Magma intrusion and deformation predictions: Sensitivities to the Mogi assumptions
Magma intrusion and deformation predictions: Sensitivities to the Mogi assumptions
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DOI：
10.1029/2006jb004860
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发表时间：
2007-06-26
影响因子：
3.9
通讯作者：
Masterlark, Timothy
中科院分区：
文献类型：
--
作者：
Masterlark, Timothy
MOGI(1958)的岩浆侵入模型被广泛用于预测活火山的观测变形。该模型模拟了嵌入均匀各向同性泊松固体半空间(HIPSHS)的小型球形膨胀源(SES)。这项研究使用分析模型和有限元模型(FEMS)相结合的方法来计算Sess引起的地表深度位移，该模型不需要HIPSHS假设。干涉合成孔径雷达(InSAR)数据表明，阿拉斯加的奥克莫克火山在1997年喷发期间，由于熔岩喷发，下沉了一米多。使用HIPSHS模型的反演方法可以精确地定位破火山口中心下3100米深处的SES。一系列可供选择的模型配置放松了HIPSHS假设的组合套件，并顺序地隔离了每个假设的影响。正演模拟预测对地形效应和层状弹性性质相对不敏感，对各向异性弹性性质和泊松比比较敏感，对火山口内弱物质的存在非常敏感。逆方法与解析和有限元生成的脉冲响应函数相结合，隔离了每个HIPSHS假设对SES深度和压力估计的影响。结果对模拟弱破火山口的模式配置特别敏感，其估计的SES深度(4500米)比HIPSHS模式的估计要深得多。对于具有高信噪比的形变数据，例如Okmok火山的联合喷发InSAR数据，由于Mogi(1958)假设而产生的正反向形变预测误差可能大大超过观测不确定性。
Mogi's (1958) magma intrusion model is widely used to predict observed deformation of active volcanoes. The model simulates a small spherical expansion source (SES) embedded in a homogeneous, isotropic, Poisson-solid half-space (HIPSHS). This study computes surface displacement due to SESs at depth using a combination of analytical and finite element models (FEMs), for which the HIPSHS assumptions are not required. Interferometric synthetic aperture radar (InSAR) data suggest that Okmok volcano, Alaska, subsided more than a meter owing to lava extrusion during its 1997 eruption. Inverse methods, which use an HIPSHS model, precisely locate an SES at a depth of 3100 m beneath the center of the caldera. A series of alternative model configurations relax the combined suite of HIPSHS assumptions and sequentially isolate the effects of each assumption. Forward modeling predictions are relatively insensitive to topographic effects and layered elastic properties, somewhat sensitive to anisotropic elastic properties and Poisson's ratio, and very sensitive to the presence of weak materials within a caldera. Inverse methods, combined with analytical and FEM-generated impulse response functions, isolate the influence of each HIPSHS assumption on SES depth and pressure estimations. Results are particularly sensitive to a model configuration simulating a weak caldera, for which the estimated SES depth (4500 m) is significantly deeper than the estimate for the HIPSHS model. For deformation data having high signal-to-noise ratios, such as the co-eruption InSAR data for Okmok volcano, both forward and inverse deformation prediction errors attributed to the Mogi (1958) assumptions can greatly exceed observation uncertainties.