Coseismic Slip Distribution of the 2 July 2013 M-w 6.1 Aceh, Indonesia, Earthquake and Its Tectonic Implications

This study investigates the coseismic slip distribution of the 2 July 2013 M-w 6.1 Aceh earthquake using Global Positioning System (GPS) data, measured geological surface offsets, and an aftershock distribution for a period of four days after the mainshock. We use the aftershock distribution to constrain the fault-plane strike of a right-lateral fault identified as the Pantan Terong segment. We estimate the coseismic slip distribution with dip angle information from the Global Centroid Moment Tensor (CMT) (model 1) and U.S. Geological Survey (USGS) (model 2) catalogs. We also estimate the coseismic slip distribution using another two fault models. Model 3 is constructed on a left-lateral fault, the Celala segment, which is perpendicular to the Aceh segment of the Sumatran fault, and model 4 is constructed using the multiple faults in models 2 and 3. We further estimate the coseismic slip distribution of this earthquake by employing an elastic dislocation model, inverting only the GPS displacements for model 3 and jointly inverting GPS displacements and geological surface offsets for models 1, 2, and 4 Minimum misfit between data and model is obtained with model 3, suggesting that the earthquake slip occurred along a left-lateral fault. Analysis of stress transfer caused by the 2013 earthquake indicates that the stress level along the Pantan Terong segment is > 0.4 bar and the southeast part of Aceh segment was brought -0.3 bar closer to failure, suggesting a possible earthquake occurrence in the future. This work demonstrates that the seismicity-derived fault plane fails to predict the surface displacement, and that the inferred Celala segment produces positive stress on Pantan Terong segment and potentially triggered all the aftershocks.