Radiated Energy and the Physics of Earthquake Faulting

On the third day of a recent AGU Chapman Conference, held in Portland, Maine, near the Two Lights fault zones and the Fort Foster brittle zone, conference participants spent the gray June day scrambling over rocky ledges above the crashing surf along the coast of the Atlantic Ocean. With field trip leader Mark Swanson, who with his students has studied the area in detail over the past 20 years, participants examined evidence of ancient earthquakes from about 300 million years ago when these rocks were 8 to 10 kilometers deep. This evidence included pseudotachylytes—glass generated by heating during fault slip at midcrustal depths.