Effective stress and pore pressure in the Nankai accretionary prism off the Muroto Peninsula, southwestern Japan

Tsuji, Takeshi; Tokuyama, Hidekazu; Pisani, P. Costa; Moore, Gregory F.

doi:10.1029/2007jb005002

Cited by 98 publications

(88 citation statements)

References 92 publications

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“…These values of ψ result in excess pore pressures at 75 m below the décollement increasing from ∼2.1 to 37.0 MPa, from the trench to 40 km landward (Figure 8c). For comparison, a study by Tsuji et al [2008], using a method similar to that of Tobin and Saffer [2009] reported excess pore pressure beneath the décollement increasing from ∼5–20 MPa from the trench to ∼20 km landward.…”

Section: Resultsmentioning

confidence: 99%

Pore pressure development beneath the décollement at the Nankai subduction zone: Implications for plate boundary fault strength and sediment dewatering

Skarbek

Saffer

2009

J. Geophys. Res.

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[1] Despite its importance for plate boundary fault processes, quantitative constraints on pore pressure are rare, especially within fault zones. Here, we combine laboratory permeability measurements from core samples with a model of loading and pore pressure diffusion to investigate pore fluid pressure evolution within underthrust sediment at the Nankai subduction zone. Independent estimates of pore pressure to $20 km from the trench, combined with permeability measurements conducted over a wide range of effective stresses and porosities, allow us to reliably simulate pore pressure development to greater depths than in previous studies and to directly quantify pore pressure within the plate boundary fault zone itself, which acts as the upper boundary of the underthrusting section. Our results suggest that the time-averaged excess pore pressure (P*) along the décollement ranges from 1.7-2.1 MPa at the trench to 30.2-35.9 MPa by 40 km landward, corresponding to pore pressure ratios of l b = 0.68-0.77. For friction coefficients of 0.30-0.40, the resulting shear strength along the décollement remains <12 MPa over this region. When noncohesive critical taper theory is applied using these values, the required pore pressure ratios within the wedge are near hydrostatic (l w = 0.41-0.59), implying either that pore pressure throughout the wedge is low or that the fault slips only during transient pulses of elevated pore pressure. In addition, simulated downward migration of minima in effective stress during drainage provides a quantitative explanation for down stepping of the décollement that is consistent with observations at Nankai.Citation: Skarbek, R. M., and D. M. Saffer (2009), Pore pressure development beneath the décollement at the Nankai subduction zone: Implications for plate boundary fault strength and sediment dewatering,

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Section: Resultsmentioning

confidence: 99%

Pore pressure development beneath the décollement at the Nankai subduction zone: Implications for plate boundary fault strength and sediment dewatering

Skarbek

Saffer

2009

J. Geophys. Res.

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“…Although these Paleozoic rocks dominate the surface geology, outcrops of Triassic plutons lie along the coastline. Some of these intrusions contain fayalite, indicating a mantle-derived magmatic source (Vásquez and Franz, 2008). The intrusions were emplaced when the margin was undergoing post-orogenic collapse and rifting, marking the transitional period between Gondwanan amalgamation and contemporary Andean-style subduction (Vásquez et al, 2011).…”

Section: Characteristics Of the Central Chile Subduction Zonementioning

confidence: 99%

Anatomy of a megathrust: The 2010 M8.8 Maule, Chile earthquake rupture zone imaged using seismic tomography

Hicks

Rietbrock

Ryder

et al. 2014

Earth and Planetary Science Letters

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Knowledge of seismic velocities in the seismogenic part of subduction zones can reveal how material properties may influence large ruptures. Observations of aftershocks that followed the 2010 M w 8.8 Maule, Chile earthquake provide an exceptional dataset to examine the physical properties of a megathrust rupture zone. We manually analysed aftershocks from onshore seismic stations and ocean bottom seismometers to derive a 3-D velocity model of the rupture zone using local earthquake tomography. From the trench to the magmatic arc, our velocity model illuminates the main features within the subduction zone. We interpret an east-dipping high P-wave velocity anomaly (>6.9 km/s) as the subducting oceanic crust and a low P-wave velocity (<6.25 km/s) in the marine forearc as the accretionary complex. We find two large P-wave velocity anomalies (∼7.8 km/s) beneath the coastline. These velocities indicate an ultramafic composition, possibly related to extension and a mantle upwelling during the Triassic. We assess the role played by physical heterogeneity in governing megathrust behaviour. Greatest slip during the Maule earthquake occurred in areas of moderate P-wave velocity (6.5-7.5 km/s), where the interface is structurally more uniform. At shallow depths, high fluid pressure likely influenced the up-dip limit of seismic activity. The high velocity bodies lie above portions of the plate interface where there was reduced coseismic slip and minimal postseismic activity. The northern velocity anomaly may have acted as a structural discontinuity within the forearc, influencing the pronounced crustal seismicity in the Pichilemu region. Our work provides evidence for how the ancient geological structure of the forearc may influence the seismic behaviour of subduction megathrusts.

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“…Research has long shown that velocity shows dependency on static stress conditions [e.g., Toksöz et al, 1976;Christensen and Wang, 1985;Tsuji et al, 2008]. Several studies have observed the velocity change associated with stress change due to earthquakes by using multiplet earthquake analysis [e.g., Poupinet et al, 1984] or controlled source experiments [e.g., Nishimura et al, 2000;Niu et al, 2008].…”

Section: Introductionmentioning

confidence: 99%

Monitoring seismic velocity change caused by the 2011 Tohoku‐oki earthquake using ambient noise records

Minato

Tsuji

Ohmi

et al. 2012

Geophysical Research Letters

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100

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We estimated the changes in seismic velocity in the southern Tohoku district of Japan during the six‐month period centered on the 11 March 2011 Tohoku‐oki earthquake, using scattered waves retrieved by autocorrelation of ambient seismic noise. The estimated velocity decrease after the earthquake, and after two large aftershocks in the study area, was as great as 1.5% in the area nearest to the mainshock. The velocity changes displayed gradual healing. The spatial distribution of the velocity change showed a correlation with both the changes in static strain, derived from GPS records, and the peak particle velocity experienced during the three earthquakes, derived from strong‐motion records. Therefore, our results show that velocity changes possibly contain information from deep in the crust bearing on coseismic stress release, in addition to shallower effects due to strong ground motion.

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Effective stress and pore pressure in the Nankai accretionary prism off the Muroto Peninsula, southwestern Japan

Cited by 98 publications

References 92 publications

Pore pressure development beneath the décollement at the Nankai subduction zone: Implications for plate boundary fault strength and sediment dewatering

Pore pressure development beneath the décollement at the Nankai subduction zone: Implications for plate boundary fault strength and sediment dewatering

Anatomy of a megathrust: The 2010 M8.8 Maule, Chile earthquake rupture zone imaged using seismic tomography

Monitoring seismic velocity change caused by the 2011 Tohoku‐oki earthquake using ambient noise records

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