Infrasonic waves in the ionosphere generated by a weak earthquake

Abstract

A computer code has been developed to simulate the generation of infrasonic waves (frequencies considered ≤80 Hz) by a weak earthquake (magnitude ∼3.6), their propagation through the atmosphere and their effects in the ionosphere. We provide estimates of the perturbations in the ionosphere at the height (∼160 km) where waves at the sounding frequency (3.59 MHz) of a continuous Doppler radar reflect. We have found that the pressure perturbation is 5.79×10 −7 Pa (0.26% of the ambient value), the temperature perturbation is 0.088 K (0.015% of the ambient value) and the electron density perturbation is 2×10 8 m −3 (0.12% of the ambient value). The characteristic perturbation is found to be a bipolar pulse lasting ∼25 s, and the maximum Doppler shift is found to be ∼0.08 Hz, which is too small to be detected by the Doppler radar at the time of the earthquake.