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。它们有多深？它们是像股票一样的，还是大致等维的身体、技能或lacoliths？确定岩浆向地表输送的管道的大小、形状和位置，以及岩浆体积和化学成分如何控制前兆地震活动和变形，也很重要。理想情况下，它将有可能区分导致火山爆发的动荡时期和以入侵结束的动荡时期，以及未来火山爆发的规模和爆炸性。区分由浅层热液活动引起的动荡与岩浆过程产生的动荡在一些硅质系统中至关重要，比如长谷火山口和黄石公园。Earthscope将在未来十年提供数量和质量不断增加的大地测量数据，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。该项目通过开发新的逆方法来解决这些问题，通过变形数据确定岩浆储层的位置和形状。研究人员不是假设一个特定的岩浆源形状，而是开发出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来模拟没有物理动机的岩浆房。相反，目前的研究寻找弹性地球内部具有均匀压力的封闭表面作为岩浆房的代表。他们反演最佳拟合的点源集，然后寻找导致相同表面变形的等效加压腔。这产生了一个物理驱动的模型，基于观察到的变形，原则上是完全一般的。此外，本项目还采用时变反演技术来估计岩浆系统的时空演化。这些方法统称为网络反演滤波器，能够对岩脉和断层的时空演变进行成像。同时反演变形数据和重复重力测量使研究人员能够估计地下流体的密度。这可以使人们可靠地区分岩浆流体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.