Outer-rise normal fault development and influence on near-trench décollement propagation along the Japan Trench, off Tohoku

Abstract

Multichannel seismic reflection lines image the subducting Pacific Plate to approximately 75 km seaward of the Japan Trench and document the incoming plate sediment, faults, and deformation front near the 2011 Tohoku earthquake epicenter. Sediment thickness of the incoming plate varies from <50 to >600 m with evidence of slumping near normal faults. We find recent sediment deposits in normal fault footwalls and topographic lows. We studied the development of two different classes of normal faults: faults that offset the igneous basement and faults restricted to the sediment section. Faults that cut the basement seaward of the Japan Trench also offset the seafloor and are therefore able to be well characterized from multiple bathymetric surveys. Images of 199 basement-cutting faults reveal an average throw of approximately 120 m and average fault spacing of approximately 2 km. Faults within the sediment column are poorly documented and exhibit offsets of approximately 20 m, with densely spaced populations near the trench axis. Regional seismic lines show lateral variations in location of the Japan Trench deformation front throughout the region, documenting the incoming plate's influence on the deformation front's location. Where horst blocks are carried into the trench, seaward propagation of the deformation front is diminished compared to areas where a graben has entered the trench. We propose that the décollement's propagation into the trench graben may be influenced by local stress changes or displacements due to subduction of active normal faults. The location and geometry of the up-dip décollement at the Japan Trench is potentially controlled by the incoming outer-rise faults.

Outer trench slope flexure and faulting at Pacific basin subduction zones

“…Attempts at explaining this apparent conflict have emphasized the role of inelastic yielding in the weakening of the plate at the trench outer slope (Wessel 1992;Bry & White 2007;Craig & Copley 2014). Evidence for stresses within the plate exceeding the elastic limit includes the prevalence of surface fractures in high-resolution bathymetry (Massell 2002;Mofjeld et al 2004), dipping reflectors in seismic reflection profiles (Ranero et al 2003;Boston et al 2014) and the occurrence of earthquakes with normal fault mechanisms (Craig et al 2014a;Emry & Wiens 2015) In our modelling approach, we prescribe the initial elastic thickness by setting it to be equal to the mechanical thickness, which is the depth at which the ductile yield stresses decrease to some arbitrary threshold. In our case this limit is set to be at 1 per cent of the overburden pressure (Cloetingh & Burov 1996;Hunter & Watts 2016).…”

Magnetotelluric imaging of a fossil paleozoic intraoceanic subduction zone in western Junggar, NW China

“…The hidden Karamay‐Urho Fault was deduced to become a shearing‐dominated fault after the subduction failed and subvertically extend into the oceanic lithospheric remnant, illuminated by shallow flower‐shaped fractures and depth Moho offsetting, respectively. The transition may represent the adjustment of subsequent horizontal compression [ Boston et al ., ] and/or cooling of oceanic lithosphere after underthrusting terminated. Following the lines of evidence, the zone of Karamay‐Urho Fault to F1 represents the fore‐arc primal accretionary prism (Figure ).…”

Intra- and intertrench variations in flexural bending of the Manila, Mariana and global trenches: implications on plate weakening in controlling trench dynamics

“…When the bending-induced stress exceeds the yield strength of the lithosphere, pervasive faulting could occur trenchward of the outerrise region (e.g. Jones et al 1978;Masson 1991;Ranero et al 2003Ranero et al , 2005Obana et al 2012;Gou et al 2013;Naliboff et al 2013;Boston et al 2014;Craig et al 2014;Zhou et al 2015). Faulting could in turn cause a significant reduction in the effective elastic thickness of the subducting plate Bodine & Watts 1979;Watts 2001;Ranero et al 2005;Contreras-Reyes & Osses 2010;Zhang et al 2014;Hunter & Watts 2016).…”