Slip rate and mode of the Feldbiss normal fault (Roer Valley Graben) after removal of groundwater effects

Abstract

The Feldbiss fault is the main active fault bounding to the southwest the Roer Valley Graben of NW Europe. In order to investigate the reasons of the discrepancy between its short-and long-term slip rate estimates, we have repeatedly surveyed a 2. Occasionally associated with minor seismicity, this aseismic slip event could betray a thickening of the transitional region located below the upper crustal zone of stable sliding. It causes a total fault slip of 5-10 cm in a few tens of years, releasing smoothly all, or a great part of, the strain accumulated during the previous 1-2 ky of fault quiescence.

PSInSAR remote sensing observations of deformation behaviour at Salisbury Plain, UK.

“…Deformation value ranges ca. +/-10 mm a -1 across 50km 2 ) were consistent with those expected from tectonic and groundwater effects in intraplate areas (Demoulin, 2006)., and with ranges recovered using InSAR in nearby, less densely vegetative, areas (Mason et al, 2015). PS density was low at 1063 PS/km 2 , as expected from such a vegetated area.…”

Improving radar interferometry for monitoring fault-related surface deformation

“…Continuous seismicity, (several earthquakes of magnitude ∼5 have been recorded since 1932) and geomorphological studies (see, e.g., Michon and van Balen (2005)) prove that the Roer Valley Rift System is active. Despite being the focus of many different studies (see e.g., Houtgast and van Balen (2000); ; Michon and van Balen (2005); van and Demoulin (2006)), the rift behavior, specially, slip rates, are still cause of debate. There exist large discrepancies between slip rates estimated at short (10-100 yr) and geological (10 5 -10 6 yr) time scales.…”

“…There exist large discrepancies between slip rates estimated at short (10-100 yr) and geological (10 5 -10 6 yr) time scales. For example, leveling measurements whose results have covered the last few decades suggest a slip rate of ∼1 mm/yr (Groenewoud et al, 1991;Demoulin, 2006). Meanwhile, techniques that give an average rate over millions of years (e.g., trenching), estimate one, and even two, orders of magnitude lower Houtgast et al, 2003Houtgast et al, , 2005.…”

Seasonal height change influence in GPS and gravimetric campaign data

“…This differential effect appears to be smaller than the absolute effect of loading by a factor of ∼7 but, since it is given in absolute value, it contains no sense (up/down) information and is unable to reveal which groundwater effect predominates at the local scale. This may be known only when individual GW data are available at each levelled station, showing then that the pore pressure effect prevails in the differential mode (Demoulin, 2006). The reason for the predominance of either groundwater effect in the measurements lies chiefly in the nature and the spatial scale of the displacements measured.…”

“…Two main near-surface influences on ground height changes H are known to be atmospheric and groundwater loading (van Dam et al, 1994(van Dam et al, , 2001Dong et al, 2002). Indeed, since we were not dealing with local-scale relative heights, we assumed that, among the effects of groundwater variations on H, the loading effect predominated over the pore pressure effect (Demoulin, 2006). Rather than modelling these various effects, we searched for statistical correlation between height changes and variations in atmospheric pressure and groundwater level.…”