Seismic source mechanisms of tremor recorded on Arenal volcano, Costa Rica, retrieved by waveform inversion

Moment tensor inversions of volcanic tremor are synthetically tested and subsequently applied to a dataset recorded on Arenal volcano in 2005. We selected 15 harmonic tremor events showing an emergent but very clear onset with a fundamental frequency range of 0.8–1.5 Hz. These events constitute an excellent opportunity to broaden our knowledge of tremor generation models. The inversions were performed for a common source location, the position of which was retrieved through the evaluation of the joint probability density function of the misfit values obtained by the moment tensor inversion of all the events and all predefined source locations (grid search). Events are located beneath the summit crater, in a shallow position. The inversion procedure was tested through the use of synthetic tremor, generated using full wavefield numerical simulations. The maximum amplitude decomposition method is used to analyse the solutions of the synthetic tests. The results highlight the stability of the moment tensor solution when the whole length of the signal is used in the inversion procedure. Hence the whole length of the tremor is utilised to retrieve the source mechanism generating the 15 tremor events. A sliding window is utilised to investigate the time variability of our solution. A crack dipping 20° to the North–Northeast is reconcilable with all 15 tremor events. This mechanism is found to be constant for the entire length of each tremor and for different events.

► A moment tensor inversion of 15 tremor recorded on Arenal in 2005 was performed. ► We constrained the inversion by using synthetic tests. ► Results highlight the need of using the whole length of the tremor signals. ► Wrong source mechanisms are generated for partial length of the signal. ► Results of the real data-set indicate constant mechanisms for all the events