23. SYNTHESIS OF THE BARBADOS DÉCOLLEMENT SEISMIC REFLECTION RESPONSE FROM DRILLING-BASED GEOPHYSICAL OBSERVATIONS AND PHYSICAL PROPERTIES 1
23. SYNTHESIS OF THE BARBADOS DÉCOLLEMENT SEISMIC REFLECTION RESPONSE FROM DRILLING-BASED GEOPHYSICAL OBSERVATIONS AND PHYSICAL PROPERTIES 1
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23. 根据基于钻探的地球物理观测和物理特性综合巴巴多斯滑脱地震反射响应 1
DOI：
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
J. Moore
中科院分区：
文献类型：
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作者：
T. Shipley;G. Moore;H. Tobin;J. Moore
一项三维地震反射实验揭示了与巴巴多斯海沟脱壳反射有关的波形和振幅的独特分布。海洋钻井项目Leg 156的一个目标是校准地震反射响应，这被认为与断裂带性质的变化有关。948站点的特征是与沉降相关的正常极性反射。采样和测井显示了一个40米厚的断裂带，随着粘土矿物从富含蒙脱石到富含伊利石的变化，该断裂带的密度增加。根据测井数据得出的合成地震图显示，尽管测井、封隔器和长期压力测量证实存在异常高压，但岩性驱动的密度变化是产生正常极性反射的原因。由于技术上的困难，Site 947的目标是表征更常见的高振幅负极性波形，但没有完成。然而，在巡航开始时进行的密度测井显示，在海底540-554米（mbsf）处存在14米厚的1.6克/厘米3层。钻头到达距滑脱层60 m范围内，测井密度达到565.5 mbsf。低密度层与滑脱的断层展带相关，具有与负极性滑脱相似的地震特征，可以作为类比。虽然没有直接校准Site 947的沉降是不令人满意的，但断层展显示的特征与巡航前的建模一致，这需要一个12至14米厚的低阻抗层来解释观察到的波形。这些非常低的密度可能是由于水力压裂过程中引入的额外流体和流化沉积物造成的，这些流体和流化沉积物是由静岩压力维持的。对极低密度的要求表明，在较厚的滑脱层内存在bb0 ~ 12m厚的静压水力裂缝带。负极性波形振幅的变化主要与增强的流体含量有关。振幅图显示了一条宽的东北向河道，可能集中了沿滑脱的流体输送。然而，许多断层带与滑脱相交，这可能造成障碍，阻止流体沿滑脱快速流动。
A three-dimensional seismic reflection experiment has revealed a distinctive distribution of waveforms and amplitudes associated with the decollement reflection in the Barbados Trench. One objective of Ocean Drilling Program Leg 156 was to calibrate this seismic reflection response, which was thought to be related to variations in fault zone properties. Site 948 is characterized by a normal polarity reflection that is correlated to the decollement. Sampling and logging reveal a 40-m-thick fault zone, with density that increases across the zone as the clay mineralogy changes from smectite rich to illite rich downhole. A synthetic seismogram, derived from the logging data, shows that the lithology-driven density shift is responsible for generatin g the normal polarity reflection even though the log, packer, and long-term pressure measurements confirm the presence of abnormally high pressures. The objective of Site 947, to characterize the more common, high-amplitude negative polarity waveform, was not completed due to technical difficulties. However, a density log, run at the beginning of the cruise, did reve al a 14-m-thick 1.6 g/cm 3 layer 540-554 m below seafloor (mbsf). The bit reached within 60 m of the decollement, and the density log went to 565.5 mbsf. The low-density layer correlates with a fault splay off the decollement, having similar seismic characteristics to that of the negative polarity decollement and can serve as an analogue. Although it is unsatisfying not to h ave directly calibrated the decollement at Site 947, the fault splay revealed characteristics that are consistent with modeling don e before the cruise that required a 12- to 14-m-thick low impedance layer to account for the observed waveform. These very low densities are probably created by introduction of additional fluids and fluidized sediments during hydrofracturing, which are maintained by lithostatic pressure. The requirement for extremely low density indicates that a >12-m-thick lithostatic pressure d hydrofractured zone occurs within the thicker decollement. The variations in the amplitude of the negative polarity waveform relate mainly to the amount of enhanced fluid content. The mapped pattern of amplitudes suggests a broad northeast-trending channel that possibly focused fluid transport along the decollement. However, numerous fault splays intersect the decollement, which may cause barriers that prevent rapid fluid flow along the decollement.