Studying active tectonics and volcano-tectonic processes using aerial (UAVs) and field-based Structure from Motion techniques
Active tectonics and volcano-tectonic processes are related to earthquakes, fracturing, fault motion (such as creeping), volcanic eruptions, caldera or flank collapse and magmatic intrusions, such as dyking. Satellite data using optical or thermal sensors provide first order information about faulting and volcanic activity, however, there is a resolution gap below the meter-scale, critical to detect and analyse small structures over broad areas and to better assess how faults, magma intrusions and collapses nucleate and evolve. During large deformations (earthquakes, dyke intrusions, collapses), the near-field area where satellite radar signal (InSAR) becomes incoherent remains poorly studied. In addition, classical field surveys and data collection are, very often, not feasible due to difficult logistic condition, hazardous accesses and/or inaccessible areas. Therefore, there is a need to collect higher resolution data to better understand faulting and volcanic processes at scales from cm to several meters, that complement classical field studies and satellite data. The scientific community has adopted modern direct and indirect methods to develop in the last decade, like the Structure from Motion (SfM) techniques.
SfM techniques have been applied using imagery acquired from field and aerial survey, using cameras and mobile phones, Unmanned Aerial Vehicles (UAVs, i.e. drones), balloons, airplanes and helicopters. This technique produces digital surface models (DSM), ortho-mosaic imagery, dense point clouds and 3D models, creating a high-resolution environment reconstruction for a single outcrop or a wide area. The session will focus on the application of the SfM techniques for research in the field of structural geology, with particular regard to active tectonics and volcano-tectonic processes. The session covers, without being limited to, the following topics: i) case studies where the SfM has been employed; ii) SfM methods, 3D reconstruction and successive analysis; iii) innovative application for SfM for survey, such as ground deformation analysis; iv) integration and comparison of SfM-derived, field and satellite data; v) new tools and methods for data analysis on SfM-derived models; and vi) future works and applications of SfM techniques.
The surface traces of historical earthquakes on the optical images are easily obscured by dense vegetation. Fortunately, the vegetation can be filtered and removed mostly or completely from LiDAR-derived cloud point data. We incorporate tectono-geomorphic interpretations of optical image, digital elevation model (DEM)-derived hillshades, contour maps, and field observations of tectono-geomorphic features and trenches to identify surface traces created by a historical earthquake. Based on DEM data, we used LaDiCaoz_v2_1 and 3D_Fault_Offsets to quantify offsets of tectonically displaced geomorphic markers. These approaches help us to recover an Mw7.5 historical earthquake at the southeast margin of the Tibetan Plateau, but the seismogenic fault had been considered as a weakly active fault and the magnitude of this earthquake was cited as M6.8 in the catalog of Chinese historic strong earthquakes from BC 2300 to AD 1911.
How to cite:
Han, Z., Dong, S., and Guo, P.: Identification of the surface traces of historical earthquakes: one example from the southeast margin of the Tibetan Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3792, https://doi.org/10.5194/egusphere-egu2020-3792, 2020.
The Wuhai Basin is in the northwestern corner of the Ordos Block. Analyzing the geometry, and kinematic and dynamic characteristics of the boundary fault, the Zhuozishan West Piedmont Fault (ZWPF), will elucidate the regional tectonic environment and guide earthquake prevention and disaster reduction projects. Six presentative sites were selected for topographic measurements, from northern, middle and southern parts. Displacements of the ZWPF were calculated by measuring the top surface elevation of a widely distributed lacustrine layer in the footwall from outcrops at the sites (using UAV), and in the hanging wall from boreholes. The vertical slip rate of the ZWPF was then calculated based on the displacement and age of the lacustrine layer. Three to four normal fault-controlled terraces have developed on the footwall of the ZWPF, and the top surface of the lacustrine layer is at 1092–1132 m elevation. Data from boreholes showed that the top surface of the lacustrine layer is at an elevation of 1042–1063 m in the hanging wall. Vertical slip rates since 70 ka were estimated as 0.5±0.2 to 1.0±0.2 mm/a. The highest rate of vertical slip was observed at Fenghuang Ridge, in the central part of the fault system, and the vertical slip rate reduced to the south. In the northern Wuhai Basin, normal faulting still controls the piedmont landscape. However, NW-SE trending reverse faults and secondary folding have resulted from dextral strike-slip movement of the fault. The Wuhai Basin developed as a dextral-tensional negative flower structure. This study indicated that stress conditions of the northwestern margin of the Ordos Block include NE–SW compression and NW–SE extension, and an S-shaped rift zone has dominated the scale, structure, and evolution of the Yinchuan, Wuhai and Hetao Basins, and the active mode of faulting in these basins.
How to cite:
Liang, K., Ma, B., and Tian, Q.: Using UAV and drilling to detect Quaternary activity of the Zhuozishan West Piedmont Fault, provides insight into the structural development of the Wuhai Basin and Northwestern Ordos Block, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12617, https://doi.org/10.5194/egusphere-egu2020-12617, 2020.
Due to its position at the boundary between American and European plates, Iceland represents an ideal natural laboratory to study active rifting processes, where rifting mechanisms are complicated by the superimposition of tectonic and magmatic stresses. In order to contribute to the study of such processes, we focused our attention on the southern sector of the Theistareykir Fissure Swarm (ThFS), an active volcanic rift belonging to the Northern Volcanic Zone of Iceland, affected by both volcanic and seismic hazard.
We studied an area which is about 22 km2-large, situated 12 km south of the intersection of the ThFS with the Husavik Flatey Fault (HFF), a dextral strike-slip lineament belonging to the Tjornes Fracture Zone (TFZ). The area is characterized by the presence of normal faults and a dense swarm of extension fractures, affecting prevalently post-glacial, Holocene lavas, dated 8-10 and 11-12 ka. Only in the western sector of the area a Late Quaternary interglacial lava crops out, while the northeastern sector is covered by a Weichselian subglacial hyaloclastite. The southern sector of the area has been investigated with classical field survey, whereas in the northern part a 3.87 km2-large area has been reconstructed using the Structure from Motion (SfM) techniques, combined with an Unmanned Aerial Vehicle (UAV), obtaining orthomosaics, DSMs and 3D models with a centimetric resolution through 4189 UAV photos, collected in 7 different missions during summer 2018.
In the whole area, we recognized and mapped a total of 624 structures (comprising 583 extension fractures and 41 normal faults), and we took various measurements at 626 structural stations along extension fractures, and 132 along normal faults. Regarding extension fractures, we collected the strike and, in 441 cases where it was possible, the opening direction and the amount of opening; along normal faults we measured the strike, dip and vertical offset.
Our approach allowed to calculate stretch values across the rift comprised between 1.002 and 1.013, and an average opening direction value of 104.4°N, normal to the average extension fracture strike measured at the structural stations (14°N), suggesting a pure extensional opening in the studied area. Actually, in 281 cases out of our 441 stations along extension fractures we noticed a lateral component > 5°. Furthermore, 49% of data is not consistent with tectonics, neither with regard to the extensional fracture strike, nor with regard to opening directions. This suggests that stresses linked to regional tectonics are not the only cause of deformation, which could have been affected by different processes like dyke intrusion, deglaciation, and inflation/deflation of the Theistareykir volcano magma chamber.
How to cite:
Corti, N. and Tibaldi, A.: Structural analysis of the Theistareykir Fissure Swarm (NE Iceland) using field survey integrated with UAV-based - Structure from Motion techniques, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1621, https://doi.org/10.5194/egusphere-egu2020-1621, 2020.
Volcano-tectonic events in extensional environments release over days or weeks tectonic strain deficit accumulated over several decades or hundreds of years.
Thanks to its position, on top of both an extensional plate boundary and a mantle plume, several volcano-tectonic events occur in Iceland, and they have relatively accurately reported since the first settlements in ~ 870 AD. The eruptions and graben formation observed during these events are related to magma transport in the crust, which also causes the reactivation of pre-existing structures.
However, the Earth’s upper crust is classically modelled as homogeneous and fully elastic and not as a pre-fractured medium. This study aims to analyse the role of pre-existing crustal structures on the propagation of magma in extensional environments.
The 13 main Icelandic volcano-tectonic events, mostly concentrated in the North, East, and West Volcanic Zones, show a return period in the order of 200 years on average. The suggested cyclic nature of strain deficit loading and subsequent release is consistent with the stepwise nature of strain release at divergent plate boundaries: the crustal opening associated with dike emplacement during volcano-tectonic events is of the same order of magnitude of the strain deficit accumulated since the previous event in the same area.
On this basis, we identified structurally relevant and logistically accessible fieldwork areas in the North Volcanic Zone to perform detailed structural mapping based on UAV-drone imagery. In August 2019 we carried out a UAV survey in Fjallagjá, a graben ~15-20 m deep and ~1 km wide that extends parallel to Sveinagjá graben for ~18 km, in the Askja volcanic system. During the volcano-tectonic event in 1875 in Askja volcanic system, Sveinagjá graben was activated and it subsided 3 to 6 m.
The UAV is a fixed-wing with a ground resolution down to 1 cm·px-1 (flying at 100 m above ground), with an on-board PPK antenna. We installed a GNSS base, wich, in combination with the PPK correction, allows a centimetre-accuracy of the georeferencing of the drone images, with no need for aerial targets as GCPs. With this setup we managed to perform 21 flights, covering an area of ~15 km2.
The processing of the drone images resulted in DEMs and orthorectified mosaics of the fieldwork area, allowing to perform a detailed morphological and structural analysis, looking at fracures, topography effects, and potential kinematic indicators. Specific attention is paid to obliquity between sets of structures. The aim is to reconstruct the paleostress history of this area of the plate boundary.
The use of UAV high-resolution mapping paves the way to an efficient broadening of the fieldwork area and makes available a near-field structural analysis dataset much wider than previously possible.
How to cite:
Panza, E., Ruch, J., and Martin, F.: Structural mapping and analysis of rifting events using UAVs in the North Volcanic Zone (Iceland), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19168, https://doi.org/10.5194/egusphere-egu2020-19168, 2020.
Kyriaki Drymoni, Fabio Luca Bonali, John Browning, Agust Gudmundsson, Luca Fallati, Varvara Antoniou, and Paraskevi Nomikou
Field studies are vital for mapping and understanding active geological processes on Earth. Such studies commonly inform analogue and numerical modelling setups and provide insights over a variety of scales. However, geological field studies have several limitations as they are sensitive both to field-based conditions (e.g. weather conditions, geomorphology, weathering, erosion and access) and the experience of the researchers conducting the work. All of these limitations can add significant error or uncertainty to geological measurements. At the same time, new geological measurement techniques (e.g. photogrammetry) are easy to access, fast and friendly to use, but also often depend on ground truthing parameters.
In this study, we compared two different methods for mapping and surveying volcanotectonic processes related to dyking events: classical field analysis and boat-based photogrammetry. We tested the two approaches on dykes located within a section of a steep cliff face that makes up part of the Santorini caldera. The caldera wall is accessible by land only in the upper most parts and so most measurements require access by boat or by abseiling down the cliff faces. The latter is very dangerous and not recommended.
The core of the work is to carefully compare field data with the equivalents collected on photogrammetry-derived 3D model, focusing on the sea level area in order to compare reliable dataset. Data comparison is focused on dyke attitudes, thicknesses, petrological descriptions, along the 4-km length profile of the northern caldera wall of Santorini volcano.
We collected a series of high-resolution images, around 800 pictures in total, aimed at 3D modelling the dyke swarm using photogrammetry methods. They have been collected using a 20 MPX hand-held camera equipped with commercial GPS from a boat, moving parallel and to a constant distance from to the caldera wall.
Comparison of both datasets allowed insights into 1) the completeness and, 2) the limitations of each technique. Here we assess the various advantages to design a novel multidimensional methodology that allows fast, accurate and low-cost data generation in difficult working conditions, such as at steep cliff faces and flooded terrains.
How to cite:
Drymoni, K., Bonali, F. L., Browning, J., Gudmundsson, A., Fallati, L., Antoniou, V., and Nomikou, P.: Field analysis Vs boat-based photogrammetry derived data in volcanotectonics: an example from the Santorini dyke swarm, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12116, https://doi.org/10.5194/egusphere-egu2020-12116, 2020.
Sam Thiele, Alexander Cruden, and Steven Micklethwaite
Sheet-intrusions are the most common means of magma transport in basaltic volcanoes, so knowledge of their propagation paths is critical for volcanic hazard analyses. Recent advances in unmanned aerial vehicle (UAV) technology and modern photogrammetric techniques such as structure from motion have made it possible to capture and analyse exposed intrusions in unprecedented detail. Using these methods we have captured digital outcrop models of the spectacularly exposed basaltic dyke-swarm that formed the plumbing system of Volcán Taburiente on La Palma (Canary Islands, Spain), and mapped 500 dykes over a total exposed length of > 50 km. We then applied a semi-automatic method implemented in CloudCompare to extract dyke orientation and thickness measurements, as well as associated uncertainty, every ~10 cm along ~60 % of the dyke margins, resulting in more than ten million individual estimates. These highlight a broadly radial dyke swarm with a focal point in the southern section of Caldera Taburiente. The near-continuous exposure also allowed us to estimate the vertical and circumferential strain induced by the dyke swarm and show that although the dykes are radial, N-S orientations are more frequent and probably gave Volcán Taburiente an elongate geometry. A simple Maxwell visco-elastic model can account for the observed strain without requiring a basal detachment or gravitational spreading, and also replicate the observed dyke-aperture distribution.
How to cite:
Thiele, S., Cruden, A., and Micklethwaite, S.: Drones, dykes and too much data: mapping the Taburiente dyke swarm, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13651, https://doi.org/10.5194/egusphere-egu2020-13651, 2020.
This presentation describes a workflow to enhance the 3D model of a geological outcrop cut across by a regional strike-slip fault located in the Venezuelan Andes.
This fault (Boconó Fault) has been active since the Early Holocene time and has affected the landscape by displacing the rivers course and the geometry of ancient glacial moraines.
One of these moraines (Los Zerpa) was studied in detail in 1983 by geologist C. Schubert, who described its evolution with a series of hand drawn panels.
In 2015 the same area was acquired by the author with a drone survey and rendered as a digital 3D model. More recently the same model has been improved by adding also the interpretation made in the 80’s, adapted to 3D in the form of geometrical elements (lineaments and surfaces) and animations showing the different stages of evolution.
The fault model can now be publicly accessed over the internet and the users can observe and animate its evolution in 3D and understand the geological processes more intuitively (https://riccardorocca.github.io/home/Los_Zerpa.html).
This workflow is proposed as an example that can be applied to other 3D models of geological faults and other geological features, so that the geological concepts can be represented more intuitively and made accessible to a large audience. With these improvements the models would be a more valuable support to, for instance, published papers and virtual field-trips.
How to cite:
Rocca, R.: Representing fault evolution by animating a drone 3D model with computer game software (Boconó Fault, Venezuelan Andes)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11426, https://doi.org/10.5194/egusphere-egu2020-11426, 2020.
Emanuela De Beni, Daniele Andronico, Massimo Cantarero, Riccardo Civico, Elisabetta Del Bello, Federico Di Traglia, Malte Eggersglüß, Thor Hansteen, Kaj Hoernle, Jeffrey Johnson, Tom Kwasnitschka, Luca Pizzimenti, Tullio Ricci, Piergiorgio Scarlato, Karen Strehlow, and Jacopo Taddeucci
Stromboli Volcano was very active in the summer of 2019: Two paroxysms dramatically changed the summit craters of the volcano on July 3 and August 28. The first intense paroxysmal eruptive sequence involved both the North and the Central-South (C-S) crater areas and has generated an eruptive plume rising 4 km above the summit (924 m a.s.l.) while the incandescent material set fire to vegetation on the flanks of the volcano. Volcanic products from the laterally directed explosions and from the collapse of the external crater terrace generated two pyroclastic flows that travelled down the Sciara del Fuoco (SdF) and for several hundred of meters out to sea. Between July 3 and August 28, the activity was characterised by lava flows in the Southern sector of the SdF and by very intense Strombolian activity at a set of small scoria cones that grew around the vents, particularly in the N crater area. The second paroxysmal eruption occurred on August 28 again involving the two crater areas and producing an eruptive column that rose 4 km above the summit. Material from the eruption and from the collapse of the rim of the C-S area contributed to the generation of a pyroclastic flow that travelled down the SdF and out to sea. Important morphological variations to the crater terrace were evident after the two paroxysms.
We used UAVs to monitor morpho-structural changes of the Stromboli volcano following the paroxysmal eruptions; in particular, five high-resolution UAV survey campaigns have been performed since May 2019. The aerial images were acquired using two different UAVs, a DJI Mavic 2 Pro and a Wingcopter. Using Structure-from-Motion (SfM) techniques we generated DEMs (Digital Elevation Model) and orthoimages with a resolution ranging between 0.2 and 0.5 m. An additional 1 m-resolution DEM was extracted from available tri-stereo Pleiades satellite imagery and chosen as pre-paroxysm surface. Using the orthoimages it was possible to map the distribution of eruption products and determine the morpho-structural changes. Furthermore, the topographic approach (subtraction between two different surfaces DEMs) with a cut-and-fill procedure was chosen to calculate the volume gain (in the southern sector of the SdF) and loss (in the crater areas).
This work demonstrates the usefulness of the combined use of UAVs and SfM techniques to map volcanic products, to highlight morphological changes and perform volume estimations. The data collected during these field efforts and the temporal comparisons of the DEMs represent a fundamental contribution to both volcanic hazard assessment and risk mitigation, and can be used to support civil protection operations.
How to cite:
De Beni, E., Andronico, D., Cantarero, M., Civico, R., Del Bello, E., Di Traglia, F., Eggersglüß, M., Hansteen, T., Hoernle, K., Johnson, J., Kwasnitschka, T., Pizzimenti, L., Ricci, T., Scarlato, P., Strehlow, K., and Taddeucci, J.: UAV surveys illuminate the morpho-structural and volume changes from the 2019 paroxysmal eruptions of Stromboli volcano (Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19715, https://doi.org/10.5194/egusphere-egu2020-19715, 2020.
1Insubria University, Department of Human and Innovation Sciences 2University of Milan-Bicocca, Department of Earth and Environmental Science, Milan, Italy 3CRUST- Interuniversity Center for 3D Seismotectonics with Territorial Applications, Italy
Iceland offers an unparalleled chance to observe the most powerful natural phenomena related to the combination of tectonic and magmatic forces, such as active rifting, volcanic eruptions, sub-volcanic intrusions. We have focused on a number of geosites which are found in the Northern Volcanic Zone (NVZ) of Iceland; here, the following volcano-tectonic features can be observed: i) the Theystareykir Fissure Swarm (ThFS), an active rift system with a central volcano, several major faults and numerous eruptive fissures; ii) the Krafla Fissure Swarm (KFS), another major rift system marked by the presence of monogenetic cones, dip-slip faults, eruptive fissures, extension fractures and the active Krafla volcano.
In order to showcase a few, outstanding examples of the above, we have made use of UAVs integrated by the Structure-from-Motion (SfM) Photogrammetry. As is well known, the combination of UAV-digital image collection and SfM techniques has been increasingly applied to geological and environmental research. We have applied this approach to the collection of high-definition images and with the purpose of constructing 3-D models, which may be considered “Virtual Outcrops (VO)”.
We highlight that such 3-D models can be navigated in immersive Virtual Reality mode, and hence can be a key tool not only for research purposes: in fact, this is a novel, cutting-edge approach which is suitable for improving geosite popularization and geoscience communication, allowing for the engagement of a wider audience, including potential end-users from the younger generation.
How to cite:
Pasquaré Mariotto, F. and Tibaldi, A.: UAV- and SfM-related techniques applied to volcano-tectonics for virtual outcrops construction and geoscience communication. Examples from the North Volcanic Zone, Iceland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4210, https://doi.org/10.5194/egusphere-egu2020-4210, 2020.
Varvara Antoniou, Paraskevi Nomikou, and Othonas Vlasopoulos
Generally, key geological outcrops are inaccessible for classical mapping due to the hard-logistic conditions of their location in remote or dangerous areas like active volcanoes or fault zones. The UAV-based photogrammetry is a helpful technique to overcome such difficulties in site investigation. It allows a very high-detailed 3D model reconstruction of relevant outcrops, providing also the possibility to cover wider areas.
In this study, we tested the use of a “Selfie drone” aimed at outcrops reconstruction for 3D mapping of volcano-tectonic features. Two different sites in Santorini volcanic complex with different characteristics have been chosen: i) the Vlychada Beach, located in the southern part of the island, characterized by vertical cliffs that offer great exposure of the pumice layers from the well-known Late Bronze Age (LBA) (Minoan) eruption and ii) a historical volcanic crater located in the northern part of Nea Kameni island, related to the 1570 A.D. eruption, with a diameter of about 85 m, which is mostly inaccessible within its internal part and cannot be studied by classical field methods.
The “Selfie drone” which was used for the photo collection, is a 0.300-kg quadcopter equipped with a 12 Megapixel camera, EXIF information (Exchangeable Image File Format) and GPS coordinates. This drone has a flight time of approximately 16 minutes. A total of about 1900 photos has been collected, considering both sites, that have been reconstructed using photogrammetry techniques.
The resulting 3D models are characterized by a sub-centimetric texture resolution, allowing detailed mapping of the Minoan pumice layers, fractures, crater geometry, and related volcanic deposits, proving the usefulness of “Selfie drones” for geological – tectonic mapping.
How to cite:
Antoniou, V., Nomikou, P., and Vlasopoulos, O.: Using “Selfie drones” for 3D mapping of volcano-tectonic features in Santorini, Greece, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3948, https://doi.org/10.5194/egusphere-egu2020-3948, 2020.
In 1905, two M ~ 8 continental strike-slip earthquakes occurred along the Bulnay fault system, in the northwestern part of Mongolia. After a first earthquake that ruptured the Tsetserleg oblique fault strand, the second event ruptured the main Bulnay fault 14 days later. With a total rupture of 676 km, these two earthquakes constitute the largest continental strike-slip earthquake sequence ever documented. Hence, the Mongolian earthquake ruptures offer a unique opportunity to document large-magnitude earthquake continental ruptures. Indeed, due to dry climatic conditions, limited erosion and anthropization, the surface ruptures have been preserved almost unaltered. This allows for accurate documentation of the rupture trace and coseismic slip distribution along the Bulnay fault, based on field observation and satellite imagery.
Along the Tsetserleg rupture, the available coseismic offset measurement data coming from high-resolution satellite imagery show a significant variability, ranging between 1.5 and 4 m for the horizontal component. It is presently difficult to assess the most representative value for the 1905 slip, which in turn impacts the magnitude estimation for this event. Another factor to take into account is the possibility of a vertical slip component, which is only poorly constrained.
In order to have a better estimate of the 3D coseismic slip, drone images were acquired on selected sites along the Bulnay 1905 rupture, near the junction with Tsetserleg fault, and along the Tsetserleg rupture. We favored sites showing structural complexities and significant surface fracture development (succession of cracks and ridges, stepovers, branching zones…).
High-resolution DEMs and orthophotomosaics were produced using the MicMac software. The geometrical characteristics of the complexities and their fracture network were then measured in order to compute the volumetric changes associated to the 1905 earthquake. These data were finally converted to 3D surface slip estimates. On certain sites, we also discussed the presence of features inherited from previous ruptures, overprinted by the 1905 earthquake.
How to cite:
Benjelloun, Y., Klinger, Y., Antoine, S., Baatarsuren, G., Bollinger, L., Cheon, Y., Choi, J.-H., and Davaasuren, G.: Analysis of surface rupture complexity sheds light on coseismic slip during the last earthquakes along the Bulnay-Tsetserleg fault zone (Mongolia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5325, https://doi.org/10.5194/egusphere-egu2020-5325, 2020.
Amerigo Corradetti, Stefano Tavani, Miller Zambrano, Emanuele Tondi, and Thomas Seers
Fault roughness is a general term used to indicate dimension and distribution of fault asperities. Due to the role that fault asperities play on slip dynamics and frictional behavior during the seismic cycle, fault roughness constitutes a key element to understand earthquakes nucleation. Since it is not possible to recover fault roughness from seismogenic sources, faults at surface are generally used as analogues. However, those faults are in most cases subject to weathering and their roughness can lose seismogenic representativeness. Active faults episodically expose “fresh” fault zones constituting the best targets for seismogenic roughness evaluations.
Here we present the study conducted on a splay of the Mt. Vettore fault system in the Central Apennines (Italy), along a vertical transect that includes both a weathered and a freshly exposed portion of the fault. The latter was exposed after the dramatic Mw 6.5 shock that hit the area on the 30th of October 2016. We produced a high detailed model of a part of the fault by means of structure from motion-multiview stereo (SfM-MVS) photogrammetry to assess its roughness parameters and to determine how these are affected by weathering.
Our results show that weathering increases the value of the fractal parameters. Accordingly, we conclude that using high resolution point clouds it is possible to recognize patches of fault having similar exposition time to weathering.
How to cite:
Corradetti, A., Tavani, S., Zambrano, M., Tondi, E., and Seers, T.: Roughness evaluation on a splay of the active fault system responsible of the massive 2016 seismic sequence of Central Apennines (Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10636, https://doi.org/10.5194/egusphere-egu2020-10636, 2020.
This study attempted to use unmanned aerial vehicle (UAV) photogrammetry for structural mapping at limited exposure outcrops in the west coast area of Buan, South Korea. The west coast area of Buan has a large tidal range, and there are restrictions for traditional structure mapping. High spatial resolution (about 4.5 cm per pixel) UAV images were obtained at low tide from a selected study site. The UAV survey identified 50 brittle structures (fractures and faults that were divided into three groups) and changes in the bedding trace. The bedding trace demonstrates various directional verging of the fold geometry that indicates slump-fault structures. While more research is still necessary, this study demonstrated that UAV mapping techniques are very useful for geological structural analysis in coastal areas.
How to cite:
Lee, H.-J. and Ko, K.: Detecting geological structures in coastal area of Buan, South Korea using unmanned aerial vehicle images, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6257, https://doi.org/10.5194/egusphere-egu2020-6257, 2020.
We analysed at very high detail the surface deformation along a volcanotectonic structure in the Krafla Fissure Swarm, located in the North Iceland Rift. The structure affects the Pleistocene Hituholar volcano and 12 ka old lava flows. The work has been carried out through the Structure from Motion technique (SfM) applied to UAV surveys, integrated with a lithostratigraphic and structural field survey. The resulting Orthomosaic and Digital Surface Model (DSM) have a resolution of 2.6 and 10 cm, respectively. The zone of deformation is characterised by topographic bulging, parallel extension fractures, and narrow grabens with locally floor uplift, which can be explained as the effect of shallow propagation of a dyke northward from the Krafla magma chamber. In fact, the study area has been interested by northward dyke propagation from the central Krafla volcano during several rifting events, among which the recentmost occurred in 1975-1984 (Krafla fire). The analysis of the very wide area covered by our UAV surveys indicates that changes in the pattern of surface deformation occur in correspondence of contacts between deposits with different rheological properties: the transition from very stiff lavas to soft hyaloclastites produces a change from extension fracturing to normal faulting. Moreover, we detected a series of extension fractures with NE-SW strike and left-lateral slip component, and NNW-SSE strike and right-lateral component, which are rotated clockwise and anticlockwise respect to the main NNE-SSW graben trend, and extend outward to the sides of the main deformation zone up to 17 m. We interpret these structures as originated in front of the dyke tip during its propagation and being successively bypassed by the dyke advancement. In case of an active volcanic zone, the comprehension of the surface deformation and of the significance of strike-slip faulting occurrence can help to determine how and where magma is propagating. Thus, these evidences may help to decipher geophysical data and surface structural data during volcano monitoring.
How to cite:
Tibaldi, A., Russo, E., and Fallati, L.: Holocene dyke-induced surface deformation at Krafla (Iceland) revealed by UAV-based high resolution 3D models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2604, https://doi.org/10.5194/egusphere-egu2020-2604, 2020.
In northern Iceland the European-North American plate boundary is broad and complex but includes a remarkable subaerial triple-junction intersection between the Husavik-Flatey Fault (HFF) dextral transform and rifting in the Northern Volcanic Zone. Fortuitously, the triple junction occurs in a sheet of ~12 ka pahoehoe lavas; a tabula rasa recording innumerable fault features displayed in exquisite detail. High-resolution drone imagery, coupled with 120 field measurements of fault slip directions and opening amounts, made possible the mapping and analysis of this detail and, importantly, enabled recognition and exclusion of potentially misleading primary deformation features associated with emplacement of the lavas. Rift-transform interactions in this natural laboratory have remained spatially stable throughout post-glacial time, although with transform-affinity faults reactivated to accommodate rift extension and transform ‘encroachment’ into the rift domain. First-order en-echelon Riedel fault complexes are recognised, linked by transpressional faulting and compressional strike-slip relay ramps, as well as second-order R shears, R’ and P shears, and previously undescribed R’ Riedel-in- Riedel relationships. A pahoehoe flow front offset along a first-order Riedel fault complex records slip at ~3.8 mm a−1, which may be consistent with the published GPS-based current slip-rate estimate of ~6.8 mm a−1 across the HFF as a whole.
How to cite:
Rust, D. and Whitworth, M.: A unique ~12 ka subaerial record of rift-transform triple-junction tectonics, NE Iceland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5788, https://doi.org/10.5194/egusphere-egu2020-5788, 2020.
Rémi Matrau, Daniele Trippanera, and Sigurjón Jónsson
Drone imaging can be effective in determining earthquake fault offsets and landslide motion in areas where higher image resolution is needed than available in satellite data. Here we use drone mapping to study the Holocene tectonic activity along the Húsavík-Flatey Fault (HFF) in northern Iceland as well as a coastal landslide in the vicinity of the fault, which poses a tsunami threat. Together with the subparallel Grímsey Oblique Rift, the partially offshore HFF accommodates ~18 mm/yr transfer motion between two parts of the Mid-Atlantic Ridge. However, it remains unclear how much of that transfer motion has occurred on the HFF during Holocene. This is important to determine for seismic hazard assessments of North Iceland, as the HFF is located much closer to several coastal communities than the offshore Grímsey Oblique Rift.
We used a DJI Phantom 4 drone to survey 5.8 km of faults onshore in 5 separate areas that together cover 2.9 km2. We processed ~6000 drone images using the photogrammetry software Agisoft PhotoScan to compute high resolution 3D Digital Surface Models (DSMs) and high resolution 2D ortho-mosaics. We placed 5 to 10 Ground Control Points (GCPs) in each survey area to reduce distortions and to apply corrections for the ortho-rectification. While errors on absolute horizontal positions (without the GCP corrections) are not large (sub-meter to a meter), errors on the absolute vertical positions can be substantial (several tens of meters). The GCP locations were determined using differential GPS and the open source package RTKLIB, and then later added in the 3D model reconstruction. Depending on the flight parameters (altitude, speed, camera rate…) and the reconstruction process, we obtained DSMs and ortho-mosaics with resolutions ranging from 2.5 to 10 cm. We used these high-resolution DSMs and ortho-mosaics to map postglacial morphologies and tectonic features along the HFF, and to measure offset structures along the fault segments, which we used to assess the Holocene slip rate of the HFF. We measured more than 30 offsets ranging from a few meters up to 80 m, which yields a minimum Holocene slip rate of 7.0 - 7.5 mm/yr, compatible with rates derived from modeling of present-day GPS observations.
In addition, we surveyed a coastal landslide that is 280 m x 130 m in size and located about 10 km south of the fault. A sudden movement of the landslide, e.g. triggered by earthquake shaking, would cause a tsunami and could threaten neighboring coastal areas, including the town of Húsavík. We aim at characterizing the volumetric and topographic evolution of the landslide to understand if the landslide is actively creeping and if it could be destabilized by an earthquake. To do this, we compare our drone-image DSM with a DSM computed from older aerial images and will use this first drone survey as a benchmark to monitor the evolution of the landslide.
How to cite:
Matrau, R., Trippanera, D., and Jónsson, S.: Holocene deformation within the Húsavík-Flatey Fault zone in north Iceland from drone imagery and field investigations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6640, https://doi.org/10.5194/egusphere-egu2020-6640, 2020.