Versatile Modeling Of Deformation (VMOD) Inversion Framework: Application to 20 Years of Observations at Westdahl Volcano and Fisher Caldera, Alaska, US.

We developed an open source, extensible Python‐based framework, that we call the Versatile Modeling Of Deformation (VMOD), for forward and inverse modeling of crustal deformation sources. VMOD abstracts from specific source model implementations, data types and inversion methods. We implement the most common geodetic source models which can be combined to model and analyze multi‐source deformation. VMOD supports Global Navigation Satellite System (GNSS), InSAR, electronic distance measurement, Leveling and tilt data. To infer source characteristics from observations, VMOD implements non‐linear least squares and Markov Chain Monte‐Carlo Bayesian inversions, including joint inversions using different sources of data. VMOD's structure allows for easy integration of new geodetic models, data types, and inversion strategies. We benchmark the forward models against other published results and the inversion approaches against other implementations. We apply VMOD to analyze deformation at Unimak Island, Alaska, observed with continuous and campaign GNSS, and ascending and descending InSAR time series generated from Sentinel‐1 satellite radar acquisitions. These data show an inflation pattern at Westdahl volcano and subsidence at Fisher Caldera. We use VMOD to test a range of source models by jointly inverting the GNSS and InSAR data sets. Our final model simultaneously constrains the parameters of two sources. Our results reveal a depressurizing spheroid under Fisher Caldera ∼4–6 km deep, contracting at a rate of ∼2–3 Mm3/yr, and a pressurizing spherical source underneath Westdahl volcano ∼6–8 km deep, inflating at ∼5 Mm3/yr. This and past applications of VMOD to volcanic unrest benefit from an extensible framework which supports jointly inversions of data sets for parameters of easily composable multi‐source models. Plain Language Summary: We developed a computational framework called the Versatile Modeling Of Deformation (VMOD) to calculate surface deformation created by buried pressure, tensile and shear sources, or find parameter values for a model that fits observed surface deformation. The framework has three main components. One component handles the model, one component handles the data, and the remaining component handles the algorithm that finds the most probable values for the parameters of a given model. Deformation can be observed using different techniques such as Global Navigation Satellite System (GNSS) or satellite images. The framework supports most of these techniques and allows users to add new techniques or deformation models. We validate our framework with literature results and contrast it with similar software used in the volcano deformation community. We apply the framework to analyze a deformation episode at Westdahl volcano and Fisher Caldera on Unimak Island, Alaska. The deformation is captured by GNSS and satellite radar images. Our results suggest a deflating spheroid ∼4–6 km deep with a rate of ∼2–3 Mm3/yr for Fisher Caldera and a inflating spherical source underneath Westdahl volcano ∼6–8 km deep, at a rate of ∼5 Mm3/yr. This and previous experiences highlight the advantages of multi‐source model deformation observations from different techniques. Key Points: We introduce a Python‐based object‐oriented modeling and inversion framework for geodetic data (Versatile Modeling Of Deformation (VMOD))VMOD's expandable framework design enables easy integration of new observation types, new deformation models, or inversion strategiesWe validate VMOD against literature and a community exercise, and use it to infer deformation sources at Fisher Caldera and Westdahl volcano [ABSTRACT FROM AUTHOR]