Report of the panel on plate motion and deformation, section 2

Given here is a panel report on the goals and objectives, requirements and recommendations for the investigation of plate motion and deformation. The goals are to refine our knowledge of plate motions, study regional and local deformation, and contribute to the solution of important societal problems. The requirements include basic space-positioning measurements, the use of global and regional data sets obtained with space-based techniques, topographic and geoid data to help characterize the internal processes that shape the planet, gravity data to study the density structure at depth and help determine the driving mechanisms for plate tectonics, and satellite images to map lithology, structure and morphology. The most important recommendation of the panel is for the implementation of a world-wide space-geodetic fiducial network to provide a systematic and uniform measure of global strain

Satellite Laser Ranging in the 1990s: Report of the 1994 Belmont Workshop

An international network of 43 stations in 30 countries routinely collects satellite ranging data which is used to study the solid Earth and its interactions with the oceans, atmosphere, and Moon. Data products include centimeter accuracy site positions on a global scale, tectonic plate motions, regional crustal deformation, long wavelength gravity field and geoid, polar motion, and variations in the Earth's spin rate. By calibrating and providing precise orbits for spaceborne microwave altimeters, satellite laser ranging also enables global measurement of sea and ice surface topography, mean sea level, global ocean circulation, and short wavelength gravity fields and marine geoids. It provides tests of general relativity and a means or subnanosecond time transfer. This workshop was convened to define future roles and directions in satellite laser ranging

International global network of fiducial stations: Scientific and implementation issues

In this report, an ad hoc panel of the National Research Council's Committee on Geodesy, Board of Earth Sciences and Resources (1) evaluates the scientific importance of a global network of fiducial sites, monitored very precisely, using a combination of surface- and space-geodetic techniques; (2) examines strategies for implementing and operating such a network; and (3) assesses whether such a network would provide a suitable global infrastructure for geodetic and other geophysical systems of the next century. The panel concludes that a global network of fiducial sites would be a valuable tool for addressing global change issues and play a critical role in providing a reference frame for scientific Earth missions. The panel suggests that existing global networks be integrated and anticipates that such a network would grow from about 30 to the ultimate size of about 200 fiducial sites. It is noted that such a global network will provide a long-term infrastructure for geodetic and geophysical studies. The panel expects that these fiducial sites would evolve into terrestrial observatories or laboratories that would permit more comprehensive studies of the Earth than those now possible

Solid Earth science in the 1990s. Volume 3: Measurement techniques and technology

Reports are contained from the NASA Workshop on Solid Earth Science in the 1990s. The techniques and technologies needed to address the program objectives are discussed. The Measurement Technique and Technology Panel identified (1) candidate measurement systems for each of the measurements required for the Solid Earth Science Program that would fall under the NASA purview; (2) the capabilities and limitations of each technique; and (3) the developments necessary for each technique to meet the science panel requirements. In nearly all cases, current technology or a development path with existing technology was identified as capable of meeting the requirements of the science panels. These technologies and development paths are discussed

Precision GPS ephemerides and baselines

The required knowledge of the Global Positioning System (GPS) satellite position accuracy can vary depending on a particular application. Application to relative positioning of receiver locations on the ground to infer Earth's tectonic plate motion requires the most accurate knowledge of the GPS satellite orbits. Research directed towards improving and evaluating the accuracy of GPS satellite orbits was conducted at the University of Texas Center for Space Research (CSR). Understanding and modeling the forces acting on the satellites was a major focus of the research. Other aspects of orbit determination, such as the reference frame, time system, measurement modeling, and parameterization, were also investigated. Gravitational forces were modeled by truncated versions of extant gravity fields such as, Goddard Earth Model (GEM-L2), GEM-T1, TEG-2, and third body perturbations due to the Sun and Moon. Nongravitational forces considered were the solar radiation pressure, and perturbations due to thermal venting and thermal imbalance. At the GPS satellite orbit accuracy level required for crustal dynamic applications, models for the nongravitational perturbation play a critical role, since the gravitational forces are well understood and are modeled adequately for GPS satellite orbits

NASA Geodynamics Program

Activities and achievements for the period of May 1983 to May 1984 for the NASA geodynamics program are summarized. Abstracts of papers presented at the Conference are inlcuded. Current publications associated with the NASA Geodynamics Program are listed

NASA geodynamics program

The status, progress, and future plans of the program are given. A list of publications of research results supported by the program is included

Solid earth science in the 1990s. Volume 2: Panel reports

This is the second volume of a three-volume report. Volume 2, Panel Reports, outlines a plan for solid Earth science research for the next decade. The science panels addressed the following fields: plate motion and deformation, lithospheric structure and evolution, volcanology, Earth structure and dynamics, Earth rotation and reference frames, and geopotential fields

Estimation of Very long Base Lines by GPS -Geodesy for Indian Plate Kinematic Studies

Under the Indo-German Collaborative, Bilateral Exchange Programme, a Project to study the ongoing Indian plate motion has been initiated between the National Geophysical Research Institute (NGRI, CSIR) and the Geodetic Institute of the University of Bonn, Germany. In this project, a permanent tracking/reference station was established at NGRI, Hyderabad by installing a Turbo Rogue GPS -SNR 8000 Receiver and the corresponding data taking and storing facilities. The GPS measurements in the IGS Global Network are meant to monitor intercontinental and intra plate crustal motion and to determine velocity vectors, eventually to derive information concerning the stresses in the Earth's crust, in particular in the Southern Himalayas. The GPS-campaigns used in the data analysis cover a time period of approximately 3 years, during which observations were taken at least twice a week. The data transfer had to be carried out off-line by mailing diskettes, which meant that the analysis had to be performed in a post-operative way. The adopted strategy was to retrieve the data from a selected set of IGS-permanent stations on the Eurasian continent as well as in Australia and South Africa. The refined GPS data processing and analysis by using Bernese software were carried out at the Geodetic Institute. The first data set up to Jan. 1997 was prepared and a Global Network solution was carried out to estimate Very Long baselines between Hyderabad and other IGS selected stations. Subsequently, the processing of 300 epochs was carried out in a semi automatic way using the Bernese Processing Engine (BPE). Special care was taken to eliminate incomplete or otherwise defective data sets before the final run. Two different types of solutions were performed, the first one by an epoch by epoch solution which shows the time evolution of coordinates and baseline lengths, and the second one for simultaneous coordinate and velocity vector estimation. The first solution was helpful to visualize the repeatability of the results for each epoch and to derive realistic error estimates for the site motions. In chapter 9, (Results and Discussion), we discuss the significance of the most important results achieved so far. Our processing of 3 year's data from Sept. 95 to Sept. 98 by global network solution involves estimation of baselines of 500 km (Hyderabad-Bangalore) to 7000 km (Hyderabad-Yaragadee) lengths. One important result is that the baselines up to 6000km yield quite reliable repeatabilities within 2cm. Thus, the baseline between Hyderabad and Irkutzk (Russia) is shortening at a rate of 5cm/year, with a high level of significance. The baseline between Hyderabad and Bangalore shows a compression in NNE-SSW direction over the past 3 years, yielding a first constraint for the inner plate stability of the Indian plate of 2mm/yr ± 1mm/yr. This information could gain importance in respect to the inner plate seismicity (cf. recent Latur earthquake). On the other hand, the baselines beyond 6000km suffer from reduced simultaneous visibility and, correspondingly, suffer substantial accuracy losses. In summary, the most significant result of our analysis is that the baseline vectors from Hyderabad to other stations beyond Himalaya are shortening. This phenomenon is fitting into the basic theory of Indian plate motion. Velocity vectors thus computed for all the stations used in the analysis are comparable with the NUVEL -1A global plate model. This means that a first breakthrough in determining plate motion rates for the Indian Subkontinent has been achieved.Bestimmung Langer Basislinien mit GPS für Untersuchungen zur indischen Plattenkinematik Ziel des dieser Arbeit zugrundeliegenden Projektes im Rahmen einer deutsch-indischen Kooperation war die Messung von geodätischen Basislinien mit Hilfe von GPS zwischen dem indischen Subkontinent und den benachbarten Kontinenten zur Untersuchung der plattentektonischen Erdkrustenbewegungen im indo-eurasischen Raum. Die Belange Indiens standen bei diesem Projekt im Vordergrund, da bekanntlich die Kollision des indischen Subkontinentes mit Eurasien, die vor ca. 40 bis 60 Millionen Jahren begann, auch gegenwätig noch zu Erdbeben mit z.T. katastrophalen Folgen führt. Die Ziele der aktuellen geodätischen Meßprogramme sind gerichtet auf die heutigen Bewegungsparameter, um daraus Schlüsse über die aktuellen Spannungen in der Erdkruste, vor allem im Bereich des südlichen Himalaya, ziehen zu können. Die GPS-Meßkampagnen erstrecken sich über einen Zeitraum von ca. 3 Jahren, wobei in Hyderabad in Durchschnitt an zwei Tagen pro Woche beobachtet wurde. Bei der Station Hyderabad bestand zunächst die Absicht, alle Meßdaten sofort, d.h. quasi on-line, in das IGS Auswertezentrum einfließen zu lassen. Da dies jedoch aufgrund der besonderen technischen Einschränkungen in Hyderabad (kein ftp-link) nicht möglich war, mußte eine Strategie der nachträglichen Einbeziehung der Station in das IGS-Weltnetz entwickelt werden. Diese Strategie besteht in der Beschaffung von Daten der Stationen eines speziell ausgewählten Sub-Netzes und der gemeinsamen Auswertung dieser Stationen im Sub-Netz. Diese Auswertung umfaßt einen Datensatz, der sich über ca. drei Jahre erstrekt und neben Hyderabad 8 weitere IGS-Stationen enthält. Die Auswertung geschah in zwei Etappen, einer ersten mit "manueller" Bearbeitung ausgewählter Datensätze die jeweils einen Tag umfassten und einer zweiten mit weitgehend automatischem Ablauf, bei der alle vorhandenen Epochen bearbeitet wurden. Die in Kap. 9 (Results and Discussion) vorgestellten Ergebnisse sind in vieler Hinsicht hochinteressant. Zunächst ist an den zeitlichen Änderungen der Basislängen (diese sind am wenigsten von Rotationen der Bezugssysteme betroffen) gut zu erkennen, daß bei Basislängen bis zu etwa 6000km eine relativ gute Wiederholungsgenauigkeit erzielt werden kann und z.T. hochsignifikante Änderungsraten erhalten werden. Die Ergebnisse der Meßreihe von knapp drei Jahren Länge zeigt bereits eine eindeutige Tendenz der Bewegung in nordöstliche Richtung von ca 5 cm/Jahr. Ein weiteres beachtliches Ergebnis stellt die kleine aber merkliche Verkürzung der Distanz zwischen Hyderabad und Bangalore dar, was auf eine Kompression der indischen Platte in Richtung NNO-SSW hinweist. Diese Information kann große Bedeutung erlangen im Zusammenhang mit den Erdbeben im inneren Bereich der indischen Platte (z.B. Latur). Bei Basislängen über 6000km verschlechtert sich diese Genauigkeit dramatisch bis zu einem Grade, wo keine signifikante Raten mehr bestimmbar sind (Basislinien Hyderabad-Yaragadee und Hyderabad-Hartebeesthoek). Wesentliche Faktoren sind hier natürlich die geringe simultane Sichtbarkeit der GPS-Satelliten sowie im Falle von Hartebeesthoek, Südafrika die großen Datenausfälle. Zusammenfassend läßt sich sagen, daß es gelungen ist, mit den drei Jahre umfassenden GPS-Daten der Station Hyderabad die indische Plattenbewegung relativ zur eurasischen Platte nachzuweisen. Gleichzeitig wurden realistische Genauigkeitsschätzungen für die quasi-permanenten GPS-Messungen im globalen IGS-Rahmen bestimmt und die Signifikanz der ermittelten Bewegungsraten nachgewiesen. Damit ist ein Durchbruch zu einer erstmaligen umfassenden Bestimmung der Plattenbewegungsrate des indischen Subkontinents in Relation zu Eurasien gelungen