Viscous roots of active seismogenic faults revealed by geologic slip rate variations
Viscous roots of active seismogenic faults revealed by geologic slip rate variations
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DOI：
10.1038/ngeo1991
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发表时间：
2013-12-01
影响因子：
18.3
通讯作者：
Steer, P.
中科院分区：
文献类型：
--
作者：
Cowie, P. A.;Scholz, C. H.;Steer, P.
地壳深部和上地幔的粘性流动有助于浅部地壳沿发震断层的应变积累(1)。很难评估这种对断层载荷的贡献，因为不清楚粘性变形是发生在局部剪切带还是更广泛地分布(2)。此外，粘性流动的应变积累率与施加的应力呈幂律关系，但很少有对活动断层长期幂律指数的直接估计。在这里，我们测量了全新世意大利亚平宁地区地震活跃的伸展断层在连续滑动期间沿断层面产生的地形和偏移。我们表明，这些数据可以用来推导应力驱动变形和断层应变率之间的关系，平均约1.5万年（kyr）。我们发现这种关系遵循一个定义良好的幂律，其指数在3.0-3.3 （1 σ）的范围内。该指数与地壳深部的非线性粘性变形，以及浅层发震断裂所促进的应变局部化是一致的。虽然我们不能排除一些分布变形，但我们认为亚平宁山脉的断层应变和地震复发在很大程度上是由深部局部剪切带的粘性流动控制的。
Viscous flow in the deep crust and uppermost mantle can contribute to the accumulation of strain along seismogenic faults in the shallower crust(1). It is difficult to evaluate this contribution to fault loading because it is unclear whether the viscous deformation occurs in localized shear zones or is more broadly distributed(2). Furthermore, the rate of strain accumulation by viscous flow has a power law dependence on the stress applied, yet there are few direct estimates of what the power law exponent is, over the long term, for active faults. Here we measure topography and the offset along fault surfaces created during successive episodes of slip on seismically active extensional faults in the Italian Apennines during the Holocene epoch. We show that these data can be used to derive a relationship between the stress driving deformation and the fault strain rate, averaged over about 15 thousand years (kyr). We find that this relationship follows a well-defined power law with an exponent in the range of 3.0-3.3 (1 sigma). This exponent is consistent with nonlinear viscous deformation in the deep crust and, crucially, strain localization promoted by seismogenic faulting at shallower depths. Although we cannot rule out some distributed deformation, we suggest that fault strain and thus earthquake recurrence in the Apennines is largely controlled by viscous flow in deep, localized shear zones, over many earthquake cycles.