## 5 Discussion  
### Rift Architecture and Kinematics  
The studied rift segment is located along the north-western part of the KFS and is characterised by the presence of grabens arranged en-echelon with a left-stepping geometry. In the study area, two main grabens are present: one, to the north, affects the Holocene lavas only, and disappears in correspondence of the other graben. This second graben is located further south and affects mostly the hyalocalistic ridge and, to a lesser extent, prolongs into the surrounding Holocene lava succession.  
The southern graben is a few tens of meters wide at its northern and southern terminations, whereas its width increases up to 300 m in its central part. This geometry in plan view cannot be related to the presence of the volcanic ridge respect to the surrounding flat area for two reasons: (i) Classical studies showed that the presence of a volcanic edifice strongly influences fault orientation by deflecting and converging faults that tend to become radial at the cone, assuming an hourglass pattern [87; 88]; in our case instead, faults tend to diverge in correspondence of the ridge. (ii) In plan view, inclined normal faults tend to diverge in correspondence of a topographic high, like a volcanic cone, but in our case it is possible to observe that faults diverge and graben width increases to the north exactly in correspondence of the contact between the hyalocalites and the lava flows, and to the south in the flat area occupied by the lavas. Moreover, the difference in altitude between the ridge and the surrounding flat area is modest and cannot account for the bulge of fault traces as simply because of fault outcrop following topography. We propose that the increase of graben width in correspondence of the hyalocalsite ridge could instead be related to the mechanical contact between the stiffer lava succession and the softer hyalocalites: the rheological contrast between the two rock units leads to faults that tend to follow the outline of the contact, favouring concentric faults. This is similar to what has been noticed after simulating a magma chamber and diffuse rift extension [88]: in this case, the presence of a magma chamber affects the faults orientation that close to the intrusion edge change their direction, mimicking the intrusion shape by curving around it.  
Focusing on the kinematics of extension fractures, the collected data suggest an av. spreading direction of N97.7\({}^{\circ}\) E, with a range of N46.3-142.3\({}^{\circ}\) E for the Holocene times (Figure 7). This av. value is lower than those given in the literature that range between N104\({}^{\circ}\) E and N115\({}^{\circ}\) E [54; 57; 58; 59; 60]. The av.  
spreading value calculated in the present research is closer to those that take into account geological data that cover a larger time window [17; 54; 60; 61]) with respect to only GPS data [57; 58; 59], suggesting a slight overall anticlockwise rotation of the spreading direction in the NW part of the Krafla rift.  
The overall fracture azimuth is suggested to be orthogonal to the spreading vector range discussed in the above section: in fact, longer and more developed fractures show an azimuth N-S to NNE-SSW (Figure 6a,b,e), as suggested for the active Krafla fissure swarm [60].  
Finally, we paid attention to the presence of strike-slip components along the extension fractures, where the av. value suggests an overall very limited left-lateral component, even though the majority of data are characterized by values with right-lateral components (Figure 8e,f). We believe that this component is the result of local perturbations by dylking at shallow depths, as shown for the 2014-2015 Bar@arbunga dylking event [89] and as suggested in the ThFS [16; 17]. In support of this hypothesis, the area has been subjected to recent historical rifting events characterized by N-propagating dykes [48], and [PERSON] et al. [37] described textbook examples of dyke-induced deformation at the surface in the eastern part of the area presented in this study.