Seismic properties of rocks exposed in the POLAR profile region—constraints on the interpretation of the refraction data

Kern, H.; Walther, C.; Flüh, Ernst R.; Marker, Mogens

doi:10.1016/0301-9268(93)90074-c

Cited by 36 publications

(25 citation statements)

References 14 publications

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“…Possible velocity variations of glass, biotite, and amphibole are not considered, and the velocity of opaque mineral is taken as that of magnetite. The velocity of kelyphite in Table 4 is assumed to be 10% lower than Schenk, 1985, 1988;Kern et al, 1993Kern et al, , 1996aKern et al, , b, 1999Rudnick and Fountain, 1995]. Studies of Kern [1978] and Kern and Richter [1981 ] show that thermally induced microfracturing is increasingly suppressed as pressure is raised and stops at pressures of a few hundred megapascals.…”

Section: Comparison Of Velocities For Xenoliths and Rocks From Metamomentioning

confidence: 99%

Measured and calculated seismic velocities and densities for granulites from xenolith occurrences and adjacent exposed lower crustal sections: A comparative study from the North China craton

Gao¹,

Kern²,

Liu³

et al. 2000

J. Geophys. Res.

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Abstract. Granulites from the Neogene xenolith-bearing Hannuoba alkaline basalt and from the Manjinggou-Wayaokou exposed lower crustal section in the Archean Huai'an terrain, which occurs within and surrounds the Hannuoba basalt, provide a unique opportunity for a comparative stuQ' on petrophysical properties and composition of the lower crust represented by these two types of samples. P and S wave velocities and densities of 12 Hannuoba lower crustal xenoliths and one associated spinel lherzolite xenolith as well as nine granulites and granulite-facies metasedimentary rocks from the Archean Huai'an terrain were measured in laboratory at pressures up to 600 MPa and temperatures up to 600øC. Calculations of P and S wave velocities were also made for the same suite of samples based on modal mineralogy and single-crystal velocities whose variations with composition are considered by using microprobe analyses and velocities of end members. The measured and calculated Vp at room temperature and 600 MPa, where the microcrack effect is considered to be almost eliminated, agree within 4% for rocks from the Manjinggou-Wayaokou section and the adjacent Wutai-Jining upper crustal to upper lower crustal section. In contrast, the xenoliths show systematically lower measured Vp by up to 15% relative to calculated velocities, even if decompression-induced products of kelyphite and glass are taken into account. The lower measured velocities for xenoliths are attributed to grain boundary alteration and residual porosity. This implies that although granulite xenoliths provide direct information about lower crustal constitution and chemical composition, they are not faithful samples for studying in situ seismic properties of the lower crust in terms of measured velocities due to alterations during their entrainment to the surface, which changes their physical properties significantly. In this respect, granulites from high-grade terrains are better samples because they are not subjected to significant changes during their slow transport to the surface and because physical properties depend primarily on mineralogy in addition to pressure and temperature. On the other hand, calculated velocities for granulite xenoliths are consistent with velocities for granulites from terrains, suggesting that they can be also used to infer lower crust composition by correlating with results from seismic refraction studies.

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Section: Comparison Of Velocities For Xenoliths and Rocks From Metamomentioning

confidence: 99%

Measured and calculated seismic velocities and densities for granulites from xenolith occurrences and adjacent exposed lower crustal sections: A comparative study from the North China craton

Gao¹,

Kern²,

Liu³

et al. 2000

J. Geophys. Res.

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“…High VffVs ratios can be related to high pore pressure, attitude of the foliation parallel to the ray path, or low quartz content [Kern et al, 1993;Hughes et al, 1993;Musacchio, 1993]. High pore pressure results in a greater decrease of S wave velocity than the decrease in P wave velocity, hence a high V•,/Vs ratio.…”

Section: Composition Of the Crustmentioning

confidence: 99%

Composition of the crust in the Grenville and Appalachian Provinces of North America inferred from V_P/V_S ratios

Musacchio¹,

Mooney²,

Luetgert³

et al. 1997

J. Geophys. Res.

111

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“…Therefore, the most plausible explanation is that the lowvelocity area is a fractured zone inside the fault that can correspond to the fault damage zone (FDZ). The velocities outside the fault zone are typical S-wave velocities in the felsic rocks of the uppermost crystalline crust documented in a petrophysical study of Finnish bedrock by Kern et al (1993). The rough estimate of the width of this zone corresponds to a smaller wavelength in the considered frequency band of 0.1-1 Hz and is about 1.5 km.…”

Section: Discussionmentioning

confidence: 73%

Structure of the Suasselkä postglacial fault in northern Finland obtained by analysis of local events and ambient seismic noise

et al. 2017

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Abstract. Understanding the inner structure of seismogenic faults and their ability to reactivate is particularly important in investigating the continental intraplate seismicity regime. In our study we address this problem using analysis of local seismic events and ambient seismic noise recorded by the temporary DAFNE array in the northern Fennoscandian Shield. The main purpose of the DAFNE/FINLAND passive seismic array experiment was to characterize the presentday seismicity of the Suasselkä postglacial fault (SPGF), which was proposed as one potential target for the DAFNE (Drilling Active Faults in Northern Europe) project. The DAFNE/FINLAND array comprised an area of about 20 to 100 km and consisted of eight short-period and four broadband three-component autonomous seismic stations installed in the close vicinity of the fault area. The array recorded continuous seismic data during September 2011-May 2013. Recordings of the array have being analysed in order to identify and locate natural earthquakes from the fault area and to discriminate them from the blasts in the Kittilä gold mine. As a result, we found a number of natural seismic events originating from the fault area, which proves that the fault is still seismically active. In order to study the inner structure of the SPGF we use cross-correlation of ambient seismic noise recorded by the array. Analysis of azimuthal distribution of noise sources demonstrated that during the time interval under consideration the distribution of noise sources is close to the uniform one. The continuous data were processed in several steps including single-station data analysis, instrument response removal and time-domain stacking. The data were used to estimate empirical Green's functions between pairs of stations in the frequency band of 0.1-1 Hz and to calculate corresponding surface wave dispersion curves. The Swave velocity models were obtained as a result of dispersion curve inversion. The results suggest that the area of the SPGF corresponds to a narrow region of low S-wave velocities surrounded by rocks with high S-wave velocities. We interpret this low-velocity region as a non-healed mechanically weak fault damage zone (FDZ) formed due to the last major earthquake that occurred after the last glaciation.

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Seismic properties of rocks exposed in the POLAR profile region—constraints on the interpretation of the refraction data

Cited by 36 publications

References 14 publications

Measured and calculated seismic velocities and densities for granulites from xenolith occurrences and adjacent exposed lower crustal sections: A comparative study from the North China craton

Measured and calculated seismic velocities and densities for granulites from xenolith occurrences and adjacent exposed lower crustal sections: A comparative study from the North China craton

Composition of the crust in the Grenville and Appalachian Provinces of North America inferred from V_P/V_S ratios

Structure of the Suasselkä postglacial fault in northern Finland obtained by analysis of local events and ambient seismic noise

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Seismic properties of rocks exposed in the POLAR profile region—constraints on the interpretation of the refraction data

Cited by 36 publications

References 14 publications

Measured and calculated seismic velocities and densities for granulites from xenolith occurrences and adjacent exposed lower crustal sections: A comparative study from the North China craton

Measured and calculated seismic velocities and densities for granulites from xenolith occurrences and adjacent exposed lower crustal sections: A comparative study from the North China craton

Composition of the crust in the Grenville and Appalachian Provinces of North America inferred from VP/VS ratios

Structure of the Suasselkä postglacial fault in northern Finland obtained by analysis of local events and ambient seismic noise

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Composition of the crust in the Grenville and Appalachian Provinces of North America inferred from V_P/V_S ratios