Not so planar faults: on the impact of faulting complexity and type on earthquake rupture dynamics

The increasing quality and completeness of global moment tensor solutions allow to advance our comprehension of seismicity delving into the connection between earthquake occurrence, tectonics, and faulting. Since, at least theoretically, each seismic event can be described using a time-dependent moment tensor averaging over different spatial orientations of various fault patches; then, if the rupture is roughly nonplanar, shear sliding may not be appropriate to modelling the whole seismic event. This implies a drop of the double-couple components. Therefore, we focus our attention on the different compositions of the moment tensors of moderate and large seismic events of global and regional catalogues as a function of the tectonic setting looking for the effect predicted by theory. We have found that thrusts host earthquakes with more elevated double-couple percentages with respect to strike-slip and normal faults. The compensated-linear-vector-dipole component decreases as the size of earthquakes increases in reverse faulting, while this trend is weaker or absent in other classes of seismicity. We have also noticed that the double-couple component positively correlates with the b-value and it is negatively related to the corner magnitude of the frequency-size distribution, which is compatible with a systematic magnitude underestimation in low double-couple earthquakes. Our results suggest that, at least for large seismic events featured by suspiciously high non-double-couple components (above 30%, e.g., 30/10/2016 Mw 6.5 Norcia and 13/11/2016 Mw 7.8 Kaikoura events) should be considered to better assess their size accurately also because of possible impact on seismic forecasting.