Repeating deep earthquakes: Evidence for fault reactivation at great depth

We have identified three groups of deep earthquakes showing nearly identica l waveforms in the Tonga stab. Relocation with a cross-correlation method s hows that each cluster is composed of 10 to 30 earthquakes along a plane 10 to 30 kilometers in length. Some of the earthquakes are colocated, demonst rating repeated rupture of the same fault, and one pair of events shows ide ntical rupture complexity, suggesting that the temporal and spatial rupture pattern was repeated. Recurrence intervals show an inverse time distributi on, indicating a strong temporal control over fault reactivation. Runaway t hermal shear instabilities may explain temporally clustered earthquakes wit h similar waveforms located along slip zones weakened by shear heating. Ear thquake doublets that occur within a few hours are consistent with events r ecurring before the thermal energy of the initial rupture can diffuse away.