AbstractsEngineering

The main focus of this work is to build 3-D FEM models with structural complexities in order to simulate volcanic systems in a more realistic way. We use Rabaul as an example to show the application of the methods and strategies proposed to an active volcano. Rabaul caldera is a volcanic system whose dynamics still need to be understood to effectively predict the behavior of future eruptions. In comparison to the simplified analytic models used so far, more realistic models, such as Finite Elements Models (FEMs), are needed to more accurately explain recent deformation and understand the magmatic system. By inverting InSAR data collected between 2007 and 2010 (using linear inversions based on FEMs), we investigate the sources of surface displacement and provide insights about the actual shallow magmatic system. FEMs are numerical models that let us include realistic features such as topography and mechanical heterogeneities. We provide strategies to use geophysical and geological information to build complex 3-D parts and assemble them into 3-D models. We then compare the effects of different material properties configurations and of different source shapes on the deformational signal and on the strength source estimates (fluid flux or pressure). Ultimately, we provide a strategy for performing a linear inversion based on an array of FEM sources that allows us to identify a distribution of flux of fluid (or change in pressure) over a volume, without imposing an a-priori source shape and depth. We use Rabaul as an example to show the 3-D model’s validity and applicability to active volcanic areas. The methodology is based on generating a library of forward numerical displacement solutions, where each entry is the displacement generated by injecting a mass of fluid of known density and bulk modulus into a source of the array. The sources are simulated as fluid-filled cavities that can accept a specified flux of magma. As the array of sources is an intrinsic geometric aspect of all forward models and the sources are activated one at a time, the domain only needs to be discretized once. This strategy precludes the need for remeshing for each activated source and greatly reduces computational requirements. By using an array of sources, we are not investigating the geometric and pressure parameters of a simplified, unique source with a regular shape. Instead, we are investigating a distribution of flux of fluids over a volume of potential sources responsible for the pressure changes in the medium as dictated by the data. The results allow us to image the complex shape of the deformation source without having to use any a-priori or simplified sources. This takes source modeling a step towards more realistic source models. The application of the methodology to Rabaul shows a shallow magmatic system under the caldera made of two interconnected lobes located at the two opposite sides of the caldera. These lobes are suggested to be the feeding reservoirs of the ongoing Tavuvur volcano eruption, on the eastern side, and…