Velocity-porosity relationships in oceanic basalt from eastern flank of the Juan de Fuca Ridge: The effect of crack closure on seismic velocity
Velocity-porosity relationships in oceanic basalt from eastern flank of the Juan de Fuca Ridge: The effect of crack closure on seismic velocity
复制标题
胡安德富卡海岭东侧海洋玄武岩的速度-孔隙度关系：裂缝闭合对地震速度的影响
DOI：
10.1071/eg08001
复制
发表时间：
2008
影响因子：
0.9
通讯作者：
G. Iturrino
中科院分区：
文献类型：
--
作者：
T. Tsuji;G. Iturrino
摘要为了建立大洋玄武岩的现场速度—孔隙度关系，考虑裂缝特征，在高达40 MPa的围压条件下，对胡安德富卡山脊东侧翼的玄武岩样品进行了纵波和横波速度测量。假设速度随围压的变化是由微裂纹闭合引起的，我们利用Kuster-Toksöz理论估计了微裂纹长径比谱。结果表明，不同样品的归一化长宽比光谱具有相似的特征。根据归一化纵横比谱，我们通过计算每个孔隙度的纵横比谱，构建了理论速度-孔隙度关系。此外，考虑围压作用下的微裂纹闭合，可以得到速度-孔隙度随围压的函数关系。考虑长宽比光谱的理论关系与观测到的在大气压下测量的100多个离散样品的关系是一致的，并且在宽孔隙度范围内通常观察到的压力依赖关系。实验数据与理论估算值的一致性表明，从胡安德富卡脊东侧获得的玄武岩样品的速度-孔隙度关系及其压力依赖性可以用裂缝特征（即归一化长径比谱）和裂缝闭合来描述。
Abstract To construct in situ velocity-porosity relationships for oceanic basalt, considering crack features, P- and S-wave velocity measurements on basaltic samples obtained from the eastern flank of the Juan de Fuca Ridge were carried out under confining pressures up to 40 MPa. Assuming that the changes in velocities with confining pressures are originated by micro-crack closure, we estimated micro-crack aspect ratio spectra using the Kuster-Toksöz theory. The result demonstrates that the normalised aspect ratio spectra of the different samples have similar characteristics. From the normalised aspect ratio spectrum, we then constructed theoretical velocity-porosity relationships by calculating an aspect ratio spectrum for each porosity. In addition, by considering micro-crack closure due to confining pressure, a velocity-porosity relationship as a function of confining pressure could be obtained. The theoretical relationships that take into account the aspect ratio spectra are consistent with the observed relationships for over 100 discrete samples measured at atmospheric pressure, and the commonly observed pressure dependent relationships for a wide porosity range. The agreement between the laboratory-derived data and theoretically estimated values demonstrates that the velocity-porosity relationships of the basaltic samples obtained from the eastern flank of the Juan de Fuca Ridge, and their pressure dependence, can be described by the crack features (i.e. normalised aspect ratio spectra) and crack closure.