Before PBO: An Overview of Continuous Strain and Tilt Measurements in the United States

Abstract

Unlike Japan, the United States has not had a large sustained program to make continuous measurements of crustal deformation—until the the Plate Boundary Observatory (PBO) initiative (Section 10) that began in 2003. Most earlier measurements instead were initiatives by individual scientists or particular agencies. In many cases early and promising results have been followed by demonstrations that apparent signals were in fact noise. Partly because of this, few programs have lasted more than a few years, two examples being measurements with shallow strainmeters in the 1960’s and shallow tiltmeters in the 1970’s. I use some of these historical examples, and concepts from studies of scientific experimentation, to suggest some general conclusions about this type of measurement.