ISOLA-BaBoo, a code for full moment tensor inversion with uncertainty estimation; application to the 2025 Anydros earthquakes

Full moment tensors are important for revealing non-shear mechanisms of earthquake faulting. Nevertheless, non-double-couple components represent sensitive source parameters, less robust than strike, dip, rake, and moment. Thus, inversion of full moment tensors must be accompanied by uncertainty analyses. Here, we present a new version of traditional ISOLA software for inverting complete waveforms, in which uncertainty is analyzed with Bayesian bootstrap. This approach is particularly useful for obtaining uncertainty of model parameters without assuming a specific (e.g., Gaussian) distribution of data error and evaluating its covariance matrix. We assume that the set of recorded waveforms is representative, noise is low relative to the signal, and the velocity model is free of systematic error. The method is applied to 25 earthquakes of the 2025 Anydros crisis, Aegean Sea, Greece. Most of the analyzed events are Mw>4.5, and they consistently indicate a shear-tensile process, i.e., crack opening on mostly normal faults. The stress field calculated from these and previously published focal mechanisms is transtensional. The fault friction coefficient is low (~0.15). We preliminarily interpret the observed moment tensors as pointing to a fluid-assisted rupture process in a complex network of tectonic faults, likely triggered by a dike emplacement.