Were those sensors in place in the ‘50’s?
It looks like the project started in the late 1970s.
The CISN uses different types of sensors (short-period, broadband, and strong-motion) in different environments (surface and/or free field, structures, boreholes) with different recording and communications systems.
The tables figures below illustrate the range and distribution of seismic instrumentation in California and western Nevada deployed by CISN partners and collaborators. These numbers and maps were put together by David Oppenheimer, of the USGS Menlo Park, as part of a planning meeting for future CISN instrumentation held in June 2002.
California and western Nevada by the numbers (as of June 2002):
•614 short-period sensors
•198 broadband sensors
•1563 strong-motion sensors (~460 without communications)
•708 instrumented structures (lifelines, dams, buildings)
•38 borehole installations