[S-CG41] Evolution and movement of the crustal surface and application of geo- and thermochronology

[SCG41-P07] WNW-ESE shortening in the Niigata-Kobe Tectonic zone explained by 2D visco-elasto-plastic collision numerical models

*Erika Moreno¹, Vlad Manea², Marina Manea², Nobuaki Suenaga³, Shoichi Yoshioka¹ (1.Kobe University, 2.CGEO, Universidad Nacional Autónoma de México, 3.Kyoto University)

Keywords:Numerical simulations, Thermal anomalies, Horizontal compression , Continental crust evolution

The Niigata-Kobe-Tectonic-Zone (NKTZ) extends approximately 500 km from Niigata Prefecture to Kobe along the coast of the Japan Sea in NE-SW direction. According to the GNSS data operated by Geospatial Information Authority of Japan (GEONET), the NKTZ is experiencing a spatially non-uniform strain rate and a continuous shortening in the WNW-ESE direction. The highest concentration of strain rate has been observed in the NE, particularly in Niigata Prefecture, where earthquakes with magnitude M > 6 have been recorded. The NKTZ is composed of three main geological and tectonic settings, differentiated by the amount of strain rates, density of volcanism, orientation of the complex fault system, interaction of the subducted plates and the amount of sediment deposited on the bedrock. The NE part of the NKTZ is separated from the Central and SW parts by the great Itoigawa-Shizuoka tectonic line, which is strongly influenced by the subduction of the Pacific (PAC) plate and the interaction between the North American (NA) and Amurian (AM) plates. The central area of the NKTZ is affected by the interaction between the Philippine Sea (PHS) plate and the PAC plate, and the presence of high density of volcanism caused by the dehydration of both slabs beneath Central Japan. Finally, SW region is affected by the subduction of the young, warm and buoyant PHS slab and is characterized by a low density of volcanism. Some studies have tried to explain the WNW-ESE contraction, mainly associating it with the strong compression caused by the interaction of the AM, NA, PAC and PHS plates. However, recent studies recognized that this model does not fully explain the WNW-ESE shortening reported by GEONET along the NKTZ, and existing numerical models only use visco-elastic approaches. In this study, we propose two-dimensional high-resolution thermomechanical numerical with visco-elasto-plastic rheology under a horizontal compressive regime. Our main objective is to analyze how the crust deforms when different mechanical, physical and thermal properties are taken into consideration. Three profiles were selected to cross the NE, central and SW parts of the NKTZ, aligned with the direction of compression, to analyze the pattern of WNW-ESE shortening present in the NKTZ. The half rate of horizontal compression is 1 cm/yr. We developed two initial model setups that approximate the geological and tectonic conditions of the NKTZ region, and includes a stratified crust, asthenosphere and asthenospheric thermal anomalies. The initial model setup for the profile that crosses the Niigata Prefecture in the WNW-ESE direction, includes a sedimentary layer of about ~ 6 km and the upper continental crustal reaching a depth of about 22 km, which would correspond to the maximum depth at which crustal seismicity is recorded. The second initial model setup, represents the second and third profiles across the Central and SW of the NKTZ and are oriented along the same shortening direction. We prescribed initial thermal anomalies (DT of 150 °C) as homogeneous with a spherical shape (diameter of 20 - 30 km). They correspond to highly hydrated regions identified by low- anomalies of seismic wave velocity. For the three selected profiles, our preliminary results are compared with strain rate and the topography of the region.