Gravitational raft tectonics in the Tumbes-Guayaquil forearc basin, Northern Andes (North Peru-South Ecuador)

Understanding the dynamics of forearc basins is a challenge to improve knowledge of their influence on subduction zone earthquakes and tsunamis. The structural architecture of the Tumbes and Guayaquil forearc depocenters in the Northern Andes is revealed by subsurface data and the construction of serial cross-sections. Seismic reflection profiles and well data reveal that the overall forearc depocenters by widespread gravitational raft tectonics instabilities. These instabilities occurred principally during the Late Neogene to Quaternary period. We emphasize kilometric-scale upper listric normal fault dip regionally basinward paired with downdip thrust wedge. These structures branch downward on a regional décollement level developed in the upper Oligocene ductile shales above subduction zone. The development of this tectonic style appears to be significantly controlled by the coeval of tectonics, high sedimentation rate in the basin and pore pressures processes. Our findings are original enough as these kinds of instabilities are much more often observed in passive margins. Finally, the large active movements of sedimentary masses could also be triggered by seismicity and could generate potential tsunamis that could reach the neighboring coastal zone, including the Guayaquil city.