Seismic wave attenuation (1/Qp) in the crust underneath the Eastern and eastern Southern Alps (Europe): imaging effects of faults, fractures, and fluids

Abstract

Abstract We present a novel three-dimensional model of compressional wave attenuation (1/Q P ) for the Eastern and eastern Southern Alps in Europe that includes the eastern part of the Adriatic indenter, termed here the Dolomites Sub-Indenter. Our approach employed waveform data from the SWATH-D network, a dense temporary network operational between 2017 and 2019, as well as selected stations of the larger AlpArray Seismic Network. A spectral inversion method using frequency-independent quality factor Q P , was applied to derive 3578 path-averaged attenuation values (t*) from 126 local earthquakes. These were then inverted using the damped least square inversion (local earthquake tomography) for the attenuation structure. The resulting Q P model, which builds on and complements a previously calculated 3-D velocity model (V P and V P /V S ), exhibits good resolution down to ~ 20 km depth. Several anomalies can be correlated with the distribution of other physical parameters (V P and V P /V S ) and regional tectonic features. Notably, the Friuli-Venetian region exhibits the highest attenuation (lowest Q P ) anomaly, coinciding with low V P values and increased V P /V S . This anomaly is likely associated with a high density of faults and fractures, as well as the presence of fluid-filled sediments along the active thrust front in the eastern segment of the Southern Alps. Another intriguing observation is the low attenuation (high Q P ) anomaly along the northwestern edge of the Dolomites Sub-Indenter (NWDI), located south of the Periadriatic fault and east of the Giudicarie fault, where seismicity is notably absent. This anomaly coincides with Permian magmatic rocks at the surface and may be a measure of their strength at depth. Graphical Abstract

Keywords

• Alpine orogeny
• Crustal structure
• Seismic attenuation
• Seismic tomography
• Body waves