Continuous GPS

The observation of the present-day deformation of the Earth's surface with high spatial and temporal resolution makes up a major part of IPOC. For this purpose, continuously recording GPS stations were installed in Northern Chile. While seismological data shed light on just short time scales and geological records capture only very long time scales, precise geodetic measurements are capable of acquiring a detailed picture of the entire earthquake cycle. This includes not merely the interseismic compression but also a possible "slow" earthquake that may occur in different depth along the seimogenic zone. Moreover, the redistribution of strain connected with the spatio-temporal clustering of earthquakes can also be observed.
Aim of this component is to provide a continuous stream of GPS time series for joint interpretation with conventional seismic data. Traditional seismic data obtain the surface displacement by a double integration of acceleration measurements (strong motion instruments) or by deconvolution of the instrument response and integration of the velocity measurements (broadband instruments). The accuracy of absolute displacements derived with seismic instruments is poor due to the bandwidth and the dynamic range limits of seismometers. In contrast geodetic methods (GPS instruments) do not have this problem: here the ground displacement is measured directly. Unlike the seismometer, the GPS receiver never saturates, however, seismic measurement provides a powerful constraint on the much noisier GPS measurements.
The combination of high-rate GPS displacements and traditional seismic data will extend the frequency range of surface displacement data that classically produced daily coordinate time series. Contrasting to seismic data, geodetic data requires extensive processing before geophysical interpretations can be made. This includes the production of time series, velocities and strain maps.

For details on sites, data availability and quality follow here.

Installations
Eight of IPOC stations (PB01 – PB08, HMBCX, PSGCX and MNMCX) are equipped with permanent recording GPS receivers (TOPCON GB-1000). They continuously measure at sampling rates of both, 1 second and 30 second. Measurements at 30 second are stored externally - the memory last for at least 16 month. Measurements at 1 second are stored internally on a 'first in first out' basis and are transmitted jointly with seismic data - if data communication is available. 1-second-data are overwritten after 16 days in the absence of a communication link.