Acoustic and mechanical properties of Nankai accretionary prism core samples
Acoustic and mechanical properties of Nankai accretionary prism core samples
复制标题
DOI：
10.1029/2010gc003169
复制
发表时间：
2011-04
期刊：
影响因子：
3.7
通讯作者：
H. Raimbourg;Y. Hamano;S. Saito;M. Kinoshita;A. Kopf
中科院分区：
文献类型：
--
作者：
H. Raimbourg;Y. Hamano;S. Saito;M. Kinoshita;A. Kopf
我们研究了最近通过海洋钻探计划/综合海洋钻探计划（ODP/IODP）钻探在南开海槽汇聚边缘恢复的未变形沉积物和增生地层，以揭示从初始沉积到初期变形的物理性质变化。我们通过独立施加围压和孔隙压力的各向同性加载试验，得出了沿 Muroto (ODP 1173) 和 Kii 横断面 (IODP C0001、C0002、C0006 和 C0007) 各个钻探地点的样品的声学 (Vp) 和机械（单轴孔隙弹性柔量、压实幅度）特性。我们量化了 Vp 对有效压力 (Peff) 和围压 (Pc) 的依赖性，这可用于校正 Vp 的大气压力测量值。外推至原位条件的岩心样本上获得的实验 Vp 略高于测井得出的速度，这可归因于速度色散或大型断层和弱带对较长波长波的影响。在高孔隙度（30%–60%）测试的沉积物中，速度首先由孔隙度控制，而不是由岩性控制，这与我们对排水骨架不可压缩性的静态测量一致，远小于流体不可压缩性。剪切模量可能不是框架不可压缩性，而是 Vp 的二阶控制，解释了实际 Vp 与 Wood（1941）悬架模型预测之间的大部分差异。我们还从各向异性、成岩作用和固结方面量化了南开样品的力学状态。声学和机械参数在垂直和水平方向上显示出相似的值，证明了测试材料的各向异性非常低。当考虑上四国盆地沉积物（1173号遗址）的多孔样本作为成岩胶结材料的例子时，一些机械和声学属性似乎可以作为晶间胶结存在的可靠实验指标。我们还在 IODP 站点 C0001（增生棱镜单元）的样品中检测到了早期胶结。在固结方面，我们根据应用相对于推断的原位值较大的 Peff 时的压实量，区分了两类材料响应（浅的可变形样品和深的难变形样品），其转变可能与临界孔隙率有关。
We studied undeformed sediment and accreted strata recently recovered by Ocean Drilling Program/Integrated Ocean Drilling Program (ODP/IODP) drilling in Nankai Trough convergent margin to unravel the changes in physical properties from initial deposition to incipient deformation. We have derived acoustic (Vp) and mechanical (uniaxial poroelastic compliance, compaction amplitude) properties of samples from various drill sites along the Muroto (ODP 1173) and Kii transects (IODP C0001, C0002, C0006, and C0007) from isotropic loading tests where confining and pore pressure were independently applied. We quantified the dependence of Vp on both effective (Peff) and confining (Pc) pressure, which can be used to correct atmospheric pressure measurements of Vp. Experimental Vp obtained on core samples extrapolated to in situ conditions are slightly higher than logging‐derived velocities, which can be attributed either to velocity dispersion or to the effect of large‐scale faults and weak zones on waves with longer wavelength. In the high‐porosity (30%–60%) tested sediments, velocities are controlled at first order by porosity and not by lithology, which is in agreement with our static measurements of drained framework incompressibility, much smaller than fluid incompressibility. Rather than framework incompressibility, shear modulus is probably the second‐order control on Vp, accounting for most of the difference between actual Vp and the prediction by Wood's (1941) suspension model. We also quantified the mechanical state of Nankai samples in terms of anisotropy, diagenesis, and consolidation. Both acoustic and mechanical parameters reveal similar values in vertical and horizontal directions, attesting to the very low anisotropy of the tested material. When considering the porous samples of the Upper Shikoku Basin sediments (Site 1173) as examples of diagenetically cemented material, several mechanical and acoustic attributes appeared as reliable experimental indicators of the presence of intergrain cementation. We also detected incipient cementation in samples from IODP Site C0001 (accretionary prism unit). In terms of consolidation, we distinguished two classes of material response (shallow, deformable samples and deep, hardly deformable ones) based on the amount of compaction upon application of a Peff large with respect to the inferred in situ value, with a transition that might be related to a critical porosity.