We improve constraints on the slip distribution and geometry of faults involved in the complex, multisegment, M w 8.6 April 2012 Wharton Basin earthquake sequence by joint inversion of high-rate GPS data from the Sumatran GPS Array (SuGAr), teleseismic observations, source time functions from broadband surface waves, and far-field static GPS displacements. This sequence occurred under the Indian Ocean, ∼400 km offshore Sumatra. The events are extraordinary for their unprecedented rupture of multiple cross faults, deep slip, large strike-slip magnitude, and potential role in the formation of a discrete plate boundary between the Indian and Australian plates. The SuGAr recorded static displacements of up to ∼22 cm, along with time-varying arrivals from the complex faulting, which indicate that the majority of moment release was on young, WNW trending, right-lateral faults, counter to initial expectations that an old, lithospheric, NNE trending fracture zone played the primary role. The new faults are optimally oriented to accommodate the present-day stress field. Not only was the greatest moment released on the younger faults, but it was these that sustained very deep slip and high stress drop (>20 MPa). The rupture may have extended to depths of up to 60 km, suggesting that the oceanic lithosphere in the northern Wharton Basin may be cold and strong enough to sustain brittle failure at such depths. Alternatively, the rupture may have occurred with an alternative weakening mechanism, such as thermal runaway.

We have compiled the first self‐consistent GPS‐based earthquake catalog for the Sumatran plate boundary. Using continuous daily position time series from the Sumatran GPS Array (SuGAr), we document 30 earthquakes which occurred within or outside the SuGAr network from August 2002 through the end of 2013, and we provide estimates of both vertical and horizontal coseismic offsets associated with 1 M9.2, 3 M8, 6 M7, 19 M6, and 1 M5.9 earthquakes, as well as postseismic decay amplitudes and times associated with 9 M > 7 earthquakes and 1 M6.7 earthquake. For most of the previously studied earthquakes, our geodetic catalog provides more complete coseismic displacements than those published, showing consistent patterns of motion across a large range of distances. For many of the moderate to large earthquakes, we publish their coseismic displacements for the first time, providing new constraints on their locations and slip distributions. For the postseismic time series, we have tackled the challenge of separating the signals for individual events from the overlapping effects of many other earthquakes. As a result, we have obtained either new or much longer time series than previously published. Based on our long time series, we find logarithmic decay times ranging from several days to more than 20 years, and sometimes a second decay time is needed, suggesting that when studying large to great Sumatran earthquakes, we need to consider multiple postseismic mechanisms. Our geodetic catalog provides rich spatial and temporal Sumatran earthquake cycle information for future studies of the physics and dynamics of the Sumatran plate boundary.

The 12 September 2007 Mw 8.4 Bengkulu earthquake in Sumatra marked the first in a modern series of large earthquakes along the Mentawai section of the Sunda megathrust. Understanding the spatial distribution of coseismic slip and ensuing afterslip is important for assessing seismic hazard in neighboring unruptured regions of the megathrust. We reestimate the spatial distribution of coseismic slip during this earthquake with improved coseismic offsets from the Sumatran GPS Array (SuGAr) and estimate afterslip following this earthquake with SuGAr postseismic time series spanning ∼6.3 years after the earthquake. We invert for the spatiotemporal distribution of afterslip with the principal component analysis‐based inversion method (PCAIM), and we take into account viscoelastic deformation by incorporating into the inversion the estimation of strain within ductile deforming blocks located at asthenospheric depths. Our results suggest cumulative afterslip concentrated within, updip, and downdip of the 2007 coseismic rupture area and shallow afterslip that borders and overlaps the 2010 Mw 7.8 Mentawai earthquake rupture zone. The cumulative contribution of stress changes due to the coseismic event and the ensuing afterslip likely increased strain rates in the shallow portion of the megathrust adjacent to the Mentawai earthquake rupture area, potentially promoting its rupture in 2010.