Depth extent of the fault-zone seismic waveguide: effects of increasing velocity with depth

Wu, Jiedi; Hole, J. A.; Snoke, J. Arthur; Imhof, Matthias G.

doi:10.1111/j.1365-246x.2008.03755.x

Cited by 15 publications

(29 citation statements)

References 33 publications

(91 reference statements)

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“…Ben‐Zion et al 2003; Peng et al 2003; Lewis et al 2005). A recent numerical analysis of FZ trapped wave pointed out that determination of fault structure at seismogenic depth requires analysis of data at higher frequencies than the FZ trapped wave (Wu et al 2008). In this study, we used precursors before the direct S waves, the S diff waves, which are sensitive to LVZ depth (Li et al 2007).…”

Section: Discussionmentioning

confidence: 99%

Shallow low-velocity zone of the San Jacinto fault from local earthquake waveform modelling

Yang

Zhu

2010

Geophysical Journal International

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S U M M A R YWe developed a method to determine the depth extent of low-velocity zone (LVZ) associated with a fault zone (FZ) using S-wave precursors from local earthquakes. The precursors are diffracted S waves around the edges of LVZ and their relative amplitudes to the direct S waves are sensitive to the LVZ depth. We applied the method to data recorded by three temporary arrays across three branches of the San Jacinto FZ. The FZ dip was constrained by differential traveltimes of P waves between stations at two side of the FZ. Other FZ parameters (width and velocity contrast) were determined by modelling waveforms of direct and FZ-reflected P and S waves. We found that the LVZ of the Buck Ridge fault branch has a width of ∼150 m with a 30-40 per cent reduction in V p and a 50-60 per cent reduction in V s . The fault dips 70 ± 5 • to southwest and its LVZ extends only to 2 ± 1 km in depth. The LVZ of the Clark Valley fault branch has a width of ∼200 m with 40 per cent reduction in V p and 50 per cent reduction in V s . The Coyote Creek branch is nearly vertical and has a LVZ of ∼150 m in width and of 25 per cent reduction in V p and 50 per cent reduction in V s . The LVZs of these three branches are not centred at the surface fault trace but are located to their northeast, indicating asymmetric damage during earthquakes.

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Section: Discussionmentioning

confidence: 99%

Shallow low-velocity zone of the San Jacinto fault from local earthquake waveform modelling

Yang

Zhu

2010

Geophysical Journal International

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“…Guided waves are hardly distinct for sources below the subducted crust. Li & Vidale (1996), Ben‐Zion (1998), Jahnke et al (2002), Igel et al (2002a), Fohrmann et al (2004) and Wu et al (2008) modelled wave propagation for sources outside a fault zone to investigate, if trapped waves can also be generated by energy transmission into the LVL. They conclude that amplitudes of guided waves are weaker or hardly generated, if sources are located beside a LVL that is continuous with depth.…”

Section: Discussionmentioning

confidence: 99%

“…In this case, seismic wave energy can also be recorded on top of the adjacent layers at any distance to the waveguide (Li & Vidale 1996; Igel et al 1997) and sources beside the LVL produce stronger guided waves by energy transmission into the waveguide (Igel et al 1997). Wu et al (2008) demonstrated that the trapping efficiency of a waveguide changes, if increasing velocities with depth both inside and outside the structure are considered.…”

Section: Introductionmentioning

confidence: 99%

Numerical modelling of seismic wave propagation along the plate contact of the Hellenic Subduction Zone��the influence of a deep subduction channel

Essen¹,

Braatz²,

Ceranna

et al. 2009

Geophysical Journal International

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S U M M A R YWe model seismic wave propagation from intermediate depth earthquakes in a subduction zone using a 2-D Chebyshev pseudospectral method. Particular attention is directed to the influence of a deep, low-viscosity subduction channel on top of the plate contact where metamorphic rocks may be exhumed by forced return flow. The study is motivated by observations of complicated dispersive and high-amplitude P-and S-wave trains in the forearc of the Hellenic Subduction Zone. The basic model is a subducted slab with a thin oceanic crust forming a lowvelocity layer. Our model setup closely follows recent results on the structure of the Hellenic Subduction Zone obtained from receiver functions and surface wave studies. They exhibit an abrupt change of the dip of the downgoing slab at about 70 km depth. The subduction channel is modelled as a thin, wedge-shaped layer of intermediate seismic velocity above a slower oceanic crust and below a faster overlying mantle wedge. We also look into the effects of a continuous phase transition from basalt to eclogite in the subducted oceanic crust and near-surface crustal structures. In all models, wave propagation is characterized by dispersive guided channel waves trapped in the low-velocity subducted crust. They produce high-amplitude arrivals in the forearc. A fast guided wave train (gP) originates from the direct P wave and a slower one (gS) from the direct S wave. Guided waves are radiated into the overlying mantle where the dip of the slab is abruptly changing. Seismogram sections for models without a subduction channel typically show two spatially separated guided wave trains, one following the oceanic crust and one travelling more steeply towards the forearc high. A subduction channel above the plate contact enhances the radiation effect of gP waves at the slab bend due to the weaker velocity contrast and inhibits the separation of the wave trains. In models with additional near-surface crustal structures the wave field is dominated by reverberations. However, guided waves remain discernible in seismogram sections because of their high amplitudes. When a basalt to eclogite phase transition is considered, guided waves are preferentially generated in the presence of a subduction channel. A pronounced gP-wave train develops particularly for sources inside this channel. On the contrary, guided waves are hardly distinct for sources below the subducted crust.

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“…Rather than relating d to a cutoff in surface roughness, we identify it as the half width of a volumetric “damage zone,” where small‐scale stress heterogeneity is attenuated by low rock strength (Figure 16). Damage zones with dimensions of tens to hundreds of meters are widely recognized features of exhumed strike‐slip faults [ Chester and Logan , 1986; Chester et al , 1993; Ben‐Zion and Sammis , 2003; Chester et al , 2005; Rockwell and Ben‐Zion , 2007], and they have been used to explain vertical low‐velocity zones of comparable dimensions inferred from fault zone guided waves [ Li et al , 1990]; these low‐velocity zones extend at least to several kilometers [ Ben‐Zion et al , 2003; Peng et al , 2003; Lewis et al , 2005] and perhaps deeper [ Li et al , 2004; Wu et al , 2008]. Drill samples across the Nojima fault, which ruptured in the 1995 Kobe earthquake, indicate that shear strength is significantly reduced and the permeability increased within a damage zone surrounding the fault core [ Lockner et al , 1999].…”

Section: Rough Fault Loading Modelmentioning

confidence: 99%

Distribution of seismicity across strike‐slip faults in California

Powers¹,

Jordan²

2010

J. Geophys. Res.

108

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[1] The distribution of seismicity about strike-slip faults provides measurements of fault roughness and damage zone width. In California, seismicity decays with distance from strike-slip faults according to a power law. This scaling relation holds out to a fault-normal distance x of 3-6 km and is compatible with a "rough fault loading" model in which the inner scale d measures the half width of a volumetric damage zone and the roll-off rate g is governed by stress variations due to fault roughness. According to Dieterich and Smith's 2-D simulations, g approximates the fractal dimension of alongstrike roughness. Near-fault seismicity is more localized on faults in northern California (NoCal, d = 60 ± 20 m, g = 1.65 ± .05) than in southern California (SoCal, d = 220 ± 40 m, g = 1.16 ± .05). The Parkfield region has a damage zone half width (d = 120 ± 30 m) consistent with the SAFOD drilling estimate; its high roll-off rate (g = 2.30 ± .25) indicates a relatively flat roughness spectrum: ∼k −1 versus k −2 for NoCal, k −3 for SoCal. Our damage zone widths (the first direct estimates averaged over the seismogenic layer) can be interpreted in terms of an across-strike "fault core multiplicity" that is ∼1 in NoCal, ∼2 at Parkfield, and ∼3 in SoCal. The localization of seismicity near individual faults correlates with cumulative offset, seismic productivity, and aseismic slip, consistent with a model in which faults originate as branched networks with broad, multicore damage zones and evolve toward more localized, lineated features with low fault core multiplicity, thinner damage zones, and less seismic coupling. Our results suggest how earthquake triggering statistics might be modified by the presence of faults.Citation: Powers, P. M., and T. H. Jordan (2010), Distribution of seismicity across strike-slip faults in California,

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Depth extent of the fault-zone seismic waveguide: effects of increasing velocity with depth

Cited by 15 publications

References 33 publications

Shallow low-velocity zone of the San Jacinto fault from local earthquake waveform modelling

Shallow low-velocity zone of the San Jacinto fault from local earthquake waveform modelling

Numerical modelling of seismic wave propagation along the plate contact of the Hellenic Subduction Zone��the influence of a deep subduction channel

Distribution of seismicity across strike‐slip faults in California

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Depth extent of the fault-zone seismic waveguide: effects of increasing velocity with depth

Cited by 15 publications

References 33 publications

Shallow low-velocity zone of the San Jacinto fault from local earthquake waveform modelling

Shallow low-velocity zone of the San Jacinto fault from local earthquake waveform modelling

Numerical modelling of seismic wave propagation along the plate contact of the Hellenic Subduction Zone���the influence of a deep subduction channel

Distribution of seismicity across strike‐slip faults in California

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Numerical modelling of seismic wave propagation along the plate contact of the Hellenic Subduction Zone��the influence of a deep subduction channel