The Mark 3 very long baseline interferometer system was used in monitoring the following geodetic phenomena: the regional deformation and strain accumulation related to large earthquakes in the plate boundary region of the western United States; contemporary relative plate tectonic motions of the North American, Pacific, South American, Eurasian, and Australian Plates; the internal deformation of continental and oceanic lithospheric plates with particular emphasis on North America and the Pacific; the rotational dynamics of the Earth and their possible correlation to earthquakes, plate motions, and other geophysical phenomena; and motions and deformation occurring in regions of high earthquake activity

Coates, R.

English

NASA Technical Reports Server

NASA GEODETIC APPLICATIONS OF THE MARK III VLBI SYSTEM 
Robert Coates 
NASA Goddard Space Flight Center 
ABSTRAa 
For the past 5 years, NASA has been developing the Mark III Very Long Baseline Interferometer 
(VLBI) System for very high accuracy geodetic applications, such as measurements of the contem- 
porary tectonic plate motions, large-scale plate stabilities, regional fault motions, Earth rotation 
changes, and polar motion. Initial deployments at fixed observatories in United States have estab- 
lished an initial reference grid for determinations of stability of the North American Plate and for 
measurements of polar motion and UT 1. Cooperating stations with new Mark III systems at Onsala, 
Sweden, and Effelsberg, Germany, observing with the U.S. stations, are to measure the relative plate 
motion between the North American and the Eurasian Plates. NASA plans to involve additional 
cooperating institutions throughout the world to develop a global VLBI network for plate motion 
determinations. NASA is developing mobile VLBI systems utilizing the Mark III for measurements 
of regional fault motions and crustal distortions. Initial deployments will be in the fault regions in 
western United States. Discussions have been initiated with foreign organizations regarding cooper- 
ative programs for measurement of fault motions in other active regions of the world. 
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426 RADIO INTERFEROMETRY 
INTRODUCTION 
In the 1960’s, NASA started supporting the development of the two space techniques, very long 
baseline interferometry (VLBI) and space laser ranging, for geodetic applications. NASA’s interest 
was in the development of space technology that would permit the measurement of the dynamic 
motions of the Earth’s crust that are believed to be the causes of earthquakes. The global distribu- 
tion of large earthquakes shows that the earthquakes are most prevalent along the edges of the 
major tectonic plates. The relative motions between these plates causes severe distortions of the 
boundaries between the plates. This results in earthquakes. Thus, it is felt that the measurement of 
the relative plate motions and the crustal distortions along the boundaries of the plates will contri- 
bute significantly to a much better understanding of the processes which lead to earthquakes. 
NASA has concentrated on the development of the VLBI and space laser ranging because these two 
space techniques offer the potential for making measurements over very long distances with accur- 
acies of better than a part in 108. The measurements with these techniques can be made over water 
and rough terrain. Thus, they seem to be ideal techniques for the measurement of plate motion, 
regional deformation, and other dynamic motions of the earth. 
CRUSTAL DYNAMICS PROJECT 
A coordinated federal program for the application of this space technology to crustal dynamics and 
earthquake research has been formulated. * The participating agencies are the National Aeronautics 
and Space Administration (NASA), National Ocean and Atmospheric Administration (NOAA), the 
United States Geological Survey (USGS), the National Science Foundation, and the Department of 
Defense (DOD). All of these agencies have a role in earth dynamics and are interested in applying 
VLBI and lasers to their particular area of activity. NASA has been leading the technology develop- 
ment, and is the focal point for the initial phase of implementation of the VLBI and lasers for 
crustal dynamics. The NOAA National Geodetic Survey (NGS) is initiating a program to implement 
an operational VLBI system for polar motion and UT1 measurements. In addition, they plan to 
implement mobile VLBI for very high accuracy geodetic surveys in North America. The United 
States Geological Survey and the National Science Foundation have prime responsibility for earth- 
quake research investigations. Their interest in utilizing VLBI is to obtain new and significant mea- 
surements and interpretations of the earthquake phenomena. The Department of Defense has a 
responsibility for high accuracy geodetic survey and mapping, as well as operational UT and polar 
motion determination. 
The success of the NASA developments of VLBI and space laser ranging has prompted NASA to 
establish a Crustal Dynamics Project for the application of these space techniques to the study of the 
earth-dynamics motions as related to earthquakes. Both the Goddard Space Flight Center and the 
Jet Propulsion Laboratory are involved in the project. Goddard is responsible for the management 
*National Aeronautics and Space Administration, National Oceanic and Atmospheric Administration, U.S. Geological Survey, 
National Science Foundation, and Defense Mapping Agency, “The Coordinated Federal Program for the Application of Space 
Technology to Crustal Dynamics and Earthquake Research,” November 1978. 
ADHERENCE AND COHERENCE IN NETWORKS AND PLANS 427 
of the project, the science coordination and management, the VLBI technology developments, the 
implementation and operations of fixed VLBI observatory stations, and the laser ranging develop- 
ment and operation. The Jet Propulsion Laboratory is responsible for the mobile VLBI develop- 
ment and operations, plus related Deep Space Network (DSN) activities. In addition to NASA, the 
Crustal Dynamics Project involves many close cooperative efforts from many other institutions. As 
an example, the development of the Mark III VLBI for geodetic applications has had the participa- 
tion of the Haystack Observatory, the Massachusetts Institute of Technology, the National Radio 
Astronomy Observatory, the Smithsonian Astrophysical Observatory (SAO), the National Geodetic 
Survey, the Owens Valley Radio Observatory, The Harvard College Observatory, and the Chalmers 
Institute. 
The scientific objectives of the Crustal Dyanmics Project are to improve our knowledge and under- 
standing of: 
l The regional deformation and strain accumulation related to large earthquakes in the plate 
boundary region of the western United States. 
0 Contemporary relative plate tectonic motions of the North American, Pacific, South Ameri- 
can, Eurasian, and Australian Plates. 
l The internal deformation of continental and oceanic lithospheric plates with particular em- 
phasis on North America and the Pacific. 
0 The rotational dynamics of the Earth and their possible correlation to earthquakes, plate 
motions, and other geophysical phenomena. 
l Motions and deformation occurring in regions of high earthquake activity. 
In order to achieve these objectives, a rather extensive measurement program utilizing both the 
VLBI and space laser ranging will be required. Frequent high accuracy measurements of baselines 
between many stations in active areas near the plate boundaries are required for the determination 
of the regional deformation and strain accumulation in these active regions. Regular measurements 
of baselines between a global set of stations on the different plates are required for the determina- 
tion of the relative tectonic plate motions. Repeated measurements of baselines between several 
stations on the same plate are needed for the measurement of the internal deformation of the plates. 
The determination of polar motion and Earth-rotation variations requires daily measurement of PM 
and UT1 with a global set of stations in stable locations. 
An integral part of the Crustal Dynamics Project is the test and validation of the capabilities of the 
space systems for making high accuracy geodetic measurements. As an example, one of the test ex- 
periments to be conducted later on this year is a five-station intercomparison between the VLBI 
and space laser ranging. Figure 1 shows the location of the five VLBI stations and the five laser 
stations. The systems are co-located at Westford, Massachusetts; Ft. Davis, Texas; Owens Valley, 
California; and Goldstone, California. In this intercomparison both the Mark III VLBI systems* and 
*T. A. Clark, “Mark III System Overview,” Proceedings of Radio Interferometry Techniques for Geodesy Conference, June 1979, 
NASA CP 2115,198O. 
.__...~ - 
428 RADIO INTERFEROMETRY 
Figure 1. Map of the station locations for the 1979 intercomparison 
of satellite laser ranging and VLBI geodetic measurements. 
the space laser systems will make a series of measurements for the determination of the baselines 
between the stations. The VLBI and laser results will then be intercompared in order to determine 
if there are any systematic effects apparent from these measurements. These baselines are expected 
to intercompare at the 5 centimeter level. 
These intercomparison stations are planned to be used continuously by one technique or the other 
throughout the life of the project in the role of permanent base stations to be used in the determin- 
ation of regional crustal deformation, internal deformation of the North American plate, and tec- 
tonic plate motions relative to the North American plate. It should be noted that the Westford site, 
the Ft. Davis site, and a new site in Richmond, Florida, make up the NGS Polar-motion Analysis 
by Radio Interferometric Surveying (Polaris) network * for operational polar motion and UT1 
determination. 
Figure 2 is a map of the different tectonic regions of the United States and locations of recom- 
mended sites for VLBI and laser measurements for the determination of the regional deformation in 
*W., E. Carter, “Project POLARIS,” Proceedings of Radio Interferometry Techniques for Geodesy Conference, June 1979, NASA 
CP 2115,198O. 
ADHERENCE AND COHERENCE IN NETWORKS AND PLANS 429 
Figure 2. Possible locations of sites for measurements of the regional crustal 
deformation in the western United States and the internal deformation of the 
North American plate. 
the western United States and the internal deformation of the North American plate. At the present 
time, this recommendation is a “strawman” proposal by a group of NASA scientists. It is expected 
that sites similar to these will be firmed up in the next few months through discussions with the 
scientific community and other government agencies. The final deployment will probably be simi- 
lar to figure 2. This map shows several fixed and mobile sites that are already in operation, plus 
many new locations to be established for mobile systems or transportable systems. A total of 41 
locations are identified, with the majority of locations in the seismically active western half of the 
United States. 
Figure 3 shows the present deployment of space laser ranging stations around the globe. This in- 
cludes NASA stations, SAO stations, European Range Observations to Satellites (EROS) stations, 
and lunar laser ranging stations. This distribution provides several stations on the North American 
plate, South American plate, the Pacific plate, the Australian plate, and the Eurasian plate for mea- 
surements of global plate motions and polar motion/UT 1. 
430 RADIO INTERFEROMETRY 
PACIFIC PLATE 
NAXCA 1 
PLATE 
ANTARCTIC PLATE 
. 
Figure 3. 1979 deployment locations of space laser ranging systems, 
In figure 4, the solid dots are the locations of fixed VLBI stations in 1979 which will be used for 
geodetic measurements. This shows the five VLBI base stations in North America that were dis- 
cussed above, the DSN stations in Australia and Spain, and the European stations at Onsala, Sweden, 
and Effeisberg, Germany, This initial deployment will begin the measurements of the plate motions 
between the three respective plates, the internal deformations of the North American and Eurasian 
plates, and polar mo tiion/UT 1. 
The development of geodetic VLBI capability at the two European stations has been accomplished 
through cooperative joint efforts of several United States and European agencies and institutions. 
The host institutions are the Chalmers Institute of Technology for the Onsala station and the Max- 
Planck-Institut fiir Radioastronomie for the Effelsberg station. The Mark III VLBI systems are being 
assembled from subsystems funded by the NASA Crustal Dynamics Project, the host institution: 
the U.S. Geological Survey and the U.S. Air Force. The Crustal Dynamics Project VLBI team fro] 
Goddard Space Flight Center, Haystack Observatory, and Mas&husetts Institute of Technology 
responsible for the implementation of the Mark III unique equipment. 
+ intent of the Cnlstal Dynamics Project to encourage organizations throughout the work 
- :r;+;~~ to make a global joint effort possible for the measurements of F 
ADHERENCE AND COHERENCE IN NETWORKS AND PLANS 431 
ANTARCTIC PLATE 
Figure 4. 1979 locations of VLBI fixed stations (solid dots), and locations of a few of the radio astronomy or space 
tracking antenna facilities (open circles) which could be considered for future geodetic VLBI applications. 
motions, crustal motions, and polar motion/UT 1. To illustrate the tremendous potential that exists 
for global VLBI participation, the open circles in figure 4 are a few of the existing radio astronomy 
or space tracking facilities which could be considered for geodetic VLBI applications. In the devel- 
opment of the Mark III VLBI system, NASA has designed the configuration to be self-contained so 
that it can be easily moved into an antenna facility for geodetic or astronomical observing sessions 
and then moved to another facility for other observations. This configuration provides the flex- 
ibility to make use of the many existing antenna facilities around the world. 
Besides the seismically active region in the western United States discussed earlier, there are many 
other regions of high earthquake activity along plate boundaries throughout the world. Some of 
these tectonically important areas are indicated in figure 5. The deployment of mobile VLBI sys- 
tems in these active regions in a manner similar to that illustrated in figure 2 will provide important 
information about the deformation in these regions. By monitoring these deformations and other 
seismic and geodetic measurements, geophysical models of the region can be developed that will 
provide insight into the reasons for the occurrence of earthquakes in the region. Through extensive 
cooperation with other organizations and countries, NASA would like to stimulate the development 
432 RADIO INTERFEROMETRY 
Figure 5. Tectonically important areas of high earthquake activity. 
of regional measurement plans with mobile systems in these seismically active areas. This will en- 
hance the scientific understanding of earthquake processes as related to the dynamics of the Earth. 
SUMMARY 
The NASA Crustal Dynamics Project is an effort to develop and demonstrate the capabilities of the 
VLBI and laser ranging techniques for unique high accuracy geodetic measurements which have the 
potential for significant scientific measurements of the dynamics of the Earth. The thrust of the 
project is to implement minimal networks to demonstrate the capability and to work with user or- 
ganizations all over the world to encourage them to build up their own capabilities for carrying on 
these very significant measurements. 
REFERENCES 
Carter, W. E., “Project POLARIS,” Proceedings of Radio Interferometry Techniques for Geodesy 
Conference, June 1979, NASA CP 2115, 1980. 
ADHERENCE AND COHERENCE IN NETWORKS AND PLANS 433 
Clark, T. A., “Mark-III System Overview,” Proceedings of Radio Interferometry Techniques for 
Geodesy Conference, June 1979, NASA CP 2115,198O. 
National Aeronautics and Space Administration, National Oceanic and Atmospheric Administration, 
U.S. Geological Survey, National Science Foundation, and Defense Mapping Agency, “The 
Coordinated Federal Program for the Application of Space Technology to Crustal Dynamics 
and Earthquake Research,” November 1978. 


NASA geodetic applications of the Mark 3 VLBI system

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