Intrinsically Variable Blind Thrust Faulting

Abstract

We propose that most fault slip rate variability across a range of time and spatial scales is due to intrinsic faulting processes, rather than extrinsic changes in surface loads or stress boundary conditions. This hypothesis is tested by comparing very high geologic resolution slip histories of blind thrust faults from three transects in the Northern Apennines, Italy. We investigated whether these slip histories document synchronous, or independent, behavior of the disconnected, blind thrust faults that core mountain front anticlines bordering the Po foreland. The slip history for these thrusts is reconstructed by applying forward structural modeling to deformed growth strata and fluvial terraces preserved on the limbs of the growing anticlines. We present a new age model using magnetostratigraphy and cyclostratigraphy for a section of growth strata exposed in the Panaro River and supplement this with age models for two other published transects. The blind thrust fault at each transect exhibits variable slip behavior over the past 3 Myr, but for most of that time the variability was both asynchronous and independent of boundary condition changes, such as Plio-Pleistocene sediment accumulation variability. However, a major deceleration in slip rates at all three locations is temporally coincident with the overfilling of the Po foreland beginning in the early Pleistocene. We attribute the deceleration to a switch from shortening on shallowly detached thrusts to shortening on a crustal-scale basement-involved fault. This switch has implications for the time and spatial scales at which extrinsic boundary conditions may contribute to deformation variability.

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

“…For all the analyzed structures, we observed a marked slip rate reduction occurred during the Calabrian (seq-PS2), evidenced by the slope change of the fitted curves shown in Figure 10, in agreement with a general reduction of the Northern Apennines thrust fronts activity observed during the Pleistocene (Gunderson et al, 2013;Maesano et al, 2013Maesano et al, , 2015Bresciani and Perotti, 2014;Maesano and D'Ambrogi, 2016) coincident with the overfilling of the Po Plain -Northern Adriatic foredeep beginning in the Early Pleistocene (Gunderson et al, 2018). On average, slip rates obtained here are consistent with previous works and findings in adjacent areas (Maesano et al, 2013(Maesano et al, , 2015 and represent, in most cases, a finer temporal scan of thrust activity.…”

“…The different approaches to slip rate calculation and the variability of the results can be treated considering all the uncertainties involved and providing a probabilistic approach to the results (Zechar and Frankel, 2009;Styron, 2019). The determination of slip rates of blind faults is mostly based on the analysis of deformed syn-tectonic markers either on surface exposures (Ward and Valensise, 1996;Vannoli et al, 2004;Gunderson et al, 2013Gunderson et al, , 2018Livio et al, 2014;Tiberti et al, 2014) or in the subsurface (Dolan et al, 2003;Wang et al, 2014;Maesano et al, 2015Maesano et al, , 2020Bergen et al, 2017), and requires a good three-dimensional geometrical definition of the underlying fault (Shaw et al, 2002).…”

Peat layer accumulation and post‐burial deformation during the mid‐late Holocene in the Po coastal plain (Northern Italy)

“…The geometry of strata that accumulate in proximal-foreland and wedge-top basins can provide clues to the rates and timing of deformation resulting from combined sediment compaction, flexural subsidence and local tectonic activity (Burbank & Raynolds, 1988;Clevis, deJager, Nijman, & DeBoer, 2004;Ford, 2004;Gunderson et al, 2014;Jones, Heller, Roca, Garcés, & Cabrera, 2004;Lickorish & Butler, 1996;Suppe, Chou, & Hook, 1992;Vergés, Marzo, & Munoz, 2002;Zapata & Allmendinger, 1996). Studies focusing on outcropping, ancient sedimentary successions (Anadòn, Cabrera, Colombo, Marzo, & Riba, 1986;Artoni & Casero, 1997;Butler & Lickorish, 1997;De Celles et al, 1991;Ford, Williams, Artoni, Vergès, & Hardy, 1997) or on seismic profiles (Argnani & Frugoni, 1997;Cook et al, 1979;Gunderson, Anastasio, Pazzaglia, & Kodama, 2018;Gunderson, Anastasio, Pazzaglia, & Picotti, 2013;Massoli, Koyi, & Barchi, 2006;McIntosh et al, 2005), provided information about long-term (10 4 -10 6 year) deformation (Charreau, Avouac, Chen, Dominguez, & Gilder, 2008;Holl & Anastasio, 1993;Meigs, Verges, & Burbank, 1996). At very short time scales (10 0 -10 1 year), land surface deformation is typically investigated through GPS or InSAR measurements (Allmendinger, Loveless, Pritchard, & Meade, 2009;Cenni et al, 2013).…”

Deformation patterns of upper Quaternary strata and their relation to active tectonics, Po Basin, Italy

“…The Quaternary geodynamic evolution and the tectonic processes active along the northern Apennines thrust fronts and in the adjacent Po-Adriatic foredeep domains have been analysed and discussed at length by several authors (e.g. Picotti & Pazzaglia, 2008;Fantoni & Franciosi, 2010;Bresciani & Perotti, 2014;Gunderson et al, 2018).…”

“…Picotti & Pazzaglia, 2008; Fantoni & Franciosi, 2010; Bresciani & Perotti, 2014; Gunderson et al. , 2018).…”