Effects of the Bear Valley and San Juan Bautista earthquakes of 1972 on Geodimeter line lengths

Measurements of lines of the California Geodimeter network in the vicinity of the epicenters of four 1972 earthquakes (magnitudes 4.7, 4.7, 4.8, and 5.1) along the San Andreas fault system indicate that no significant anomalous changes in line length preceded or accompanied those earthquakes. Within the precision of measurement, the data are consistent with a linear change in line length with time. Measurements of two 20-km-long lines made 2 days before and 1 day after a magnitude 4.7 earthquake showed no significant change even though the epicenter of the earthquake was only about 15 km from each of the three stations at the end points of the lines.