Reflections on the development and applications of the 1970 paper on Tectonic Stress and the Spectra of Seismic Shear waves from Earthquakes

Abstract:

The JGR paper was written when Jim had just left Caltech and started a new appointment at the Institute of Geophysics and Planetary Physics (IGPP) at U C San Diego. The puzzle of the Heat Flow Paradox was a focus of research. Jim wanted to develop a model in which the stress history and the amount of frictional heat generation was zero. The paper was written as a model in which a few as possible arbitrary unknown losses of energy occurred. This would allow an estimate of the far field energy radiation expected. IGPP was developing digital seismic instruments, and Jim envisioned a model that could be used to compare with evolving very high quality data.

Just before moving to IGPP, at CalTech, Jim started to build an elastic foam rubber model in which the displacements could easily be observed. Jim wanted to avoid models in which the displacement or rupture progress was arbitrarily specified, i.e., Jim wanted to see a spontaneous rupture. He was also wanting to find a model that could be compared with measurements in the foam rubber model.

We will briefly discuss other considerations in building the model, and subsequent studies in the foam rubber model, field studies of pulverized rock and PBRs (precariously balanced rocks), and other applications related to strong ground motions and seismic hazard, which have led to interesting conclusions about the nature of stresses in the earth.