Abstract
<p class="western" align="justify"><span style="font-family: 'Bitstream Charter', serif;"><span>By extending the conventional Beam-Forming frequency-wavenumber power spectral estimate to the case of arbitrarily-shaped wavefronts, we obtained images of rupture propagation during the 2016 August 24, Mw=6.0 central Italy earthquake. Using a set of strong-motion accelerometers, we evaluate the beam power along the travel time curves associated with synthetic sources spanning a model fault surface. This allows deriving time-dependent images of the distribution of energy radiation throughout the fault plane. Results indicate bi-lateral rupture propagation toward SE and NW, in rough agreement with surface co-seismic displacement and surface damage pattern. To a first order, our results are also consistent with those obtained from full-waveform inversion of strong-motion data.</span></span></p>
Highlights
According to the TimeDomain Moment Tensor (TDMT) solution dispatched by INGV soon after the event, the earthquake was caused by normal faulting with planes striking along the Apennines direction, i.e. SSENNW (GdL INGV, 2016; Fig. 1)
beam forming (BF) power spectra are calculated over subse quent 2slong time windows shifting along the seismograms with 1s increment
This apparent paradox, that would imply a retreat of the rupture front, can be interpreted in terms of the interference between waves simul taneously radiated by the previouslyidenti fied, separate rupture fronts expanding toward opposite directions
Summary
Subsequent analyses of the GPS and Synthetic Aperture Radar (SAR) deformation patterns [GdL IREACNR & INGV, 2016] and aftershocks distribution al low constraining the causative fault to the southwesterndipping nodal plane of the TDMT solution This mechanism is consistent with the structural features of this sector of the Apennines, characterized by NNWSSEtrend ing, westdipping extensional Quaternary faults which are responsible for most of the de structive earthquakes that struck Italy over the last decades. Preliminary inspection of the threecomponent recordings evidenced that the Swaves suffered important loss of coher ence even for small interstation distances Those waves are characterized by a low frequency content (~0.3 Hz on velocity seismograms), which make them not appropri ate for investigating the dynamical evolution of the source over short time intervals.
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