scholarly journals Shear wave splitting at the Hawaiian hot spot from the PLUME land and ocean bottom seismometer deployments

2012 ◽  
Vol 13 (2) ◽  
pp. n/a-n/a ◽  
Author(s):  
John A. Collins ◽  
Cecily J. Wolfe ◽  
Gabi Laske
Keyword(s):  
Shear Wave ◽  
Hot Spot ◽  
Shear Wave Splitting ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Wave Splitting

Fracture characterisation using frequency-dependent shear-wave splitting analysis of azimuthal anisotropy: application to fluid flow pathways at the Scanner Pockmark area, North Sea

2020 ◽  
Author(s):  
Adam Robinson ◽  
Gaye Bayracki ◽  
Calum MacDonald ◽  
Ben Callow ◽  
Giuseppe Provenzano ◽  
...  
Keyword(s):  
Shear Wave ◽  
North Sea ◽  
Seismic Anisotropy ◽  
Shear Wave Splitting ◽  
Azimuthal Anisotropy ◽  
Geophysical Data ◽  
Fluid Migration ◽  
Ocean Bottom ◽  
Air Gun ◽  
Wave Splitting

<p>Scanner pockmark, located in the Witch Ground Graben region of the North Sea, is a ~900 m by 450 m, ~22 m-deep elliptical seafloor depression at which vigorous and persistent methane venting is observed. Previous studies here have indicated the presence of chimney structures which extend to depths of several hundred meters, and which may represent the pathways along which upwards fluid migration occurs. A proposed geometry for the crack networks associated with such chimney structures comprises a background pattern outside the chimney with unconnected vertical fractures preferentially aligned with the regional stress field, and a more connected, possibly concentric fracture system within the chimney. The measurement of seismic anisotropy using shear-wave splitting (SWS) allows the presence, orientation and density of subsurface fracture networks to be determined. If the proposed model for the fracture structure of a chimney feature is correct, we would expect, therefore, to be able to observe variations in the anisotropy measured inside and outside of the chimney.</p><p>Here we test this hypothesis, using observations of SWS recorded on ocean bottom seismographs (OBS), with the arrivals generated using two different air gun seismic sources with a frequency range of ~10-200 Hz. We apply a layer-stripping approach based on observations of SWS events and shallow subsurface structures mapped using additional geophysical data to progressively determine and correct for the orientations of anisotropy for individual layers. The resulting patterns are then interpreted in the context of the chimney structure as mapped using other geophysical data. By comparing observations both at the Scanner pockmark and at a nearby reference site, we aim to further contribute to the understanding of the structures and their role in governing fluid migration. Our interpretation will additionally be informed by combining the field observations with analogue laboratory measurements and new and existing rock physics models.</p><p>This work has received funding from the NERC (CHIMNEY; NE/N016130/1) and EU Horizon 2020 programme (STEMM-CCS; No.654462).</p>

scholarly journals Shear wave splitting across the Iceland hot spot: Results from the ICEMELT experiment

2002 ◽  
Vol 107 (B12) ◽  
pp. ESE 23-1-ESE 23-12 ◽  
Author(s):  
Ingi T. Bjarnason ◽  
Paul G. Silver ◽  
Georg Rümpker ◽  
Sean C. Solomon
Keyword(s):  
Shear Wave ◽  
Hot Spot ◽  
Shear Wave Splitting ◽  
Wave Splitting

scholarly journals Shear-Wave Splitting in the Alpine Region

2021 ◽  
Author(s):  
Götz Bokelmann ◽  
Gerrit Hein ◽  
Petr Kolinsky ◽  
Irene Bianchi ◽  
AlpArray Working Group
Keyword(s):  
Shear Wave ◽  
Seismic Anisotropy ◽  
Eastern Alps ◽  
Shear Wave Splitting ◽  
Western Alps ◽  
Alpine Region ◽  
Mantle Flow ◽  
Ocean Bottom ◽  
Wave Splitting ◽  
Ocean Bottom Seismometers

<p>To constrain seismic anisotropy under and around the Alps in Europe, we study SKS shear-wave splitting from the region densely covered by the AlpArray seismic network. We apply a technique based on measuring the splitting intensity, constraining well both the fast orientation and the splitting delay. 4 years of teleseismic earthquake data were processed automatically (without human intervention), from 724 temporary and permanent broadband stations of the AlpArray deployment including ocean-bottom seismometers. We have obtained an objective image of anisotropic structure in and around the Alpine region, at a spatial resolution that is unprecedented. As in earlier studies, we observe a coherent rotation of fast axes in the western part of the Alpine chain, and a region of homogeneous fast orientation in the central Alps.  The spatial variation of splitting delay times is particularly interesting. On one hand, there is a clear positive correlation with Alpine topography, suggesting that part of the seismic anisotropy (deformation) is caused by the Alpine orogeny. On the other hand, anisotropic strength around the mountain chain shows a distinct contrast between western and eastern Alps. This difference is best explained by the more active mantle flow around the Western Alps. We discuss earlier concepts of Alpine geodynamics in the light of these new observational constraints. </p>

Solving Shear-Wave Splitting in PS Data Processing of 3D 4C OBN Seismic Survey Offshore Nunukan, Indonesia

2020 ◽  
Author(s):  
A. Waluyo
Keyword(s):  
Shear Wave ◽  
Shear Wave Splitting ◽  
Azimuthal Anisotropy ◽  
Seismic Survey ◽  
Tectonic Activity ◽  
Ocean Bottom ◽  
Survey Area ◽  
Seismic Image ◽  
Wave Splitting ◽  
Data Continuity

A 350-km2 3D 4C ocean-bottom node (OBN) offshore survey was acquired in December 2018, in Nunukan, North Kalimantan, Indonesia (Figure 1) with the processing work completed during 2019. Indonesia as a whole and the Nunukan survey area are situated in an active tectonic area where the Pacific Plate in the east and the Australian Plate in the south are actively pressing toward the Asian Plate. The tectonic activity is the main source of regional and local stress in the survey area. The dominant stress direction is Northeast-Southwest (NE-SW) (Figure 1). This stress exhibits azimuthal anisotropy in seismic waves, defined as the dependence of seismic wave speeds on propagation azimuth. In homogenous media, once the two horizontal geophone components of OBN acquisition have been properly rotated to the source-detector direction (radial) and a direction perpendicular to it (transverse), the converted waves (PS) energy will be maximum at the radial and minimum at the transverse directions. However, in azimuthal anisotropy media, shear waves split into fast and slow velocity components and the transverse data can appear to have more energy than the radial, as we observed clearly in the Nunukan OBN PS data. Ignoring the shear-wave splitting can result in degrading the PS seismic image. Herein, we outline how we addressed the azimuthal anisotropy in the Nunukan 3D OBN data. Without a shear-wave splitting correction, the PS seismic image lost data continuity of target horizons, making any attempt to correlate it with the PP image extremely difficult. The shear-wave splitting correction provided a much better PS image with improved structural data continuity and higher vertical resolution, giving greater confidence for PP-PS event correlation.

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