Erft / Swist fault.
Composite source DECS003 corresponds to the Erft and Swist faults (Figure S4). These faults have been mapped in detail by Ahorner (1962), who discerned several overlapping sections. From north to south, the main sections are the Quadrather fault, Horremer fault, Erft fault, northern Swist fault, and southern Swist fault. The stepover widths between the three northern sections and between the two southern sections are less than 1 km, while the separation between the Erft and Swist faults is slightly larger (~1.5 km). This stepover width is considered to be too small to arrest fault rupture, and for this reason the Erft and Swist faults are combined in a single source. The total length of the Erft/Swist source is ~56 km. The Swist fault disappears to the south near the village of Meckenheim. This latitude corresponds with the southern limit of extensive Quaternary river terraces of the Lower Rhine Embayment, and also with the disappearance of the (Bouguer) gravimetric low that characterizes the RVG (Figure 3 in manuscript). The LRG terminates here in the heart of the Rhenish Shield.
| Fault section | Trench site | Year | Institute | Reference |
|---|---|---|---|---|
| northern Swist fault section | Metternich | 2004 | GDNRW | Skupin et al. (2008) |
Based on the map of Ahorner (1962), the long-term vertical displacement rate of DECS003 is 0.031 – 0.070 mm/yr. Ahorner (2001) also reported average offsets for the top of the Upper Terrace of the Rhine River (~700 kyr) on all faults that are part of the Erft/Swist fault. If we take into account fault overlap by summing the offsets of parallel faults, we obtain a length-weighted average offset of 32.6 m for this surface, equivalent to a vertical displacement rate of 0.047 mm/yr. This value probably slightly underestimates the real deformation rate, because the total length of the thus considered faults is 66 km, whereas the length of source DECS003 is only 56 km. A comparable value of 0.055 mm/yr can be obtained from a schematic profile across the Erft fault by Boenigk and Frechen (2006). These values are in agreement with the longer-term rate.
| ID | Type of evidence | Offset (m) | Time period | Deformation rate (mm/yr) | Reference |
|---|---|---|---|---|---|
| 20 | Displacement of base of “Ältere Hauptterrasse” of the Rhine R. |
Mean: 80.9 (n=17) Max: 95 + 45 |
Since 2.0 – 2.58 Ma | 0.031 – 0.070 | Based on data from Ahorner (1962) |
| 21 | Displacement of top of “Ältere Hauptterrasse” of the Rhine R. |
Mean: 32.6 Max: 60 |
Since ~700 kyr | 0.047 – 0.086 | Based on data from Ahorner (2001) |
| 22 | Displacement of Weichselian loess deposits | 2 – 3 | 20 – 30 kyr | 0.067 – 0.150** | Ahorner (1996); Ahorner (2001) |
| 23 | Displacement of base of UT2 terrace | ~35 | Since 640 kyr | 0.055 | Based on sketch in Boenigk and Frechen (2006) |
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