2008 USGS seismic hazard maps 3

[msucog]

the new usgs maps are out. be sure to recognize that the maps are not exactly the same as ibc maps. however, it does appear that there will be changes to the design parameters. in several locations, the changes will go to about 80% of the current PGA, Ss and S1 values. other locations in high seismic areas may see an increase. i guess the actual changes will not be incorporated into ibc until the 2009 version comes out.

http://earthquake.usgs.gov/research/hazmaps/

here's where you can go to see the difference in value between the '02 and '08 maps. there's some significant changes.

http://earthquake.usgs.gov/research/hazmaps/products_data/2008/maps/ratio.php

 

[muuddfun]

Right now they are not very usable, they need to incorporate them into the Java applet they have to get any decent grid spacing in our area. I tried to do it by hand scaling from the map the other day and it was useless. I am sticking with the old maps for now.

 

[msucog]

"i am sticking with the old maps for now"---and you should until ibc adopts them. i put this thread up because when it's time for them to be adopted by ibc, your clients could benefit by you knowing what sort of changes are coming. since there's 10-20% differences between the current and new maps, there likely will be changes in site classes and SDC for the same location depending on which version is "current" at that time. your clients could see you as a great friend with the "heads up" sort of information.

usgs maps should not necessarily be used to determine Ss and S1 in accordance with IBC. the IBC maps based on the usgs maps should be used.

the second link shows how much of a change in values you might see.

 

[msquared48]

In the second link, when I click on the Washington link for the maximum ground acceleration, it is interesting to note that the oblong red region of the Cascadia Subduction Zone off the coast is not even on the color scale legend.

Are they telling us something here? doDODOdo doDODOdo doDODOdo ......

Mike McCann
MMC Engineering

 

[msucog]

they jacked up the values it looks 10-30% at certain locations very near or in certain orientation to high seismic areas (cascadia, new madrid, etc). it's my understanding that the cascadia is the next "big one".
if you look at the report (

http://pubs.usgs.gov/of/2008/1128/)

i think there's some good info for around that area.

http://earthquake.usgs.gov/eqcenter/recenteqsus/

there sure is a whole of activity the past few weeks...up from ~800 eq to 1400+ in the u.s.. i watch it pretty regular and it sure seems like something is brewing lately. maybe it's better to be a bunch of little eq instead of one big, massive one.

 

[msucog]

"there sure is a whole of activity the past few weeks...up from ~800 eq to 1400+ in the u.s.. i watch it pretty regular and it sure seems like something is brewing lately. maybe it's better to be a bunch of little eq instead of one big, massive one. "

i guess it was a massive one (M7.9) in china this time...

 

[msquared48]

The thing I worry about is the swarms in Las Vegas, off the Oregon Coast, and in the Aleutians, and the Cascadia Subduction Zone is inside the triangle. Just an observation -

It's all related to energy. Earthquakes, volcanic eruptions - it's all untimately linked to the geothermal activity of the earths interior.

Mike McCann
MMC Engineering

 

[msucog]

it certainly is odd the string of sizable earthquakes around the globe the past month or so. from china to alaska, nv, illinois and several other places. it sure seems to my simple mind that there's a lot of "background noise" along with the occassional (but more than usual as far as i recall) bigger thuds. it seems to be one big chain reaction...i suppose it probably kind of is since we are but one earth.

i suppose that it is a reminder we are all just specks of matter on a massive and sometimes violent ocean and there's not a damn thing we can do about but watch...regardless of how "good" we think we are.

either way, it is definitely interesting to watch while attempting to comprehend the absolutely magnificent breadth and magnitude (i can't think of any other more appropriate words to explain it) of what must be occurring below our feet...it all sort of puts to scale just how "true" one of my borings can possible be.