Well Gauges as Seismographs

Abstract

A NUMBER of workers¹ have noted that distant earthquakes are registered on automatic water stage recorders operated on deep wells. In each of these cases, the time scale was so small that the earthquake record was merely a thick line transverse to the direction of time movement. We recently fixed a gauge in a well at Lodi, California, with a Bosch-Omori seismograph drum, rate 15 mm./min., and smoked paper recording. The well is known as 3612A2. It is located at lat. 38° 07 38 N., long. 1217deg; 16 29 W. in the Mokelumne area of the San Joaquin Valley. It is of circular cross section, diameter 6 in., depth 76.0 ft. below ground surface which is at an altitude of 46.9 ft. above mean sea-level. This well, which is not cased below the water surface, is in unconsolidated alluvial deposits of Pleistocene and Pliocene age. It presumably penetrates to a confined aquifer or aquifers. No log is available. The gauge is composed of a copper float, 4J in. in diameter, which operates a stationary 8 in. float-wheel by means of a cord and counterweight. A 4-in. diameter axle mounted on the float-wheel shaft is connected at its upper periphery by a copper ribbon to an auxiliary wheel in the same plane and at the same elevation, on the other side of the recording drum, tension in the ribbon being maintained by a second counterweight below the auxiliary wheel. An aluminium stylus attached to the copper ribbon thus moves horizontally a distance equal to one half that which the float moves vertically. This stylus records on smoked paper on the drum. The minutes are marked on the record by means of a pendulum contact-making clock (supplied by Spindler and Hoyer with Bosch-Omori seismographs), actuating a relay circuit coupled to a solenoid, which energises the magnetic counterweight. Thus the stylus is displaced each minute. The clock correction is obtained daily.