scholarly journals Structure and kinematics of an extensional growth fold, Hadahid Fault System, Suez Rift, Egypt

Solid Earth ◽  
2020 ◽  
Vol 11 (3) ◽  
pp. 1027-1051
Author(s):  
Christopher A.-L. Jackson ◽  
Paul S. Whipp ◽  
Robert L. Gawthorpe ◽  
Matthew M. Lewis
Keyword(s):  
Structural Complexity ◽  
Surface Displacement ◽  
Normal Fault ◽  
Fault System ◽  
Length Scale ◽  
Slip Ratio ◽  
Continental Extension ◽  
Structural Style ◽  
Progressive Loss ◽  
Geometry And Kinematics

Abstract. Normal faulting drives extensional growth folding of the Earth's upper crust during continental extension, yet we know little of how fold geometry relates to the structural segmentation of the underlying fault. We use field data from the Hadahid Fault System, Suez Rift, Egypt, to investigate the geometry and kinematics of a large (30 km long, up to 2.5 km displacement), exceptionally well-exposed normal fault system and to test and develop models for extensional growth folding. The Hadahid Fault System comprises eight up to 5 km long segments that are defined by unbreached or breached monoclines. These segments are soft-linked, hard-linked, or defined by a more subtle along-strike transition in overall structural style. High overlap : separation (O:S) ratios between its segments suggest the Hadahid Fault System comprises a single, now hard-linked structure at depth. We demonstrate that a progressive loss of at-surface displacement along-strike of the Hadahid Fault System results in surface-breaking faults and breached monoclines being replaced by unbreached monoclines developed above blind faults. However, shorter along-strike length-scale variations in structural style also occur, with unbreached monoclines developed between breached monoclines. The origin of this variability is unclear, but it might reflect local variations in host rock material properties that drive short length-scale variations in fault propagation-to-slip ratio, and thus the timing and location of fold breaching. We show that folding is a key expression of the strain that accumulates in areas of continental extension, arguing that tectono-sedimentary models for rift development should capture the related structural complexity.

scholarly journals Structure and kinematics of an extensional growth fold, Hadahid Fault System, Suez Rift, Egypt

2019 ◽  
Author(s):  
Christopher Aiden-Lee Jackson ◽  
Paul S Whipp ◽  
Robert Gawthorpe ◽  
Matthew M Lewis
Keyword(s):  
Structural Complexity ◽  
Surface Displacement ◽  
Normal Fault ◽  
Fault System ◽  
Length Scale ◽  
Slip Ratio ◽  
Continental Extension ◽  
Structural Style ◽  
Progressive Loss ◽  
Geometry And Kinematics

Normal faulting drives extensional growth folding of the Earth’s upper crust during continental extension, yet we know little of how fold geometry relates to the structural segmentation of the underlying fault. We use field data from the Hadahid Fault System, Suez Rift, Egypt to investigate the geometry and kinematics of a large (30 km long, up to 2.5 km displacement), exceptionally well-exposed normal fault system to test and develop models for extensional growth folding. The Hadahid Fault System comprises eight, up to 5 km long segments that are defined by unbreached or breached monoclines. These segments are soft-linked, hard-linked, or defined by a more subtle along-strike transition in overall structural style. High overlap:separation (O:S) ratios between its segments suggest the Hadahid Fault System comprises a single, now hard-linked structure at-depth. We demonstrate that a progressive loss of at-surface displacement along strike of the Hadahid Fault System results in surface-breaking faults and breached monoclines being replaced by unbreached monoclines developed above blind faults. However, shorter along-strike length-scale variations in structural style also occur, with unbreached monoclines developed between breached monoclines. The origin of this variability is unclear, but might reflect local variations in host rock material properties that drive short length-scale variations in fault propagation-to-slip ratio, and thus the timing and location of fold breaching. We show that folding is a key expression of the strain that accumulates in areas of continental extension, and argue that tectono-sedimentary models for rift development should capture the related structural complexity.

scholarly journals Structure and kinematics of an extensional growth fold, Hadahid Fault System, Suez Rift, Egypt

2019 ◽  
Author(s):  
Christopher A.-L. Jackson ◽  
Paul S. Whipp ◽  
Robert L. Gawthorpe ◽  
Matthew M. Lewis
Keyword(s):  
Structural Complexity ◽  
Normal Fault ◽  
Fault System ◽  
Length Scale ◽  
Soft Or ◽  
Slip Ratio ◽  
Continental Extension ◽  
Structural Style ◽  
Progressive Loss ◽  
Geometry And Kinematics

Abstract. Normal faulting drives extensional growth folding of the Earth's upper crust during continental extension, yet we know little of how fold geometry relates to the structural segmentation of the underlying fault. We use field data from the Hadahid Fault System, Suez Rift, Egypt to investigate the geometry and kinematics of a large (30 km long, up to 2.5 km displacement), exceptionally well-exposed normal fault system to test and develop models for extensional growth folding. The Hadahid Fault System comprises eight, up to 5 km long segments that are defined by unbreached, breached, or partly breached monoclines. These segments are soft- or hard-link, or defined by a more subtle transition in overall structural style. High overlap : separation (O : S) ratios between its segments suggest the Hadahid Fault System comprises a single, now hard-linked structure at-depth. We demonstrate that a progressive loss of displacement along strike of the Hadahid Fault System results in surface-breaking faults and breached monoclines being replaced by unbreached monoclines developed above blind faults. However, shorter along-strike length-scale variations in structural style also occur, with unbreached monoclines developed between breached monoclines. The origin of this variability is unclear, but might reflect local variations in host rock material properties that drive short length-scale variations in fault propagation-to-slip ratio, and thus the timing and location of fold breaching. We show that folding is a key expression of the strain that accumulates in areas of continental extension, and argue that tectono-sedimentary models for rift development should capture the related structural complexity.

scholarly journals The 31 March 2020 Mw 6.5 Stanley, Idaho, Earthquake: Seismotectonics and Preliminary Aftershock Analysis

2020 ◽  
Author(s):  
Lee M. Liberty ◽  
Zachery M. Lifton ◽  
T. Dylan Mikesell
Keyword(s):  
Surface Displacement ◽  
Volcanic Belt ◽  
Normal Fault ◽  
Fault System ◽  
Basin And Range Province ◽  
Ground Shaking ◽  
The North ◽  
Show Evidence ◽  
Tectonic Framework ◽  
Tectonic Belt

Abstract We report on the tectonic framework, seismicity, and aftershock monitoring efforts related to the 31 March 2020 Mw 6.5 Stanley, Idaho, earthquake. The earthquake sequence has produced both strike-slip and dip-slip motion, with minimal surface displacement or damage. The earthquake occurred at the northern limits of the Sawtooth normal fault. This fault separates the Centennial tectonic belt, a zone of active seismicity within the Basin and Range Province, from the Idaho batholith to the west and Challis volcanic belt to the north and east. We show evidence for a potential kinematic link between the northeast-dipping Sawtooth fault and the southwest-dipping Lost River fault. These opposing faults have recorded four of the five M≥6 Idaho earthquakes from the past 76 yr, including 1983 Mw 6.9 Borah Peak and the 1944 M 6.1 and 1945 M 6.0 Seafoam earthquakes. Geological and geophysical data point to possible fault boundary segments driven by pre-existing geologic structures. We suggest that the limits of both the Sawtooth and Lost River faults extend north beyond their mapped extent, are influenced by the relic trans-Challis fault system, and that seismicity within this region will likely continue for the coming years. Ongoing seismic monitoring efforts will lead to an improved understanding of ground shaking potential and active fault characteristics.

scholarly journals Pre-inversion normal fault geometry controls inversion style and magnitude, Farsund Basin, offshore southern Norway

Solid Earth ◽  
2020 ◽  
Vol 11 (4) ◽  
pp. 1489-1510
Author(s):  
Thomas B. Phillips ◽  
Christopher A.-L. Jackson ◽  
James R. Norcliffe
Keyword(s):  
Late Cretaceous ◽  
Focal Point ◽  
Three Dimensional ◽  
Normal Fault ◽  
Fault System ◽  
Prior History ◽  
Plate Boundaries ◽  
Northern Margin ◽  
Long Wavelength ◽  
Structural Style

Abstract. Compressional strains may manifest along pre-existing structures within the lithosphere, far from the plate boundaries along which the causal stress is greatest. The style and magnitude of the related contraction is expressed in different ways, depending on the geometric and mechanical properties of the pre-existing structure. A three-dimensional approach is thus required to understand how compression may be partitioned and expressed along structures in space and time. We here examine how post-rift compressional strains are expressed along the northern margin of the Farsund Basin during Late Cretaceous inversion and Palaeogene–Neogene pulses of uplift. At the largest scale, stress localises along the lithosphere-scale Sorgenfrei-Tornquist Zone, where it is expressed in the upper crust as hangingwall folding, reverse reactivation of the basin-bounding normal fault, and bulk regional uplift. The geometry of the northern margin of the basin varies along strike, with a normal fault system passing eastward into an unfaulted ramp. Late Cretaceous compressive stresses, originating from the convergence between Africa, Iberia, and Europe, selectively reactivated geometrically simple, planar sections of the fault, producing hangingwall anticlines and causing long-wavelength folding of the basin fill. The amplitude of these anticlines decreases upwards due to tightening of pre-existing fault propagation folds at greater depths. In contrast, later Palaeogene–Neogene uplift is accommodated by long-wavelength folding and regional uplift of the entire basin. Subcrop mapping below a major, uplift-related unconformity and borehole-based compaction analysis show that uplift increases to the north and east, with the Sorgenfrei-Tornquist Zone representing a hinge line rather than a focal point to uplift, as was the case during earlier Late Cretaceous compression. We show how compressional stresses may be accommodated by different mechanisms within structurally complex settings. Furthermore, the prior history of a structure may also influence the mechanism and structural style of shortening that it experiences.

scholarly journals Pre-inversion normal fault geometry controls inversion style and magnitude, Farsund Basin, offshore southern Norway

2020 ◽  
Author(s):  
Thomas Brian Phillips ◽  
Christopher A.-L. Jackson ◽  
James R. Norcliffe
Keyword(s):  
Late Cretaceous ◽  
Focal Point ◽  
Three Dimensional ◽  
Normal Fault ◽  
Fault System ◽  
Prior History ◽  
Plate Boundaries ◽  
Northern Margin ◽  
Long Wavelength ◽  
Structural Style

Abstract. Inversion may localise along pre-existing structures within the lithosphere, far from the plate boundaries along which the causal stress is greatest. Inversion style and magnitude is expressed in different ways, depending on the geometric and mechanical properties of the pre-existing structure. A three-dimensional approach is thus required to understand how inversion may be partitioned and expressed along structures in space and time. We here examine how inversion is expressed along the northern margin of the Farsund Basin during Late Cretaceous inversion and Neogene uplift. At the largest scale, strain localises along the lithosphere-scale Sorgenfrei-Tornquist Zone; this is expressed in the upper crust as hangingwall folding, reverse reactivation of the basin-bounding normal fault, and bulk regional uplift. The geometry of the northern margin of the basin varies along-strike, with a normal fault system passing eastward into an unfaulted ramp. Late Cretaceous compressive stresses, originating from the Alpine Orogeny to the south, selectively reactivated geometrically simple, planar sections of the fault, producing hangingwall anticlines and causing long-wavelength folding of the basin fill. The amplitude of these anticlines decreases upwards due to tightening of pre-existing fault propagation folds at greater depths. In contrast, Neogene shortening is accommodated by long-wavelength folding and regional uplift of the entire basin. Subcrop mapping below a major, Neogene uplift-related unconformity and bore-based compaction analysis show that uplift increases to the north and east, with the Sorgenfrei-Tornquist Zone representing a hingeline to inversion rather than a focal point, as was the case during the Late Cretaceous. We show how compressional stresses may be accommodated by different inversion mechanisms within structurally complex settings. Furthermore, the prior history of a structure may also influence the mechanism and structural style of inversion that it experiences.

scholarly journals Neogene-Quaternary tectonic regime and macroseismic observations in the Tyrnavos-Elassona broader epicentral area of the March 2021, intense earthquake sequence

2021 ◽  
Vol 58 ◽  
pp. 200
Author(s):  
Dimitrios Galanakis ◽  
Sotiris Sboras ◽  
Garyfalia Konstantopoulou ◽  
Markos Xenakis
Keyword(s):  
Normal Fault ◽  
Fault Scarp ◽  
Focal Mechanisms ◽  
Fault System ◽  
Spatiotemporal Evolution ◽  
Surface Rupture ◽  
Alluvial Deposits ◽  
Epicentral Area ◽  
Ground Shaking ◽  
Macroseismic Observations

On March 3, 2021, a strong (Mw6.3) earthquake occurred near the towns of Tyrnavos and Elassona. One day later (March 4), a second strong (Mw6.0) earthquake occurred just a few kilometres toward the WNW. The aftershock spatial distribution and the focal mechanisms revealed NW-SE-striking normal faulting. The focal mechanisms also revealed a NE-SW oriented extensional stress field, different from the orientation we knew so far (ca. N-S). The magnitude and location of the two strongest shocks, and the spatiotemporal evolution of the sequence, strongly suggest that two adjacent fault segments were ruptured respectively. The sequence was followed by several coseismic ground deformational phenomena, such as landslides/rockfalls, liquefaction and ruptures. The landslides and rockfalls were mostly associated with the ground shaking. The ruptures were observed west of the Titarissios River, near to the Quaternary faults found by bore-hole lignite investigation. In the same direction, a fault scarp separating the alpidic basement from the alluvial deposits of the Titarissios valley implies the occurrence of a well-developed fault system. Some of the ground ruptures were accompanied by extensive liquefaction phenomena. Others cross-cut reinforced concrete irrigation channels without changing their direction. We suggest that this fault system was partially reactivated, as a secondary surface rupture, during the sequence as a steeper splay of a deeper low-to-moderate angle normal fault.

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