Observations of an ionospheric perturbation arising from the Coalinga Earthquake of May 2, 1983

An ionospheric peturbation that was produced by the Coalinga earthquake of May 2, 1983, was detected by a network of high‐frequency radio links in northern California. The ionospheric refraction regions of all five HF propagation paths, at distances between 160 and 285 km (horizontal range) from the epicenter, were affected by a ground‐motion‐induced acoustic pulse that propagated to ionospheric heights. The acoustic pulse was produced by the earthquake‐induced seismic waves rather than the vertical ground motion above the epicenter. These observations appear to be the first ionospheric disturbances to be reported this close to an earthquake epicenter.