Earthquake cycle deformation and the Moho: Implications for the rheology of continental lithosphere
Earthquake cycle deformation and the Moho: Implications for the rheology of continental lithosphere
复制标题
地震周期变形和莫霍面：对大陆岩石圈流变学的影响
DOI：
10.1016/j.tecto.2013.07.029
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发表时间：
2013-12
期刊：
影响因子：
2.9
通讯作者：
Ryder, I.
中科院分区：
文献类型：
--
作者：
Wright, T. J.;Elliott, J. R.;Wang, H.;Ryder, I.
在过去20年中，地震荷载周期大地测量的数量和质量都有了显著提高。在本文中，我们汇编和审查这些观测和测试是否地壳厚度施加任何控制。我们发现78个震源机制大陆地震来自卫星大地测量，187个估计的地震间的“锁定深度”，和23个地震（或序列）的震后变形已被观察到。从全球范围来看，我们估计孕震厚度为14 ± 5和14 ± 7 km。我们发现，莫霍面深度与大地测量确定的孕震层厚度之间不存在全局关系。我们还发现，在全球范围内，孕震厚度与地壳温度结构的代用指标之间没有明确的关系。这表明，在大洋岩石圈中如此明显的温度效应，在大陆中被岩性、应变率和/或粒度的显著变化所掩盖。布格重力弹性厚度系统大于大地孕震厚度，但它们之间没有相关性。相比之下，自由空间方法的弹性厚度通常小于大地测量法估计的孕震层厚度。震后观测显示出相当大的区域差异，但大多数长期的大地震研究推断粘弹性松弛在下地壳和/或上地幔的松弛时间为几个月到几百年。这显然与弹性厚度的较高估计值相矛盾。因此，我们对大地测量数据的分析支持“crème brélée”模型，即大陆岩石圈的强度主要在上部孕震层。然而，大地测量观测的分布偏向于较弱的地区，断层也可以修改局部流变。因此，震后的结果可能是在一个坚固的地壳或地幔中取样的薄弱区域。
The last 20 years has seen a dramatic improvement in the quantity and quality of geodetic measurements of the earthquake loading cycle. In this paper we compile and review these observations and test whether crustal thickness exerts any control. We found 78 earthquake source mechanisms for continental earthquakes derived from satellite geodesy, 187 estimates of interseismic “locking depth”, and 23 earthquakes (or sequences) for which postseismic deformation has been observed. Globally we estimate seismogenic thickness to be 14 ± 5 and 14 ± 7 km from coseismic and interseismic observations respectively. We find that there is no global relationship between Moho depth and the seismogenic layer thickness determined geodetically. We also found no clear global relationship between seismogenic thickness and proxies for the temperature structure of the crust. This suggests that the effect of temperature, so clear in oceanic lithosphere, is masked in the continents by considerable variation in lithology, strain-rate, and/or grain size. Elastic thicknesses from Bouguer gravity are systematically larger than the geodetic seismogenic thicknesses but there is no correlation between them. By contrast, elastic thicknesses from free-air methods are typically smaller than the geodetic estimates of seismogenic layer thickness. Postseismic observations show considerable regional variations, but most long-term studies of large earthquakes infer viscoelastic relaxation in the lower crust and/or upper mantle with relaxation times of a few months to a few hundred years. These are in apparent contradiction with the higher estimates of elastic thickness. Our analysis of the geodetic data therefore supports the “crème brûlée” model, in which the strength of the continental lithosphere is predominantly in the upper seismogenic layer. However, the distribution of geodetic observations is biased towards weaker areas, and faults can also modify the local rheology. Postseismic results could therefore be sampling weak regions within an otherwise strong crust or mantle.
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