Earthquake Characteristics and Structural Properties of the Southern Tyrrhenian Basin from Full Seismic Wave Simulations

Abstract

Modelling the response of seismic wavefields to sharp lateral variations in crustal discontinuities is essential for seismic tomography application and path effects correction in earthquake source characterization. This is particularly relevant when wavefields cross back-arc oceanic basins, i.e. mixed continental-oceanic settings. High-frequency (>0.05 Hz) seismic waves resonate and get absorbed across these settings due to a shallow Moho, crustal heterogeneities, and energy leakage. Here, we provide the first high-frequency wave-equation model of full seismograms propagating through realistic 3D back-arc basins. Inversion by parameters trial based on correlation analyses identifies P-, S- and coda-wave as attributes able to estimate jointly 3D Moho variations, sediment thickness, and earthquake source characteristics using data from a single regional earthquake. We use as data waveforms produced by the Accumoli earthquake (Central Italy, 2016), propagating across the Southern Tyrrhenian basin and recorded across Southern Italy. The best model comprises a deep Moho ($$\sim$$ ∼ 18 km) in the middle of the basin and a crustal pinch with the continental crust in Sicily. The deep Moho corresponds to the Issel Bridge, a portion of continental crust trapped between the Vavilov and Marsili volcanic centres. The Accumoli earthquake is optimally described at a depth of 7.3 km using a boxcar with rise time of 6 s. Our results show that the early S-wave coda comprises trapped and reverberating phases sensitive to crustal interfaces. Forward modelling these waves is computationally expensive; however, adding these attributes to tomographic procedures allows modelling both source and structural parameters across oceanic basins.

Head Waves in Modified Weiskopf Sandy Medium

“…For example, in the course of deep Earth exploration, these waves are observed at the seismic wave propagation in the geophysical formations [59][60][61][62][63][64][65][66][67][68][69], enabling the identification of both the Earth's crust and mantle fine structure [66,68]. On a smaller scale, SP waves propagating along the free Earth's surface are generated by shallow earthquakes and undersurface explosions [36,[70][71][72][73][74][75]. These waves play an important role in the identification of underground or surface explosions from shallow earthquakes with the corresponding seismograms [36]; even very shallow earthquakes with focuses lying at a depth of several kilometers produce prominent SP waves, while explosions, especially near surface ones, produce no SP waves in seismograms [20,36].…”