The American Geophysical Union held their Fall Meeting in San Francisco this week. My wife heard a report on some of the happenings of interest to the general public on the radio this afternoon. One of the reports described the NetQuakes program being undertaken by the U.S. Geological Survey.
The NetQuakes program asks volunteers to host small seismographs at their homes in order to increase the number of seismographs in the San Francisco Bay area. These appear to be strong motion sensors based on triaxial accelerometers and record data only when triggered by an acceleration of 0.25% g. The triggered waveforms are sent to the USGS via wifi through the vounteer’s internet connection and are immediately analyzed for possible earthquake events. The triggered waveforms are also displayed on a page off of the NetQuakes homepage.
As I was exploring the NetQuakes site, I noticed that several, but not all the stations showed a coherent signal at about 10:16:30 on Dec 18, 2009. I clicked on on one, J021-NC. Then I went the USGS Earthquake Hazards page to look for small California earthquakes at that time. I looked first at the listing for Magnitude 3+ events but didn’t find any at the proper time, which I should have expected from the limited number of stations reporting the event. When I looked at the Magnitude 1+ list I found a Magnitude 1.8 earthquake just a few miles from the J021-NC station. The station names can be determined by clicking on the location map at the location indicators…pretty cool and it should give them very fast earthquake severity and location information.