Stress–strain ‘paradox’, plate coupling, and forearc seismicity at the Cascadia and Nankai subduction zones

Wang, K.

doi:10.1016/s0040-1951(99)00301-7

Cited by 84 publications

(89 citation statements)

References 65 publications

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“…Although crustal shortening in the direction of plate convergence (nearly 'margin-normal') is dominant in the interseismic period, most of accumulated strain is released at the time of the great interplate earthquake. Eventually, strain regime in the forearc block is far from 'margin-normal' compression in a long time scale (Wang, 2000).…”

Section: Subsurface Structure and Faulting Of The Mtlmentioning

confidence: 99%

Subsurface structure and faulting of the Median Tectonic Line, southwest Japan inferred from GPS velocity field

et al. 2014

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The Median Tectonic Line (MTL) is the longest arc-parallel fault system in southwest Japan whose right-lateral strike-slip is related to oblique subduction of the Philippine Sea plate (PH). We constructed a dense Global Positioning System network along a 200 km-long traverse line across the MTL in 1998 to estimate deep fault structure and slip distribution. Horizontal velocities were determined at 65 sites through campaign measurements and show crustal shortening in the direction of the plate convergence. Using multi-rectangular segments and depthdependent coupling at the plate interface, we calculate and remove elastic deformation caused by the PH subduction. The residual velocity field shows right-lateral strike-slip block motion of about 5 mm/yr across the MTL, consistent with geological estimates. However, the block boundary does not coincide with the surface trace of the MTL, being displaced 20-30 km to the north. The residual velocity field is reproduced by a model with a 35-45• northwarddipping fault plane, full locking of the upper portion to a depth of 15 km, and steady slip of 5 mm/yr below. GPS results are supported by imaging of an inclined fault plane revealed by seismic profiling and currently low activity of shallow earthquakes.

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Section: Subsurface Structure and Faulting Of The Mtlmentioning

confidence: 99%

Subsurface structure and faulting of the Median Tectonic Line, southwest Japan inferred from GPS velocity field

et al. 2014

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“…Strike-slip forearc earthquakes indicating er• < erz have prevailed since the last great subduction events [Kimura and Okano, 1995], and we are presently about half way though an average interseismic period for Nankai. The value of er• will increase in the future prior to the next subduction event but is not expected to exceed erz significantly or at all [Wang, 1999]. Therefore the temporal average of er• should be about the value of erz or less.…”

Section: Strain Because It Is the Comparison Between The Marginnormamentioning

confidence: 99%

Mechanics of low‐stress forearcs: Nankai and Cascadia

Wang¹,

He²

1999

J. Geophys. Res.

136

125

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Abstract.The Nankai and Cascadia subduction zones have low-stress forearcs, where the margin-normal horizontal compressive stress is similar to or less than the vertical stress except in the accretionary prisms. In the absence of active back-arc spreading, the forearc margin-normal stress is controlled mainly by the total shear force along the subduction fault (or the plate coupling force) and the gravitational force. The plate coupling force creates compression, and the gravitational force, in the presence of margin topography, creates lateral tension. We give a simple expression that relates the forearc stress to topography and average fault strength, with the latter represented by an effective coefficient of friction /•. We also use a finite element model of two converging plates in frictional contact to model the forearc stresses. The analyses indicate that a low-stress forearc requires not only the subduction fault to be very weak but also the mechanically coupled fault area to be narrow in the downdip direction and shallow in depth. For Nankai and Cascadia, where the coupled fault areas are narrow and shallow because of the young and hot subducting plates,/• is about 0.05 or less and in •tny case less than 0.09. The low fault strength is probably not a unique property of low-stress forearcs, since the same low/• values combined with wider and deeper coupled areas can be shown to create large margin-normal compression. In addition, there does not seem to be any relation between subduction earthquake magnitudes and plate coupling forces. Great earthquakes occur at subduction zones having low-stress forearcs such as Nankai an d C ascadia.

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“…As pointed out by Wang (2000), the long-term strain regime in the forearc is far from arc-normal contraction.…”

Section: Interseismic Velocities and Coseismic Displacementsmentioning

confidence: 96%

Present-day deformation across the southwest Japan arc: Oblique subduction of the Philippine Sea plate and lateral slip of the Nankai forearc

et al. 2014

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We estimate long-term/permanent crustal deformation in the Nankai forearc, southwest Japan, that accumulated over one earthquake deformation cycle in the Nankai subduction zone. A short-term deformation due to an oblique subduction of the Philippine Sea plate is modeled based on coseismic fault slips associated with interplate thrust earthquakes at the Nankai Trough, and subtracted from the interseismic crustal velocity field observed by GPS. The long-term/permanent deformation left in the data shows arc-parallel movement of the forearc at a rate of 5-10 mm/yr. We interpret that the forearc movement, driven by the oblique plate convergence, is accommodated by steady aseismic slip on the deep portion of the fault plane of the Median Tectonic Line (MTL) on the rear boundary of the Nankai forearc. The rate of the forearc movement is consistent with the geological slip rate of the MTL in the late Quaternary, and also with that expected from deflection of the slip vector of the 1946 Nankai earthquake from the current plate convergence vector.

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Stress–strain ‘paradox’, plate coupling, and forearc seismicity at the Cascadia and Nankai subduction zones

Cited by 84 publications

References 65 publications

Subsurface structure and faulting of the Median Tectonic Line, southwest Japan inferred from GPS velocity field

Subsurface structure and faulting of the Median Tectonic Line, southwest Japan inferred from GPS velocity field

Mechanics of low‐stress forearcs: Nankai and Cascadia

Present-day deformation across the southwest Japan arc: Oblique subduction of the Philippine Sea plate and lateral slip of the Nankai forearc

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