Nonvolcanic Deep Tremor Associated with Subduction in Southwest Japan

Obara, Kazushige

doi:10.1126/science.1070378

Cited by 1,224 publications

(1,411 citation statements)

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“…Rough tremor source locations spread in a broad area, often with a clear migration along subduction zone strike with time. Calculated depths are in the range of 20-40 km [Obara, 2002]. Similar seismic signals have been recently observed in the Cascadia subduction zone.…”

Section: Introductionsupporting

confidence: 62%

Array measurements of deep tremor signals in the Cascadia subduction zone

Rocca

McCausland

Galluzzo

et al. 2005

Geophysical Research Letters

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Preliminary analysis of deep tremor recorded during July, 2004, in the Cascadia Subduction zone shows that small aperture arrays can resolve the slowness and back azimuth of seismic waves with a useful resolution. Data were collected by three dense arrays of short‐period seismometers specifically deployed in the Puget Sound area under an US‐Italy‐Canada cooperative effort. Slowness analyses at the three arrays indicate that the 2–4 Hz tremor wave‐field is composed of waves propagating with apparent velocities higher than 4 km/s. Combining this with polarisation analysis show these waves to be transverse (SH) waves. However, P‐waves, though smaller in amplitude, can be detected by different slowness values obtained for the radial and transverse components. The intersection of wave vectors determined by the back azimuth and slowness values measured at the three arrays provides a preliminary estimate of source location for a sample of the recorded deep tremor.

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Section: Introductionsupporting

confidence: 62%

Array measurements of deep tremor signals in the Cascadia subduction zone

Rocca

McCausland

Galluzzo

et al. 2005

Geophysical Research Letters

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“…We suggest that ductile failure of ultramylonite zones may provide a viable mechanism inducing earthquakes in the lower crust [Maggi et al, 2000]. Likewise, ductile failure is a possible mechanism explaining the occurrence of intermediate and deep nonvolcanic tremors in subduction zones [Obara, 2002;Obara and Hirose, 2006;Ito and Obara, 2006;Ito et al, 2007;Brown et al, 2009] and fault zones [Nadeau and Dolenc, 2005], which are commonly assumed to be generated by dehydration reactions and/or fluid pressure pulses.…”

Section: Geological Applicationmentioning

confidence: 99%

Superplasticity and ductile fracture of synthetic feldspar deformed to large strain

Rybacki¹,

Wirth²,

Dresen³

2010

J. Geophys. Res.

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[1] We performed high-strain torsion experiments on fine-grained (≈4 mm) anorthite aggregates in a Paterson-type gas deformation apparatus. The dense hydrous (≈0.1 wt% H 2 O) samples contain < 3 vol% Si-enriched residual glass located at triple junctions. Specimens were twisted at constant rate to a maximum shear strain of about 5 at experimental conditions of 100-400 MPa confining pressure, temperatures of 950°C-1200°C, and shear strain rates of ≈2 × 10 −5 , 5 × 10 −5 , and 2 × 10 −4 s −1 . Resulting maximum shear stresses at the sample periphery were in the range of ≈2-80 MPa. The samples showed strain hardening at slow deformation rate and strain weakening at fast strain rate, respectively. Fitting the stress strain rate data to a power law yields linear viscous behavior. Microstructural analysis shows locally enhanced dislocation density, suggesting diffusion-assisted and/or dislocation-assisted grain boundary sliding as the dominant deformation mechanism. Deformed samples exhibit abundant cavities, nucleated mostly at grain triple junctions and at grain boundaries in response to cooperative grain boundary sliding. At shear strains ≥ 2, growth and coalescence of the cavities form an anastomozing network of regularly spaced strings oriented at about 30°to the direction of maximum compressive stress and ∼15°to the shear plane. Strain is localized along these shear bands associated with a shape-preferred orientation of high-aspect ratio feldspar grains and with segregation of initial pore fluids (residual glass) into the bands. More than one third of the samples were deformed to terminal failure that occurred suddenly at shear strains of ≈3-5. The experiments indicate that cavitation damage may facilitate fluid flow and deep seismicity in highly strained shear zones.Citation: Rybacki, E., R. Wirth, and G. Dresen (2010), Superplasticity and ductile fracture of synthetic feldspar deformed to large strain,

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“…Slow slip events (sometimes referred to as slow earthquakes) had been recognized for some time in the literature using strainmeters (Linde et al, 1996) and seismometers (e.g., Kanamori and Stewart, 1979), although their importance and locations only became apparent when networks of GPS stations started recording and documenting their widespread occurrence. Associated with slow slip, a new source of seismic energy (called non-volcanic tremor) in the forearc was discovered by Obara (2002) off southwest Japan, which appeared as coherent noise propagating across arrays of seismograph stations. Rogers and Dragert (2003) then found similar signals in the forearc of the Cascadia subduction zone that occurred concurrently with slow slip events and both phenomena recurred episodically, which led to the term "Episodic Tremor and Slip", or…”

Section: Accepted M Manuscriptmentioning

confidence: 99%

Teleseismic constraints on the geological environment of deep episodic slow earthquakes in subduction zone forearcs: A review

2016

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More than a decade after the discovery of deep episodic slow slip and tremor, or slow earthquakes, at subduction zones, much research has been carried out to investigate the structural and seismic properties of the environment in which they occur. Slow earthquakes generally occur on the megathrust fault some distance downdip of the great earthquake seismogenic zone in the vicinity of the mantle wedge corner, where three major structural elements are in contact: the subducting oceanic crust, the overriding forearc crust and the continental mantle. In this region, thermo-petrological models predict significant fluid production from the dehydrating oceanic crust and mantle due to prograde metamorphic reactions, and their consumption by hydrating the mantle wedge. These fluids are expected to affect the dynamic stability of the megathrust fault and enable slow slip by increasing pore-fluid pressure and/or reducing friction in fault gouges.Resolving the fine-scale structure of the deep megathrust fault and the in situ distribution of fluids where slow earthquakes occur is challenging, and most advances have been made using A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPTteleseismic scattering techniques (e.g., receiver functions). In this paper we review the teleseismic structure of six well-studied subduction zones (three hot, i.e., Cascadia, southwest Japan, central Mexico, and three cool, i.e., Costa Rica, Alaska, and Hikurangi) that exhibit slow earthquake processes and discuss the evidence of structural and geological controls on the slow earthquake behavior. We conclude that changes in the mechanical properties of geological materials downdip of the seismogenic zone play a dominant role in controlling slow earthquake behavior, and that near-lithostatic pore-fluid pressures near the megathrust fault may be a necessary but insufficient condition for their occurrence.

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Nonvolcanic Deep Tremor Associated with Subduction in Southwest Japan

Cited by 1,224 publications

References 4 publications

Array measurements of deep tremor signals in the Cascadia subduction zone

Array measurements of deep tremor signals in the Cascadia subduction zone

Superplasticity and ductile fracture of synthetic feldspar deformed to large strain

Teleseismic constraints on the geological environment of deep episodic slow earthquakes in subduction zone forearcs: A review

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