Important Geodetic Station Reinstalled for Earthquake Monitoring at the University of Concepción

On November 21, 2019, the GNSS (Global Navigation Satellite System) observation station was re-installed at the former TIGO (Transportable Integrated Geodesical Observatory, currently located in Argentina (AGGO) see http://www.aggo-conicet.gob.ar) integrated Geodetic station, on the premises of the University of Concepción. This was a joint effort between the University of Concepción (UdeC), the National Seismological Center (CSN) and the GEOCOM company, Trimble's representative in Chile, to continuously monitor the deformation to which this area is subjected.

GNSS Station

This station was initially installed in 2002, marking the beginning of operations of the German Geodetic Observatory TIGO, and operated until April 2015, after which it was moved to La Plata, Argentina. A GNSS system allows the reception of signals from different satellite constellations (the most well-known being the GPS system) to obtain the station's position with great accuracy, which provides important information for understanding processes related to earthquakes and Earth deformation. Hayo Hase, Director of the TIGO observatory, said at the time: "At the end of TIGO project operations, together with BKG, we left the GNSS structure available at this point to continue studies for science and humanity," an objective that is now being realized with the re-activation of this site. Thus, today we can have a record of how the position of this site has varied from 2002 to the present, providing unique information to quantify the deformation associated with the 2010 earthquake.

As one of the geodetic techniques for observing geocentric position using artificial satellites (GNSS), TIGO installed several stations in the Concepción area, the main one being located at UdeC, which is designated within the global network as CONZ 41719M002, where there are also gravity measurements, SLR (Satellite Laser Ranging) and VLBI (Very Long Baseline Interferometry). Figure 1 shows the antenna installation.

Observation

The station has a multi-frequency and multi-constellation receiver that simultaneously observes GPS, GLONASS, GALILEO, and BEIDOU, providing a daily average of data from 35 satellites. This is one of the new requirements of the IGS (International GNSS Service) for global network stations and is one of the attributes of this site. Figure 2 shows the different constellations available.

Seismic Cycle

The largest earthquakes on the planet occur in subduction zones, where an oceanic tectonic plate slides under a continental plate, as is the case in Chile. The seismic cycle is a repetitive process during which energy accumulates for decades to centuries (interseismic phase) and is suddenly released by earthquakes (coseismic phase). In the years following the release, a postseismic phase occurs where part of the stresses induced by the earthquake continue to gradually accommodate. Recent studies indicate that movement patterns in the crust during the accumulation period allow for the identification of areas where energy accumulation is greater, which are generally the areas where more energy is released in a large earthquake.

Through GNSS observations, we can continuously estimate the geocentric position of a station. This position is compared daily with respect to the origin of the measurements. With this, we obtain the variation in the station's position as a function of time. This variation in position, or displacement, is directly linked to the surface deformation caused by the interaction between the Nazca and South American plates and allows us to monitor changes in deformation during the different phases of the seismic cycle.

The CONZ station is one of the few GNSS stations in Chile that recorded crustal deformation before, during, and after the 2010 earthquake, allowing observation of the seismic cycle in its three stages: interseismic, coseismic, and postseismic. Figure 3 shows these three parts of the seismic cycle, including recent estimates.

During the 2010 earthquake, the CONZ station shifted almost 3 meters to the west, 60 cm to the south, and experienced an approximate 5 cm subsidence. After the earthquake, the magnitude of post-seismic deformation could be recorded, which decays after the earthquake, a process that lasts several years until inter-seismic deformation predominates again. Thanks to the reinstallation of this station, it will be possible to identify when this area will again enter an inter-seismic energy accumulation phase, thus evidencing the changes in crustal displacements that occur in this process.

Data Distribution

The generated data will be published on the CSN website at http://gps.csn.uchile.cl, and these observations will also contribute to the global IGS network.

GEOCOM GNSS Network

For its part, CONZ will integrate the GEOCOM GNSS Network by emitting a continuous stream of raw GNSS observations that are being processed to send multi-station and single-station differential corrections for RTK observations using the NTRIP Caster that GEOCOM has maintained for over a decade.

By Juan Carlos Báez | Marcos Moreno | Ariel Silva | Héctor Contreras