Chapter 9: Evolution of the Hat Creek Fault System, Northern California
Chapter 9: Evolution of the Hat Creek Fault System, Northern California
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第 9 章：北加州帽子溪断层系统的演化
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发表时间：
2016
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通讯作者：
M. Blakeslee
中科院分区：
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作者：
S. Kattenhorn;B. Krantz;E. Walker;M. Blakeslee
50 km（31 mi）长的帽子溪断层位于沿着北方加州的莫多克高原西缘，是一条几何形状复杂的分段正断层，它至少使更新世熔岩偏移570 m（1870 ft）的累积落差。三个亚平行，NNW走向的陡坎（边缘，中间，和最近）反映了一个渐进的向西迁移的表面破裂的位置，逐步抵消年轻的更新世火山沉积物在一个1000万年的断层历史。50公里（31英里）长的边缘陡崖主要由右阶部分组成，最大落差为12370米（1214英尺），位于1925年的熔岩中。中间陡崖长17.5公里，位于环岸以西0.4至3.5公里处，由左阶段组成，最大落差为177米。新崖长30.5公里（19英里），位于旧崖底部以西几十米处，由最大落差56米（184英尺）的左阶段组成。现代陡坎的最北端部分抵消了53.5 ± 2 ka的玄武质熔岩，而其余部分抵消了24 ± 6 ka的玄武岩流，这些玄武岩流喷发到帽子溪谷，表明陡坎系统较年轻。断层通过年轻熔岩的垂直传播产生了振幅高达30米（98英尺）的断层痕迹单斜。单斜通常会被一个垂直的扩张断层崖沿着沿着其上枢纽破坏。与重复地震相关的震动逐渐破坏了这些单斜，导致解体或部分完全崩溃。断裂模式和断层段的几何形状和链接被用来推断运动学和应力历史。边缘系统和中间系统的最古老的部分表明最初的NE-SW向ENE-WSW延伸。后来的边缘，中间，和最近的部分响应E-W扩展，与以前记录的应力状态的级联弧后。一个小盾状火山（煤渣丘）附近的中间和最近的断层段的复杂性表明，目前休眠的岩浆系统所造成的应力场的空间变异性。沿新近陡坎沿着的新近右旋斜向运动学的证据，意味着轻微的西北-东南向延伸，可能反映了从内华达州西部的步行者车道带向系统的右旋剪切的转移。我们的解释要求在过去的1000万年里，帽溪断层附近的水平主应力顺时针旋转了1045 °，这意味着在相对较短的地质时期内，分段的正断层系统可能会发展出显著的复杂性。
Abstract The 50 km (31 mi) long Hat Creek fault, located along the western margin of the Modoc Plateau in northern California, is a geometrically complex segmented normal fault that offsets Pleistocene lavas by at least 570 m (1870 ft) of cumulative throw. Three subparallel, ∼NNW-trending sets of scarps (Rim, Intermediate, and Recent) reflect a progressive westward migration of surface rupture locations that offset progressively younger Pleistocene volcanic deposits during a ∼1 Myr fault history. The 50 km (31 mi) long Rim scarp comprises predominantly right-stepping segments with a maximum throw of ∼370 m (1214 ft) in ∼925 ka lavas. The 17.5 km (10.9 mi) long Intermediate scarp occurs 0.4 to 3.5 km (0.2–2.2 mi) west of the Rim, comprising left-stepping segments with a maximum throw of ∼177 m (581 ft). The 30.5 km (19 mi) long Recent scarp occurs several tens of meters west of the bases of older scarps, and is composed of left-stepping segments with a maximum throw of 56 m (184 ft). The northernmost segment of the Recent scarp offsets 53.5 ± 2 ka basaltic lavas, whereas the remaining segments offset 24 ± 6 ka basalt flows that erupted into Hat Creek Valley, indicating a youthful scarp system. Vertical propagation of the fault through young lavas produced fault-trace monoclines with amplitudes of up to 30 m (98 ft). The monoclines are commonly breached along their upper hinges by a vertical, dilational fault scarp. Shaking associated with repeated earthquakes progressively broke down these monoclines, causing disaggregation or partial to complete collapse. Fracture patterns and fault segment geometries and linkages were used to deduce the kinematic and stress history. The oldest segments of the Rim and Intermediate systems suggest initial NE-SW to ENE-WSW extension. Later Rim, Intermediate, and Recent segments responded to E-W extension, consistent with the previously documented stress state of the Cascades backarc. Complexity in Intermediate and Recent fault segments near a small shield volcano (Cinder Butte) suggests spatial variability in the stress field caused by a currently dormant magmatic system. Evidence for recent dextral-oblique kinematics along the Recent scarp, implying a slightly WNW-ESE extension, may reflect the transfer of dextral shear into the system from the Walker Lane Belt in western Nevada. Our interpretations require ∼45° of clockwise rotation of the horizontal principal stresses in the vicinity of the Hat Creek fault over the past ∼1 Myr, implying that significant complexity can develop in segmented normal fault systems over relatively short periods of geologic time.