Magnitude --> Ground Acceleration

You can't determine the ground acceleration with a seismometer, you have to have an accelorometer or strong motion seismometer. The strong motion seismometers are specifically made for local strong shaking whereas the typical seismometer is way too sensitive to measure strong shaking locally. And those that measure the ground shaking from a distance won't tell you the ground motion at the local site.

Its been that way for a long time. And here in the Midwest (I'm in St. Louis, MO) we're not much closer to having a network of strong motion accelorometers here. I know of only one in recent history and that is presently being installed on the new cable stay bridge in Cape Girardeau, MO.

California has recently begun a program to install strong motion recorders and keep a database of records. It is COSMOS and was headed up by long-time seismologist Bruce Bolt.

Thanks a lot for your post. I noticed how the seismogram was clipped because the ground motion was too large for the seismometer. That's why they reported the duration magnitude, right?

On the University of Memphis CERI website, they have a list of seismograph stations. At this link,


it looks like there are a lot of strongmotion sensors. Do you think that these stations were able to measure the quake accurately?

Do you know of any websites that have accelerometer data showing absolute ground motion accelerations?

Thanks,
Shemp

On that website with the list of locations for strong motion stations, it shows one in Memphis that's at a weigh station on I-40. Why in the world would they put one right by a road that always has semi trucks rumbling by??

Shemp,

I didn't see anywhere on the list of strong motion sensors where the data is available.

Regarding the weigh station, its important to have the sensor somewhere its not going to be tampered with. As for the truck induced vibrations this would likely be low and can certainly be filtered out.

Incidentally, I've not heard of the duration magnitude before. Could you elaborate.

I noticed that the Moment magnitude of this quake was reported at Mw = 4.0 so a little lower than the 4.5 reported earlier. The latter may have been a local magnitude. The moment magnitude will give an actual correlation to the amount of energy associated with that quake.

This website briefly describes duration magnitude.