Monitoring of crustal movements in the San Andreas fault zone by a satellite-borne ranging system
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Date
1976-08
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Ohio State University. Division of Geodetic Science
Abstract
The Close Grid Geodynamic Measurement System is conceived as an orbiting ranging device with a ground base grid of reflectors or transponders (spacing 1.0 to 30 km), which are projected to be of low cost (maintenance free and unattended), and which will permit the saturation of a local area to obtain data useful to monitor crustal movements in the San Andreas fault zone. This investigation includes a station network of 75 stations covering an area between 36°N and 38°N latitudes, and 237°E and 239°E longitudes, with roughly half of the stations on either side of the faults. In addition, the simulation of crustal movements through the introduction of changes in the relative positions between grid stations, weather effect for intervisibility between satellite and station and loss of observations thereof, and comparative evaluation of various observational scheme/pattern have been critically studied. The study considers laser radar as the main ranging system pending final selection from many possible candidates and the ranges used have been generated for standard deviations of 2 and 10 cm. The satellite orbit is inclined at 110° and slightly eccentric (c = 0.04) with orbital altitudes varying from 370 km to 930 km. Geometric and short arc modes are the two main methods for handling ranges and solution/adjustment of the system. The constant rate of crustal motion has been assumed as 3 cm per year both in latitudinal and longitudinal directions. No vertical motion is considered. Using this rate, two time epochs, t0 and t1 ( = t0 + 12 months) are considered to investigate motion recovery. The results have been analyzed in two stages: (1) Recovery analysis in terms of the differences between the actual and the recovered chords between any two stations to select the most optimum design of experiment, (2) Statistical analysis in terms of the conventional α and β errors for the recovery of motion rate for the selected design of experiment. The geometric mode with minimum of five grid and three distant (fundamental) stations and mixed ranging to satellite and airplane seems to be most promising. The fundamental stations are distinguished from the grid station in their location and this location should be 'distant' enough from the area of crustal movement so that they can be considered stationary over the time span of the motion involved. The recovery of motion rate for magnitude is quite straightforward, while for direction each case may require consideration on its own merit. The study also recognizes the sensitivity of the results/deductions obtained thereof to any design of experiment associated with them. For the specified setup, time interval between two sets of station recovery for different motion rate or ranging accuracies has also been suggested. [Some mathematical expressions are not fully represented in the metadata. Full text of abstract available in document.]
Description
Prepared for the National Aeronautics and Space Administration, Washington, D.C.: Grant No. NGR 36-008-204, OSURF Project No. 3820-A1