Abstract:To test the “bed of nails” model, we have made detailed measurements of P wave velocities in five low‐porosity, crystalline rocks at effective pressures to 500 MPa and fit two equations based on the model to the laboratory data. The first equation, V(P) = V0(1 + P/ Pi)(1 ‐ m)/2, applies at relatively low pressures because it assumes that the grain modulus is very much larger than the crack modulus. It can be fit to four of the five data sets. The fit to the data for a monomineralic epidote yields values for V0… Show more
“…A reduction in velocities beneath the rift at periods sensitive to the crust and uppermost mantle could be explained by localized fracturing and deformation associated with extension (Carlson & Gangi 1985) or elevated temperatures. These observations are counter to what is observed in magmatic rifts, where lower crustal velocities are higher beneath the rift than outside it owing to extensive magmatic intrusion to the lower and middle crust (e.g.…”
Section: The North and Central Basins Of Lake Malawi: Localization Ofmentioning
“…A reduction in velocities beneath the rift at periods sensitive to the crust and uppermost mantle could be explained by localized fracturing and deformation associated with extension (Carlson & Gangi 1985) or elevated temperatures. These observations are counter to what is observed in magmatic rifts, where lower crustal velocities are higher beneath the rift than outside it owing to extensive magmatic intrusion to the lower and middle crust (e.g.…”
Section: The North and Central Basins Of Lake Malawi: Localization Ofmentioning
“…The upper crust was excluded from the estimation, because upper crustal velocities are considered to be strongly affected by several parameters other than crustal composition, such as variable fracture distribution and porosity [e.g., Carlson and Gangi, 1985;Kelemen and Holbrook, 1995]. This indicates that our estimated average velocity represents the composition of the middle to lower crust.…”
Section: Along-arc Structural Variationmentioning
confidence: 99%
“…In the depth range of the upper crust, several other factors control velocities, such as porosity changes due to variations in the degree of fracturing [Carlson and Gangi, 1985;Ganchin et al, 1998]. Therefore velocity data from the upper crust are unsuitable for the determination of the composition of that layer.…”
[1] The processes that create continental crust in an intraoceanic arc setting are a matter of debate. To address this issue, we conducted an active source wide-angle seismic study to examine along-arc structural variations of the Izu intraoceanic arc. The data used were acquired over a 550-km-long profile along the volcanic front from Sagami Bay to Tori-shima. The obtained structural model showed the existence of felsic to intermediate composition middle crust with a P wave velocity (Vp) of 6.0-6.5 km s À1 in its upper part and 6.5-6.8 km s À1 in its lower part. The thickness of the middle crust varied markedly from 3 to 13 km. The underlying lower crust also consisted of two layers (Vp of 6.8-7.2 km s À1 in the upper part and Vp of 7.2-7.6 km s À1 in the lower part). The upper of these layers was interpreted to consist of plutonic gabbro, and the lower layer was interpreted to be mafic to ultramafic cumulates. Average crustal velocities calculated from our model showed remarkable lateral variation, which correlated well with arc volcanism. Low average crustal seismic velocities ($6.7 km s À1
“…Since dynamic as well as static Young's moduli increase with depth (e.g. Carlson and Gangi 1985;Holt et al 2005), Young's modulus at reservoir depth should therefore be higher than at the surface. Thus, Young's modulus at reservoir depth has been highly underestimated.…”
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