Heterogeneous stress state of island arc crust in northeastern Japan affected by hot mantle fingers

Abstract

By considering a thermal structure based on dense geothermal observations, we model the stress state of the crust beneath the northeastern Japan island arc under a compressional tectonic regime using a finite element method with viscoelasticity and elastoplasticity. We consider a three‐layer structure (upper crust, lower crust, and uppermost mantle) to define flow properties. Numerical results show that the brittle‐viscous transition becomes shallower beneath the Ou Backbone Range compared with areas near the margins of the Pacific Ocean and the Japan Sea. Moreover, several elongate regions with a shallow brittle‐viscous transition are oriented transverse to the arc, and these regions correspond to hot fingers (i.e., high‐temperature regions in the mantle wedge). The stress level is low in these regions due to viscous deformation. Areas of seismicity roughly correspond to zones of stress accumulation where many intraplate earthquakes occur. Our model produces regions with high uplift rates that largely coincide with regions of high elevation (e.g., the Ou Backbone Range). The stress state, fault development, and uplift around the Ou Backbone Range can all be explained by our model. The results also suggest the existence of low‐viscosity regions corresponding to hot fingers in the island arc crust. These low‐viscosity regions have possibly affected viscous relaxation processes following the 2011 Tohoku‐oki earthquake.

Asthenosphere Flow Modulated by Megathrust Earthquake Cycles

“…Laboratory rock experiments constrain the rheological properties of olivine (Karato & Jung, 2003;Mei & Kohlstedt, 2000) and serpentinite (Hilairet et al, 2007;Reinen et al, 1991) well, but the in situ conditions remain elusive. As a result, there is no consensus on the effective viscosity at steady state, the water content (and its spatial variations), and the pathways to arc volcanism (Hu et al, 2014;Lee & Wada, 2017;Ohzono et al, 2012;Shibazaki et al, 2016) in the backarc.…”

(U–Th)/He thermochronometric mapping across the northeast Japan Arc: towards understanding mountain building in an island-arc setting

“…A comparison between short-and long-term denudation/uplift rates is discussed separately in the three tectonic units described below. Furthermore, geodynamic modeling were concerned using a finite element method based on rheology for the entire NE Japan Arc (e.g., Shibazaki et al 2008Shibazaki et al , 2016. Shibazaki et al (2016), provide an estimate of long-term uplift rates assuming some boundary conditions and geophysical parameters.…”

“…Furthermore, geodynamic modeling were concerned using a finite element method based on rheology for the entire NE Japan Arc (e.g., Shibazaki et al 2008Shibazaki et al , 2016. Shibazaki et al (2016), provide an estimate of long-term uplift rates assuming some boundary conditions and geophysical parameters. We also compared our denudation rates from thermochronometric data with those modeling results.…”

“…Uplift rates were estimated at ~ 0.2 to ~ 0.4 mm/year over ~ 10 5 year based on the elevations and emergent ages of the fluvial/ marine terraces (e.g., Tajikara and Ikeda 2005;Okuno et al 2014). Moreover, geodynamic modeling, using the finite element method (Shibazaki et al 2016), provided uplift rates up to 0.4 mm/year on a 10 6 years timescale. Denudation rates at < 0.05 mm/year were obtained based on our thermochronometric data, indicating one order of magnitude discrepancy in rates between short-and long term (described later).…”

“…year from displacements across the eastern margin faults of Kitakami lowland and the western margin faults of Yokote basin on 10 5−6 years timescales (Awata 1988;Ikeda et al 2002;Doke et al 2012). Geodynamic modeling using the finite element method (Shibazaki et al 2016) offered uplift rates of ~ 0.4-1.0 mm/year on a 10 6 years timescale. Our denudation rates in this study were estimated at ~ 0.2-1.4 mm/year, which are consistent with the independently derived short-term rates outlined above.…”