Crustal deformation observatory: Part B, precision geodesy

The primary purpose of this investigation this past year was to establish and monitor a precise leveling array at Pinon Flat Geophysical Observatory to monitor tilt strain. The leveling array is one of several strain measurement techniques established at the observatory by several investigators for side-byside testing. Precise leveling is an optical method of measuring vertical strain in contrast to the various tiltmeters which measure electronically or electro-optically. The advantages of establishing several strain measuring techniques at one location is to obtain a high degree of redundancy so that the precision of each technique can be better evaluated.

A secondary and on-going objective of the leveling is the observation of closely-spaced benchmarks to determine factors affecting their stability. Tectonic interpretations from analyses of historic levelings are frequently suspect because of benchmark instability (Karcz and others, 1976).