Paleoseismology and paleotsunamis of the NE Japan subduction zone and relationships with the 2011, M9 Tohoku earthquake: Constraints on the seismic cycle – PALET

L’approche choisie dans PALET est de combiner différentes méthodes d’investigations en paléosismologie et étude des paléotsunami qui permettrons de rechercher les traces des séismes de magnitude égale ou supérieure à 9, et d’en déduire le cycle sismique associé. Les investigations et évidences de terrain associées aux modèles numériques permettrons de mieux comprendre les processus physiques des ruptures sismiques et de développer les applications à l’évaluation et prévision de l’aléa sismique.
Nous proposons l’utilisation de nouvelles méthodologies : 1) La géologie des zones sismiques et paléosismologie avec analyse des tranchées en 2 et 3 dimensions à travers les ruptures de surface, 2) l’application des profiles géoradar (GPR) combinée avec les « Géoslices », 3) la recherche des paléotsunamis couplée aux mesures de soulèvements et de subsidence côtiers durant le pleistocène supérieur et l’Holocène, et 3) la modélisation du cycle sismique et le transfert de contrainte au cours du Pleistocène supérieur et l’Holocène.

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The PALET project addresses the issue of long-term faulting behaviour and earthquake prevision of the NE Japan coastline and the site inshore of the 2011 M9 mega-thrust Tohoku earthquake. The goal of the project is to combine different approaches in paleoseismology and paleo-tsunami research to find evidence for the past giant events and to reveal its “super cycle” in the geologic record if they exist. Based on the field findings together with numerical simulations, we then understand the physical process of earthquake occurrence and expand the application in earthquake prevision and hazard evaluation.
In PALET, we devise the following three strategies; 1) to find and date paleotsunami deposits along the Sanriku-to-Fukushima coastal regions, 2) to reveal the history of the surface rupturing events of normal faults in Fukushima region which suggests the similar extensional event after the 2011-type earthquake, and 3) to compare the Holocene and 12-ka marine terraces with the observed data of coseismic and postseismic uplift and subsidence occurred in 2011. To execute such strategies, we employ several new geologic methodologies;
(1) the geology of earthquakes and paleoseismology with 2D-3D trenching, (2) the use of high-resolution Ground Penetrating Radar combined with Geoslices, and (3) the modelling of seismic cycle and related earthquake stress change over the late-Pleistocene and Holocene. These outcomes from the methodologies are here integrated through field investigations and modelling and by means of the fault parameters obtained from four tasks (and two partners). PALET can be an important source of data and motivation for a wide community of involved geoscientists in seismology, geodesy, geology, rock mechanics, mechanical modelling, and seismic hazard and risk.