We have provided the first estimate of scattering and intrinsic attenuation for the Gargano Promontory (Southern Italy) analyzing 190 local earthquakes with ML ranging from 1.0 to 2.8. To separate the intrinsic $${Q}_{i}$$ Q i and scattering $${Q}_{s}$$ Q s quality factors with the Wennerberg approach (1993), we have measured the direct S waves and coda quality factors ($${Q}_{\beta }$$ Q β , $${Q}_{c}$$ Q c ) in the same volume of crust. $${Q}_{\beta }$$ Q β parameter is derived with the coda normalization method (Aki 1980) and $${Q}_{c}$$ Q c factor is derived with the coda envelope decay method (Sato 1977). We selected the coda envelope by performing an automatic picking procedure from $${T}_{\mathrm{start}}=1.5{T}_{S}$$ T start = 1.5 T S up to 30 s after origin time (lapse time $${T}_{L}$$ T L ). All the obtained quality factors clearly increase with frequency. The $${Q}_{c}$$ Q c values correspond to those recently obtained for the area. The estimated $${Q}_{i}$$ Q i are comparable to the $${Q}_{c}$$ Q c at all frequencies and range between 100 and 1000. The $${Q}_{s}$$ Q s parameter shows higher values than $${Q}_{i}$$ Q i , except for 8 Hz, where the two estimates are closer. This implies a predominance of intrinsic attenuation over the scattering attenuation. Furthermore, the similarity between $${Q}_{i}$$ Q i and $${Q}_{c}$$ Q c allows us to interpret the high $${Q}_{c}$$ Q c anomaly previously found in the northern Gargano Promontory up to a depth of 24 km, as a volume of crust characterized by very low seismic dumping produced by conversion of seismic energy into heat. Moreover, most of the earthquake foci fall in high $${Q}_{i}$$ Q i areas, indicating lower level of anelastic dumping and a brittle behavior of rocks.

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We have provided the first estimate of scattering and intrinsic attenuation for the Gargano Promontory (Southern Italy) analyzing 190 local earthquakes with ML ranging from 1.0 to 2.8. To separate the intrinsic \({Q}_{i}\) and scattering \({Q}_{s}\) quality factors with the Wennerberg approach (1993), we have measured the direct S waves and coda quality factors (\({Q}_{\beta }\), \({Q}_{c}\)) in the same volume of crust. \({Q}_{\beta }\) parameter is derived with the coda normalization method (Aki, 1980) and \({Q}_{c}\) factor is derived with the coda envelope decay method (Sato, 1977). We selected the coda envelope by performing an automatic picking procedure from \({T}_{start}=1.5{T}_{S}\) up to 30 s after origin time (lapse time \({T}_{L}\)). All the obtained quality factors clearly increase with frequency. The \({Q}_{c}\) values correspond to those recently obtained for the area. The estimated \({Q}_{i}\) are comparable to the \({Q}_{c}\) at all frequencies and range between 100 and 1000. The \({Q}_{s}\) parameter shows higher values than \({Q}_{i}\), except for 8 Hz, where the two estimates are closer. This implies a predominance of intrinsic attenuation over the scattering attenuation. Furthermore, the similarity between \({Q}_{i}\) and \({Q}_{c}\) allows us to interpret the high \({Q}_{c}\) anomaly previously found in the northern Gargano Promontory up to a depth of 24 km, as a volume of crust characterized by very low seismic dumping produced by conversion of seismic energy into heat. Moreover, most of the earthquake foci fall in high \({Q}_{i}\) areas, indicating lower level of anelastic dumping and a brittle behavior of rocks.

<div> <p><span>We found a previously unreported later seismic phase from intermediate-depth and deep earthquakes of the Southern Tyrrhenian subduction zone recorded by European seismic stations. </span><span>Later phases are useful to constrain local-scale discontinuities, especially in subduction zones, but their observation is infrequent, since it depends on seismic stations distribution and slab geometry. Their detection, therefore, is a great opportunity to improve our knowledge of subduction systems and Earth’s interior. They also represent a powerful mean to retrieve the chemical composition of such deep structures.</span><span> </span></p> </div><div> <p><span>We analysed thousands of waveforms of the strongest earthquakes occurred in the Southern Tyrrhenian subduction system and recorded by European seismic stations from 1990 to 2020.</span><span> </span></p> </div><div> <p><span>The unknown seismic phase is visible at stations from 6 to 9 degrees from the epicentre, towards the north. Only earthquakes located in a well-defined region of the slab, in the depth range of 215–320 km, generate this secondary phase. We built a direct 2D P-velocity model of the Tyrrhenian slab to reproduce observed travel times and ray paths of direct and later phases. We interpret the later phase as a compressional (P) wave that propagates downward in a narrow, high P-wave velocity layer within the deepest part of the subducting slab. We proprose that the high P-wave velocity layer in the subducting slab could be related to the presence of the dense hydrous magnesium silicate phase A, which is probably the main (meta) stable hydrous phase in the upper-mantle deep slab. Our findings provide further insights on the Southern Tyrrhenian slab structure and h</span><span>ave also relevant implications on water transport in the Earth’s mantle and slab petrology.</span></p> </div>