Physics of Earthquakes: The Real Earthshaking Science*

The study of earthquakes is driven by the desire to understand our dynamic planet and to minimize the devastation that earthquakes can cause. Earthquake science spans a huge range of temporal and spatial scales. The largest earthquakes rupture faults that are 100s to 1000s of kilometers long but start from nucleation regions so small that they have never been reliably observed. Earthquake faults move at only millimeters to centimeters a year but earthquake ruptures propagate at speeds of kilometers a second, and most earthquakes last less than a minute.
I will begin by introducing the basic concepts and observations of earthquake occurrence, and the widely-accepted, friction-based physical understanding of fault failure and rupture. I will then discuss how more recent observations and modeling are providing improved insights into this earthshaking science.
Fault rocks obtained from drilling through the San Andreas Fault and other major earthquake ruptures are providing evidence of the frictional strength of these plate boundary faults. Great earthquakes are being recorded by more, better instruments than ever before providing unprecedented resolution of the rupture process. The increase in anthropogenically-induced earthquakes forms an unintentional semi-controlled experiment to probe the triggering process. Improved geodetic observations are revealing that earthquakes are only part of a continuum of fault rupture types, with durations varying from seconds to minutes, days and even months.
Dynamic modeling of individual earthquakes on super computers can now produce realistic simulations of earthquake rupture and shaking. Earthquakes do not occur in isolation but interact as a consequence of both the dynamic and static stress changes they cause. Progress is also being made on modeling earthquakes as part of a complex system of deformation.