Subsurface Magmatic Processes in the Western Galapagos Islands from High-Resolution Interferometric Radar Deformation Measurements

1992年至1999年期间对西加拉帕戈斯群岛进行的Zebker 0001096干涉合成孔径雷达观测表明，伊莎贝拉岛和费尔南迪纳岛上的七座火山中至少有六座发生了变形，其中一些变形的速度非常快。四座火山正在以每年0.9米的速度膨胀，其中包括伊莎贝拉岛南部的塞拉内格拉火山。1992-99年间，内格拉山脉的总抬升超过2.5m，这是由于火山下方1.5-3.0公里处浅层岩浆房的压力增加所致。另外两座火山，伊莎贝拉岛的Cerro Azul火山和费尔南迪纳火山，在观察期内喷发。这些火山表现出喷发前膨胀、共喷发的通货紧缩和浅层侵入的局部变形的复杂格局。令人惊讶的是，数十年前的熔岩流目前仍在继续消退。高分辨率、空间密度高的InSAR数据可用于约束地下岩浆活动。初步结果表明，一些观测信号可以用简单的对称压力源很好地模拟，而另一些则不能用这种模型来解释。来自塞纳内格拉火山的数据似乎需要伴随着通货膨胀的间歇性断层或其他非弹性变形。研究人员建议结合新的观测和雷达干涉测量的模型开发，调查目前的活动及其与地下过程的关系。他们将利用这些观测来限制火山下方岩浆室的几何和体积变化，限制储藏室和侵入/喷发岩脉之间的流动动力学，以及与持续的岩浆室膨胀相关的断层和非弹性变形的作用。他们还将审查这些过程的时间变异性，如InSAR测量所证明的那样。要分析加拉帕戈斯火山活动的这些高分辨率InSAR观测，需要创建和验证干涉图，开发适用于InSAR数据的反演方法，并扩展这些方法，以推导出覆盖岩石中地下活动和非弹性响应的详细模型。具体地说，该小组将：1)开发利用InSAR观测的密集性质的分析方法；2)通过研究更真实的岩浆室几何形状来扩展模拟能力；3)检查在加拉帕戈斯一些破火山口观察到的非弹性响应；4)测试是否有证据表明不同火山的岩浆系统是耦合的或相互作用的；5)研究对长达20年的熔岩流沉降的特殊观测。

Zebker 0001096 Interferometric synthetic aperture radar (InSAR) observations of the Western Galapagos during 1992-1999 show that at least six out of the seven volcanoes on the islands of Isabela and Fernandina have been deforming, some at unusually high rates. Four volcanoes are inflating, including Sierra Negra on southern Isabela Island at rates of up to 0.9 m/year. The total uplift of Sierra Negra during 1992-99 is more than 2.5 m. The uplift is caused by pressure increases in shallow magma chambers beneath the volcanoes at depths 1.5-3.0 km. Two other volcanoes, Cerro Azul on Isabela Island and Fernandina volcano, erupted during the observation period. These volcanoes show a complicated pattern of pre-eruptive inflation, co-eruptive deflation, and localized deformation due to shallow intrusions. Amazingly, decades-old lava flows are continuing to subside at the present time. The high-resolution spatially-dense InSAR data can be used to constrain subsurface magmatic processes. Preliminary results indicate that some of the observed signals are well-modeled by simple symmetric pressure sources, while others cannot be explained by such models. Data from Sierra Negra volcano appear to require episodic faulting, or other inelastic deformation, accompanying inflation. The investigators propose to investigate the current activity and its relation to subsurface processes using a combination of new observations and model development, as enabled by radar interferometry. They will use the observations to constrain the geometry and volume changes of magma chambers beneath the volcanoes, the dynamics of flow between storage chambers and intrusive/eruptive dikes, and the role of faulting and inelastic deformation associated with sustained magma chamber inflation. They also will examine temporal variability in these processes as evidenced in the InSAR measurements. Analysis of these high-resolution InSAR observations of Galapagos volcanism requires creation and validation of interferograms, development of inverse methods suited to InSAR data, and extension of these methods to derive detailed models of subsurface activity and inelastic response in the overlying rock. Specifically, the team will i) develop analytical methods that capitalize on the dense nature of the InSAR observations, ii) extend modeling capability by examining more physically realistic magma chamber geometries, iii) examine inelastic response observed in some Galapagos calderas, iv) test whether there is evidence that the magmatic systems at the various volcanoes are coupled or interacting, and v) study the extraordinary observation of subsidence of lava flows that are up to 20 years old.