scholarly journals Mimicking Alpine thrusts by passive deformation of synsedimentary normal faults: a record of the Jurassic extension of the European margin (Mont Fort nappe, Pennine Alps)

2020 ◽  
Vol 113 (1) ◽  
Author(s):  
Adrien Pantet ◽  
Jean-Luc Epard ◽  
Henri Masson
Keyword(s):  
Normal Faults ◽  
Field Observations ◽  
Tectonic Unit ◽  
Normal Faulting ◽  
Alpine Tectonics ◽  
Paleozoic Basement ◽  
Passive Deformation ◽  
Nw Italy ◽  
Fault Scarps ◽  
Rifted Margin

Abstract The Mont Fort nappe, former uppermost subunit of the Grand St-Bernard nappe system, is an independent tectonic unit with specific structural and stratigraphic characteristics (Middle Penninic, NW Italy and SW Switzerland). It consists in a Paleozoic basement, overlain by a thin, discontinuous cover of Triassic-Jurassic metasediments, mainly breccias, called the Evolène Series. The contact of this Series over the Mont Fort basement is debated: stratigraphic or tectonic? We present new observations that support the stratigraphic interpretation and consequently imply that the Evolène Series belongs to the Mont Fort nappe. We moreover show that the Mont Fort nappe was strongly affected by normal faulting during Jurassic. These faults went long unnoticed because Alpine orogenic deformation blurred the record. Alpine strain erased their original obliquity, causing confusion with an Alpine low-angle thrust. These Jurassic faults have been passively deformed during Alpine tectonics, without inversion or any other kind of reactivation. They behaved like passive markers of the Alpine strain. Detailed field observations reveal the link between observed faults and specific breccia accumulations. Areas where the Evolène Series is missing correspond to sectors where the fault scarps were exposed on the bottom of the sea but were too steep to keep the syn- to post-faulting sediments. The Mont Fort nappe thus represents an example of a distal rifted margin. The succession of synsedimentary extensional movements followed by orogenic shortening generated a situation where passively deformed normal faults mimic an orogenic thrust.

scholarly journals Seismicity, focal mechanism, and stress tensor analysis of the Simav region, western Turkey

2020 ◽  
Vol 12 (1) ◽  
pp. 479-490
Author(s):  
Ahu Kömeç Mutlu
Keyword(s):  
Moment Tensor ◽  
Aftershock Sequence ◽  
Movement Direction ◽  
Normal Faults ◽  
Normal Faulting ◽  
Stress Inversion ◽  
Western Turkey ◽  
Stress Orientations ◽  
Extension Direction ◽  
Inversion Analysis

AbstractThis study focuses on the seismicity and stress inversion analysis of the Simav region in western Turkey. The latest moderate-size earthquake was recorded on May 19, 2011 (Mw 5.9), with a dense aftershock sequence of more than 5,000 earthquakes in 6 months. Between 2004 and 2018, data from earthquake events with magnitudes greater than 0.7 were compiled from 86 seismic stations. The source mechanism of 54 earthquakes with moment magnitudes greater than 3.5 was derived by using a moment tensor inversion. Normal faults with oblique-slip motions are dominant being compatible with the NE-SW extension direction of western Turkey. The regional stress field is assessed from focal mechanisms. Vertically oriented maximum compressional stress (σ1) is consistent with the extensional regime in the region. The σ1 and σ3 stress axes suggest the WNW-ESE compression and the NNE-SSW dilatation. The principal stress orientations support the movement direction of the NE-SW extension consistent with the mainly observed normal faulting motions.

The 4 December 2015 Mw 7.1 Normal-Faulting Antarctic Plate Earthquake and Its Seismotectonic Implications

2020 ◽  
Vol 110 (3) ◽  
pp. 1090-1100
Author(s):  
Ronia Andrews ◽  
Kusala Rajendran ◽  
N. Purnachandra Rao
Keyword(s):  
Body Wave ◽  
Focal Depth ◽  
Normal Fault ◽  
Normal Faults ◽  
Oceanic Plate ◽  
Normal Faulting ◽  
Transform Faults ◽  
Wave Inversion ◽  
Spreading Ridges ◽  
Southeast Indian Ridge

ABSTRACT Oceanic plate seismicity is generally dominated by normal and strike-slip faulting associated with active spreading ridges and transform faults. Fossil structural fabrics inherited from spreading ridges also host earthquakes. The Indian Oceanic plate, considered quite active seismically, has hosted earthquakes both on its active and fossil fault systems. The 4 December 2015 Mw 7.1 normal-faulting earthquake, located ∼700  km south of the southeast Indian ridge in the southern Indian Ocean, is a rarity due to its location away from the ridge, lack of association with any mapped faults and its focal depth close to the 800°C isotherm. We present results of teleseismic body-wave inversion that suggest that the earthquake occurred on a north-northwest–south-southeast-striking normal fault at a depth of 34 km. The rupture propagated at 2.7  km/s with compact slip over an area of 48×48  km2 around the hypocenter. Our analysis of the background tectonics suggests that our chosen fault plane is in the same direction as the mapped normal faults on the eastern flanks of the Kerguelen plateau. We propose that these buried normal faults, possibly the relics of the ancient rifting might have been reactivated, leading to the 2015 midplate earthquake.

scholarly journals Structural cross sections through the Corinth-Patras detachment fault-system in Northern Peloponnesus (Aegean Arc, Greece)

2001 ◽  
Vol 34 (1) ◽  
pp. 235 ◽  
Author(s):  
N. FLOTTÉ ◽  
D. SOREL
Keyword(s):  
Cross Sections ◽  
Detachment Fault ◽  
Fault System ◽  
Normal Faults ◽  
Field Observations ◽  
Structural Mapping ◽  
The North ◽  
Gulf Of Corinth ◽  
Aegean Arc

Structural mapping in northern Peloponnesus reveals the emergence of an E-W striking, more than 70km long, low angle detachment fault dipping to the north beneath the Gulf of Corinth. This paper describes four north-south structural cross-sections in northern Peloponnesus. Structural and sedimentological field observations show that in the studied area the normal faults of northern Peloponnesus branch at depth on this major low angle north-dipping brittle detachment. The southern part of the detachment and the related normal faults are now inactive. To the north, the active Helike and Aigion normal faults are connected at depth with the seismically active northern part of the detachment beneath the Gulf of Corinth.

scholarly journals Structure of massively dilatant faults in Iceland: lessons learned from high resolution UAV data

2019 ◽  
Author(s):  
Christopher Weismüller ◽  
Janos L. Urai ◽  
Michael Kettermann ◽  
Christoph von Hagke ◽  
Klaus Reicherter
Keyword(s):  
High Resolution ◽  
Normal Fault ◽  
Lessons Learned ◽  
Normal Faults ◽  
Large Set ◽  
Recent Sediment ◽  
Field Observations ◽  
East African ◽  
Continuous Transition ◽  
Opening Width

Abstract. Normal faults in basalts develop massive dilatancy up to several tens of meters close to the Earth's surface and show corresponding interactions with groundwater and lava flow. These massively dilatant faults (MDF) are widespread in extensional settings like Iceland or the East African Rift, but their detailed geometry is not well understood, despite their importance for fluid flow in the subsurface, geohazards or geothermal energy. We present a large set of digital elevation models (DEM) of the surface geometries of MDF with 5–15 cm resolution, acquired along the Icelandic Rift zone using unmanned aerial vehicles (UAV). UAV provide a much higher resolution than aerial/satellite imagery and a much better overview than ground-based fieldwork, thus bridging the gap between outcrop scale and regional observations. Our data present representative outcrops of MDF, formed in basaltic sequences linked to the Mid Ocean Ridge. We acquired photosets of overlapping images along about 20 km of MDF and processed these using photogrammetry to create high resolution DEMs and ortho-rectified images. We use this dataset to map the faults and their damage zones to measure length, opening width and vertical offset of the faults and identify surface tilt in the damage zones. Ground truthing of the data was done by field observations. Mapped vertical offsets show typical trends of normal fault growth by segment coalescence. However, opening widths in map-view show variations at much higher frequency, caused by segmentation, collapsed relays and tilted blocks. These effects cause a commonly higher than expected ratio of vertical offset and opening width for a steep normal fault at depth. Based on field observations and the relationships of opening width and vertical offset, we define three endmember morphologies of MDF: (i) dilatant faults with opening width and vertical offset, (ii) tilted blocks (TB), and (iii) opening mode (mode I) fissures. Field observation of normal faults without visible opening invariably shows that these have an opening filled by recent sediment. TB dominated normal faults tend to have a largest opening width with respect to vertical offsets. Fissures have opening widths up to 15 m with throw below a 2 m threshold. Plotting opening width versus vertical offset of the fractures shows that there is a continuous transition between the endmembers. We conclude that fractures associated with MDF belong to one larger continuum and the three endmembers are thus not necessarily indicative for fracture maturity.

scholarly journals A reappraisal of active tectonics along the Fethiye-Burdur trend, southwestern Turkey

2021 ◽  
Author(s):  
Edwin Nissen ◽  
Mussaver Didem Cambaz ◽  
Élyse Gaudreau ◽  
Andrew Howell ◽  
Ezgi Karasözen ◽  
...  
Keyword(s):  
Active Tectonics ◽  
Normal Fault ◽  
Recent Change ◽  
Strike Slip ◽  
Gravitational Potential Energy ◽  
Normal Faults ◽  
Normal Faulting ◽  
Arrival Times ◽  
Anatolian Plateau ◽  
Recent Earthquakes

We investigate active tectonics in southwestern Turkey along the trend between Fethiye, near the eastern end of the Hellenic subduction zone, and Burdur, on the Anatolian plateau. Previously, regional GPS velocity data have been used to propose either (1) a NE-trending zone of strike-slip faulting coined the Fethiye-Burdur Fault Zone, or (2) a mix of uniaxial and radial extension accommodated by normal faults with diverse orientations. We test these models against the available earthquake data, updated in light of recent earthquakes at Acıpayam (20 March 2019, Mw 5.6) and Bozkurt (8 August 2019, Mw 5.8) — the largest in this region in the last two decades — and at Arıcılar (24 November 2017, Mw 5.3). Using Sentinel-1 InSAR and seismic waveforms and arrival times, we show that the Acıpayam, Bozkurt and Arıcılar earthquakes were buried ruptures on pure normal faults with subtle or indistinct topographic expressions. By exploiting ray paths shared with these well-recorded modern events, we relocate earlier instrumental seismicity throughout southwestern Turkey. We find that the 1971 Mw 6.0 Burdur earthquake likely ruptured a NW-dipping normal fault in an area of indistinct geomorphology near Salda Lake, contradicting earlier studies that place it on well-expressed faults bounding the Burdur basin. Overall, the northern Fethiye-Burdur trend is characterized by orthogonal normal faulting, consistent with radial extension and likely responsible for the distinct physiography of Turkey's 'Lake District'. The southern Fethiye-Burdur trend is dominated by ESE-WNW trending normal faulting, even though most faults evident in the topography strike NE-SW. This hints at a recent change in regional strain, perhaps related to eastward propagation of the Gökova graben into the area or to rapid subsidence of the Rhodes basin. Overall, our results support GPS-derived tectonic models that depict a mix of uniaxial and radial extension throughout southwestern Turkey, with no evidence for major, active strike-slip faults anywhere along the Fethiye-Burdur trend. Normal faulting orientations are consistent with a stress field driven primarily by contrasts in gravitational potential energy between the elevated Anatolian plateau and the low-lying Rhodes and Antalya basins.

scholarly journals On the complexity of surface ruptures during normal faulting earthquakes: excerpts from the 6 April 2009, L'Aquila (central Italy) earthquake (<i>M</i><sub>w</sub> 6.3)

2013 ◽  
Vol 5 (2) ◽  
pp. 2043-2079
Author(s):  
L. Bonini ◽  
D. Di Bucci ◽  
G. Toscani ◽  
S. Seno ◽  
G. Valensise
Keyword(s):  
Surface Deformation ◽  
Central Italy ◽  
Normal Faults ◽  
Normal Faulting ◽  
Seismogenic Fault ◽  
Earthquake Catalogues ◽  
Central Italy Earthquake ◽  
Seismological Data ◽  
Seismogenic Source ◽  
Earthquake Potential

Abstract. Over the past few years the assessment of the earthquake potential of large continental faults has increasingly relied on field investigations. State-of-the-art seismic hazard models are progressively complementing the information derived from earthquake catalogues with geological observations of active faulting. Using these observations, however, requires full understanding of the relationships between seismogenic slip at depth and surface deformation, such that the evidence indicating the presence of a large, potentially seismogenic fault can be singled out effectively and unambiguously. We used observations and models of the 6 April 2009, Mw 6.3, L'Aquila, normal faulting earthquake to explore the relationships between the activity of a large fault at seismogenic depth and its surface evidence. This very well-documented earthquake is representative of mid-size yet damaging earthquakes that are frequent around the Mediterranean Basin, and is somehow paradigmatic of the nature of the associated geologic evidence along with observational difficulties and ambiguities. Thanks to available high-resolution geologic, geodetic and seismological data aided by analogue modeling, we reconstructed the full geometry of the seismogenic source in relation with surface and sub-surface faults. We find that the earthquake was caused by seismogenic slip in the range 3–10 km depth, and that the slip distribution was strongly controlled by inherited discontinuities. We also contend that faulting was expressed at the surface by pseudo-primary breaks resulting from coseismic crustal bending and by sympathetic slip on secondary faults. Based on our results we propose a scheme for hierarchizing normal faults through which all surface occurrences related to faulting at depth can be interpreted in the frame of a single, mechanically coherent model. Appreciating such complexity is crucial to avoid severe over- or under-estimation of the local seismogenic potential.

Emplacement mechanisms of a dyke swarm across the Brittle-Ductile transition

2020 ◽  
Author(s):  
Hans Jørgen Kjøll ◽  
Olivier Galland ◽  
Loic Labrousse ◽  
Torgeir B. Andersen
Keyword(s):  
Host Rock ◽  
Mafic Magma ◽  
Large Igneous Province ◽  
Dyke Swarm ◽  
Field Observations ◽  
Transport Pathways ◽  
Influx Rate ◽  
Brittle Ductile Transition ◽  
Iapetus Ocean ◽  
Rifted Margin

&lt;p&gt;Dykes are the main magma transport pathways through the Earth&amp;#8217;s crust and, in volcanic rifts, they are considered the main mechanism to accommodate tectonic extension. Most models consider dykes as hydro-fractures propagating as brittle tensile, mode I cracks opening perpendicular to the least principal stress. This implies that dykes emplaced in rifts are expected to be sub-vertical and accommodate crustal extension. Here we present detailed field observations of a well-exposed dyke swarm that formed near the brittle-ductile transition at a magma-rich rifted margin during opening of the Iapetus Ocean. It was related to a ca 600 million year-old large igneous province. Our observations show that dykes were not systematically emplaced by purely brittle deformation and that dyke orientation may differ from the typical mode 1 pattern. Distinct dyke morphologies related to different emplacement mechanisms have been recognized including: 1) Brittle dykes that exhibit straight contacts with the host rock, sharp tips, and en-echelon segments with bridges exhibiting angular fragments; 2) Brittle-ductile dykes with undulating contacts, rounded tips, folding of the host rock and contemporaneous brittle and ductile features; 3) Ductile &amp;#8220;dykes&amp;#8221; with rounded shapes and mingling between partially molten host rock and the intruding mafic magma. The brittle dykes exhibit two distinct orientations separated by ~30&amp;#176; that are mutually cross-cutting, demonstrating that the dyke swam did not consist of only vertical sheets oriented perpendicular to regional extension, as expected in rifts. By using the host-rock layers as markers, a kinematic restoration to quantify the average strain accommodating the emplacement of the dyke complex was performed. This strain estimate shows that the dyke swarm accommodated &gt;100% horizontal extension, but also 27% vertical thickening. This suggests that the magma influx rate was higher than the tectonic stretching rate, which imply that magma was emplaced forcefully, as supported by field observations of the host-rock deformation. Finally, observations of typical &amp;#8220;brittle&amp;#8221; dykes that were subsequently deformed by ductile mechanisms as well as dykes that were emplaced by purely ductile mechanisms suggest that the fast emplacement of the dyke swarm triggered a rapid shallowing of the brittle-ductile transition. The abrupt dyke emplacement and associated heating resulted in weakening of the crust that probably facilitated the continental break-up, which culminated with opening of the Iapetus Ocean.&lt;/p&gt;

Contrasting transient and steady-state rivers crossing active normal faults: new field observations from the Central Apennines, Italy

2007 ◽  
Vol 19 (4) ◽  
pp. 529-556 ◽  
Author(s):  
Alexander C. Whittaker ◽  
Patience A. Cowie ◽  
Mikaël Attal ◽  
Gregory E. Tucker ◽  
Gerald P. Roberts
Keyword(s):  
Steady State ◽  
Normal Faults ◽  
Field Observations ◽  
Central Apennines ◽  
Transient And Steady State

scholarly journals Structure of massively dilatant faults in Iceland: lessons learned from high-resolution unmanned aerial vehicle data

Solid Earth ◽  
2019 ◽  
Vol 10 (5) ◽  
pp. 1757-1784 ◽  
Author(s):  
Christopher Weismüller ◽  
Janos L. Urai ◽  
Michael Kettermann ◽  
Christoph von Hagke ◽  
Klaus Reicherter
Keyword(s):  
High Resolution ◽  
Normal Fault ◽  
Lessons Learned ◽  
Normal Faults ◽  
Large Set ◽  
Recent Sediment ◽  
Field Observations ◽  
East African ◽  
Continuous Transition ◽  
Opening Width

Abstract. Normal faults in basalts develop massive dilatancy in the upper few hundred meters below the Earth's surface with corresponding interactions with groundwater and lava flow. These massively dilatant faults (MDFs) are widespread in Iceland and the East African Rift, but the details of their geometry are not well documented, despite their importance for fluid flow in the subsurface, geohazard assessment and geothermal energy. We present a large set of digital elevation models (DEMs) of the surface geometries of MDFs with 5–15 cm resolution, acquired along the Icelandic rift zone using unmanned aerial vehicles (UAVs). Our data present a representative set of outcrops of MDFs in Iceland, formed in basaltic sequences linked to the mid-ocean ridge. UAVs provide a much higher resolution than aerial/satellite imagery and a much better overview than ground-based fieldwork, bridging the gap between outcrop-scale observations and remote sensing. We acquired photosets of overlapping images along about 20 km of MDFs and processed these using photogrammetry to create high-resolution DEMs and orthorectified images. We use this dataset to map the faults and their damage zones to measure length, opening width and vertical offset of the faults and identify surface tilt in the damage zones. Ground truthing of the data was done by field observations. Mapped vertical offsets show typical trends of normal fault growth by segment coalescence. However, opening widths in map view show variations at much higher frequency, caused by segmentation, collapsed relays and tilted blocks. These effects commonly cause a higher-than-expected ratio of vertical offset and opening width for a steep normal fault at depth. Based on field observations and the relationships of opening width and vertical offset, we define three endmember morphologies of MDFs: (i) dilatant faults with opening width and vertical offset, (ii) tilted blocks (TBs) and (iii) opening-mode (mode I) fissures. Field observation of normal faults without visible opening invariably shows that these have an opening filled with recent sediment. TB-dominated normal faults tend to have the largest ratio of opening width and vertical offset. Fissures have opening widths up to 15 m with throw below a 2 m threshold. Plotting opening width versus vertical offset shows that there is a continuous transition between the endmembers. We conclude that for these endmembers, the ratio between opening width and vertical offset R can be reliably used to predict fault structures at depth. However, fractures associated with MDFs belong to one larger continuum and, consequently, where different endmembers coexist, a clear identification of structures solely via the determination of R is impossible.

The world-wide oceanic rise-ridge system

1965 ◽  
Vol 258 (1088) ◽  
pp. 109-122 ◽  
Keyword(s):  
Heat Flow ◽  
World Wide ◽  
High Heat ◽  
The Other ◽  
Normal Faults ◽  
Normal Faulting ◽  
High Heat Flow ◽  
Flood Basalts ◽  
The World ◽  
Ridge System

About half the length of the * oceanic ’ rise-ridge system is centred in ocean basins. On the other hand, almost the whole system is approximately disposed in circles around continental shields. Exceptional heating of the system is indicated by high heat flow and the extrusion of extraordinary volumes of flood basalts. The concentration of volcanoes, however, is little greater than normal for ocean basins. Longitudinal normal faulting and transverse wrench faulting are characteristic of the system. Both types formed early in the life of the system and are still active. Wrench faults offset belts of normal faulting and the crests of rises and ridges in many places but are not themselves known to be offset by normal faults. The ancient Darwin Rise has subsided in the southwestern Pacific. Its history differs in some respects from other rises although it too was heated and faulted. A hypothesis of origin of the system is briefly discussed.

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