Volcanic and Seismic source Modelling (VSM) - An open tool for geodetic data modelling

Natural processes and anthropogenic activities often generate changes in the stress state of the crust, and, consequently, measurable surface deformation. Volcanic activity produces surface displacements as a result of phenomena including magma recharge/deployment and migration, and fluid flow. The accurate measurement of surface deformation is one of the most relevant parameters to measure tectonic stress accumulation and for studying the seismic cycle. Improved monitoring capabilities also capture surface deformations related to coastal erosion and its connection to climate change, landslides and deep seated gravitational slopes, and other hydrogeological hazards. In addition, anthropogenic activity such as mining and water pumping cause measurable soil displacement.

Ground deformations are measured by space and terrestrial techniques, reaching sub-millimetric accuracy. Synthetic Aperture Radar (SAR) satellites have been quickly developing in the last decades. GNSS data allows to map nearly 3D deformation patterns, but often the network consists of few benchmarks. The joint use of SAR and GNSS data compensate the intrinsic limitations of each technique. Levelling measures the geodetic height of a benchmark. Borehole dilatometers and clinometers provide derivative measurements of the surface displacements.

Theoretical models of deformation sources are commonly employed to investigate the surface displacements observed, for example, in volcanic areas or related to a seismic event. A volcanic source can be represented by a confined part of crust with a certain shape inflating/deflating because of a change in the internal magma/gas pressure. The static seismic source is ideally represented by a tabular discontinuity in the crust undergoing relative movement of both sides. Furthermore, gas reservoir exploitation, water pumping and soil consolidation, can be represented using the same models.

Volcanic and Seismic source Modelling (VSM) is an open-source Python tool to model ground deformation detected by satellite and terrestrial geodetic techniques. It allows the user to choose one or more geometrical sources as forward model among sphere, spheroid, ellipsoid, fault, and sill. It supports geodetic from several techniques: interferometric SAR, GNSS, levelling, Electro-optical Distance Measuring, tiltmeters and strainmeters. Two sampling algorithms are available, one is a global optimization algorithm based on the Voronoi cells and the second follows a probabilistic approach to parameters estimation based on the Bayes theorem. VSM can be executed as Python script, in Jupyter Notebook environments or by its Graphical User Interface. Its broad applications range from high level research to teaching, from single studies to near real-time hazard estimates. Potential users range from early career scientists to experts. It is freely available on GitHub (https://github.com/EliTras/VSM). In this contribution I show the functionalities of VSM and test cases.