Fluctuations of water‐surface in observation‐wells and at stream gaging‐stations in the Mokelumne Area, California, during the earthquake of December 20, 1932

Abstract

On December 20, 1932, much of the western United States felt a pronounced earthquake‐shock which caused noticeable fluctuations of the water‐surface in several observation‐wells and at two stream gaging‐stations in the Mokelumne Area, central California. These effects of the earthquake are reported briefly in this paper. According to Dr. Byerly (personal communication, February 9, 1933), in charge of the seismograph‐station of the University of California at Berkeley, the earthquake‐ vibrations at that place began at 10 h 11 m 00 s p.m., Pacific Standard Time, December 20, 1932, and continued three hours on the records of his most sensitive instruments. He reports further that the maximum double amplitude of the Earth‐motion at Berkeley was of the order of two mm and that the north‐south and east‐west components of the amplitude were approximately equal. In the Mokelumne Area, which centers about the City of Lodi, 57 miles north 70° east from the seismograph‐station at Berkeley, the pronounced initial Earth‐shock caused chandeliers to sway, upset some bric‐a‐brac, and in at least one building opened a few cracks in the interior plastering. At Stockton, 15 miles south of Lodi, the glass of at least one display‐window in a shop was cracked.