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#191843 - 01/15/10 03:43 PM A 7.0 Earthquake?
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5305
Loc: Blue Collar Country
Time for a reality check - perhaps you California folks might be able to answere my question.

We've been treated to all manner of imageg from the recent quake in Haiti, and blanket statements as to the lack of building standards there.

Yet ... 7.0 is a pretty good quake. So, I'm curious: Is modern construction expected to survive a 7.0 Quake in, say, LA or San Francisco?

If so, what does 'survive' mean? Just haveing the dust shook off, or merely not falling on your head, or something in-between?

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#191844 - 01/15/10 04:46 PM Re: A 7.0 Earthquake? [Re: renosteinke]
Tesla Offline
Member

Registered: 06/16/04
Posts: 1280
Loc: Sacramento, CA
There is no building code that can assure occupants that a given structure will survive a 7.0 quake for the following reasons:

Distance from the fault -- you might be right on top of it...

The nature of the soil -- bad for you if the ground turns 'quick'...

The nature of adjacent soils -- hillsides may come to you -- or completely slide into the sea...

Minor fires after the quake become extreme hazards because equipment, communications and roads are impeded...

.....

The most important things that a homeowner should do and which are surprisingly cost effective is to address shear action and wave motion.

This is done by retrofitting shear walls -- especially to any framing between the foundation and the first main floor. In many warmer areas this 'half-stage' is open for ventilation. Experience and testing shows that such elements fold down like dominos. A shear wall retrofit is as simple as screwing OSB across most of the cripple studs. Construction adhesive completes the attachment. You get the benefit even if only half of the surface area is covered -- so you don't need to sheet the whole panel.

Wave motion is addressed by Simpson Strong-Tie hold-downs widely available at the orange box -- or equivalent brands. These function to hold the framing to the foundation -- corners being a particular concern -- and to stop the roof from flying off. This last feature doubles as protection from ultra-high winds, too.

Millions of homes pre-date shear wall construction mandates. If that means you then you'd be very well advised to attend to it when the weather permits.

If your house doesn't hop off the foundation or separate at the platform or roof line you should do okay.

If a quake hits, shut off the gas ASAP. Fire after the quake must be suppressed promptly. A couple of bottles of fire-extinguisher is not a bad investment.
_________________________
Tesla

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#191845 - 01/15/10 05:11 PM Re: A 7.0 Earthquake? [Re: Tesla]
HotLine1 Offline

Member

Registered: 04/03/02
Posts: 6804
Loc: Brick, NJ USA
Off of Reno's thoughts, but relevant to the subject matter. Talking to a local EC this AM regarding a 'minor' issue, he says to me that he will take care of it when he gets back from Haiti!!

He's going for a week to do what he can with a local organization.
_________________________
John

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#191879 - 01/16/10 11:55 PM Re: A 7.0 Earthquake? [Re: HotLine1]
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Has anyone here ( the same as me) noticed that we seem to be having a lot more severe earthquakes these days?
I mean, in a period of say 5 years, there have been some devastating earth-quakes around the "Pacific Ring of Fire" and bits in between.

Survival, as John speaks of, can mean simply looking at having a decent supply of clean water available to drink after a disaster has struck.
Emergency Management over here state that you must be able to look after yourself and your family for a period of 3 days to a week, that includes water, food and shelter (the 3 basics of survival).

Being prepared for an emergency, is half the battle won.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#191880 - 01/17/10 12:37 AM Re: A 7.0 Earthquake? [Re: Trumpy]
gfretwell Online   content

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
I always have several cases of bottled water sitting around ... but we have emergencies here
_________________________
Greg Fretwell

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#191884 - 01/17/10 02:03 AM Re: A 7.0 Earthquake? [Re: gfretwell]
techie Offline
Member

Registered: 05/17/05
Posts: 240
Loc: palo alto, ca usa
In the Loma Prieta quake in 89, some areas suffered no damage, while some areas miles from the epicenter suffered major damage. Factors included building (and structure) construction methods, and underlying soil types.

The Marina district of San Francisco, about 40 miles from the epicenter, suffered major damage due to soil liquifaction (much of the area was built on landfill..).

The Cypress structure on I-880 collapsed due to lack of rebar wraps within the support columns (there was plenty of vertical rebar, but nothing to keep the concrete from blowing out the column sides during a major quake.)

Well constructed wood framed housing tended to fair well due to the
flexibility of the structure, while non-reinforced brick tended to perform poorly.

There were a number of mobile homes that probably would have survived, had they not slid off their foundations.

In the Northridge quake in 1991, there were a number of apartment buildings that collapsed due to lack of shearwalls on the lower levels (they were built over garage/carport areas.. )

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#191888 - 01/17/10 09:06 AM Re: A 7.0 Earthquake? [Re: techie]
gfretwell Online   content

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
Florida doesn't really have earthquakes but it would be interesting. I suspect our soil (sand) would liquefy but the code compliant houses are fairly well strapped with steel, from the foundation to the roof. I suspect that you might just find your house had moved over to the neighbors lot.
_________________________
Greg Fretwell

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#191892 - 01/17/10 11:52 AM Re: A 7.0 Earthquake? [Re: gfretwell]
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5305
Loc: Blue Collar Country
I see that the Northridge quake had a magnitude of 6.7, and Loma Prieta of 6.9. Since the scale is logrithmic, this means that the Northridge quake was but half the power of the one in Haiti.

I'm willing to equate Loma Prieta with the haiti quake, only because different sources give quite a range of values for both quakes.

So, we can say with some honesty that we have had a quake similar to the one in Haiti strike an area -both geologically and urban- similar to Haiti.

In our quake we suffered less than 100 dead, and damage was nothing close to that seen in Haiti. The bulk of housing fared well - let alone 'top dollar' public buildings.

This proves that, yes, you can reasonably build for a quake of this size. There is absolutely no reason for this to catastrophe have happened. By comparing the disasters, we can say that the current codes and practices of California have been validated.

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#191894 - 01/17/10 12:13 PM Re: A 7.0 Earthquake? [Re: renosteinke]
electure Offline

Member

Registered: 12/24/00
Posts: 4226
Loc: Fullerton, CA USA
A 7.0 magnitude isn't the only thing involved.

Vertical and horizontal acceleration rates, & as techie mentioned above, soil liquefaction, are all modifying factors to damage sustained by an earthquake.

The Richter scale reading must be taken in context with the other factors.

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#191895 - 01/17/10 12:31 PM Re: A 7.0 Earthquake? [Re: electure]
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5305
Loc: Blue Collar Country
One can only assume that the folks doing the 'seismic designing' and writing the standards know all about these other factors.

Media hype could lead one to believe that the Haiti quake was far more massive than anything ever seen, and that no place could expect to ride it out. The Richter scale measurements suggest otherwise- that there have been quakes of similar power, striking built-up areas, that have been survived.

Haiti fell apart. San Francisco did not. Either it's dumb luck, or the standards have been validated. We can't just say one quake was 'more powerful' when the measurements suggest they were comparable.

Unless, of course, one wishes to argue that there are too many variables, and that the standards are meaningless. Then you would have to also claim any improvents observed after adopting standards are just dumb luck.

I'll carry this a few steps farther ...
After this quake, inspection of the failed structures will document a lack of any effort made to protect the structures against quakes of any level.

I'll bet that a review of history will show that a quake of this size, in that area, was neither unique nor unexpected.

I'll also go so far as to say that any designer, or contractor, who did not take earthquakes into account when he built those failed buildings was irresponsible, even criminally negligent.

Nor is such a dispute unheard of. I am personally aware of a bridge contractor who quit a contract mid-stream over such a design dispute. Now THERE's a man with a conscience!

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