The physical properties of rock within Oceanic Core Complexes (OCC) provide information about the history of magmatism, deformation and alteration associated with detachment faulting and unroofing of their gabbroic sequences. New core and logging data from Atlantis Bank (AB) OCC are compared with prior deep sea drilling data from this site on the Southwest Indian Ridge, as well as from Atlantis Massif (AM) OCC on the Mid-Atlantic Ridge. The average seismic velocity at each site is typical for gabbroic rock. Downhole core and log variations are found to depend on both porosity and alteration. Porosity at millimeter to meter scale impacts P-wave velocities (6.0–6.4 km/s) in the upper several hundred meters at both OCC. Below ~ 600–800 m depth, in situ velocities are higher (6.6–6.9 km/s) for the remainder of the 1.5 km drilled to date, except in zones where alteration is significant. Variability of 0.5–1 km/s over depth intervals of a few meters is persistent where mineral alteration exceeds 10–20%, whereas variability drops to ± 0.1 km/s for intervals affected by little to no alteration. Seismic anisotropy is negligible overall, with just a few intervals showing consistent fast azimuth and magnitude of a few percent. The depth extent of alteration, probably related to the zone deformed below the detachment when active, is ~ 600–800 meters at both AB and AM.

中文翻译：

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海洋岩心复合体中辉长岩段的地震特性：海底钻探的约束

大洋核心复合体（OCC）中岩石的物理性质提供了与岩浆层序的断裂断层和顶板化有关的岩浆作用，变形和蚀变的历史信息。来自亚特兰蒂斯银行（AB）OCC的新岩心和测井数据与西南印第安海岭本站点以及大西洋中脊亚特兰蒂斯地块（AM）OCC的先前深海钻探数据进行了比较。辉长岩在每个站点的平均地震速度是典型的。发现井下岩心和测井变化取决于孔隙率和蚀变。毫米至米级的孔隙度会影响两个OCC上部几百米的P波速度（6.0-6.4 km / s）。在约600-800 m的深度以下，迄今钻探的1.5 km的剩余部分中，原位速度较高（6.6–6.9 km / s），除了变化明显的区域外。在矿物变化超过10–20％的情况下，在几米的深度范围内，变化的持续性为0.5–1 km / s，而在几乎没有变化的情况下，变化性下降至±0.1 km / s。地震各向异性总体上可以忽略不计，仅有几个间隔显示出一致的快速方位角和百分之几的震级。改变的深度范围，可能与活动时在分离线以下变形的区域有关，在AB和AM处均为〜600-800米。仅有几个间隔显示出一致的快速方位角和百分之几的幅度。在AB和AM处，变化的深度范围可能与活动区以下的变形带有关，约为600-800米。仅有几个间隔显示出一致的快速方位角和百分之几的幅度。在AB和AM处，变化的深度范围可能与活动区以下的变形带有关，约为600-800米。