dc.contributor.author
Charoensawan, Jirapat
dc.contributor.author
Adam, Ludmila
dc.contributor.author
Ofman, Michael
dc.contributor.author
Toy, Virginia
dc.contributor.author
Simpson, Jonathan
dc.contributor.author
Zhong, Xin
dc.contributor.author
Schuck, Bernhard
dc.date.accessioned
2021-08-06T13:33:27Z
dc.date.available
2021-08-06T13:33:27Z
dc.identifier.uri
https://refubium.fu-berlin.de/handle/fub188/31553
dc.identifier.uri
http://dx.doi.org/10.17169/refubium-31285
dc.description.abstract
P-wave anisotropy is significant in the mylonitic Alpine Fault shear zone. Mineral- and texture-induced anisotropy are dominant in these rocks but further complicated by the presence of fractures. Electron back-scattered diffraction and synchrotron X-ray microtomography (micro-CT) data are acquired on exhumed schist, protomylonite, mylonite, and ultramylonite samples to quantify mineral phases, crystal preferred orientations, microfractures, and porosity. The samples are composed of quartz, plagioclase, mica and accessory garnet, and contain 3–5% porosity. Based on the micro-CT data, the representative pore shape has an aspect ratio of 5:2:1. Two numerical models are compared to calculate the velocity of fractured rocks: a 2D wave propagation model, and a differential effective medium model (3D). The results from both models have comparable pore-free fast and slow velocities of 6.5 and 5.5 km/s, respectively. Introducing 5% fractures with 5:2:1 aspect ratio, oriented with the longest axes parallel to foliation decreases these velocities to 6.3 and 5.0 km/s, respectively. Adding both randomly oriented and foliation-parallel fractures hinders the anisotropy increase with fracture volume. The anisotropy becomes independent of porosity when 80% of fractures are randomly oriented. Modeled anisotropy in 2D and 3D are different for similar fracture aspect ratios, being 30 and 15%, respectively. This discrepancy is the result of the underlying assumptions and limitations. Our numerical results explain the effects that fracture orientations and shapes have on previously published field- and laboratory-based studies. Through this numerical study, we show how mica-dominated, pore-free P-wave anisotropy compares to that of fracture volume, shape and orientation for protolith and shear zone rocks of the Alpine Fault.
en
dc.format.extent
16 Seiten
dc.rights.uri
https://creativecommons.org/licenses/by/4.0/
dc.subject
P-wave velocity
en
dc.subject
Alpine Fault
en
dc.subject
electron backscattered diffraction
en
dc.subject
numerical modeling
en
dc.subject
synchrotron X-ray microtomography
en
dc.subject.ddc
500 Naturwissenschaften und Mathematik::550 Geowissenschaften, Geologie::550 Geowissenschaften
dc.title
Fracture Shape and Orientation Contributions to P-Wave Velocity and Anisotropy of Alpine Fault Mylonites
dc.type
Wissenschaftlicher Artikel
dcterms.bibliographicCitation.articlenumber
645532
dcterms.bibliographicCitation.doi
10.3389/feart.2021.645532
dcterms.bibliographicCitation.journaltitle
Frontiers in Earth Science
dcterms.bibliographicCitation.volume
9
dcterms.bibliographicCitation.url
https://doi.org/10.3389/feart.2021.645532
refubium.affiliation
Geowissenschaften
refubium.affiliation.other
Institut für Geologische Wissenschaften / Fachrichtung Geochemie, Hydrogeologie, Mineralogie
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refubium.resourceType.isindependentpub
no
dcterms.accessRights.openaire
open access
dcterms.isPartOf.eissn
2296-6463
refubium.resourceType.provider
WoS-Alert