A numerical approach for modelling fault-zone trapped waves

Gulley, Anton; Kaipio, Jari P.; Eccles, J. D.; Malin, Péter

doi:10.1093/gji/ggx199

Cited by 12 publications

(7 citation statements)

References 53 publications

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“…For the P-SV phases, FZTW have properties similar to Rayleigh-type resonance or leaky modes (e.g. Malin et al 2006;Gulley et al 2017). The latter appear between the P-and S-body waves with appreciable amplitudes on the radial and vertical components (Ellsworth & Malin 2011).…”

Section: Fault Zone Trapped Wavesmentioning

confidence: 98%

Internal structure of the San Jacinto fault zone in the trifurcation area southeast of Anza, California, from data of dense seismic arrays

Qin

Ben‐Zion

Qiu

et al. 2017

Geophysical Journal International

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We image the internal structure of the San Jacinto fault zone (SJFZ) in the trifurcation area southeast of Anza, California, with seismic records from dense linear and rectangular arrays. The examined data include recordings from more than 20 000 local earthquakes and nine teleseismic events. Automatic detection algorithms and visual inspection are used to identify P and S body waves, along with P-and S-types fault zone trapped waves (FZTW). The location at depth of the main branch of the SJFZ, the Clark fault, is identified from systematic waveform changes across lines of sensors within the dense rectangular array. Delay times of P arrivals from teleseismic and local events indicate damage asymmetry across the fault, with higher damage to the NE, producing a local reversal of the velocity contrast in the shallow crust with respect to the large-scale structure. A portion of the damage zone between the main fault and a second mapped surface trace to the NE generates P-and S-types FZTW. Inversions of high-quality S-type FZTW indicate that the most likely parameters of the trapping structure are width of ∼70 m, S-wave velocity reduction of 60 per cent, Q value of 60 and depth of ∼2 km. The local reversal of the shallow velocity contrast across the fault with respect to large-scale structure is consistent with preferred propagation of earthquake ruptures in the area to the NW.

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Section: Fault Zone Trapped Wavesmentioning

confidence: 98%

Internal structure of the San Jacinto fault zone in the trifurcation area southeast of Anza, California, from data of dense seismic arrays

Qin

Ben‐Zion

Qiu

et al. 2017

Geophysical Journal International

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“…The methodology discussed in Gulley et al (2017) is used for the computation of the FZTW responses. This method starts with the 3-D transversely isotropic elastic wave equation (Aki & Richards 2009) and assumes that the velocity model is varying in the acrossfault (z) direction only and that the wave is travelling in the x − z plane.…”

Section: O M P U Tat I O N a L A P P Roa C H Ov E Rv I E Wmentioning

confidence: 99%

“…5. These eigenmodes represent the amplitude of the wave for each frequency as it travels along the waveguide (Gulley et al 2017). This removal of the higher frequencies occurs because the lower frequency trapped modes penetrate further into the countryrock as indicated by Fig.…”

Section: Varying Source and Receiver Locations In The Fault-perpendicmentioning

confidence: 99%

“…(1c), δ does not affect the SH velocities so we only need to test this approximation on the F R guided waves. In order to do this, we continue to use the finite element method (Gulley et al 2017; see Section 2) to compute the dispersion curves for = 0.15 in the country-rock, = 0.3 is the maximum value in the fault zone and δ = /4. This simulation is compared with a simulation using the approximation δ = /2 and the error in the approximation is taken as the difference between these two simulations.…”

Section: High Angle Approximation For the Anisotropy Parameter δmentioning

confidence: 99%

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The effect of gradational velocities and anisotropy on fault-zone trapped waves

Gulley

Eccles

Kaipio

et al. 2017

Geophysical Journal International

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“…Love‐type trapped waves have been recorded and analyzed at many fault and rupture zones in California (e.g., Catchings et al, 2016; Cochran et al, 2009; Lewis et al, 2005; Li et al, 1990, 1994; Peng et al, 2003; Yang et al, 2011), Japan (e.g., Mamada et al, 2004; Mizuno & Nishigami, 2006), Turkey (e.g., Ben‐Zion et al, 2003), Italy (e.g., Avallone et al, 2014; Rovelli et al, 2002), Israel (Haberland et al, 2003), and other locations. A less common type of trapped waves involves leaky modes (normal modes with phase velocities higher than body wave velocities) or Rayleigh‐type signals that appear on the radial and vertical components with appreciable amplitudes between the direct P and S waves (Gulley et al, 2017; Malin et al, 2006). These waves have been observed at the Parkfield section of the San Andreas fault (e.g., Ellsworth & Malin, 2011) and several locations along the San Jacinto fault zone (e.g., Qin et al, 2018; Qiu et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Analysis of Fault Zone Resonance Modes Recorded by a Dense Seismic Array Across the San Jacinto Fault Zone at Blackburn Saddle

et al. 2020

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We present observations and modeling of spatial eigen-functions of resonating waves within fault zone waveguide, using data recorded on a dense seismic array across the San Jacinto Fault Zone (SJFZ) in southern California. The array consists of 5-Hz geophones that cross the SJFZ with~10-30 m spacing at the Blackburn Saddle near the Hemet Stepover. Wavefield snapshots after the S wave arrival are consistent for more than 50 near-fault events, suggesting that this pattern is controlled by the fault zone structure rather than source properties. Data from example event with high signal to noise ratio show three main frequency peaks at~1.3,~2.0, and~2.8 Hz in the amplitude spectra of resonance waves averaged over stations near the fault. The data are modeled with analytical expressions for eigen-functions of resonance waves in a low-velocity layer (fault zone) between two quarter-spaces. Using a grid search-based method, we investigate the possible width of the waveguide, location within the array, and shear wave velocities of the media that fit well the resonance signal at~1.3 Hz. The results indicate a~300 m wide damaged fault zone layer with~65% S wave velocity reduction compared to the host rock. The SW edge of the low-velocity zone is near the mapped fault surface trace, indicating that the damage zone is asymmetrically located at the regionally faster NE crustal block. The imaging resolution of the fault zone structure can be improved by modeling fault zone resonance modes and trapped waves together.

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A numerical approach for modelling fault-zone trapped waves

Cited by 12 publications

References 53 publications

Internal structure of the San Jacinto fault zone in the trifurcation area southeast of Anza, California, from data of dense seismic arrays

Internal structure of the San Jacinto fault zone in the trifurcation area southeast of Anza, California, from data of dense seismic arrays

The effect of gradational velocities and anisotropy on fault-zone trapped waves

Analysis of Fault Zone Resonance Modes Recorded by a Dense Seismic Array Across the San Jacinto Fault Zone at Blackburn Saddle

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