scholarly journals Elastic anisotropies of rocks in a subduction and exhumation setting

Solid Earth ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 1801-1828
Author(s):  
Michael J. Schmidtke ◽  
Ruth Keppler ◽  
Jacek Kossak-Glowczewski ◽  
Nikolaus Froitzheim ◽  
Michael Stipp
Keyword(s):  
Subduction Zones ◽  
Elastic Anisotropy ◽  
Accretionary Prism ◽  
P Wave ◽  
European Alps ◽  
Data Set ◽  
Wave Velocities ◽  
Wide Range ◽  
P Wave Velocities ◽  
Felsic Rocks

Abstract. Subduction and exhumation are key processes in the formation of orogenic systems across the world, for example, in the European Alps. For geophysical investigations of these orogens, it is essential to understand the petrophysical properties of the rocks involved. These are the result of a complex interaction of mineral composition and rock fabric including mineral textures (i.e., crystallographic preferred orientations). In this study we present texture-derived elastic anisotropy data for a representative set of different lithologies involved in the Alpine orogeny. Rock samples were collected in the Lago di Cignana area in Valtournenche, in the Italian northwestern Alps. At this locality a wide range of units of continental and oceanic origin with varying paleogeographic affiliations and tectono-metamorphic histories are accessible. Their mineral textures were determined by time-of-flight neutron diffraction. From these data the elastic properties of the samples were calculated. The data set includes representative lithologies from a subduction-exhumation setting. In subducted lithologies originating from the oceanic crust, the P-wave anisotropies (AVPs [%]) range from 1.4 % to 3.7 % with average P-wave velocities of 7.20–8.24 km/s and VP / VS ratios of 1.70–1.75. In the metasediments of the former accretionary prism the AVPs range from 3.7 % to 7.1 %, average P-wave velocities are 6.66–7.23 km/s and VP / VS ratios are 1.61–1.76. Continental crust which is incorporated in the collisional orogen shows AVP ranging from 1.4 % to 2.1 % with average P-wave velocities of 6.52–6.62 km/s and VP / VS ratios of 1.56–1.60. Our results suggest that mafic and felsic rocks in subduction zones at depth may be discriminated by a combination of seismic signatures: lower anisotropy and higher VP / VS ratio for mafic rocks, and higher anisotropy and lower VP / VS ratio for felsic rocks and metasediments.

scholarly journals Elastic anisotropies of rocks in a subduction and exhumation setting

2021 ◽  
Author(s):  
Michael J. Schmidtke ◽  
Ruth Keppler ◽  
Jacek Kossak-Glowczewski ◽  
Nikolaus Froitzheim ◽  
Michael Stipp
Keyword(s):  
Subduction Zones ◽  
Elastic Anisotropy ◽  
Tectonic Setting ◽  
P Wave ◽  
European Alps ◽  
Data Set ◽  
Wave Velocities ◽  
Wide Range ◽  
P Wave Velocities ◽  
Felsic Rocks

Abstract. Subduction and exhumation are key processes in the formation of orogenic systems across the world, for example, in the European Alps. For geophysical investigations of these orogens, it is essential to understand the petrophysical properties of the rocks involved. These are the result of a complex interaction of mineral composition and rock fabric including mineral textures (i.e. crystallographic preferred orientations). In this study we present texture-derived elastic anisotropy data for a representative set of different lithologies involved in the Alpine orogeny. Rock samples were collected in the Lago di Cignana area in Valtournenche, in the Italian Northwestern Alps. At this locality a wide range of units of continental and oceanic origin with varying paleogeographic affiliations and tectono-metamorphic histories are accessible. Their mineral textures were determined by time-of-flight neutron diffraction at the Frank Laboratory of Neutron Physics at the JINR in Dubna, Russia. From these data the elastic properties of the samples were calculated. The data set includes representative lithologies from a subduction-exhumation-setting. In subducted lithologies originating from the oceanic crust, the elastic anisotropies range from 1.4 to 5.0 % with average P-wave velocities of 7.01–8.24 km/s and VP / VS-ratios of 1.71–1.76. In the metasediments of the former accretionary prism the elastic anisotropies range from 4.7 to 8.2 %. This tectonic setting displays average P-wave velocities of 6.47–7.23 km/s and VP / VS-ratios of 1.60–1.76. Continental crust which is incorporated in the collisional orogen shows elastic anisotropies ranging from 1.8 to 2.8 % with average P-wave velocities of 6.42–6.51 km/s and VP / VS-ratios of 1.56–1.60. Our results suggest that mafic and felsic rocks in subduction zones at depth may be discriminated by a combination of seismic signatures: lower anisotropy and higher VP / VS ratio for mafic rocks, higher anisotropy and lower VP / VS ratio for felsic rocks and metasediments.

scholarly journals Upscaling of elastic properties in carbonates: A modeling approach based on a multiscale geophysical data set

2020 ◽  
Author(s):  
Jerome Fortin ◽  
Cedric Bailly ◽  
Mathilde Adelinet ◽  
Youri Hamon
Keyword(s):  
Elastic Properties ◽  
Wave Velocity ◽  
Representative Elementary Volume ◽  
P Wave ◽  
Elementary Volume ◽  
Data Set ◽  
Wave Velocities ◽  
P Wave Velocity ◽  
Ultrasonic Measurements ◽  
Seismic Scale

<p>Linking ultrasonic measurements made on samples, with sonic logs and seismic subsurface data, is a key challenge for the understanding of carbonate reservoirs. To deal with this problem, we investigate the elastic properties of dry lacustrine carbonates. At one study site, we perform a seismic refraction survey (100 Hz), as well as sonic (54 kHz) and ultrasonic (250 kHz) measurements directly on outcrop and ultrasonic measurements on samples (500 kHz). By comparing the median of each data set, we show that the P wave velocity decreases from laboratory to seismic scale. Nevertheless, the median of the sonic measurements acquired on outcrop surfaces seems to fit with the seismic data, meaning that sonic acquisition may be representative of seismic scale. To explain the variations due to upscaling, we relate the concept of representative elementary volume with the wavelength of each scale of study. Indeed, with upscaling, the wavelength varies from millimetric to pluri-metric. This change of scale allows us to conclude that the behavior of P wave velocity is due to different geological features (matrix porosity, cracks, and fractures) related to the different wavelengths used. Based on effective medium theory, we quantify the pore aspect ratio at sample scale and the crack/fracture density at outcrop and seismic scales using a multiscale representative elementary volume concept. Results show that the matrix porosity that controls the ultrasonic P wave velocities is progressively lost with upscaling, implying that crack and fracture porosity impacts sonic and seismic P wave velocities, a result of paramount importance for seismic interpretation based on deterministic approaches.</p><p>Bailly, C., Fortin, J., Adelinet, M., & Hamon, Y. (2019). Upscaling of elastic properties in carbonates: A modeling approach based on a multiscale geophysical data set. Journal of Geophysical Research: Solid Earth, 124. https://doi.org/10.1029/2019JB018391</p>

scholarly journals Verification of the seismic P-wave velocities under Moho boundary: Central Poland case study, LUMP profile

2018 ◽  
Vol 67 (1) ◽  
pp. 41-57
Author(s):  
Monika Dec ◽  
Marcin Polkowski ◽  
Tomasz Janik ◽  
Krystyna Stec ◽  
Marek Grad
Keyword(s):  
P Wave ◽  
Wave Velocities ◽  
Central Poland ◽  
Moho Boundary ◽  
P Wave Velocities
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