Temporal and spatial variations in seismic anisotropy and V/V ratios in a region of slow slip

Zal, Hubert; Jacobs, Katrina; Savage, Martha K.; Yarce, J.; Mroczek, Stefan; Graham, Kenny; Todd, Erin; Nakai, J. S.; Iwasaki, Yu; Sheehan, A. F.; Mochizuki, Kimihiro; Wallace, Laura; Schwartz, S. Y.; Webb, Spahr C.; Henrys, S.

doi:10.1016/j.epsl.2019.115970

Cited by 36 publications

(86 citation statements)

References 42 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The fast axes of Vp exhibit a clear spatial pattern: While they are mostly oriented in the trench‐normal (i.e., plate convergence) direction in the accretionary wedge, they are rotated to the trench‐parallel direction on the seaward side of the trench and in the landward north Tuaheni basin (Figures 5 and 9a). This regional variation is consistent with the results of shear wave splitting analysis (Zal et al, 2020; Figure 9b) and the regional stress field estimated by focal mechanism solutions (Townend et al, 2012). Occurrence of fast axes in the accretionary wedge agrees well with the directions of maximum horizontal stress inferred from borehole breakouts at Drilling Sites U1518 and U1519 (Figure 9a).…”

Section: Resultssupporting

confidence: 90%

“…This change may be related to the Tuaheni Ridge and the edge of the North Tuaheni basin, in an area where forearc extension has been previously mapped (Böttner et al, 2018; Figures 9c and 12a). The variation in seismic anisotropy is consistent with the results of shear wave splitting analysis (Zal et al, 2020; Figure 9b). While the depth variation in anisotropy was not well constrained by Zal et al (2020), our results demonstrate that the upper few kilometers in the overriding plate is the region which determines this spatial pattern.…”

Section: Discussionsupporting

confidence: 90%

“…Seismic anisotropy at shallow depths in subduction zones is an important indicator of the stress state and is commonly interpreted to be caused by preferentially oriented cracks in a compressional stress regime associated with plate subduction (Tonegawa et al, 2017; Zal et al, 2020). Our findings that (i) significant anisotropy occurs associated with the active splay faults and the deformation front and (ii) the fast axes in the accretionary wedge lie parallel to the plate convergence direction suggest that the regional stress field and preferentially oriented cracks in the fault‐bound blocks primarily control the seismic anisotropy.…”

Section: Discussionmentioning

confidence: 99%

“…Along the~500-km-long Hikurangi subduction zone, the oceanic Hikurangi Plateau, a large igneous province of Cretaceous age, is subducting beneath the North Island of New Zealand (e.g., Wood & Davy, 1994). The Hikurangi Plateau includes numerous seamounts and other volcanic features and is composed of basaltic basement thickly overlain by sedimentary layers of Mesozoic to Cenozoic ages (Barnes et al, 2020;Davy et al, 2008).…”

Section: Geological Settingmentioning

confidence: 99%

“…Eberhart‐Phillips and Reyners (2009) found that the Hikurangi margin forearc is characterized by heterogeneous anisotropy (both in magnitude and azimuth) using earthquake arrival time data. Shear wave splitting for event‐station pairs on HOBITSS ocean bottom seismometers and onshore GeoNet seismic stations yields E‐W fast azimuths in the accretionary wedge close to the trench and variable directions further landward, which may be explained by fracture and fault patterns created by subducting seamounts (Zal et al, 2020). Borehole breakouts at drill sites support that SH max at shallow depths in the accretionary wedge is orthogonal to the deformation front (Wallace et al, 2019).…”

Section: Seismic Anisotropy In the Crust Of The Northern Hikurangi Mamentioning

confidence: 99%

See 4 more Smart Citations

Three‐Dimensional P Wave Velocity Structure of the Northern Hikurangi Margin From the NZ3D Experiment: Evidence for Fault‐Bound Anisotropy

et al. 2020

Self Cite

View full text Add to dashboard Cite

We present a high-resolution three-dimensional (3-D) anisotropic P wave velocity (Vp) model in the northern Hikurangi margin offshore Gisborne, New Zealand, constructed by tomographic inversion of over 430,000 first arrivals recorded by a dense grid of ocean bottom seismometers. Since the study area covers a region where shallow slow slip events (SSEs) occur repeatedly and the subduction of a seamount is proposed, it offers an ideal location to link our understanding of structural and hydrogeologic properties at megathrust faults to slip behavior. The Vp model reveals an~30-km-wide, low-velocity accretionary wedge at the toe of the overriding plate, where previous seismic reflection studies show a series of active thrust faults branching from the plate interface. We find some locations with significant Vp azimuthal anisotropy >5% near the branching faults and the deformation front. This finding suggests that the anisotropy is not ubiquitous and homogeneous within the overriding plate, but more localized in the vicinity of active thrust faults. The fast axes of Vp within the accretionary wedge are mostly oriented to the plate convergence direction, which is interpreted as preferentially oriented cracks in a compressional stress regime associated with plate subduction. We find that the magnitudes of anisotropy are roughly equivalent to values found at oceanic spreading centers, where the extensional stress regime is dominant and the crack density is expected to be higher than subduction zones. This consideration may indicate that additional effects such as fault foliation and clay mineral alignment also contribute to upper plate anisotropy along subduction margins. Plain Language Summary We use man-made sound waves (controlled-source seismic data) to reveal in three dimensions the speed of sound within rocks and sediments that make up the northern Hikurangi margin off the east coast of North Island, New Zealand. We find that the sediments lying on top of subducting plate (accretionary wedge) have low velocities and host several branching faults. We also find that the speed of sound is faster when measured in the direction that the plates are colliding and slower when measured parallel to the faults (this phenomenon is called seismic anisotropy). This difference in speed suggests that the faults contain cracks that are aligned parallel to the direction of the plate subduction.

show abstract

Section: Resultssupporting

confidence: 90%

Section: Discussionsupporting

confidence: 90%

Section: Discussionmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

Section: Seismic Anisotropy In the Crust Of The Northern Hikurangi Mamentioning

confidence: 99%

See 3 more Smart Citations

Three‐Dimensional P Wave Velocity Structure of the Northern Hikurangi Margin From the NZ3D Experiment: Evidence for Fault‐Bound Anisotropy

et al. 2020

Self Cite

View full text Add to dashboard Cite

show abstract

Water depth dependence of long-range correlation in nontidal variations in seafloor pressure

Inoue

Ito

Wallace

et al. 2020

Preprint

Self Cite

View full text Add to dashboard Cite

Temporal fluctuations in ocean bottom pressure originate from phenomena at varying spatio-temporal scales over the Earth's surface driven by atmospheric and oceanic circulation, tides, tsunamis, and tectonic deformation of the crust. Ocean-bottom pressure gauges (OBPs) are becoming widely used to measure tectonic signals, particularly those caused by tectonic deformation in some subduction zones (e.g.,

show abstract

Variable in-situ stress orientations across the northern Hikurangi Subduction Margin

McNamara

Behboudi

Wallace

et al. 2020

Preprint

Self Cite

View full text Add to dashboard Cite

Fault slip resulting from stress accumulation is a function of the orientation and magnitudes of the three principal stresses (σ 1 >σ 2 >σ 3 ), subsurface pore pressures (P p ), existing fault orientations, and rock cohesion and friction (Anderson, 1906;M. L. Zoback et al., 1989). Stress orientations, magnitudes, and P p can in turn be altered by local topography, mechanical contrasts of subsurface geological units, and earthquake and creep activity. Studies of active tectonic systems, including shallow subduction zones, reveal both temporal and spatial perturbations in the crustal stress state related to fault geometry and activity (

show abstract

Temporal and spatial variations in seismic anisotropy and V/V ratios in a region of slow slip

Cited by 36 publications

References 42 publications

Three‐Dimensional P Wave Velocity Structure of the Northern Hikurangi Margin From the NZ3D Experiment: Evidence for Fault‐Bound Anisotropy

Three‐Dimensional P Wave Velocity Structure of the Northern Hikurangi Margin From the NZ3D Experiment: Evidence for Fault‐Bound Anisotropy

Water depth dependence of long-range correlation in nontidal variations in seafloor pressure

Variable in-situ stress orientations across the northern Hikurangi Subduction Margin

Contact Info

Product

Resources

About