Abstract
Part I. The response of standard magnetographs to earthquake waves is a seismograph effect. These instruments react as ultra-low-sensitivity seismic recorders. With little or no additional effort some magnetic observatories could be used as supplementary seismic stations at the times of great earthquakes. The effects of the Alaskan earthquake of March 28, 1964, are studied in detail in this paper. A number of similar cases are known.
Part II. Even if the response of standard magnetographs is definitely of a mechanical nature it is likely that the earthquake waves do generate real magnetic waves. Some experimental evidence (from Bergen Park, Colorado) of the existence of such waves is presented. Mechanisms for generation of the observed waves are discussed. It is shown that piezomagnetic oscillations in magnetic rock or induced currents in a region with enhanced conductivity may offer an explanation. These effects are associated with anomalous conditions in the crust. It seems evident that the properties of the “average crust” cannot explain the observed magnetic variations.
