Late‐interseismic state of a continental plate‐bounding fault: Petrophysical results from DFDP‐1 wireline logging and core analysis, Alpine Fault, New Zealand
Late‐interseismic state of a continental plate‐bounding fault: Petrophysical results from DFDP‐1 wireline logging and core analysis, Alpine Fault, New Zealand
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大陆板块边界断层的晚震间状态：DFDP-1 测井和岩心分析的岩石物理结果，新西兰高山断层
DOI：
10.1002/ggge.20236
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发表时间：
2013
期刊：
影响因子：
3.7
通讯作者：
D. Mcnamara
中科院分区：
文献类型：
--
作者：
John Townend;R. Sutherland;V. Toy;J. Eccles;C. Boulton;S. Cox;D. Mcnamara
我们在0.1-100米尺度上描述了一条主要的板块边界大陆断裂在晚震间状态下的地球物理特征。阿尔卑斯山断层每200-400年发生一次Mw∼8级地震，最后一次破裂是在公元1717年。2011年，在深断层钻探项目(DFDP-1)第一阶段期间，在冈特克里克的两个钻孔中采集了从阿尔卑斯山断层一侧延伸到另一侧的电缆地球物理测井和岩石岩芯。这些数据记录了下一次阿尔卑斯山断层地震发生的环境条件。电缆测井数据的主成分分析表明，80%的变化是由电性、声波和自然伽马属性解释的，初步的多变量分类能够从地球物理测量中重建缺失岩心的岩性。断裂带的性质表现出系统的变化，与主滑移带附近普遍的递进蚀变和粉碎过程相一致，叠加在不同的原岩成分上。我们的观测表明，该断裂带在0.1-100m尺度的弹性不对称性与用遥感地球物理方法成像的地壳尺度造山带的弹性不对称性相反。在断裂带尺度不对称性的基础上，地震破裂优势方向的双物质界面模型反映了阿尔卑斯断裂优势断裂的北东向。对阿尔卑斯山断层的结构和水力结构的持续表征将提高我们对原地条件、地震破裂过程和未来地震造成的危险之间的关系的理解。
We present a geophysical characterization at 0.1–100 m scales of a major plate‐bounding continental fault in a late‐interseismic state. The Alpine Fault produces MW∼8 earthquakes every 200–400 years and last ruptured in 1717 AD. Wireline geophysical logs and rock cores extending from one side of the Alpine Fault to the other were acquired in two boreholes drilled in 2011 at Gaunt Creek during the first phase of the Deep Fault Drilling Project (DFDP‐1). These data document ambient conditions under which the next Alpine Fault earthquake will occur. Principal component analysis of the wireline logging data reveals that >80% of the variance is accounted for by electrical, acoustic, and natural gamma properties, and preliminary multivariate classification enables the lithologies of sections of missing core to be reconstructed from geophysical measurements. The fault zone exhibits systematic variations in properties consistent with common processes of progressive alteration and comminution near the principal slip zone, superimposed on different protolith compositions. Our observations imply that the fault zone has the opposite sense of elastic asymmetry at 0.1–100 m scales to that of the crustal‐scale orogen imaged by remote geophysical methods. On the basis of the fault‐zone scale asymmetry, the bimaterial interface model of preferred earthquake rupture directions implies a northeastward direction of preferred Alpine Fault rupture. On‐going characterization of the structural and hydraulic architecture of the Alpine Fault will improve our understanding of the relationship between in situ conditions, earthquake rupture processes, and the hazards posed by future earthquakes.