Structural Mapping of Dike-Induced Faulting in Harrat Lunayyir (Saudi Arabia) by Using High Resolution Drone Imagery

Abstract

Dike intrusions produce faulting at the surface along with seismic swarms and possible eruptions. Understanding the geometry and kinematics of dike-induced fractures can provide relevant information on what controls magma emplacement and the associated hazards. Here, we focus on the Harrat Lunayyir volcanic field (western Saudi Arabia), where in 2009 a dike intrusion formed a NNW-SSE oriented, ten-kilometer-long and up to one-meter deep graben. This widens from ∼2 km in the SSE to ∼5 km in the NNW, showing a well-defined border normal fault to the west but a diffused fracture zone to the east. We conducted a fixed-wing drone survey to create high resolution (∼3.4 cm) ortho-rectified images and DEMs of the western fault and of a portion of the eastern fracture zone to determine the fracture geometry and kinematics. We then integrated these results with field observations and InSAR data from the 2009 intrusion. Both fault zones contain smaller segments (hundreds of meters long) consisting of normal faults and extension fractures, showing two dominant orientation patterns: NNW-SSE (N330 • ± 10 •) and NW-SE (N300 • ± 10 •). The NNW-ESE oriented segments are subparallel to the inferred 2009 dike strike (N340 •), to pre-historical Harrat Lunayyir eruptive fissures (N330 •) and to the overall Red Sea axis (N330 •). This suggests that these segments reflect the present-day off-rift stress field close to the Red Sea shoulder. However, the NW-SE oriented segments are oblique to this pattern and exhibit enechelon structures, suggesting different processes such as: (1) a transfer (or soft-linkage) between dike-parallel fault segments, (2) a topographic control on the fault propagation and (3) a possible reactivation of inherited regional faults. Vertical fault offsets obtained by the drone survey along the western fault vary with the local lithology and these data are not consistent everywhere with the offsets derived from the 2009 InSAR measurements. Field evidence within lava flows also shows the occurrence of previous slipping event(s) on the fault before the 2009 intrusion. Collectively, we suggest that the mismatch between the drone and InSAR datasets is related to the different spatial and temporal resolutions offered by the two techniques.

Mapping and evaluating kinematics and the stress and strain field at active faults and fissures: a comparison between field and drone data at the NE rift, Mt Etna (Italy)

“…The other faults form small grabens, one of which is present in the studied sector: this graben is 35 m wide at the southwestern foothill of the Mt Pizzillo pyroclastic cone and widens up to 80 m in correspondence to the upper portions of the cone. We suggest that this geometry is mainly due to the interference between the fault dip and the shape of the conical edifice, as observed also at Mount Laki in Iceland (Trippanera et al, 2015) or along the Harrat Lunayyir Fault in Saudi Arabia (Trippanera et al, 2019).…”

“…The use of UAVs in geoscience is quickly increasing for a series of reasons: (i) UAV data acquisition is cheaper with respect to other methods, such as airborne and terrestrial laser scanning and lidar (Cawood et al, 2017;Lizarazo et al, 2017); (ii) the proposed approach reduces work time compared to field data collection, especially in the case of the study of long structures as those of Tibaldi and Ferrari (1992), Kozhurin et al (2006), andTrippanera et al (2019); (iii) UAVs provide the possibility of reaching sites that can be inaccessible for logistic conditions or can be dangerous, such as an active volcano. Moreover, the excellent accuracy of the SfM-derived models allows us to carry out observations and measures at a level of detail in the order of centimeters and thus a scale that is comparable to field surveys.…”

“…As a parallel and complementary activity to the UAV survey, we collected several GCPs, distributed all over the area, essential to scale and reference the SfM-derived models as well as to avoid any bulging effect (James and Robson, 2012;Turner et al, 2012;Westoby et al, 2012;Smith et al, 2016;Vollgger and Cruden, 2016;James et al, 2017;Esposito et al, 2017). We targeted 34 natural targets, as already successfully performed by Bonali et al (2020), to speed up the GCP collection avoiding the deployment and recovery of artificial targets.…”

“…In the last few years, the abovementioned difficulties have been overcome by the use of structure-from-motion (SfM) photogrammetry applied to images collected by unmanned aerial vehicles (UAVs or drones) in active volcanotectonics studies (Bonali et al, 2019a(Bonali et al, , 2020Trippanera et al, 2019;Weismüller et al, 2019) and to assess volcanic hazard (Müller et al, 2017;Darmawan et al, 2018;De Beni et al, 2019). Therefore, in this work we use this technique, which allows us to reconstruct very detailed orthomosaics and digital surface models (DSMs) of the surveyed areas.…”

Iceland, an Open-Air Museum for Geoheritage and Earth Science Communication Purposes

“…Thanks to the above, UAVs have been employed, over the past decade, to enhance knowledge of different types of geohazards, ranging from seismic [67,68] to landslide [69][70][71][72][73] to volcanic [74][75][76][77] and flood hazards [78,79]. With regard to the study of active tectonics and volcano-tectonics, focused on geological objects like those documented in the present work, after the first attempts with balloons [80], UAV-captured images have become a major option in the study of active faults [81][82][83][84][85][86][87][88]. In most of these works, the use of UAVs has been integrated by Structure-from-Motion (SfM) photogrammetry [89][90][91], a powerful technique to augment traditional methods used to gather outcrop data.…”