Radiofrequency emissions observed during macroscopic hypervelocity impact experiments

Abstract

Banded low-frequency radiofrequency (r.f.) signals, very low frequency propagation and light emission have been recorded to precede, accompany and follow some large earthquakes^1–3, and mechanisms to account for these phenomena have been suggested recently^4,5, discussed briefly by Chi-Yu King (ref. 6 and references therein) and summarized by Sadovski⁷. Banded r.f. emission has also been detected in a series of laboratory tests in which samples of granite and other hard rocks were fractured under static pressure⁸. Here we report observations of banded r.f. emission generated during and after macroscopic hypervelocity impacts of small projectiles on hard rocks. We believe that our results may help to further the understanding of earthquake emissions and the mechanism of impact magnetization⁹, both of which are associated with the fracturing of rocks under some kind of stress.