Stress measurements around earthquake fault and shallow subduction zone using core samples retrieved from deep boreholes

这项研究的目的是：i)探讨岩心方法，特别是滞弹性应变恢复(ASR)方法，是否可以应用于深海钻探，例如即将进行的“南开海槽地震孕育区实验(NantroseIZE)”；以及ii)通过应用科学钻探项目台湾车龙铺断层钻探项目(TCDP)的应力测量，了解活动断层附近的地应力分布的基本特征。利用从5000m深度的大陆钻井工程中采集的定向岩心在六个独立方向上测得的滞弹性应变，分析了三维地应力。对于所有被测的岩心样品，都得到了膨胀滞弹性应变，并且各个方向的应变值都足够高，从而保证了所用测量系统的准确性。然后，这些菌株被成功地用于三维…L进一步分析了三个主应力的方向，并估计了应力的大小。作为第二个实例，为了了解集集地震后车龙铺断裂上方、内部和下方不同深度的岩石应力变化特征，我们利用TCDP反演的钻芯样品，采用三维ASR方法确定了现今的应力。获得的滞弹性应变是高质量的；应变数据可以用于三维分析，从而确定方向和估计主应力的大小。初步结果表明，主应力方向在断层上方浅层和深部之间发生变化，即TCDP孔内的现今应力分布可能受到车龙堡断裂破裂的影响。因此，可以说ASR方法非常适合于直接确定三维主应力方向和估计大深度各向同性岩石中的主应力大小。较少

Objectives of this study are, i) to examine whether core-based methods, especially the anelastic strain recovery (ASR) method, can be applied for determining the in-situ stress in cases of deep ocean drilling such as the coming "The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE)" at great depths, and ii) to understand basic features of stress distribution in the vicinity of an active fault by means of application the stress measurements on a scientific drilling project, Taiwan Chelungpu-fault Drilling Project (TCDP).First, we analyzed three-dimensional in-situ stress by using anelastic strains measured in six independent directions of oriented cores which were taken from a 5,000 m-depth continental drilling project. For all the core samples measured, the expansional anelastic strains were obtained ; and the strain values in various directions was sufficiently high for the accuracy of the measurement system used. Then, these strains were successfully used for a three-dimensiona … More l analysis of the directions of three principal stresses and estimation of the magnitudes of the stresses. As second case study, in order to understand the feature of rock stress change at different depths above, within, and beneath the Chelungpu fault after the Chi-Chi earthquake, we employed the three-dimensional ASR method to determine current stress using drill core samples retrieved from TCDP. Acquired anelastic strains were of high quality ; and the strain data could be used for three-dimensional analysis resulting in the determination of directions and the estimation of magnitudes of the principal stresses. Preliminary results showed that the directions of principal stresses changed between the shallower depth above the fault and the deeper depth beneath it, that is, the current stress distribution in the TCDP hole might be influenced by the Chelungpu-fault rupture. Consequently, it can be said that the ASR method is well suited for use in directly determining the directions of principal stresses in three dimensions and in estimating their magnitude in isotropic rocks at large/great depths. Less