PFO Geophysical Sensors


Deformation Monitoring: Instruments and Systems

Position:

Two permanent GPS receivers, part of the SCIGN network, have operated at the site since 1991. Both are on deeply anchored monuments, designated as PIN1 (the primary point), and PIN2 (the secondary point, though with fewer equipment changes). Another site, ROCH, has been run 14 km to the west of the site, also since 1991. For information on these sites, click here.

Mobile VLBI measurements were made at PFO between 1983 and 1990; for the results from these, see the Goddard VLBI page (note that VLBI designates the location as PINFLATS).

Both the PIN1 continuous GPS and VLBI points are part of the International Terrestrial Reference Frame.

Strain:

There are three long-baseline laser strainmeters in operation; all have been operating since the early 1970's. One, the NW-SE, has been fully anchored since 1983; the NS instrument has been partially anchored since 1988; the EW instrument is not anchored. Without anchoring the long-term strain signal is affected by motion of the end piers, though this does not affect the stability over periods of weeks (usually). PFO is also the site of a borehole tensor strainmeter operated by the University of Queensland. The anchoring measurements give many measurements of vertical strain.

From 1971-1991 the site was included within the USGS Geodolite network (Anza net); measurements with a 2-color laser system are still being made by the USGS over the area, as well as periodic GPS measurements.

Tilt:

There are two long-baseline liquid-level tiltmeters, one at an azimuth of 107 degrees and one north-south instrument. Both are anchored, though the optical-fiber anchors used in the NS instrument are less satisfactory.

Several borehole tiltmeter systems, emplaced at depths of 5 to 120 m, are currently in operation. Gravity: There is a gravity pier at which occasional absolute gravity measurements have been made.

Seismic:

The site is part of the IDA/IRIS component of the Global Seismic Network (station code PFO), including VBB sensors in a vault and a borehole (the vault sensors are also part of the TERRASCOPE network, which also includes strong-motion sensors.

Three-component short-period ssensors of the Anza network, which are telemetered to to San Diego in real time.

Borehole geophones, installed at ?? m depth.

Several arrays of closely-spaced seismic sensors have been operated at the site in the past.

In the central trailer, an ink drum recorder (seismograph) running off a 1-Hz Johnson-Matheson vertical seismometer.

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