Frequency-Dependent Rupture Characteristics of the 30 October 2016 Mw 6.5 Norcia, Italy Earthquake Inferred From Joint Multi-Scale Slip Inversion

The relationship between multi-scale rupture characteristics and different frequency contents of the seismic waveforms has been revealed for moderate to great earthquakes by previous researches. To better understand such a relationship, we propose a two-step strategy to perform finite fault inversion in the wavelet domain with multi seismic datasets, involving the seismic observations at both teleseismic and near-field distances. In our two-step strategy, the larger-scale pattern of the seismic rupture is first constrained by using the lower-frequency seismic waveforms and then based on the lower-frequency rupture pattern, the higher-frequency rupture features are obtained by performing inversion with higher-frequency data. We apply this two-step strategy with multi seismic datasets to study the 30 October 2016 Mw 6.5 Norcia, Italy earthquake, which is the largest event of the 2016-2017 central Italy seismic sequence. By analyzing the recovered slip patterns from different frequency bands, we notice the frequency-dependent rupture features of this earthquake. The lower-frequency slip concentrated at the shallower depths above the source, and the higher-frequency slip appeared near the edges of the lower-frequency slip patch, working as "barriers", due to fault complexities in central Italy. The frequency-dependent slip pattern of the 30 October 2016 Norcia earthquake shows a relation to the unevenly distributed pore fluid pressure, as indicated by Vp/Vs tomography from previous researches. Our results suggest that fault complexities and unevenly distributed fluids contribute to the frequency-dependent rupture of this earthquake.