Earthquakes have been understood conceptually for about 100 years. Strain and stress build until the rock fractures, sliding along a fault surface, with the fracture propagation moderated by elastic waves. Although some details about friction and the ensemble behavior of evolving fault networks still have to be worked out, the earthquake cycle follows an unchallenged master paradigm with an uneven two-step of rapid sliding and slow reloading.1 Or so we thought 10 years ago.
Earthquakes mark the relative motion between tectonic plates, large and small. Since the 1960s, the theory of plate tectonics has recognized that Earth’s lithosphere is broken into pieces of various sizes, ranging from much of the vast area under the Pacific Ocean down to as small a rock mass as one is able to consider. The definition of lithosphere—the shallower volume of rock that behaves in a plastic manner compared with the underlying viscous flow...
