Compressional and shear wave velocities and elastic constants at DSDP Leg 59 Holes

Prior to the Deep Sea Drilling Project the composition of the oceanic crust could only be inferred from seismic-refraction and gravity data and the recovery of a wide variety of dredged rocks. Through the success of the Deep Sea Drilling Project, it is now clear that the top of oceanic Layer 2 usually consists of basalt. Several laboratory studies (e.g., Fox et al., 1972; Christensen and Shaw, 1970; Hyndman and Drury, 1976) have demonstrated that the seismic velocities of oceanic basalt are similar to velocities reported from refraction studies of Layer 2 and that the variability in Layer 2 velocities has many causes, the most important being fracturing and sea-floor alteration produced by the interaction of basalt and sea water (Christensen and Salisbury, 1973).
To date, most reported measurements of velocities in oceanic basalts are from samples obtained from the main ocean basins. With the exception of an earlier study of velocities and related elastic properties of a suite of rocks from DSDP Sites 292, 293, 294, and 296 located in the Philippine Sea (Christensen et al., 1975; Fountain et al., 1975), elastic properties have not been determined for oceanic rocks from marginal basins. In this chapter compressional- and shear-wave velocities and elastic constants are reported at elevated confining pressures for basalt and volcanic breccias from Holes 447A, 448, and 448A.

在深海钻探计划（Deep Sea Drilling Project, DSDP）开展之前，人类仅能通过地震折射数据、重力数据以及多种疏浚采获岩石的回收结果，推断大洋地壳的组成成分。随着深海钻探计划取得成功，如今已明确洋壳第二层的顶部通常由玄武岩构成。多项实验室研究（如Fox等人1972年、Christensen与Shaw1970年、Hyndman与Drury1976年的研究）已证实，大洋玄武岩的地震波速度与洋壳第二层折射研究中测得的速度相近，且洋壳第二层的速度变化存在多种成因，其中最主要的是玄武岩与海水相互作用所产生的破裂作用及海底蚀变作用（Christensen与Salisbury，1973）。截至目前，已报道的大洋玄武岩速度测量数据大多采自主要大洋盆地的样品。除了一项针对菲律宾海DSDP站位292、293、294及296处一套岩石的速度与相关弹性性质的早期研究（Christensen等人，1975；Fountain等人，1975）外，学界尚未对边缘海盆地的大洋岩石开展弹性性质测定。本章报道了取自447A、448及448A钻孔的玄武岩与火山角砾岩，在围压升高条件下的纵波、横波速度及弹性常数测试结果。