Erweiterte Modellbildung zur Bestimmung von Positionszeitreihen global verteilter GPS-Stationen

Eine Vielzahl geophysikalischer Prozesse im System Erde gehen mit Massenverlagerungen einher. Änderungen in der Massenverteilung führen zu beobachtbaren Änderungen im Schwerefeld und Rotationsverhalten der Erde sowie zu einer Deformation der Erdkruste. Die messtechnische Erfassung dieser Größen erlaubt einen Rückschluss auf die beteiligten Massentransportprozesse und stellt damit eine Grundvoraussetzung für die Erdsystemforschung dar. Satellitengestützte Navigationssysteme wie z.B. das Global Positioning System (GPS) spielen in diesem Zusammenhang eine zentrale Rolle, denn sie ermöglichen eine präzise Positionsbestimmung auf globaler Ebene. Für die Bestimmung eines terrestrischen Referenzrahmens werden üblicherweise mittlere Koordinaten zu einer Referenzepoche sowie zugehörige lineare Änderungen mit der Zeit angenommen. Bei diesem Konzept führen alle nichtlinearen Stationsbewegungen, deren Effekte im Rahmen der Beobachtungsmodellierung nicht reduziert werden, zu Abweichungen gegenüber dem linearen Bewegungsmodell. Diese Abweichungen haben Einfluss auf die Positionszeitreihen der in Betracht gezogenen Stationen und erlauben einen Rückschluss auf die auflastinduzierenden Änderungen in der Massenverteilung. Die Bestimmung von Stationspositionszeitreihen mittels GPS bildet den Kern der vorliegenden Arbeit. Die Arbeit baut inhaltlich auf vier Publikationen auf, die sich unterschiedlichen Fragestellungen in Bezug auf die Positionsbestimmung mittels GPS widmen. Eine zusammenfassende Diskussion gibt einen Überblick über Massenvariationen im System Erde und auflastinduzierte Krustendeformation. Spezielle Aspekte in Bezug auf eine konsistente Modellierung von Massenvariationen und daraus abgeleiteter Deformationsanteile werden hier dargelegt. Praktische Untersuchungen erfolgen zu Änderungen in der Massenverteilung aufgrund von atmosphärischen Druckvariationen, Ozeanzirkulation und hydrologisch bedingten Wasserspeicheränderungen im Bereich der Kontinente. Der Einfluss ionosphärischer Terme höherer Ordnung auf GPS-Parameterschätzwerte wird untersucht. Diese Analyse erfolgt vor dem Hintergrund, dass bei der vermittelnden Ausgleichung generell auch systematische Effekte, die für sich genommen keine Stationspositionsänderung verursachen, trotzdem Einfluss auf geschätzte Stationskoordinaten haben. Die Sensitivität der GPS-Beobachtungen gegenüber der Auflastdeformation wird genutzt, modellierte Massenvariationen zu validieren. Mittels gegebener Massenvariationen werden Deformationszeitreihen abgeleitet. Für diese Zeitreihen werden im Zuge der Parameterschätzung Skalierungsfaktoren bestimmt und als Indikator für die Übereinstimmung zwischen modellierter und beobachteter Deformation gewertet. Änderungen der Massenverteilung im System Erde zeichnen sich unter anderem durch eine Schwerpunktverlagerung gegenüber der festen Erde aus. Wird die Massenverteilung durch eine sphärisch-harmonische Reihenentwicklung dargestellt, so sind die Terme ersten Grades mit der Schwerpunktverlagerung verknüpft. Die Grad-1-Anteile der Massenvariation können mittels satellitengravimetrischer Beobachtungen prinzipiell nicht bestimmt werden. Sie lassen sich aber mit Hilfe der GPS-Beobachtungen aus dem zugehörigen Deformationsanteil ermitteln. Der Einfluss systematischer Beobachtungsfehler auf diesem Inversionsansatz wird untersucht. Bei der Bestimmung globaler GPS-Lösungen werden die in den Beobachtungen enthaltenen Auflasteffektes prinzipiell auf alle simultan geschätzten Parameter abgebildet. Diese systematische Verfälschung erschwert die geophysikalische Interpretation von Stationspositionszeitreihen. Ein integrierter Ansatz wird entwickelt, um bestehende Vorinformation über verschiedene Massenvariationsprozesse bestmöglich einzubeziehen

GNSS - ein Werkzeug für globale und regionale geophysikalische Forschung

Beitrag zu GNSS anläßlich einer Festschrift zum 65. Geburtstag von Prof. Reinhard Dietrich

Do crustal deformations observed by GPS in Tierra del Fuego (Argentina) reflect glacial-isostatic adjustment?

Vertical site velocities determined by geodetic GPS observations in the Lago Fagnano area, Tierra del Fuego main island, are interpreted with respect to their potential relation with the glacial-isostatic crustal response to ice mass changes. The spatial pattern of the uplift rates, in combination with the horizontal crustal deformation pattern, point towards a fault-tectonic rather than glacial-isostatic origin of the determined vertical crustal deformations. This implies rather small GIA effects pointing towards relatively small Holocene ice-mass changes in Tierra del Fuego. However, these findings are considered to be preliminary. They should be confirmed by additional observations covering an extended area with GPS sites.Facultad de Ciencias Astronómicas y Geofísica

Present-day crustal deformation along the Magallanes-Fagnano Fault System in Tierra del Fuego from repeated GPS observations

The present-day deformation of the earth crust in the Argentine part of Tierra del Fuego main island (southernmost South America) is here investigated based on repeated geodetic GPS observations. The island is traversed by the active transform boundary between the South American and Scotia tectonic plates, represented by the Magallanes-Fagnano fault system. Since 1993 a regional network comprising to date 29 GPS sites has been observed almost every year. The complete set of accumulated observations was processed using the Bernese GPS software and state-of-the-art processing strategies and models. The utilization of homogeneous GPS products resulting from a reprocessing of the global IGS network warrants a stable realization of a global reference frame. For each GPS site 3-D positions and linear velocities with error estimates were obtained. A strain analysis of the horizontal velocity components revealed the zones of major deformation activity. A 30-km-wide deformation belt centred on the main trace of the fault system was identified. This belt is bordered to the north (South America) and south (Scotia) by geodynamically stable zones, which move horizontally with a relative average velocity of 4.4 ± 0.6 (east) and -0.3 ± 0.4 (north) mm a-1. Within the deformation belt a maximum strain rate in the order of 0.25 μstrain per year has been detected. A pronounced change in the deformation style from transtension (east) to transpression (west) is observed. The area of predominating shortening of the crust coincides with a local rotation minimum and relative uplift. Throughout the period covered by the GPS observations the displacements and deformations occurred to be linear with time.Facultad de Ciencias Astronómicas y Geofísica

Present-day crustal deformation along the Magallanes-Fagnano Fault System in Tierra del Fuego from repeated GPS observations

The present-day deformation of the earth crust in the Argentine part of Tierra del Fuego main island (southernmost South America) is here investigated based on repeated geodetic GPS observations. The island is traversed by the active transform boundary between the South American and Scotia tectonic plates, represented by the Magallanes-Fagnano fault system. Since 1993 a regional network comprising to date 29 GPS sites has been observed almost every year. The complete set of accumulated observations was processed using the Bernese GPS software and state-of-the-art processing strategies and models. The utilization of homogeneous GPS products resulting from a reprocessing of the global IGS network warrants a stable realization of a global reference frame. For each GPS site 3-D positions and linear velocities with error estimates were obtained. A strain analysis of the horizontal velocity components revealed the zones of major deformation activity. A 30-km-wide deformation belt centred on the main trace of the fault system was identified. This belt is bordered to the north (South America) and south (Scotia) by geodynamically stable zones, which move horizontally with a relative average velocity of 4.4 ± 0.6 (east) and -0.3 ± 0.4 (north) mm a-1. Within the deformation belt a maximum strain rate in the order of 0.25 μstrain per year has been detected. A pronounced change in the deformation style from transtension (east) to transpression (west) is observed. The area of predominating shortening of the crust coincides with a local rotation minimum and relative uplift. Throughout the period covered by the GPS observations the displacements and deformations occurred to be linear with time.Facultad de Ciencias Astronómicas y Geofísica

Lake-level variations of Lago Fagnano, Tierra del Fuego: observations, modelling and interpretation

The lake-level variations of Lago Fagnano, the largest lake in Tierra del Fuego, southernmost South America, on time scales from a few minutes to three years are investigated using a geodetic approach and applying the tools of time series analysis. Based on pressure tide gauge records at three locations in the lake precise lake-level time series are derived. The analysis of the observed variations in space, time and frequency domain leads to the separation of the principal force-response mechanisms. We show that the lake-level variations in Lago Fagnano can be described essentially as a combination of lake-level shift and tilt and of surface seiches. Regarding the lake-level response to air-pressure forcing, a significant departure from the inverse barometer model is found. Surface seiches dynamics are particularly intensive in Lago Fagnano pointing towards exceptionally low dissipative friction. An undisturbed series of seiches lasting eleven days is presented; and at least eleven longitudinal modes are identified. Based on the characterisation of the main contributions in space and time as well as their relation to the driving forces, a model for the transfer of the lake-level variations at a reference point to an arbitrary location in the lake with an accuracy of 1 cm is developed.Facultad de Ciencias Astronómicas y Geofísica

Anomalous ocean load tide signal observed in lake-level variations in Tierra del Fuego

We demonstrate the application of a 100 km long lake as a sensor for studying the tidal effects on Tierra del Fuego main island. The lake-level variations observed in Lago Fagnano reflect both the direct response to the tidal potential and the indirect effect of the ocean tidal loading. Modeling both contributions explains the observed tidal signal in the lake to about 70%. Underestimated model load tide amplitudes are found to be probably responsible for the remaining difference. We interpret this discrepancy as a hint for regional elastic lithosphere properties differing substantially from those represented by currently available global models.Facultad de Ciencias Astronómicas y Geofísica

Do crustal deformations observed by GPS in Tierra del Fuego (Argentina) reflect glacial-isostatic adjustment?

Vertical site velocities determined by geodetic GPS observations in the Lago Fagnano area, Tierra del Fuego main island, are interpreted with respect to their potential relation with the glacial-isostatic crustal response to ice mass changes. The spatial pattern of the uplift rates, in combination with the horizontal crustal deformation pattern, point towards a fault-tectonic rather than glacial-isostatic origin of the determined vertical crustal deformations. This implies rather small GIA effects pointing towards relatively small Holocene ice-mass changes in Tierra del Fuego. However, these findings are considered to be preliminary. They should be confirmed by additional observations covering an extended area with GPS sites.Facultad de Ciencias Astronómicas y Geofísica

Present-day crustal deformation along the Magallanes-Fagnano Fault System in Tierra del Fuego from repeated GPS observations

The present-day deformation of the earth crust in the Argentine part of Tierra del Fuego main island (southernmost South America) is here investigated based on repeated geodetic GPS observations. The island is traversed by the active transform boundary between the South American and Scotia tectonic plates, represented by the Magallanes-Fagnano fault system. Since 1993 a regional network comprising to date 29 GPS sites has been observed almost every year. The complete set of accumulated observations was processed using the Bernese GPS software and state-of-the-art processing strategies and models. The utilization of homogeneous GPS products resulting from a reprocessing of the global IGS network warrants a stable realization of a global reference frame. For each GPS site 3-D positions and linear velocities with error estimates were obtained. A strain analysis of the horizontal velocity components revealed the zones of major deformation activity. A 30-km-wide deformation belt centred on the main trace of the fault system was identified. This belt is bordered to the north (South America) and south (Scotia) by geodynamically stable zones, which move horizontally with a relative average velocity of 4.4 ± 0.6 (east) and -0.3 ± 0.4 (north) mm a-1. Within the deformation belt a maximum strain rate in the order of 0.25 μstrain per year has been detected. A pronounced change in the deformation style from transtension (east) to transpression (west) is observed. The area of predominating shortening of the crust coincides with a local rotation minimum and relative uplift. Throughout the period covered by the GPS observations the displacements and deformations occurred to be linear with time.Facultad de Ciencias Astronómicas y Geofísica

Lake-level variations of Lago Fagnano, Tierra del Fuego: observations, modelling and interpretation

The lake-level variations of Lago Fagnano, the largest lake in Tierra del Fuego, southernmost South America, on time scales from a few minutes to three years are investigated using a geodetic approach and applying the tools of time series analysis. Based on pressure tide gauge records at three locations in the lake precise lake-level time series are derived. The analysis of the observed variations in space, time and frequency domain leads to the separation of the principal force-response mechanisms. We show that the lake-level variations in Lago Fagnano can be described essentially as a combination of lake-level shift and tilt and of surface seiches. Regarding the lake-level response to air-pressure forcing, a significant departure from the inverse barometer model is found. Surface seiches dynamics are particularly intensive in Lago Fagnano pointing towards exceptionally low dissipative friction. An undisturbed series of seiches lasting eleven days is presented; and at least eleven longitudinal modes are identified. Based on the characterisation of the main contributions in space and time as well as their relation to the driving forces, a model for the transfer of the lake-level variations at a reference point to an arbitrary location in the lake with an accuracy of 1 cm is developed.Facultad de Ciencias Astronómicas y Geofísica