A frequency domain inversion code to retrieve time-dependent parameters of very long period volcanic sources

In this article, we present a new code for the inversion of source parameters of volcanic seismic events. The code, named VOLPIS (Volcanic Long Period Inversion for the Source), has as its main goal the retrieval of time-dependent source parameters, so that both amplitudes and time history of source components can be estimated. The methodology used has been designed to be extremely flexible, in order to be easily applied to different datasets and, eventually, used for the inversion of any other seismic source with a complex source time function. Certain physical phenomena occurring at volcanic focal regions can be expressed in terms of a generalized seismic point source, as the sum of single forces and dipole forces (moment tensor). Source time histories for different source components can be kept independent, so that superposition of different physical phenomena can be retrieved, even in cases where they occur with different timing. Otherwise, a constraint for partially or fully common source time history can be included. The algorithm is based on a frequency domain approach, where the inversion is solved separately for each complex sampled frequency. The code structure helps in simplifying the handling and processing of data, which can be adapted to data characteristics or user requirements. Significant examples of possible applications to synthetic data are included.