Physical properties and elastic constants of ODP Holes 137-504B and 140-504B upper crustal rocks@en

Seismic velocities have been measured at confining pressures of 100 MPa and 600 MPa for sheeted dike samples recovered during Ocean Drilling Program Legs 137 and 140. The compressional- and shear-wave velocities show an increase with depth at Hole 504B, which is in sharp contrast to the atmospheric pressure velocity measurements performed as part of the shipboard analyses. Rocks exposed to different types of alteration and fracture patterns show distinct changes in their physical properties. The seismic reflectors observed on the vertical seismic profile (VSP) experiment performed during Leg 111 may have been caused by low velocity zones resulting from alteration. The amount of fracturing and hydrothermal alteration in several zones also may have contributed to the acoustic impedance contrast necessary to produce the E5 reflector. Poisson's ratios calculated from laboratory velocity measurements show several low values at depths ranging from 1600 mbsf to 2000 mbsf, which tends to follow similar trends obtained from previous oceanic refraction experiments. A comparison of physical properties between samples recovered from Hole 504B and ophiolite studies in the Bay of Islands and Oman shows a good correlation with the Bay of Islands but significant differences from the measurements performed in the Oman complex.本数据集针对大洋钻探计划（Ocean Drilling Program, ODP）第137、140航次采集的席状岩墙（sheeted dike）样品，在100 MPa与600 MPa围压条件下完成了地震波速测试。504B钻孔的纵波与横波波速均随深度递增，该结果与船上分析环节常压下测得的波速数据形成显著反差。经历不同类型蚀变与破裂样式的岩石，其物理性质存在显著差异。第111航次开展的垂直地震剖面（Vertical Seismic Profile, VSP）实验中观测到的地震反射层，可能由蚀变作用形成的低速带所致。部分区域的破裂程度与热液蚀变作用，同样可能是形成E5反射层所需声阻抗差的成因之一。基于实验室波速测试计算得到的泊松比，在海底以下1600~2000米（mbsf）区间内存在多个低值点，其变化趋势与此前海洋折射实验的结果高度一致。将504B钻孔采集的样品与岛屿湾、阿曼地区蛇绿岩研究的物理性质数据对比后发现，其与岛屿湾的观测结果相关性良好，但与阿曼杂岩的实测数据存在显著差异。