Automatic near real-time determination of co-seismic displacements (Ground Tracking System) | GTS

The image shows three simplified diagrams on the determination of displacement vectors on tectonic plates with GNSS-measurements, which allow conclusions on the probability for the generation of a Tsunami. In the first case a tsunami generation may be unlikely or the tsunami may be small, due to a strike slip movement of the tectonic plates with no vertical displacement. A higher probability for a bigger tsunami is given in the other two cases with vertical movements of the plates. In the third case only a part of an involved plate is moved, which corresponds to a smaller Tsunami generation area resulting in a smaller Tsunami.
Figure 1: Simplified representation of the relation between earthquakes, tectonic plates movements, GNSS-based displacement determination and tsunami generation; in case a) the generation of a tsunami is less likely, and if a tsunami does occur it tends to be small (tectonic plates move only laterally to each other, without vertical displacement). In cases b) and c), there is a higher probability of a larger tsunami occurring, since the tectonic plates have also moved vertically in relation to each other. In case c), only part of plate 2 is moved, so the area that would trigger a tsunami is smaller. (C. Falck, GFZ)

The magnitude and location (epicenter and depth) of a strong earthquake can be determined quickly and accurately using seismological methods and technology. Seismology also allows an estimation, but until now, not an accurate determination of possible movements (deformations) of the Earth’s surface in the earthquake’s area. However, knowledge of these co-seismic deformations is particularly relevant for an early warning system to quickly answer the question of whether an earthquake has triggered a tsunami. Help comes from GNSS-instrumentation (GNSS-stations) and a special analysis system which detects and precisely determines ground motions on the Earth’s surface. The GNSS-based determination of ground movements works particularly well near the epicenter, where the magnitude of the ground movements is high. By contrast, seismological sensors near the epicenter can be overloaded, while measurements from sensors further away may only be available after a certain time due to the travel time of the seismic signals. In combination with other techniques (determination of the tsunami-inducing mechanism and the rupture area), the reliability of tsunami early warnings can be significantly improved by using GNSS-based ground motion measurements (Figure 1).

The image shows a simulated displacement vectors as they would have been displayed by the GTS on December 26th 2004 just a few minutes after the Sumatra-Andaman Earthquake. Basis for the simulation are subsequently determined movement parameters for GNSS-station locations, displayed as green symbols, caused by the movements of the tectonic plates. In point of fact, at the time of the strong earthquake and the following tsunami there was no GTS and no useable network of GNSS-stations in Indonesia.
Figure 2: Simulated display of displacement vectors as they would have been displayed by the GTS just a few minutes after the Sumatra-Andaman Earthquake on December 26th 2004. The basis for this is the displacements determined retrospectively at locations with GNSS stations (green symbols) that were caused by the movements of the tectonic plates. At the time of this strong earthquake and the subsequent tsunami in Indonesia, there was neither a GTS nor a useful network of GNSS stations. (C. Falck, GFZ)

A system for an automatic determination of ground motions, respectively co-seismic deformations, was developed by GFZ within the project GITEWS. It is supported by an automatic GNSS processing system for near real-time processing of data continuously measured from GNSS-stations in and around Indonesia. This system, which has been implemented at the Indonesian warning centre as a ground tracking system, is capable of providing initial values (3D displacement vectors) for relevant, i.e. particularly earthquake-prone, locations with GNSS instruments within three minutes of a strong earthquake. These initial values are then updated every two minutes (Figure 2).

Precise information on possible ground movements is also provided for the locations of tide gauge stations, provided that they are equipped with GNSS devices. If the location of a tide gauge station has changed, for example due to an earthquake, the water levels measured there must be corrected or discarded for early warning purposes.

Project partners:

  • BMKG (Meteorology, Climatology and Geophysics Agency, Jakarta, Indonesia)

Time frame:

  • 2005 -2011

Funding:

  • German Federal Ministry for Education and Research (BMBF), Grant 03TSU01

Project related publication:

  • Falck, C., Ramatschi, M., Subarya, C., Bartsch, M., Merx, A., Hoeberechts, J., Schmidt, G. (2010): Near real-time GPS applications for tsunami early warning systems. - Natural Hazards and Earth System Sciences (NHESS), 10, 2, 181-189. https://doi.org/10.5194/nhess-10-181-2010
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