Multichannel Alignment of <i>S</i> Waves

Bostock, M. G.; Plourde, A. P.; Drolet, Doriane; Littel, Geena

doi:10.1785/0120210076

Cited by 7 publications

(4 citation statements)

References 16 publications

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“…We used the double‐difference seismic tomography code tomoDD10 (Zhang, 2003; Zhang & Thurber, 2003) to invert for the preliminary velocity structure within the region of the 2012 M w 7.8 rupture, keeping the ∼2,700 earthquake hypocenters constant. In both hypoDD and tomoDD10 inversions, we employed both catalog differential times (ph2dt, Waldhauser & Ellsworth, 2000) and cross‐correlation differential times (Bostock et al., 2022).…”

Section: Methodsmentioning

confidence: 99%

Incipient Subduction and Slip Partitioning at High Obliquity: The Haida Gwaii Plate Boundary

Oliva,

Bostock,

Schaeffer

et al. 2024

JGR Solid Earth

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Plate motion obliquity along the dominantly transform Queen Charlotte plate boundary (QCPB) peaks offshore Haida Gwaii. To investigate the effects of obliquity on plate boundary deformation, we analyze continuous seismic waveforms from temporary and permanent stations from 1998 to 2020 to generate a catalog of ∼50,000 earthquakes across Haida Gwaii. We use an automated technique based on auto‐regressive phase detection and onset estimation to obtain the initial seismic catalog, integrate existing catalogs, invert for 3D velocity structure using data from the best constrained period, and relocate the entire catalog using the new 3D velocity model. We investigate the seismically active sections of the transcurrent Queen Charlotte fault (QCF), noting that little seismicity locates directly along its bathymetrically defined trace. Instead, seismicity illuminates a complex system of segmented structures with variable geometries along strike. Other clusters highlight active shallow faults within the highly deformed Queen Charlotte terrace. Few aftershocks appear on the thrust plane of the 2012 Mw 7.8 Haida Gwaii earthquake except near its inferred intersection with the QCF at 15–20 km depths, suggesting elevated residual stress at the juncture of slip‐partitioning. Deep crustal seismicity (up to ∼20 km depths) beneath central Haida Gwaii aligned parallel to the strike of the thrust plane may represent landward underthrusting of the Pacific plate. Our results suggest possible coseismic strike‐slip rupture on the QCF during the 2012 earthquake and add support to the thesis that highly oblique transform boundaries are viable settings for subduction initiation.

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Section: Methodsmentioning

confidence: 99%

Incipient Subduction and Slip Partitioning at High Obliquity: The Haida Gwaii Plate Boundary

Oliva,

Bostock,

Schaeffer

et al. 2024

JGR Solid Earth

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“…We employ the P-and S-waveforms for LFE templates 053, 065, and 070 at 5 stations to determine a) delays for S-and P-wave arrivals corresponding to the nominal template location, computed using the alignment procedures in [72]; b) the splitting parameters that best reduce the S-wave particle motions on the two horizontal coordinates to rectilinear motion isolated to a single channel [73]; and c) the expected P-polarity for P-waveforms on the vertical component. These quantities are used to normalize 24 hourlong waveforms for the 4 S-wave stations (KELB (2003)/KLNB (2004 and 2005), PGC, SILB, SSIB) and 1 P-wave station (SNB) employed in this study (stations KELB and KLNB differ in location by ~ 40 m).…”

Section: Detection and Locationmentioning

confidence: 99%

Tectonic tremor: the chatter of mafic underplating beneath southern Vancouver Island?

Littel,

Bostock,

Sammis

et al. 2024

Preprint

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Tremor is a low-amplitude seismic signal that usually temporally coincides with episodic slow fault slip at plate boundaries worldwide. Since the discovery of tremor in Cascadia, significant effort has been devoted to understanding its relationship to slow slip. However, its source mechanism has been widely debated, owing in large part to the challenge of locating sources accurately in depth. We assemble a tremor catalog of 4,851 events for a ~ 10 X 20 km2 area on southern Vancouver Island from slow slip episodes in 2003–2005 using a cross-station detection method adapted from previous studies, which we extend to use both P- and S- waves, thereby recovering accurate depths. Tremor occurs in distinct, quasi-planar clusters in the plate boundary region at a depth near 39 km, just beneath a layer of high reflectivity and within a zone of elevated Poisson’s ratio. We interpret this tremor to represent mafic underplating, wherein shearing generates tremor and continuously erodes basaltic material of the upper few hundred meters of the oceanic crust. Comminuted basalt with an increasingly anisotropic fabric is gradually plated onto the overriding lithosphere to form the highly reflective layer. Localized areas of material transfer within the subduction zone may manifest the distinct tremor clusters.

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“…The main reason is the difficulty in obtaining reliable time shifts with MCCC since cross‐correlation of noisy seismograms tends to obtain inaccurate time shifts and thus insignificant improvements after stacking. The cross‐correlation‐based techniques have been shown to be closely related to the framework of rank reduction via singular value decomposition, which could be further extended to align more complicated S waves (Bostock et al., 2021).…”

Section: Introductionmentioning

confidence: 99%

SMatStack to Enhance Noisy Teleseismic Seismic Phases: Validation and Application to Resolving Depths of Oceanic Transform Earthquakes

Fang,

Abercrombie

2023

Geochem Geophys Geosyst

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The depths of most moderate‐sized oceanic earthquakes are poorly constrained because of the lack of local recording stations and noisy teleseismic recordings. This hampers our understanding of slip behaviors along oceanic faults and the mechanical properties of the oceanic lithosphere. In this study, we develop a new method to enhance the weak body‐wave signals, particularly the depth phases, associated with earthquakes on oceanic transform faults using large‐aperture arrays in the teleseismic range. We simulate the enhanced teleseismic signals to refine the centroid depths of moderate‐sized earthquakes. We validate the new approach using synthetic waveforms and show it outperforms conventional methods when dealing with noisy signals. We obtain the depth estimates for three moderate‐sized earthquakes on the Chain transform fault in the equatorial Atlantic Ocean and find two of them are consistent with a local catalog derived using oceanic bottom seismometers. Application of the new method to the past decades of teleseismic recordings of moderate‐sized earthquakes on the large and slow‐slipping transform faults will provide significantly improved constraints on the width of the seismogenic zone, thus advancing our understanding of the rheology of oceanic lithosphere and earthquake processes in oceanic settings and, by comparison, their more dangerous continental counterparts. The new method is not limited to oceanic transform earthquakes, but can be easily adapted to other seismological studies in which noisy but coherent signals could be revisited for better usage.

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Multichannel Alignment of S Waves

Cited by 7 publications

References 16 publications

Incipient Subduction and Slip Partitioning at High Obliquity: The Haida Gwaii Plate Boundary

Incipient Subduction and Slip Partitioning at High Obliquity: The Haida Gwaii Plate Boundary

Tectonic tremor: the chatter of mafic underplating beneath southern Vancouver Island?

SMatStack to Enhance Noisy Teleseismic Seismic Phases: Validation and Application to Resolving Depths of Oceanic Transform Earthquakes

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