Magnitude 3.1 Earthquake

Three earthquakes, the largest having a magnitude of 3.1, occurred within two hours of each other on May 7, 2000, as detailed in the table below.

Time, PDT Magnitude Latitude Longitude Depth Approximate Locaton Distance to HFP Distance to BBG
08:05 M=2.1 36.866 -121.597 6.3 km Near San Juan Bautista 16 km 60 km
08:50 M=2.7 36.246 -120.821 6.4 km Near New Idria 82 km 42 km
09:50 M=3.1 36.244 -120.829 6.0 km Near New Idria 82 km 42 km
Helicorder display

Seismograms from two stations, HFP (Fremont Peak; 9 miles SW of Hollister, 18 miles SSE of Gilroy) and BBG (Big Mountain; 7 miles ENE of Pinnacles, 26 miles N of King City) captured all three events. The New Idria events are closer to BBG than HFP, while the San Juan Bautista event is closer to HFP than to BBG.

These distance relationships can be seen in two ways. First, the New Idria events registered higher amplitudes at BBG than at HFP, while the San Juan Bautista event had higher amplitudes at HFP than at BBG. Secondly, if you look closely you will see that the first waves from the San Juan Bautista event arrive slightly earlier at HFP than at BBG. Conversely, the first waves from the New Idria events arrived at BBG first.