A geomagnetic precursor to the 1979 Carlisle earthquake

A study of horizontal field transfer functions, in the period range 10-104 s, has been made for the 2 year period preceding the 1979 Carlisle earthquake (magnitude 5). The study using two sites, local to and remote from the earthquake epicentre, reveals that a precursory effect is observed at short periods (< 102 s) some 35 km from the main epicentre. The results indicate a change from two-dimensional geolectric anisotropy to a more conductive three-dimensional geoelectric configuration during the period immediately preceding the earthquake