The 2015 Illapel earthquake, Central Chile, a case of characteristic earthquake?

On September 16, 2015, the Chilean margin experienced a great subduction megathrust earthquake. The MW=8.2 Illapel earthquake occurred in the Metropolitan segment north of where the Juan-Fernandez ridge meets the Chile trench and subduction style and geometry change. Combining GPS displacement measurements, InSAR interferograms, strong motion and broadband seismological waveforms, and high frequency (HF) teleseismic backprojection we derive a comprehensive description of the coseismic rupture. We further determine moment tensors and obtain accurate depth estimates for mostly offshore aftershock sequence by careful observations of teleseismic depth phases. The rupture nucleated near the coast but then propagated to the north and updip, with a circular geometry of diameter 100 km and a peak slip of ~6 m below the forearc. HF seismic radiation is mostly emitted downdip of the region of most intense slip, but unlike in most previous events the high frequency emitters do not track the whole rupture but are confined to a small region. The time evolution of HF seismic radiation also arrests earlier than the long period rupture evolution, indicating that the final phase of the rupture progressed more smoothly. The aftershocks, mostly plate interface events, extend significantly beyond the limits of the main rupture in both directions. In 1943, a comparable event struck the Illapel area. The similar extent of the aftershock zone and tsunami heights therefore make this part of the margin a candidate site for generating characteristic earthquakes. The approximate match of peak slip and accumulated slip deficit in the 72 years since the 1943 event also support this interpretation. However, the 1943 event appears to have had a shorter source time function and probably a smaller magnitude, pointing to differences in the detailed rupture evolution. The coupling is mostly close to fully locked in this area at least along the coast line but nevertheless the coseismic rupture is associated with a local peak in the locking pattern, whereas a narrow partially creeping area is found just to the south of the main rupture. Although locally the recent Illaped earthquake has relieved much of the accumulated stress, the segment immediately adjacent to the north remains unbroken since 1922, and presents a serious earthquake and tsunami hazard