Abstract

The March 16, 2014 M-W 6.7 earthquake played an important role in the complex seismic sequence leading to the nucleation of the April 1st, 2014 M-W 8.2 Pisagua earthquake in northern Chile. The M-W 6.7, an upper plate reverse faulting event with nodal planes highly rotated counterclockwise with respect to the strike of the megathrust at its location, is analyzed. For each nodal plane of the regional W-phase centroid moment tensor solution, the spatiotemporal slip distribution is inverted using near-field records. The optimal space and time smoothing constraints are determined objectively based on the Akaike's Bayesian Information Criterion. We analyze seismicity on the region affected by the M-W 6.7 and M-W 8.2 Pisagua mainshock, with accurate hypo center locations obtained using a 3D heterogeneous medium. We also performed regional moment tensor inversion of events (M >= 4.0) occurred before the M-W 8.2. Our results suggest the sub-vertical fault plane dipping southward (dip similar to 70 degrees) as being the causative fault of the March 16 M-W 6.7 earthquake. The rupture propagated to the northwest, lasted 15 s, and yielded a total seismic moment of 1.36 x 10(19) Nm (M-W 6.7). Estimated slip is characterized by total rupture length of similar to 22 km, and suggest shallow slip distributed between similar to 3 km, down to 17 km depth. A comparison between coastal tide gauge records and forward tsunami modeling show similarity of the time series, thus supporting the plausibility of our estimated slip models. Our interpretation suggests that the rupture of the M-w 6.7 intraplate could be explained by stress accommodation between two segments along-dip with different mechanical properties at the interplate boundary, and inside the upper plate.