Detailed Earthquake Threat maps?

[timbernet]

I am trying to find some detailed earthquake threat maps/fault line maps....

A long time ago someone told me that Highway 26 out in the Sandy area was built on a fault line, but looking at this map from Clackamas County



it looks pretty blue (good) through the Boring/Sandy area.


Then I start looking at where I work (thinking of getting home in case of a larger earthquake) and the map isn't detailed enough for me to locate the rough area where I work... I see some blue where I think I work... but then there is a wide patch of orange, so I kinda want to zoom in and look.


I know these are rough estimates and can't guarantee a lack of structural damage, etc -- but I'd still rather be in a blue area than a orange area!


So does anyone know of an online system for querying this type of map data?

Read More

 

[elsie]

USGS might be a good place to start. <broken link removed> has several map links and a live seismic feed from Corvallis. <broken link removed> is a historical map of epicenters and shows various fault lines, but isn't very high resolution.

elsie

 

[MarkSBG]

What question are you trying to answer? "What is the seismic risk for my personal house?" or "What is Portlands seismic risk?" or something else?

 

[timbernet]

What question are you trying to answer? "What is the seismic risk for my personal house?" or "What is Portlands seismic risk?" or something else?

Seismic risk for the area around Boring and Clackamas mainly... and if what I heard about a fault line going right now Highway 26 was true or not.


I am at 700' elevation, no rivers, streams, or creeks nearby - so flooding is out.
Not a lot of trees, so forest fires are out.
20 miles away from Portland with a few hills inbetween, so, depending on the size of Nuke/Wind patterns, somewhat protected a bit there (fallout is still a threat).

35-40 miles away from Mount Hood --- other than ash, larger debris isn't an issue.

No railroad tracks for 12 miles to the north, so chemical spills on the rail line aren't a big threat for me.

SO that leaves me with what to worry about? Earthquake! (and the payloads going down Highway 26 - about 2,000' away)

Just trying to get an idea of what I am preparing for.... hole opening up in the ground and swallowing everything? (IF Highway 26 is on a fault, and I am close to 26, I am somewhat concerned about that depending on the size of quake)

OR is the worst that is going to happen is things fall of shelves and maybe some structural/foundation damage but overall a safe property?


Like I said in my original post -- I know there aren't exact answers to any of these questions. BUT, based on statistics and data gathered over the year based on terrain information, etc - I know that they can make some good guesses/estimates.


Edit to add: saw this PDF on one of those links above: <broken link removed> -- pretty interesting read!

 

[TAT2D]

My first thought was to see if I could find an overlay for Google Earth. A cursory look didn't turn up the info we're after, but it may be there somewhere and if not, given how reactive Google is to 'topical' issues, and the thousands of people that are this morning thinking, "Hmmm, wonder if that could happen here?" they may be working on putting the data together in the right format.

MrB

 

[MarkSBG]

Oregon is considered a very high seismic risk. The building codes today are based on maintaining life safety during an earthquake that comes through once about every 300 years. Oregon has not seen one of these design level earthquakes in about 300 years, so we are certainly due for a big one.

Having said that, historically, single occupant houses in the US fair pretty well during earthquakes. The forces generated in an earthquake go up as the weight of the building goes up. Houses are significantly lighter than other building types. Many of the failures that occur in houses typically includes:
- sliding off the foundation because there are not anchor bolts into a concrete footing
- collapse of the cripple wall. (This is the wall between the top of the foundation and the bottom of the first floor framing. Often this wall if poorly constructed in older construction.)
- collapse of porches and carports that are not adequately connected to the house.
- Nonstructural damage. (breaking gas lines, tipping water heaters over, contents falling from shelves, etc...)

Another factor that is very important is soil type in the area you live. Very thick clay layers (like the bay muds in San Francisco) amplify the earthquake loads. It's kind of like shaking a plate of jello. Rocky soils do not amplify these forces.

Obviously, to know your actual seismic risk, you would need to go out and hire a structural engineer knowledgable in seismic engineering.

You can go here for additional reading about Oregon and seismic activity:
<broken link removed>

Here is the location of those google maps MrB was referring to:
<broken link removed>

 

[SOG165]

Here's a bit of additional info that dovetails into what MarkSBG has provided.

<broken link removed>

SOG165

 

[RavenLunatic]

The building codes today are based on maintaining life safety during an earthquake that comes through once about every 300 years. Oregon has not seen one of these design level earthquakes in about 300 years, so we are certainly due for a big one.

Although it's true that it's been about 300 years since the last slippage of the Cascadia Subduction Zone (1700 as targeted by tsunami data from Japan and Atwater's Salt Marsh Ghost Forest and Tsunami Sand Deposit dating along the coast), the media has published much heresay about periodicity of the CSZ. Atwater's work has shown dates of CSZ slippage varying from periods as short as 300 years to over 1200 years. It certainly could slip at anytime, but with a lack of periodicity, we cannot say that it's overdue.

 

[OFADAN]

Timber where did you obtain a copy of the County Hazard map probablity?

 

[timbernet]

Timber where did you obtain a copy of the County Hazard map probablity?

The JPEG in my first post?

Right here: <broken link removed> --- The County GIS website.

 

[Karma]

I was told at one time that Salem would be facing a big problem if there was a big earthquake. Supposedly if the Detroit dam broke, the city of Salem would be under 10' or more of water in 20 minutes or so. That would be a problem for sure.