Villegas-Lanza J. C., Nocquet Jean-Mathieu, Rolandone F., Vallée Martin, Tavera H., Bondoux Francis, Tran T., Martin Xavier, Chlieh Mohamed
Source
Nature Geoscience, 2016,
9 (2), p. 150-154 ISSN 1752-0894
In subduction zones, stress is released by earthquakes and transient aseismic slip. The latter falls into two categories: slow slip and afterslip. Slow-slip events emerge spontaneously during the interseismic phase, and show a progressive acceleration of slip with a negligible contribution of synchronous tremors or microseismicity to the energy, or moment release(1-12). In contrast, afterslip occurs immediately after large and moderate earthquakes, decelerates over time, and releases between 20 and 400% of the moment released by the preceding earthquake(13-18). Here we use seismic and GPS data to identify transient aseismic slip that does not fit into either of these categories. We document a seismic-aseismic slip sequence which occurred at shallow depths along a weakly coupled part of the Andean subduction zone(19) in northern Peru and lasted seven months. The sequence generated several moderate earthquakes that together account for about 25% of the total moment released during the full sequence, equivalent to magnitude 6.7. Transient slip immediately followed two of the earthquakes, with slip slowing at a logarithmic rate. Considered separately, the moment released by transient slip following the second earthquake was more than 1,000% of the moment released during the earthquake itself, a value incompatible with classical models of afterslip. Synchronous seismic swarms and aseismic slipmay therefore definea stress-release process that is distinct from slow-slip events and afterslip.
