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

Zebker 0001096 1992-1999年期间对西加拉帕戈斯的干涉合成孔径雷达（干涉合成孔径雷达）观测表明，伊萨贝拉和费尔南迪纳岛上的七座火山中至少有六座一直在变形，有些火山的变形速度非常高。四座火山正在膨胀，其中包括伊萨贝拉岛南部的Sierra Negra火山，其膨胀速度高达每年0.9米。Sierra Negra在1992-99年期间的总抬升超过2.5 m。隆起是由火山下方1.5-3.0公里深处的浅岩浆室压力增加引起的。另外两座火山--伊萨贝拉岛上的塞罗阿苏尔火山和费尔南迪纳火山--在观测期间也发生了喷发。这些火山表现出一种复杂的模式，喷发前的膨胀，共同喷发的紧缩，和局部变形，由于浅侵入。令人惊讶的是，几十年前的熔岩流目前正在继续消退。高分辨率空间密集的干涉合成孔径雷达数据可以用来约束地下岩浆过程。初步结果表明，一些观察到的信号是很好的模拟简单的对称压力源，而其他人不能用这样的模型来解释。来自Sierra Negra火山的数据似乎需要幕式断层或其他非弹性变形，伴随着膨胀。调查人员建议，利用雷达干涉测量技术，结合新的观测和模型开发，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结果来限制火山下方岩浆房的几何形状和体积变化，储存室和侵入/喷发岩脉之间的流动动力学，以及与持续岩浆房膨胀相关的断层和非弹性变形的作用。他们还将研究这些过程中的时间变化，如干涉合成孔径雷达测量所证明的那样。分析加拉帕戈斯火山活动的这些高分辨率干涉合成孔径雷达观测结果需要创建和验证干涉图，开发适合于干涉合成孔径雷达数据的逆方法，并扩展这些方法以推导出地表下活动和上覆岩石非弹性响应的详细模型。具体而言，该团队将i）开发利用干涉合成孔径雷达观测的密集性的分析方法，ii）通过检查物理上更真实的岩浆房几何形状来扩展建模能力，iii）检查在一些加拉帕戈斯火山口观察到的非弹性响应，iv）测试是否有证据表明各种火山的岩浆系统是耦合或相互作用的，研究长达20年的熔岩流沉降的非凡观测。

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.