: Over the past 50 years, brief magnetic pulses have been detected during the weeks leading up to several earthquakes. Analysis of the pulses revealed that their frequency increased as a quake became imminent, but it was not clear whether the pulses were related to the quakes. Now Friedemann Freund of San Jose State University in California and his colleagues propose that the pulses are caused by the buildup of pressure in Earth's crust, which breaks the peroxy (oxygen–oxygen) bonds of crystals in the rock. Their lab tests reveal that the process releases electrons and creates positively charged "holes" in the crystals. The resulting electrical disturbance can propagate at up to 100 m/s. If this is happening in Earth's crust, the resulting electrical current could be the source of the magnetic pulses. However, the team's work is preliminary; the researchers hope to collect more data from future quakes that will help them better pinpoint the source of the pulses.