Analytical models of deformation and residual gravity changes due to a Mogi source in a viscoelastic medium
Analytical models of deformation and residual gravity changes due to a Mogi source in a viscoelastic medium
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DOI：
10.1016/j.tecto.2008.10.006
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发表时间：
2009-06-09
期刊：
影响因子：
2.9
通讯作者：
Ferrari, Claudio
中科院分区：
文献类型：
--
作者：
Bonafede, Maurizio;Ferrari, Claudio
对流行的 Mogi 模型进行了简要回顾，该模型描述了由于嵌入均匀弹性半空间中的小型加压球形空腔而产生的变形，讨论了与其他各向同性变形模型的异同，并提供了对伴随源膨胀的不同体积变化的解释。然后将该模型推广到粘弹性流变学。人们发现，源内重现大变形（有时在火山地区观察到）所需的超压强烈依赖于神学参数，因此，如果源周围介质的弛豫时间很短（数月），则可以获得相当低的值，而不是从弹性理论推断出的极高值。如果源的膨胀是由于来自远处的新岩浆的输入造成的，则由于源的球形几何形状，所产生的残余重力变化 Delta g 可以很容易地计算出来，并且新安置的材料的密度可以根据重力变化和隆起之间的 Delta g/w 之比来推断。该比率与超压和源半径无关，这些参数通常是定义不明确的参数，并且稍微依赖于瞬态阶段的弛豫时间。显示了阶梯状超压历史和恒定岩浆供应率的显式解。还提出了一个更现实的模型，其中粘弹性特性被限制在源周围被弹性介质包围的小球形体积内。即使准确解释火山区的变形和重力变化通常需要考虑地形、弹性分层和膨胀源的三轴几何形状，为了说明起见，仍将根据广义 Mogi 模型计算的值与 198284 年 Campi Flegrei 火山口（意大利）隆起期间的观测结果进行比较。 (C) 2008 Elsevier B.V. 保留所有权利。
The popular Mogi model, describing deformation due to a small pressurized spherical cavity embedded in a homogeneous elastic half-space, is shortly reviewed, similarities and differences with other isotropic deformation models are discussed and the interpretation of the different volume changes accompanying source inflation is provided. The model is then generalized to viscoelastic rheology. The overpressure needed within the source to reproduce the large deformation, sometimes observed in volcanic regions, is found to be strongly dependent on theological parameters, so that reasonably low values may be obtained if the relaxation time of the medium surrounding the source is short (months), instead of the extremely high values inferred from the elastic theory. If the inflation of the source is due to the input of new magma from remote distance, the resulting residual gravity change Delta g may be easily computed, thanks to the spherical geometry of the source, and the density of the newly emplaced material may be inferred from the ratio of Delta g/w, between the gravity change and the uplift. This ratio is independent of the overpressure and the radius of the source, which are generally ill defined parameters, and is slightly dependent on the relaxation time in the transient phase. Explicit solutions are shown for a step-like overpressure history and for a constant magma supply rate. A more realistic model is also proposed, in which the viscoelastic properties are restricted to a small spherical volume around the source, surrounded by an elastic medium. Even if an accurate interpretation of deformation and gravity changes in volcanic areas generally requires taking into account topography, elastic layering and the triaxial geometry of the inflation source, values computed according to the generalized Mogi model are compared with observations made during the 198284 uplift episode at Campi Flegrei caldera (Italy), for the sake of illustration. (C) 2008 Elsevier B.V. All rights reserved.