While both electric and magnetic fields are expected to accompany dynamic physical
processes in the earth’s crust, simultaneous measurements of both fields are
not routinely made. We will therefore discuss electric fields, magnetic fields, and
electromagnetic fields separately during, and preceding, earthquakes and volcanic
eruptions. Magnetic and electric fields generated by earthquakes and volcanic
eruptions are termed “seismomagnetic (SM)”, “seismoelectric (SE)”, “volcanomagnetic
(VM)” and “volcanoelectric (VE)” effects. Those preceding earthquakes
and eruptions, or occurring at other times, are termed “tectonomagnetic (TM)” and
“tectonoelectric (TE)” effects.