Disaggregation bands as an indicator for slow creep activity on blind faults

Abstract

Hidden, blind faults have a strong seismic hazard potential. Consequently, there is a great demand for a robust geological indicator of neotectonic activity on such faults. Here, we conduct field measurements of disaggregation bands above known underlying blind faults at several locations in Central Europe. We observe that the disaggregation bands have the same orientation as that of the faults, indicating their close connection. Disaggregation bands develop in unconsolidated, near-surface, sandy sediments. They form by shear-related reorganization of the sediment fabric, as a consequence of grain rolling and sliding processes, which can reduce the porosity. Using an analogue shearing experiment, we show that disaggregation bands can form at a velocity of 2 cm h−1, which is several orders of magnitude slower than seismogenic fault-slip velocities. Based on the field data and the experiments, we infer that disaggregation bands can form in the process zone of active blind faults and serve as an indicator of neotectonic activity, even if the fault creeps at very low slip velocity. Disaggregation bands could open a new path to detect hidden active faults undergoing aseismic movements.

An examination of the glaciomarginal fan of the Odranian glaciation at the Mokrzeszów site, Sudetic Foreland, SW Poland

“…The deformation model is shown in Figure 17. The orientation of the main fault and its location in the tectonic graben very likely indicate rather end deformation/disaggregation bands that developed above a larger, subsurface blind fault (see Brandes et al 2018Brandes et al , 2022aBrandes et al , 2022b. Minor deformation structures within facies Sr, Sh are similar to those described by Pisarska-Jamroży & Weckwerth (2013).…”

“…It also seems interesting that a coarse-grained fan with fan-delta settings (Lang et al 2017) was formed within the SMF (Krzyszkowski et al 1995(Krzyszkowski et al , 2000. A similar situation of glacial lake formation in a tectonically active zone was reported by Longhitano (2008) in the Southern Apennines, and by the team of Brandes & Tanner (2012) and Brandes et al (2011Brandes et al ( , 2018Brandes et al ( , 2022a in Germany.…”

“…The fault activity might be related to the reactivation of the faults due to ice loading during glaciation. The fault most probably developed the expression of syn-or post-Saalian (Odranian) activity along one of a number of basement faults (Brandes & Tanner 2012, 2022a, 2022b.…”

“…The orientation of the main fault and its location in the tectonic graben indicate rather an endogenic origin of deformation in the Mokrzeszów open pit (Krzyszkowski 1992, 1993a, Krzyszkowski & Bowman 1997. The small faults as deformation disaggregation bands may have been formed above a larger, subsurface blind fault (see Brandes et al 2018Brandes et al , 2022aBrandes et al , 2022b.…”

“…Krzyszkowski 1993a, modified) The faults are probably of tectonic origin (Mazur et al 2010, Štěpančíková et al 2010, Różycka & Migoń 2017, Stemberk et al 2019 strengthened by the instability of the sediments on a steep slope. These faults may have been formed by grain rolling and a related reorganization of the grain fabric (see: Brandes et al 2018Brandes et al , 2022aBrandes et al , 2022b, thus they are disaggregation bands and might indicate neotectonic activity above a branch fault, e.g. of the Sudetic Margin Fault, and in the tectonic Roztoka-Mokrzeszów Graben (Fig.…”