The 2012 Sumatra great earthquake sequence

recorded (moment magnitudes Mw1⁄48.6 and 8.2). Broadband seismological observations of the Mw1⁄48.6 mainshock indicate a large centroid depth ( 30 km) and remarkable rupture complexity. Detailed study of the surface-wave directivity and moment rate functions clearly indicates the partition of the rupture into at least two distinct subevents. To account for these observations, we developed a procedure to invert for multiple-point-source parameters. The optimum source model at long period consists of two point sources separated by about 209 km with magnitudes Mw1⁄48.5 and 8.3. To explain the remaining discrepancies between predicted and observed surface waves, we can refine this model by adding directivity along the WNW–ESE axis. However, we do not exclude more complicated models. To analyze the Mw1⁄48.2 aftershock, we removed the perturbation due to large surface-wave arrivals of the Mw1⁄48.6 mainshock by subtracting the corresponding synthetics computed for the two-subevent model. Analysis of the surface-wave amplitudes suggests that the Mw1⁄48.2 aftershock had a large centroid depth between 30 km and 40 km. This major earthquake sequence brings a new perspective to the seismotectonics of the equatorial Indian Ocean and reveals active deep lithospheric deformation. & 2012 Elsevier B.V. All rights reserved.