The geophysical instrumentation operated by the U.S Geological Survey and others near Parkfield is designed to monitor ongoing tectonic processes that generate earthquakes and to record the strong shaking that results from larger shocks and its effects. this discussion focuses on the former objectives; the latter is discussed in the next section "Ground Shaking and Engineering Studies on the Parkfield Section of the San Andreas Fault Zone."
Because scientists expect the anticipated earthquake to resemble the historic Parkfield earthquakes, and in particular that in 1966, the data from the 1966 shock were used to site instruments for optimun benefit before, during, and after the next shock. the primary feature used for siting was the "1966 rupture zone," which is shown as the orange fault traces on the maps in this section. This zone defines the extent of surface tectonic cracks in 1966 and includes the source areas for fore shocks to the 1934 and 1966 earthquakes (north end of the zone) as well as for apparent precursory fault creep in 1966 (near center of the zone). Scientists believe that if precursors to the next shock are observed, they most likely will be near the 1966 rupture zone.
