GTSM at San Francisco East Bay
CHT and GAT are situated in the East Bay region of San Francisco Bay.
They were installed with co-located Sacks-Evertson dilatometers as part of a 6 site(Lake Chabot, Garin Park,Coyote, Mill Creek,Sunol, Russell River) array in September-October 1992. Shortly after 1992, creepmeters [cfw(Fremont-USGS),coz(Oakland Zoo),cpp(Pinole Park), ctm(Temescal Park), and chp(Palisades)-R.Bilham,U.Colorado] were also installed.
Data for CHT is provided for channels 2, 3, and 4. Anomalous tidal response was identified on channel 1 early in the life of this instrument. All post 1986 instruments include a redundant channel (here channel 4) to be used for this purpose when necessary.
During deployment of GAT, the deployment cable was damaged approximately 30 meters from the surface by failure of a manually controlled guide pulley. A field repair was undertaken because only one target horizon was available below the casing. By May 6, 1994, fluid leakage into the cable was detected. Several attempts were made over the years to 1998 to control copper conductor corrosion, but in September 1998, complete failure of several conductors resulted in loss of downhole contact. This is one of only two GTSM instruments on grid power, and the long sections of missing data initially, were due to delays in connection to the grid, and temporary availability of solar power.
This station was taken off-line on September 2 1998.
These instruments provide strain data on:
Long term strain accumulation. Data records are available from the East Bay sites near the Hayward fault, GAT and CHT from 1993. Tilt records are also available from the Gladwin Tensor instrument at GAT and CHT from 1993.
Medium term strain changes associated with earthquake activity and other fault processes.
Coseismic strain offsets useful for constraining earthquake source mechanisms.