Porosity and sound velocity measured in sediment core CIROS-1

The CIROS-1 drillhole, which in 1986 reached a depth of 700 m below the seafloor, is still the only deep hole that can provide information on the velocity structure of the upper crust in McMurdo Sound and the Ross Sea, Antarctica. A careful review and quality control of the downhole logging data of CIROS-1 resulted in a new porosity depth function that is consistent with porosity data from the MSSTS-1 and CRP-1 drillholes. Using existing porosity-velocity equations, it was possible for the first time to obtain reliable velocity information for the upper 700 m of strata off the Victoria Land coast. The calculated synthetic seismograms, based on downhole velocity and density data, fit very well with the existing seismic lines IT90A-71, PD90-12, and NBP9601-89. The quality of the correlation confirms that the average velocity of the top 700 m of strata is about 2 000-2 300 m/s, and not 2 800-3 000 m/s, as was previously assumed. […]

CIROS-1 钻孔，该钻孔于1986年钻探至海底下方700米深度，至今仍是唯一能够提供麦克默多湾及罗斯海南极上地壳速度结构信息的深孔。对CIROS-1钻孔的井下测井数据进行细致的审查和质量控制，得出了与MSSTS-1和CRP-1钻孔的孔隙度数据相一致的新孔隙度深度函数。借助现有的孔隙度-速度方程，首次成功获得了维多利亚地海岸线上方700米地层的可靠速度信息。基于井下速度和密度数据计算出的合成地震图，与现有的地震线IT90A-71、PD90-12和NBP9601-89吻合良好。相关性质量的高标准证实，上层700米地层的平均速度约为2000-2300米/秒，而非之前所假设的2800-3000米/秒。