California's Hospitals are built on top of Earthquake fault lines. How's that for safety?

But anyway . . . the subject at hand. . . I lived through many Earthquakes in CA and the most powerful for me was the one the hit the bay ara that knocked out the bay bridge and caused houses to collapse in the Marina in San Francisco.

In my opinion, from the 6 or so remodeling demo projects I've done, whereas I've taken the house down to the studs . . . I have to give more of a thumbs up to those houses that were built as special to the owner rather than a track house by a builder AND pre mid 70s.

I had one house built in the 40s that had unbelieveable 2 x 6s and 2 x 8s used for framing. I had another house that used such long wood beams from one end of the house to another that it can't be done that way today because of cost. Also the way they framed the houses in the 40s often went beyond code for its time.

That said, the houses I've seen often built in the 60s in Northern CA are often built on piers rather than concrete slab. So, in the bay area, it's more likely that a house could fall off it's piers due to a shaker of huge proportions. I'd be concerned of this type of construction.

I've also owned a KB Home that was build in 1997 in southern California. The stucco actually held up nicely through small tremors. My concern though is that during the building of houses in the late 90s and early 2000s, there were a lot of non English speaking folks getting paid to do jobs fast . . . and I'm not too sure that the quality of the work because of the fast pace of slopping these houses together just to sell them would hold up in a large sized quake. In fact, IF real inspections were done, my house wouldn't have passed because the fire alarms were put on the same circuit as the kitchen. Code is separate circuit.

Unfortunately, you might have the luxury to go underneath the hood to determine quality of construction . . .but a lot can be determined by a look into the attic. What size beams did they use and how are they joined together???
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Postby bluemonday » Wed Mar 16, 2011 11:19 pm

DiscoBunny1979 wrote:...
That said, the houses I've seen often built in the 60s in Northern CA are often built on piers rather than concrete slab. So, in the bay area, it's more likely that a house could fall off it's piers due to a shaker of huge proportions. I'd be concerned of this type of construction.



This is a non issue if the house is properly bolted to it's perimeter concrete foundation(assuming it has one). The house may fail at other points though, pony ( cripple ) walls collapsing( lot's of older houses have these), garages collapsing at the car hole end, etc.
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Postby sscritic » Thu Mar 17, 2011 12:09 am

thechoson wrote:Do they even build these in California anymore? All the new homes seem at least 2 stories now

Absolutely!

Who can afford a new house? Not the unemployed carpenter, but the newly retired baby boomer with his fat 401(k) and social security who is selling the house he has owned for 30 years in order to downsize. If he hasn't used his old house as a piggybank, he will have a nice nest egg to put into a one-story house so he won't have to deal with stairs. In the past 15 years, one story houses were considered too expensive to build (the land cost per sqft of house was too great), but now they are one of the few styles still selling.

Babyboomers have ruled the US for the last 40 years, and they will continue to rule for the next 30. There are just too many of them for homebuilders, car manufacturers, retailers, etc. to ignore.

I went to one new development that had put 2 one story houses in their first phase of 6 houses. Those were the first to go. The next phase of 6 houses was going to have 3 one story houses. They are now running specials on the two story houses to get rid of them, but there are no discounts on the one story houses (only $675,000). I just double checked their website; they are sold out of the one story model.
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Postby DiscoBunny1979 » Thu Mar 17, 2011 12:33 am

bluemonday wrote:
DiscoBunny1979 wrote:...
That said, the houses I've seen often built in the 60s in Northern CA are often built on piers rather than concrete slab. So, in the bay area, it's more likely that a house could fall off it's piers due to a shaker of huge proportions. I'd be concerned of this type of construction.



This is a non issue if the house is properly bolted to it's perimeter concrete foundation(assuming it has one). The house may fail at other points though, pony ( cripple ) walls collapsing( lot's of older houses have these), garages collapsing at the car hole end, etc.

--------

Yes, properly bolted and if there is a perimeter foundation to begin with. Many of these homes in the bay area have had to add this bolting scenario. Many don't because of the cost. Also....if you're ever in the vacinity of the Russian River, take a look at the construction used on some of those weekenders made into full year residences that hang off of cliffs to view the river and supported only by wooden post and pier. Very scarey if you ask me. But the views from the decks are nice.
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Postby paulsiu » Thu Mar 17, 2011 8:31 am

The house that scare me would be house out in the wood on cliffs. I once visited Muir wood and notice a lot of house on the side of the cliff. I'll be really nervous that the earthquake won't break off the house or dump a bunch of trees or boulder on it.

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Re: How big of an earthquake can california houses withstand

Postby Ed 2 » Thu Mar 17, 2011 8:42 am

paulsiu wrote:Anyone know how large of an earthquake can a California house built in the 90's withstand? I was looking through some of the building code, but I don't see a figure.

Paul


I think 8.0 would make a Great damage but the biggest danger would be not an earthquake , the danger would be a looting and riots in CA after. We are not a Japan.The best remedy for it is to have a guns in your house
Last edited by Ed 2 on Thu Mar 17, 2011 10:27 pm, edited 1 time in total.
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Postby i<3Investing » Thu Mar 17, 2011 7:51 pm

I'll answer what I can... :)

Allan wrote:I assume new homes are required to be engineered designed and certified in California.


No, even the new code has exemptions for wood framed homes.. Although for liability purposes an engineer will often be brought in on a project.

LynnC wrote:My dad was a contractor and always said to buy a single story, wood framed home for quality.


Wood framed are the tanks of structures... The shear walls alone can normally handle most anything.

zinnia wrote:the Diablo Canyon nuclear plant on the California coast, which sits less than a mile from an offshore fault line, does not include a ready response for an accident triggered by an earthquake


Having done structural design for the nuclear industry, I can guarantee you they are built for scenarios that you wouldn't even begin to think of. Also, any structural calculations done for nuclear work has 2nd and 3rd party reviewers. My guess is this is just the news being the news.

Shawn wrote:The point is that ground shaking tends to saturate for larger earthquakes (e.g., more than M 6 or 7). Larger earthquakes tend to be more damaging because the shaking occurs over a much broader geographical area due to the larger dimensions of the fault rupture. It is not that the shaking itself is that much stronger (although the shaking can last longer for the bigger events).


Very true info here... I didn't mean to say that the Japan earthquake felt 1,000 times stronger than Northridge. Actually often times the buildings you thought would have fallen down years ago will remain standing after earthquakes because of the soil they sit on.

DiscoBunny1979 wrote:Just a tid bit of info for folks . . . from what I remember, most of California's Hospitals are built on top of Earthquake fault lines. How's that for safety?


Actually hospitals fall into a different category than regular structures. They are built to basically withstand the full force of a large earthquake and remain functioning. If memory serves, they are built 50% stronger than most other buildings. You also have to be an S.E. to build hospitals, which is basically the rolls royce of structural engineering (i'm not one but aspire to be one someday). I would much rather be in a hospital within 5 miles of a fault than under a coconut tree 100 miles from a fault ;)
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Postby V572625694 » Thu Mar 17, 2011 8:09 pm

I was in the Easter 2010 earthquake in San Diego, which was 7.2 on the Richter scale at the epicenter about 108 miles southeast of the city, perhaps weaker here but still quite scary. I was on the patio of a two-story house built in 2005 and felt motion. When I got home to my 12th-floor (of 21) condo later, the only damage was a drywall crack over an archway and I didn't discover that until much later. I watched the building being built in 2004-07, and there is a tremendous amount of rebar in the columns that hold up the floor plates, and it was welded together before the concrete was poured.

My office is on the 12th floor of a 13-story building constructed in 1925. A friend (tax preparer working on Sunday in tax season, of course) was in the building when the quake happened, and was certain the building would come down. He ran down the fire stairs as fast as he could, outdistancing several much younger evacuees.

I'm sitting in that building now, and it's fine, perhaps because it has a steel frame beneath its granite and brick exterior--other old buildings in San Diego were built of unreinforced concrete, but came through fine as well.
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Postby roamin survivor » Thu Mar 17, 2011 8:16 pm

thechoson wrote:Do they even build these in California anymore? All the new homes seem at least 2 stories now


Finished building my single story in Jan. Had to fight off everyone saying do 2-story; earthquakes were one factor in it.

Allan wrote:I assume new homes are required to be engineered designed and certified in California.


i<3Investing is right. Still had a structural engineer go over my plans. Very interesting stuff.

i<3Investing wrote:
LynnC wrote:My dad was a contractor and always said to buy a single story, wood framed home for quality.


Wood framed are the tanks of structures... The shear walls alone can normally handle most anything.


My dad was a contractor too and insisted I do two-story. I (re)learned about all the work going into shear walls when talking with the SE. Code currently dictates 80% of the shear walls must be wall. I have this long thin lot, so I hope the shear walls do handle the load.

DiscoBunny1979 wrote:I had one house built in the 40s that had unbelieveable 2 x 6s and 2 x 8s used for framing


I saw all of these while I was demoing the house (built in 1925). The inner walls are 2x6, but mainly for sound dampening. I'm sure they'd hold up well in a quake.

thechoson wrote:I live on the top floor of a 4 story apartment complex where the bottom floor is a parking garage. This is in the Bay Area.


I think you're okay on those provided it's at ground level; it's the ones that are below ground level that scare me the most. I believe it was in the news that those tend to not be braced correctly due to the requirements at the time. Haven't seen anything new being built with that.
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