Structural reconstruction, fault parameterization, and slip rate analysis in the northern Adriatic Sea (Italy): implications for the Plio-Pleistocene tectonic activity of long-lived offshore buried thrusts.

The northern Apennines foredeep is characterized by a Plio-Pleistocene tectonic activity whose driving structures (thrust faults and related anticlines) are always buried by a high amount of syntectonic sediments, both onshore (Po Plain) and offshore (Adriatic Sea), thereby leaving subtle or none apparent signatures in the topo-bathymetry. Compared to the rest of Italy, this area has a relatively moderate earthquake hazard, but historical reports and instrumental recordings testify for significant seismicity. Seismological analyses of recent sizeable earthquakes (e.g., the Mw 6.1, Emilia earthquake in 2012) confirmed that the seismic activity is mainly due to the outermost northern Apennines buried thrusts. In this work, we reconstructed and parameterized the 3D geometry of such buried faults in an offshore sector just south of the Po River delta by interpreting a dense network of 2D seismic reflection profiles. The availability of two regional seismic reflection profiles, coupled with a detailed reconstruction of Plio-Pleistocene horizons, allowed us to restore the deformation cumulated by these thrusts. Our analysis was aimed at (1) establishing the age of inception of the main crustal thrusts, (2) reconstruct the main Plio-Pleistocene tectonic events affecting the study area, and (3) calculate the Plio-Pleistocene slip rates at different time slices and reporting them through probability distribution functions that take into account the uncertainties associated with horizon ages and restoration parameters. Our results show that the Plio-Pleistocene tectonic activity is variably distributed on different thrust faults and decreases exponentially over time after the Gelasian. The analysis performed on the most recent reflectors suggests that a low but not negligible tectonic activity characterizes the main thrusts in the studied region in the last 4-500 ka and hints at a residual activity that may last until the present.

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3D reconstructions of fault surfaces and key stratigraphic horizons to define recent tectonic activity in the northern Apennines outer fronts and foredeep (northern Adriatic Sea, Italy)

10.5194/egusphere-egu2020-9569 ◽

2020 ◽

Author(s):

Yuri Panara ◽

Francesco Emanuele Maesano ◽

Roberto Basili ◽

Giacomo Losi ◽

Jakub Fedorik ◽

...

Keyword(s):

3D Reconstruction ◽

Cross Sections ◽

Seismic Reflection ◽

Adriatic Sea ◽

Structural Features ◽

Data Availability ◽

Tectonic Activity ◽

Northern Adriatic Sea ◽

Northern Adriatic ◽

Seismic Reflection Profiles

Fault plane attitude and dimension are important parameters for deriving seismotectonic information or input data for earthquake hazard assessment and in this sense a complete 3D view and characterization of geological and structural elements is essential. However, there is always a trade-off between structural complexity and data availability at the scale of the designed application.In the last few years, merging public and confidential seismic reflection profiles and borehole data, were used in order to carry out a 3D reconstruction of fault planes and Plio-Pleistocene stratigraphic horizons in the northern Adriatic Sea, at the front of the northern Apennine fold-and-thrust belt and associated foredeep. The study area straddles the Italian coastline and subsurface data interpretation allowed us to reconstruct the structural setting of both onshore and offshore structures. Although it is known that this area has low rates of active tectonic deformation, it hosts important seismogenic faults associated with instrumental seismicity and historical earthquakes.The dense distribution of seismic reflection profiles allowed us to perform an accurate 3D reconstruction of almost 50 fault planes, of different dimensions and order of importance. Their geometrical and structural features helped to define the most recent tectonic phases. To this end, we also mapped several Plio-Pleistocene regional unconformities and integrated them with previously published reconstructions of key horizons.In some cases, where further published data were available, it was also possible to perform detailed cross sections whose restoration allowed us to reconstruct the post-Miocene (5.33 Ma) slip-rate history of some important tectonic structures with a detail of ~1 Ma. The 3D geological model revealed several structural features like fault continuity and terminations, level of connectivity, presence of lateral ramps, along strike variations of displacement that could not be fully addressed using cross sections alone.

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Geological and geophysical study of a thin-skinned tectonic wedge formed during an early collisional stage: the Trasimeno Tectonic Wedge (Northern Apennines, Italy)

Geological Magazine ◽

10.1017/s001675681900061x ◽

2019 ◽

Vol 157 (2) ◽

pp. 213-232 ◽

Cited By ~ 1

Author(s):

Filippo Carboni ◽

Francesco Brozzetti ◽

Francesco Mirabella ◽

Francesco Cruciani ◽

Massimiliano Porreca ◽

...

Keyword(s):

Cross Section ◽

Seismic Reflection ◽

Northern Apennines ◽

Early Miocene ◽

Thrust Belts ◽

Tectonic Reconstruction ◽

Geophysical Study ◽

Shortening Rate ◽

Seismic Reflection Profiles ◽

Surface Geology

AbstractThe presence of a set of well-known turbidite successions, deposited in progressively E-migrating foredeep basins and subsequently piled up with east vergence, makes the Northern Apennines of Italy paradigmatic of the evolution of deepwater fold-and-thrust belts. This study focuses on the early Apenninic collisional stage, early Miocene in age, which led to the accretion of the turbidites of the Trasimeno Tectonic Wedge (TTW), in the central part of the Northern Apennines. Based on the interpretation of previously unpublished seismic reflection profiles with new surface geology data and tectonic balancing, we present a detailed tectonic reconstruction of the TTW. In the study area, the TTW is characterized by a W-dipping shaly basal décollement located at a depth of 1–5 km. The tectonic wedge is c. 5 km thick at its central-western part and tapers progressively eastwards to c. 1 km. The total shortening, balanced along a 33 km long cross-section, is c. 60 km, including 20 km (40%) of internal imbrication, c. 23 km of horizontal ENE-wards translation along the basal décollement and c. 17 km of passive translation caused by the later shortening of footwall units. Deformation balancing, constrained through upper Aquitanian – upper Burdigalian (c. 21–16 Ma) biostratigraphy, provides an average shortening rate of c. 8.6 mm a–1. Internal shortening of the TTW shows an average shortening rate of c. 4 mm a–1 for this period.

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

Frontiers in Earth Science ◽

10.3389/feart.2021.664288 ◽

2021 ◽

Vol 9 ◽

Author(s):

Yuri Panara ◽

Francesco Emanuele Maesano ◽

Chiara Amadori ◽

Jakub Fedorik ◽

Giovanni Toscani ◽

...

Keyword(s):

Adriatic Sea ◽

Sedimentary Cover ◽

Slip Rate ◽

Northern Apennines ◽

Middle Pleistocene ◽

Tectonic Deformation ◽

Slip Rates ◽

Northern Adriatic ◽

Slip History ◽

Over Time

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.

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The evolution of the Malvern Lineament [abstract only]

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1986.0036 ◽

1986 ◽

Vol 317 (1539) ◽

pp. 277-277 ◽

Cited By ~ 2

Keyword(s):

Seismic Reflection ◽

Tectonic Activity ◽

Normal Faults ◽

Sedimentary Deposits ◽

Westerly Direction ◽

History Of ◽

Early Palaeozoic ◽

Western Side ◽

Seismic Reflection Profiles ◽

Uplift And Erosion

The geology of the Malvern Hills has been the subject of controversy since the 1850s. Many of the problems have now been resolved by using a combination of techniques including mapping, seismic-reflection profiling, deep drilling and geochronology. The Malvern Lineament is a major north-south trending crustal structure with a complex history of tectonic activity. In early Palaeozoic times thrusting on the Malvern axis caused uplift of the area to the east of the axis and some thickening of sedimentary deposits to the west. The importance of the Llandovery unconformity along the western side of the Malvern Hills is stressed. In late Carboniferous times there was major thrusting in a westerly direction, probably associated with dextral transpression, and considerable uplift and erosion of the area to the east of the Malverns. In Permian and Triassic times an extensional lithospheric stress field was initiated. This resulted in reactivation of the earlier thrusts as major normal faults down throwing to the east and with throws, locally, in excess of 2.5 km. These faults, which dip eastwards at between 35 and 50°, are detectable on seismic-reflection profiles to a depth of about 5 km and controlled the development of the Worcester Basin, inverting the site of an older ‘high’.

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