Friction properties of the plate boundary megathrust beneath the frontal wedge near the Japan Trench: an inference from topographic variation

Abstract

The 2011 Tohoku-Oki earthquake (Mw 9.0) produced a fault rupture that extended to the toe of the Japan Trench. The deformation and frictional properties beneath the forearc are keys that can help to elucidate this unusual event.In the present study, to investigate the frictional properties of the shallow part of the plate boundary, we applied the critically tapered Coulomb wedge theory to the Japan Trench and obtained the effective coefficient of basal friction μ ′ b À Áand Hubbert-Rubey pore fluid pressure ratio (λ) of the wedge beneath the lower slope. We extracted the surface slope angle and décollement dip angle (which are the necessary topographic parameters for applying the critical taper theory) from seismic reflection and refraction survey data at 12 sites in the frontal wedges of the Japan Trench. We found that the angle between the décollement and back-stop interface generally decreases toward the north. The measured taper angle and inferred effective friction coefficient were remarkably high at three locations. The southernmost area, which had the highest coefficient of basal friction, coincides with the area where the seamount is colliding offshore of Fukushima. The second area with a high effective coefficient of basal friction coincides with the maximum slip location during the 2011 Tohoku-Oki earthquake. The area of the 2011 earthquake rupture was topographically unique from other forearc regions in the Japan Trench. The strain energy accumulation near the trench axis may have proceeded because of the relatively high friction, and later this caused a large slip and collapse of the wedge. The location off Sanriku, where there are neither seamount collisions nor rupture propagation, also has a high coefficient of basal friction. The characteristics of the taper angle, effective coefficient of basal friction, and pore fluid pressure ratio along the Japan Trench presented herein may contribute to the understanding of the relationship between the geometry of the prism and the potential for generating seismo-tsunamigenic slips.

The damage is done: Low fault friction recorded in the damage zone of the shallow Japan Trench décollement

“…in which a patch of the shallow fault zone accumulates significant elastic strain energy [Kato and Yoshida, 2011;Kennett et al, 2011;Matsubara and Obara, 2011;Koge et al, 2014] are inconsistent with the observed damage zone properties at the JFAST site, a location of inferred coseismic slip. If our interpretations are correct, great earthquakes like the 2011 M w 9.0 Tohoku-oki event could rupture to the trench without a shallow strong fault patch.…”

Simple Crack Models Explain Deformation Induced by Subduction Zone Megathrust Earthquakes

“…Observational evidence of failure mode reversal in the frontal wedge during a single megathrust event is still incomplete. Koge et al (2014) found that a portion of the wedge above the large slip area of the 2011 Tohoku earthquake with a high taper angle (indicating high basal friction) hosted normal fault activity during or after the Tohoku mainshock (indicating low basal friction, also see Cubas et al, 2013). They explained this seemingly contradictory observation by a switch of the stress state in the wedge from compressionally critical to extensionally critical, due to a basal friction evolution from statically strong to dynamically weak.…”

“…The rupture evolution from full-crack-like to half-crack-like (Fig. 8) leads to early compressional failure overprinted by later extensional failure during a single megathrust event, which might be the case for the frontal wedge during the 2011 Tohoku earthquake (Koge et al, 2014). A similar scenario may have also occurred in the Nankai Trough, based on a similar current stress state in the frontal wedge between the Nankai Trough and the Japan Trench (Lin et al, 2015).…”

“…For example, it assumes a (steady state) velocity-strengthening friction along the most seaward part of the plate interface. Such assumption may work well for understanding compressional deformation seaward of buried megathrusts, as for the central slip segment of the 2010 Maule earthquake Yue et al, 2014), but it would have a difficulty in explaining rupture to the trench and coexistence of both compressional and extensional features in the frontal wedge, as observed for the 2011 Tohoku earthquake (Koge et al, 2014).…”

Preface for the special issue of “New Perspective of Subduction Zone Earthquakes”

“…(1)The Nankai trough (14 papers; Sugihara et al 2014, Tsuji et al 2014, Idehara et al 2014, Akuhara and Mochizuki 2014, Hyodo et al 2014, Takahashi et al 2014, Yamada and Shibanuma 2015, Takeshita et al 2014, Hino et al 2015, and Toki et al 2014) (2)The Japan trench (6 papers; Aochi and Ide 2014, Koge et al 2014, Sawai et al 2014, and Boston et al 2014) (3)Other trenches and fault zones (4 papers; Maekawa et al 2014, Namiki et al 2014) and ancient accretionary complexes and faults on land (7 papers; Schumann et al 2014, Hamahashi et al 2015, Kogure et al 2014, and Hashimoto and Yamano 2014) (4)Theoretical treatments of fracture and earthquake (2 papers; Kame et al 2014 andNishiyama et al 2014) The papers are also categorized into three scientific issues, focusing on different regions within each topic:…”