Earthquake in a maze:compressional rupture branching during the April 11 2012 M8.6 Sumatra earthquake

unprecedented complexity of dynamic rupture. The surprisingly large magnitude results from the combination of deep extent, high stress drop, and rupture of multiple faults. Back-projection source imaging indicates that the rupture occurred on distinct planes in an orthogonal conjugate fault system, with relatively slow rupture speed. The east-southeast–west-northwest ruptures add a new dimension to the seismotectonics of the Wharton Basin, which was previously thought to be controlled by north-south strike-slip faulting. The rupture turned twice into the compressive quadrant, against the preferred branching direction predicted by dynamic Coulomb stress calculations. Orthogonal faulting and compressional branching indicate that rupture was controlled by a pressure-insensitive strength of the deep oceanic lithosphere. The11 April 2012 moment magnitude (Mw)8.6 earthquake off shore of Sumatra is arecord-breaking event in many respects. It is the largest strike-slip and intraplate earth-quake ever recorded and, as shown here, one of the most complicated ruptures ever imaged by modern seismology. The faulting geometry and the peculiarities of its complex rupture path offe