Description and history of mercury-tube tiltmeters used in the San Francisco Bay area, California

Abstract

Four mercury-tube type tiltmeters, operated by the U.S. Geological Survey, have been in continuous operation since 1969 in the San Francisco Bay area. This paper contains a brief description and history of these tiltmeters, and a summary of data recorded during the years 1974 to 1983. Two of these tiltmeters are located in the University of California, Berkeley, Byerley seismic vault just east of the Hayward fault, lat. 37*51.6', and long. 122°14.9' at an elevation of 276 meters, as shown in Fig. 1. The tunnel for the Byerley vault is drilled into the steeply folded beds of the Clairemont formation. This formation consists of thin bedded shales and cherts. The vault is about 2 km from the Hayward fault. The Wildcat, University, and the Strawberry Canyon faults are also located in the area. The University and Strawberry Canyon faults run perpendicular to the Hayward and Wildcat faults. The other two instruments are located in a vault in the Presidio of San Francisco, lat. 37.79, and long. 122.47. The vault was originally constructed as an ammunition bunker during the Spanish-American war. This vault has been used as a test facility by the USGS since 1968. It is Duilt on Franciscan chert and sandstone on top of a hill, overlooking the Pacific Ocean near the Golden Gate bridge. The walls are reinforced concrete approximately 1/2 meter thick, and the roof is heavily reinforced with the steel girders. The interior rooms can be isolated from one another. A thick (5 meter) overburden of sand covers the bunkers.

Low strain level acoustic emission due to seismic waves and tidal/thermoelastic strains observed at the San Francisco Presidio, California

“…122.47) was originally constructed as an ammunition bunker during the Spanish-American war. It houses strainmeters, tiltmeters, seismometers and a variety of other geophysical instruments (Jones, 1983). It is built on Franciscan chert and sandstone on top of a hill, overlooking the Pacific Ocean near the Golden Gate bridge, approximately 10 km east of the San Andreas fault.…”