Viscosity Structure of the Crust and Upper Mantle in Western Nevada from Isostatic Rebound Patterns of Lake Lahontan Shorelines
Viscosity Structure of the Crust and Upper Mantle in Western Nevada from Isostatic Rebound Patterns of Lake Lahontan Shorelines
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从拉洪坦湖海岸线的等静压回弹模式研究内华达州西部地壳和上地幔的粘度结构
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发表时间：
2005
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通讯作者：
S. Wesnousky
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作者：
B. Bills;K. D. Adams;S. Wesnousky
大型湖泊可以产生和记录显著的地壳变形。我们提出了一个分析的均衡反弹模式记录在海岸线的古湖拉洪坦，在内华达州西部，使用分层的麦克斯韦粘弹性模型。推断的粘度结构取决于加载历史。我们使用三个变量的一个有据可查的湖面高程模型作为输入，并恢复相应的粘度和密度结构的估计。一个简单的两层模型，在无粘性半空间上有一个弹性板，与观测到的高程模式非常吻合，残差方差为数据方差的30%。使用多层有限粘度模型，残差方差降低到数据方差的20%，非常接近噪声水平。在较高分辨率的模式中，在80至160公里的深度范围内，粘度低于10 Pa·s。最小粘度非常类似的值，已经看到在东部大盆地，从类似的分析邦纳维尔湖海岸线，但低粘度区是一个薄邦纳维尔下面。对地震导出的密度结构进行小的调整，可以改进对海岸线观测的拟合。此外，我们发现，小的变化，在拟议的加载模型可能会导致虚假的密度反演，并建议这种建模方法提供了一个测试的加载历史。
Large lakes can both produce and record significant crustal deformation. We present an analysis of the isostatic rebound pattern recorded in the shorelines of paleo-lake Lahontan, in western Nevada, using a layered Maxwell viscoelastic model. The inferred viscosity structure depends on loading history. We use three variants of a well documented lake surface elevation model as input and recover corresponding estimates of viscosity and density structure. A simple two layer model, with an elastic plate over an inviscid half-space, fits the observed elevation pattern quite well, with a residual variance of 30% of the data variance. Using muli-layered, finite viscosity models, the residual variance is reduced to 20% of the data variance, very nearly to the noise level. In the higher resolution models, the viscosity is below 10 Pa s over the depth range from 80 to 160 km. The minimum viscosity is very similar to the value that has been seen in the eastern Great Basin, from similar analyses of Lake Bonneville shorelines but the low viscosity zone is a thinner beneath Bonneville. Making small adjustments to a seismically derived density structure allows an improved fit to the shoreline observations. Additionally, we find that small variations in proposed loading models can result in presumably spurious density inversions, and suggest that this modeling approach provides a test for loading histories.