Probabilistic Assessment of Slip Rates and Their Variability Over Time of Offshore Buried Thrusts: A Case Study in the Northern Adriatic Sea

Abstract

When sedimentation rates overtake tectonic rates, the detection of ongoing tectonic deformation signatures becomes particularly challenging. The Northern Apennines orogen is one such case where a thick Plio-Pleistocene foredeep sedimentary cover blankets the fold-and-thrust belt, straddling from onshore (Po Plain) to offshore (Adriatic Sea), leading to subtle or null topo-bathymetric expression of the buried structures. The seismic activity historically recorded in the region is moderate; nonetheless, seismic sequences nearing magnitude 6 punctuated the last century, and even some small tsunamis were reported in the coastal locations following the occurrence of offshore earthquakes. In this work, we tackled the problem of assessing the potential activity of buried thrusts by analyzing a rich dataset of 2D seismic reflection profiles and wells in a sector of the Northern Apennines chain located in the near-offshore of the Adriatic Sea. This analysis enabled us to reconstruct the 3D geometry of eleven buried thrusts. We then documented the last 4 Myr slip history of four of such thrusts intersected by two high-quality regional cross-sections that were depth converted and restored. Based on eight stratigraphic horizons with well-constrained age determinations (Zanclean to Middle Pleistocene), we determined the slip and slip rates necessary to recover the observed horizon deformation. The slip rates are presented through probability density functions that consider the uncertainties derived from the horizon ages and the restoration process. Our results show that the thrust activation proceeds from the inner to the outer position in the chain. The slip history reveals an exponential reduction over time, implying decelerating slip-rates spanning three orders of magnitudes (from a few millimeters to a few hundredths of millimeters per year) with a major slip-rate change around 1.5 Ma. In agreement with previous works, these findings confirm the slip rate deceleration as a widespread behavior of the Northern Apennines thrust faults.

Revitalizing vintage seismic reflection profiles by converting into SEG-Y format: case studies from publicly available data on the Italian territory

“…[e.g.,Pezzo et al, 2020;Bigi et al, 2013;Mancinelli and Scisciani 2020;Maesano et al, 2013] and directly comparable with SEG-Y data provided by oil & gas companies[Panara et al, 2021]. This improvement also broadens the field of analysis for the definition of the activity of geological structures, such as the evaluation of slip rates and depositional rates, which are parameters that have a substantial impact in the assessment of the hazard associated,Figure 6.…”

“…Considering some of the critical issues just described, it is of fundamental importance that the scientific community may have open access tools for building high-quality and digital subsurface datasets, which can be utilized in research, especially in areas with significant knowledge gaps, such as geo-hazard analyses. An example of such a study would be to carry out thorough investigations for recognizing and mapping faults in the subsurface, which could then be associated with earthquakes' hypocentral locations [e.g., Buttinelli et al, 2021, Govoni et al, 2014, Barchi et al, 2021 for recent seismic sequences in the Italian territory] and active faults [e.g., Mirabella et al, 2004;Maesano et al, 2020;Panara et al, 2021]. Hence, it is necessary to handle good quality data to make robust inferences for seismotectonics.…”

“…In these areas, during the Pleistocene, the sedimentation rates were faster than the tectonic rates by one order of magnitude, leading to the complete burial of the frontal thrust of the Apennines [Maesano and D'Ambrogi, 2017]. Nonetheless, the geometry of the main intra-Pleistocene horizons both in the Adriatic and in the Po Plain [Amadori et al, 2019] has recorded the eventual activity of the underlying faults [Panara et al, 2021], and also the relocation of the seismicity in the area suggest that the frontal thrusts are still active and seismogenic [Battimelli et al, 2019]. The use of subsurface information thus may be crucial to refining the knowledge of the recent compressive deformation at the Apennines front.…”

Buried Alive: Imaging the 9 November 2022, Mw 5.5 Earthquake Source on the Offshore Adriatic Blind Thrust Front of the Northern Apennines (Italy)

“…We based the seismo-stratigraphic interpretation (Figure 2b) on available well-logs (Boheme-1, Tamara-1, Pesaro Mare-4, Cornelia-1, Elga-1, and Malachite-1); the constraints on the Plio-Pleistocene sequence were adopted from studies in adjacent areas (Amadori et al, 2019(Amadori et al, , 2020Ghielmi et al, 2013;Panara et al, 2021). The interpreted seismic profiles were integrated with subsurface maps of the Marne a Fucoidi Fm top horizon (Albian p.p.…”

“…The recent offshore activity was also attributed to NW-SE transpressional tectonics (Costa et al, 2021;Pierantoni et al, 2019). These conclusions have been highly disputed based on the integration of different observations, including geomorphology, extensive geophysical and subsurface geological datasets, historical seismicity, and focal mechanisms of major earthquakes (Basili & Barba, 2007;Burrato et al, 2003;DISS Working Group, 2021;Maesano et al, 2013;Panara et al, 2021;Vannoli et al, 2004Vannoli et al, , 2015.…”