Repeating caldera collapse events constrain fault friction at the kilometer scale
Repeating caldera collapse events constrain fault friction at the kilometer scale
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DOI：
10.1073/pnas.2101469118
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发表时间：
2021-07
期刊：
影响因子：
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通讯作者：
P. Segall;K. Anderson
中科院分区：
文献类型：
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作者：
P. Segall;K. Anderson
地震物理学要求理解在地震滑动之前和期间断层上的摩擦阻力是如何变化的。实验室岩石摩擦实验已经导致广泛使用的摩擦定律，取决于滑动速率和滑动历史。然而，这些实验仅限于比自然断层小得多的样本。高重复性，并特别良好的仪器，在Kellauea火山的破火山口坍塌事件可以被视为更大规模的岩石摩擦实验，并完全验证实验室实验。火山口坍塌是由于岩浆从地壳浅层储层中迅速流出而造成的。坍塌将重量转移到下面的岩浆库，从而维持喷发。我们的研究结果允许更准确地了解导致破火山口坍塌和高速率玄武岩喷发的条件。断层摩擦是理解地震的核心，然而实验室岩石力学实验最多限于米级。因此，问题仍然存在的适用性测量摩擦性能断层在原地。特别是，滑动弱化距离dc强烈影响地震成核期间的前兆滑动，但与断层粗糙度成比例，并且很难外推到自然界。2018年，夏威夷的卡拉韦厄火山爆发，造成了62次可重复的坍塌事件，其中山顶破火山口下降了数米，并伴随着MW 4.7至5.4的极长周期（VLP）地震。崩塌被全球定位系统和倾斜仪器记录得非常好，代表了独特的自然界大规模摩擦实验。我们模拟一个活塞坍缩到岩浆库中。活塞底部的压力和边缘的剪应力由速率和状态摩擦控制，平衡其重量。活塞的向下运动压缩了下面的岩浆，推动岩浆流动到喷发。蒙特卡罗估计的未知数验证实验室摩擦参数在公里尺度，包括稳态速度减弱的幅度。不存在加速塌陷前变形，dc ≤10 mm，甚至可能更小，这些结果支持使用实验室摩擦定律和参数模拟地震。我们确定的初始条件和材料和岩浆系统参数，导致幕式破火山口坍塌，揭示了小的差异，喷发口海拔可以导致喷发量和持续时间的重大差异。大多数历史上的玄武岩破火山口的崩溃，至少部分，偶发性的，这意味着粘滑的条件在这里得到的是普遍满足的性质。
Significance Earthquake physics require understanding how the frictional resistance on faults varies leading up to and during seismic slip. Laboratory rock friction experiments have led to widely used friction laws that depend on sliding rate and slip history. However, these experiments are restricted to samples vastly smaller than natural faults. Highly repeatable, and exceptionally well instrumented, caldera collapse events at K̄ılauea volcano can be treated as kilometer-scale rock friction experiments and entirely validate laboratory experiments. Caldera collapse is caused by rapid draining of magma from a shallow crustal reservoir. Collapse transfers weight to the underlying magma reservoir, thereby sustaining the eruption. Our results permit more accurate understanding of conditions leading to caldera collapse and high-rate basaltic eruptions. Fault friction is central to understanding earthquakes, yet laboratory rock mechanics experiments are restricted to, at most, meter scale. Questions thus remain as to the applicability of measured frictional properties to faulting in situ. In particular, the slip-weakening distance dc strongly influences precursory slip during earthquake nucleation, but scales with fault roughness and is challenging to extrapolate to nature. The 2018 eruption of K̄ılauea volcano, Hawaii, caused 62 repeatable collapse events in which the summit caldera dropped several meters, accompanied by MW 4.7 to 5.4 very long period (VLP) earthquakes. Collapses were exceptionally well recorded by global positioning system (GPS) and tilt instruments and represent unique natural kilometer-scale friction experiments. We model a piston collapsing into a magma reservoir. Pressure at the piston base and shear stress on its margin, governed by rate and state friction, balance its weight. Downward motion of the piston compresses the underlying magma, driving flow to the eruption. Monte Carlo estimation of unknowns validates laboratory friction parameters at the kilometer scale, including the magnitude of steady-state velocity weakening. The absence of accelerating precollapse deformation constrains dc to be ≤10 mm, potentially much less. These results support the use of laboratory friction laws and parameters for modeling earthquakes. We identify initial conditions and material and magma-system parameters that lead to episodic caldera collapse, revealing that small differences in eruptive vent elevation can lead to major differences in eruption volume and duration. Most historical basaltic caldera collapses were, at least partly, episodic, implying that the conditions for stick–slip derived here are commonly met in nature.