Seismogram of Napa 6.0 Magnitude Earthquake from Modesto

One of the nice things about the new Science Community Center at Modesto Junior College is that we have been given some wonderful tools for the teaching of science. We had a modest seismometer at the old facility, but the software ran off Windows 97, and had not been updated since. We purchased a new seismograph unit from Wards Science, and although it is a simple apparatus, it has been giving us some excellent data on quakes worldwide. We got a good reading on today's event in the Napa Valley, a magnitude 6.0 shaker, the largest in the Bay Area in 25 years. That was the Loma Prieta Earthquake of 1988, a magnitude 6.9 quake that killed dozens, and collapsed bridges and overpasses in Oakland and San Francisco.

The bottom image is the raw data. Each horizontal line on the screen represents one hour of recording time, and so about two days are represented. The waves reverberated through our area for about eight minutes or so. The computer program allows us to isolated the event and manipulate the appearance of the waves, so the upper image is the same data, only spread out. Modesto is located about 100 miles from Napa as the crow flies, and the largest waves were off-scale. I'm pretty sure there were people in Modesto who felt the event.