WATSONVILLE, Calif. (UPI) — Observations on the San Andreas Fault near Santa Cruz, Calif., show large earthquakes have occurred more frequently there than previously thought, a study says.
Researchers with the U.S. Geological Survey, with assistance from the California Geological Survey, conducted a paleoseismic study documenting four surface-rupturing earthquakes that occurred across the Santa Cruz Mountains section of the fault in the past 500 years.
Studies near Watsonville, Calif., found the evidence for the four temblors, the most recent being the 1906 magnitude-7.8 San Francisco earthquake, a release from the Seismological Society of America said Wednesday.
Geologists Thomas Fumal and Tim Dawson said each of the three earthquakes prior to the 1906 quake was likely a large magnitude event that ruptured most, or all, of the Santa Cruz Mountains segment of the fault and would have produced similar physical deformation as the 1906 quake.
This study suggests the San Andreas Fault produces a wider array of magnitudes than current seismic hazard models predict, and that individual segments of the fault system can produce destructive earthquakes, the researchers said.