Rumble, Rumble

[jheidt2543]

I woke up this morning to a news report of a 5.4 earthquake centered near New Salem, IL which is 330 miles away. This is a rare event in the Midwest of the USA, so rare in fact that in my part of the country the seismic effects were generally ignored until the advent of the IBC 2000.

Now under the IBC Code; I find for type II building, Ss=.145, S1=.055, assumed soil class D, SDs=.154, SD1=.088 and then I can compute the seismic shear loading on a building based on the building's dead weight for the code required return period quake.

My question is, how do I find out how the 5.4 magnitude quake relates to the code required loading? Is 5.4 10% of the design loading (I know that the Richter Scale is not a uniform scale). I would like to get a "feel" for what this size quake actually means to a building in my area.

 

[KUSUCKS]

Try this map...

http://earthquake.usgs.gov/eqcenter/shakemap/global/shake/2008qza6/

You can access actual %g values at a number of area reporting stations.

 

[JJMT]

remember the accelerations on the map are for the ground, and the accelerations used in the IBC are spectral accelerations (idealized building accelerations)

 

[SlideRuleEra]

The last four pages of USGS Circular 985, about the Charleston, SC earthquake in 1886 compares the subjective Modified Mercalli Intensity Scale with the objective Richter Scale. This will give you a "hands on" comparison of Richter magnitude to expected damage (at least damage expected to 19th century structures). Here is a link:

http://pubs.er.usgs.gov/usgspubs/cir/cir985

The document is in .djvu format, but a link to the required browser plug-in is provided.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Qshake]

jheidt2543 - Your question is a bit much to ask for since magnitude is affected by many factors and that a single buildings response will not be the same for all 5.2 magnitude earthquakes. As an example, the frequency content of the strong motion will change from location to location and from event to event.



Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[MiketheEngineer]

Regardless of the engineering - this was the first real earthquake I have encountered. Sure - we have minor ones around here quite often <4.0.

I am in St. Louis - and let me tell you - it rattled me and the house for about 10 to 15 LONG seconds. I was about ready to hide under the door frame.

It does give you an appreciation for all the extra seismic work we do!!

 

[jheidt2543]

Qshake: I understand that intensity, location and distance all affect at building's response. What I'm trying to get a "feel" for is when we have an event, like the 5.4 quake I slept through this morning, how does that relate to the "design" quake we use in the IBC Code, "... Ss=.145, S1=.055, assumed soil class D, SDs=.154, SD1=.088..."

Those of us that are "new" to seismic design requirements don't have the same "feel" for the loads that we might for dead, live, wind or snow loadings. It's one thing to live in a high seismic area, but when your on the fringe where a distant quake only makes your heart flutter a little - it's hard to know if the house is moving or you've found love again.

 

[cvg]

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

 

[MiketheEngineer]

I found love again...........

Good questions...

In St Louis - wind usually governs on your typical average 2-3 story wood structure - whereas in Cape Girardeau, MO (100 miles south) where seismic gets a bit more intense - seismic usually governs.

Theoretically - we are about equal when comparing the two...
when comparing total horizontal forces or shear.

So - say - it feels somthing like a 90 mph wind - give or take....but I would have to say the deflections sure felt higher or maybe it was just the back & forth motion...

My bed hasn't moved like that in years!!