Tectonic Geodesy
Why study this topic? The challenges
Space geodesy technologies, such as GNSS, are valuable tools for monitoring the deformation of the Earth’s crust and its surface, especially along areas of active tectonics. The high accuracy of the measurements (millimeter scale) and the capabilities of continuous data flow, have revolutionized the understanding of the physical processes that precede, take place during or follow strong earthquakes. For example, GNSS data analysis can reveal which sections of the plate-interface zone are accommodating high strains, decipher the rupture process of strong earthquakes and assess transient postseismic deformation that frequently occurs after large-magnitude earthquakes. During the last two decades, usage of high-rate GNSS data has become very common, given that, contrary to seismometers and strong motion sensors, GNSS stations can directly provide displacement waveforms without saturation or drift.
An important discovery due to GNSS data over the last 20 years or so, is the detection of silent earthquakes (or slow-slip events). These earthquakes, like typical earthquakes, release energy in response to the movement of tectonic plates but over a period of time ranging from a few days to months. In several cases it has been observed that silent earthquakes precede large earthquakes, often triggering them. Another important finding using GNSS data is that the locus of a future earthquake, its recurrence and size, largely depends on the mechanical properties (e.g. friction) of the materials that characterize either a large active fault or a plate-interface zone at different depths. Given that space geodesy technologies such as GNSS, are a valuable tool in geosciences and because Greece is located on an active subduction zone, the Institute of Geodynamics has its own permanent GNSS network. It consists of 28 continuously operating GNSS stations with a sampling interval ranging from 0.2 sec to 1 sec. These stations transmit data in real time to the facilities of the Institute of Geodynamics and are freely available to the science community.
Our key research activities
- Studying the active crustal deformation processes and geodynamics of Greece
- Rupture modeling of large earthquakes
- Calculation of slip rates and distribution of elastic stresses along active faults
- Quantification and comparison between seismic and geodetic moment rates
- Geodetic constraints on seismic hazard assessment
- Modeling of coseismic and postseismic deformation
- Time series analysis of GNSS measurements
- Utilization of high-rate GNSS data for capturing the static and dynamic displacements during earthquakes
Our operational activities, infrastructure and services
- Development and maintenance of the permanent GNSS network of NOA
- Freely available daily RINEX files (30 sec) of NOANET stations along with additional stations belonging to other institutions that trust NOA to manage their data (http://geodesy.gein.noa.gr:8000/nginfo/data/)
- Freely available high-rate GNSS data after the occurrence of large earthquakes
- Management and operation of the EPOS-GNSS national node (http://geodesy.gein.noa.gr:8000/nginfo/data/)
- Calculation and analysis of GNSS station position time series
- Real-time streaming of correction messages (e.g. RTCM) via the internet for high-precision applications in the fields of topography, construction of technical works, etc.