Understanding Volcanic Sources Through Improved Inversion of Deformation and Gravity Data

研究火山的一个重要目标是确定岩浆库的大小和形状。 有多深？它们是树干状的，还是大致等维的物体、岩床或湖石？同样重要的是要确定岩浆被输送到地表的管道的大小、形状和位置，以及岩浆体积和化学成分如何控制地震活动和变形。 理想的情况是，可以区分导致爆发的动荡时期和以入侵结束的动荡时期，以及未来爆发的规模和爆炸性。 区分浅层热液活动引起的动荡和岩浆过程产生的动荡，对长谷破火山口和黄石公园等一些火山系统至关重要。Earthscope将在未来十年内提供越来越多和质量越来越高的大地测量数据，这将有助于解决这些问题，但需要改进分析这些数据的方法，该项目正在通过开发新的反演方法来解决这些问题，以便根据变形数据确定岩浆库的位置和形状。研究人员没有假设特定的源形状，而是开发了从数据中求解岩浆房几何形状的方法。 以前的工作利用分布式点源模型岩浆房没有物理动机。 目前的研究，而不是寻找一个封闭的表面与均匀的压力内的弹性地球作为一个代表的岩浆房。 他们反演点源的最佳拟合集，然后寻找一个等效的加压腔，导致相同的表面变形。这产生了一个物理动机的模型，根据观察到的变形，在原则上是完全通用的。此外，该项目正在采用时间相关的反演技术来估计岩浆系统的时间和空间演化。 这些方法，统称为网络反演滤波器，能够成像的时空演变的堤防，和故障。变形数据的同时反演和重复的重力测量使研究人员能够估计地下流体的密度。 这可以使人们能够可靠地区分岩浆和含水流体作为变形的原因。

An important goal in studying volcanoes is to determine the size and shape of magma reservoirs. How deep are they? Are they stock-like, or roughly equi-dimensional bodies, sills, or lacoliths? It is also important to determine the size, shapes, and locations of conduits through which magma is transported to the surface, and how precursory seismicity and deformation are controlled by magma volume and chemistry. Ideally, it would be possible to distinguish between periods of unrest that lead to eruptions versus those that end with intrusion, as well as the size and explosivity of future eruptions. Distinguishing between unrest caused by shallow hydrothermal activity from that generated by magmatic processes is critical in some silicic systems such as Long Valley Caldera and Yellowstone. The increasing amount and quality of geodetic data that Earthscope will make available in the next decade will help address these questions, however improved methods are needed to analyze these data.This project is addressing these issues by developing new inverse methods to determine the location and shape of magmatic reservoirs from deformation data. Rather than assume a particular source shape, the researchers are developing methods to solve for the magma chamber geometry from the data. Previous work utilized distributed point sources to model magma chambers without physical motivation. The present study looks instead for a closed surface with uniform pressure inside an elastic earth as a representation of a magma chamber. They invert for the best fitting set of point sources and then seek an equivalent pressurized cavity that causes the same surface deformation. This yields a physically motivated model, based on observed deformation that is in principal completely general.Additionally, this project is employing time dependent inversion techniques to estimate the temporal and spatial evolution of the magmatic system. These methods, collectively referred to as Network Inversion Filters, are capable of imaging the spatio-temporal evolution of dikes, and faults. Simultaneous inversion of deformation data and repeated gravity measurements permits researchers to estimate the density of subsurface fluids. This can allow one to discriminate reliably between magmatic and aqueous fluids as causes of deformation.