Hi I've been lurking on this list for a while and have some qestions for some of the more experienced people. I have build a Shackelford-Gunderson seismometer, based on the electronics board that Larry Cochrane provides. The thing has been running for a couple of months, and I managed to bag several events. My questions all relate to what my expectations should be for the performance of the thing. The sensor is sitting on my basement floor. I live in what is probably a noisier than average location, a residential neighborhood about 500 yards from a very busy street. First, what should I expect to be able to see as a function of distance and magnitude of an event? About the weakest events that I have seen were two from Iceland, both about 6.5, both of which produced very nice and unmistakeable records. But there is a lot of activity that seems to be below my sensititivity (or noise floor). Should I be able to do better? Second, I routinely see a very long period background noise. If I run the Winquake FFT routine on a "no event" record from my system, I see a broad peak around 100 seconds with several spikes in the gram around 60 - 120 seconds. I wouldn't be surprised if a lot of this is thermal noise, but it would be nice to know if what I'm seeing is reasonably typical of seismic noise. The noise level does seem lower at night, when there isn't any activity in the house. I understand that there are continuout microseisms with a period of around 6 seconds (?). They aren't obvious in my records, perhapse because I don't have the LF gain set high enough. My LF noise level produces peaks that average around 20 or so from a 12 bit A-D converter. My other problem is a basement floor that is about as stiff as a trampoline. Haven't been able to find a spot that is immune to people walking on the floor above. Short of buying a new house or pouring concrete in the back yard, I'm probably stuck with that one. I'd appreciate anyone's comments or suggestions. I'm having fun, but have a lot to learn. Larry Conklin lconklin@............ __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>