PFO Geophysical Sensors
Deformation Monitoring: Instruments and Systems
Two permanent GPS receivers,
part of the
SCIGN network, have operated at the site since
Both are on deeply anchored monuments, designated as
PIN1 (the primary point), and
PIN2 (the secondary point, though with fewer equipment changes).
has been run 14 km to the west of the site, also since 1991.
For information on these sites, click
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.
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.
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
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.
There is a gravity pier at which occasional
measurements have been made.
The site is part of the
IDA/IRIS component of the
Global Seismic Network
including VBB sensors in a vault and a
(the vault sensors are also part of the
TERRASCOPE network, which also includes
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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