Global coseismic deformations, GNSS time series analysis, and earthquake scaling laws
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Abstract We investigate how two decades of coseismic deformations affect time series of GPS station coordinates (Global Navigation Satellite System) and what constraints geodetic observations give on earthquake scaling laws. We developed a simple but rapid model for coseismic deformations, assuming different earthquake scaling relations, that we systematically applied on earthquakes with magnitude larger than 4. We found that coseismic displacements accumulated during the last two decades can be larger than 10 m locally and that the cumulative displacement is not only due to large earthquakes but also to the accumulation of many small motions induced by smaller earthquakes. Then, investigating a global network of GPS stations, we demonstrate that a systematic global modeling of coseismic deformations helps greatly to detect discontinuities in GPS coordinate time series, which are still today one of the major sources of error in terrestrial reference frame construction (e.g., the International Terrestrial Reference Frame). We show that numerous discontinuities induced by earthquakes are too small to be visually detected because of seasonal variations and GPS noise that disturb their identification. However, not taking these discontinuities into account has a large impact on the station velocity estimation, considering today's precision requirements. Finally, six groups of earthquake scaling laws were tested. Comparisons with our GPS time series analysis on dedicated earthquakes give insights on the consistency of these scaling laws with geodetic observations and Okada coseismic approach.Keywords:
Classification of discontinuities
Coordinate time
Trilateration
Frame of reference
Realization (probability)
Reference model
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Epoch (astronomy)
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Coordinate time
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One of the fundamental goals of geodesy is to precisely define positions of points on the surface of the Earth, so it is necessary to establish a well-defined geodetic datum for geodetic measurements and positioning computations. Recently, a set of the coordinates established using GPS and referred to an international terrestrial reference frame could be used as a three-dimensional geocentric reference system for a country. Such a geocentric reference system, based on this modern concept, was carried out in Taiwan in 1997 and realised in 1998. Besides the advantages of using GPS to effectively establish this new national reference system, the coordinate qualities of these well-distributed and well-defined GPS control stations will also benefit from the convenient implementation of the maintenance of the coordinate system.
Geocentric model
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