The effects of thermomechanical heterogeneities in island arc crust on time-dependent preeruptive stresses and the failure of an andesitic reservoir
The effects of thermomechanical heterogeneities in island arc crust on time-dependent preeruptive stresses and the failure of an andesitic reservoir
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DOI：
10.1002/2014jb011079
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发表时间：
2014-06-01
影响因子：
3.9
通讯作者：
Odbert, H.
中科院分区：
文献类型：
--
作者：
Gottsmann, J.;Odbert, H.
利用苏弗里耶尔山火山（SHV）的地面变形数据，我们提出了在储层破裂和重新喷发活动之前，机械异质地壳中随温度和时间变化的应力演化的数值模拟结果。最适合的模型不允许我们区分由单个垂直拉长的储层或一系列堆叠的储层组成的岩浆管道系统。体积在 50 至 100 km(3) 之间、储层压力变化在 4 至 7 MPa 之间、储层体积变化在 0.03 至 0.04 km(3) 之间、岩浆压缩系数在 4 x 10(-11) 和 1 x 10(-9) Pa-1 之间的长形储层几何形状提供了合理的热机械模型参数来解释变形时间序列；超压比通常从均质弹性地壳模型推断出的超压要低大约一个数量级。储层破坏预计发生在储层顶部，但具有高度可压缩岩浆（大于或等于 4 x 10(-9) Pa）的储层除外，在储层破坏时预测会形成近水平床坎。引入深地壳热区可以调节应变分配到更热的下伏地壳中，并导致储层破裂时超压估计值进一步降低至 1-2 MPa 左右。推导出的体积通量与活动次火山系统热模型的约束一致，并且意味着在 SHV 下供给喷发的可压缩岩浆糊柱的动态失效。我们对结果的解释是，深地壳热区和中地壳安山岩储层周围的热包裹岩石的综合热机械效应从根本上改变了储层启动时随时间变化的地下应力和应变分配。这些效应极大地影响了火山大地测量监测记录的表面应变。
Using ground deformation data from Soufriere Hills volcano (SHV), we present results from numerical modeling of the temperature-and time-dependent stress evolution in a mechanically heterogeneous crust prior to reservoir failure and renewed eruptive activity. The best fit models do not allow us to discriminate between a magmatic plumbing system consisting of either a single vertically elongated reservoir or a series of stacked reservoirs. A prolate reservoir geometry with volumes between 50 and 100 km(3), reservoir pressure changes between 4 and 7 MPa, and reservoir volume changes between 0.03 and 0.04 km(3) with magma compressibility between 4 x 10(-11) and 1 x 10(-9) Pa-1 provide plausible thermomechanical model parameters to explain the deformation time series; around an order of magnitude less overpressure than is generally inferred from homogeneous, elastic crustal models. Reservoir failure is predicted to occur at the crest of the reservoir except for reservoirs with highly compressible magma (greater than or similar to 4 x 10(-9) Pa) for which subhorizontal sill formation is predicted upon reservoir failure. Introducing a deep-crustal hot zone modulates the partitioning of strains into the hotter underlying crust and results in a further reduction in overpressure estimates to values of around 1-2 MPa upon reservoir failure. Deduced volume fluxes are consistent with constraints from thermal modeling of active subvolcanic systems and imply dynamic failure of a compressible magma mush column feeding eruptions at SHV. Our interpretation of the results is that the combined thermomechanical effects of a deep-crustal hot zone and hot encasing rocks around a midcrustal andesitic reservoir fundamentally alter the time-dependent subsurface stress and strain partitioning upon reservoir priming. These effects substantially influence surface strains recorded by volcano geodetic monitoring.