Measuring the Movement of the San Andreas Fault Using GPS

Event Center A&B

Global Positioning Systems (GPS) data were collected from various localities in the San Bernardino Mountains area to find out the slip rates of the faults in the area. Over 5,000,000 slip-rate combinations were tested for 14 faults within a transect across the Pacific-North America plate boundary passing through San Gorgonio Pass. The chi2 criterion was used to rank models in terms of goodness of fit to the observed GPS site velocities. A running average that was shifted was used to provide a low and high envelope around the observed data to define which slip rate combinations fit the data acceptably. The acceptable slip rates of the San Andreas fault range from 8-24 mm/yr, and of the San Jacinto fault range from 0-16 mm/yr. The best fitting model has a slip rate of the San Andreas fault of 14 mm/yr with the San Jacinto fault having a slip rate of 8 mm/yr.