Stability of fault plane solutions for Mw >= 4.8 in northern Italy in 2012

TL;DR

This study critically analyzes the stability of seismic fault plane solutions for moderate earthquakes in northern Italy in 2012, emphasizing the importance of waveform inversion parameters for accurate source characterization.

Contribution

It demonstrates the impact of cutoff period choices on the stability and resolution of moment tensor solutions, highlighting the need for short-period waveform inversion.

Findings

Shorter cutoff periods improve solution resolution.

Inversion instability affects depth and fault plane solutions.

Spurious components can arise from poor resolution.

Abstract

We propose a critical analysis of the moment tensor solutions of the major seismic events that affected northern Italy in 2012. Inverting full waveforms at regional distance using the non-linear method named INPAR, we investigate period dependent resolution that affects in particular the solutions of shallow events. This is mainly due to the poor resolution of Mzx and Mzy components of the seismic tensor when inverting signals whose wavelengths significantly exceed the source depth. As a consequence, instability affects both source depth and fault plane solution retrieval, and spurious large Compensated Linear Vector Dipole components arise. The inversion performed at cutoff periods shorter than 20 s reveals in many cases different details of the rupture process, that are not resolved inverting at longer cutoff periods. Thus we conclude that inversion of full waveforms at cutoff period as short as possible should be preferred.