scholarly journals Evolution of rift systems and their fault networks in response to surface processes

2021 ◽  
Author(s):  
Derek Neuharth ◽  
Sascha Brune ◽  
Thilo Wrona ◽  
Anne Glerum ◽  
Jean Braun ◽  
...  
Keyword(s):  
Sedimentary Basins ◽  
Field Studies ◽  
Fault Analysis ◽  
Growth Patterns ◽  
Surface Processes ◽  
Fault System ◽  
Normal Faults ◽  
Continental Margins ◽  
Geodynamic Models ◽  
Fault Growth

Continental rifting is responsible for the generation of major sedimentary basins, both during rift inception and during the formation of rifted continental margins. Geophysical and field studies revealed that rifts feature complex networks of normal faults but the factors controlling fault network properties and their evolution are still matter of debate. Here, we employ high-resolution 2D geodynamic models (ASPECT) including two-way coupling to a surface processes code (FastScape) to conduct 12 models of major rift types that are exposed to various degrees of erosion and sedimentation. We further present a novel quantitative fault analysis toolbox (Fatbox), which allows us to isolate fault growth patterns, the number of faults, and their length and displacement throughout rift history. Our analysis reveals that rift fault networks may evolve through five major phases: 1) distributed deformation and coalescence, 2) fault system growth, 3) fault system decline and basinward localization, 4) rift migration, and 5) breakup. These phases can be correlated to distinct rifted margin domains. Models of asymmetric rifting suggest rift migration is facilitated through both ductile and brittle deformation within a weak exhumation channel that rotates subhorizontally and remains active at low angles. In sedimentation-starved settings, this channel satisfies the conditions for serpentinization. We find that surface processes are not only able to enhance strain localization and to increase fault longevity but that they also reduce the total length of the fault system, prolong rift phases and delay continental breakup.

How syn-rift sedimentation promotes the formation of hyper-extended margins

2020 ◽  
Author(s):  
Susanne Buiter
Keyword(s):  
Sedimentary Basins ◽  
Surface Processes ◽  
Tectonic Activity ◽  
Tectonic Deformation ◽  
Continental Margins ◽  
Rifted Margins ◽  
Continental Rifts ◽  
Break Up ◽  
Mountain Belts ◽  
Sediment Layers

<p>Seismic observations show that some rifted continental margins may have substantial amounts of offshore sediments. For example, sediment layers of several kilometres thick are found on the margins of Mid Norway, Namibia and Angola. Intriguingly, these margins are wide, being characterised by distances of several hundreds of kilometres from typical continental crustal thicknesses of 30-40 km to clearly identifiable oceanic crust. On the other hand, some margins that are sediment-starved, such as Goban Spur, Flemish Cap and Northern Norway, have short onshore-to-offshore transitions. Variations in the amount of sediments not only impact the development of offshore sedimentary basins, but the changes in mass balance by erosion and sedimentation can also interact with extensional tectonic processes. In convergent settings, such feedback relationships between erosion and tectonic deformation have long been highlighted: Erosion reduces the elevation and width of mountain belts and in turn tectonic activity and exhumation are focused at regions of enhanced erosion. But what is the role played by surface processes during formation of rifted continental margins?</p><p>I use geodynamic finite-element experiments to explore the response of continental rifts to erosion and sedimentation from initial rifting to continental break-up. The experiments predict that rifted margins with thick syn-rift sedimentary packages are more likely to form hyper-extended crust and require more stretching to achieve continental break-up than sediment-starved margins. These findings imply that surface processes can control the style of continental break-up and that the role of sedimentation in rifted margin evolution goes far beyond the simple exertion of a passive weight.</p>

scholarly journals An integrated structural and GPS study of the Jalpatagua fault, southeastern Guatemala

Geosphere ◽  
2020 ◽  
Author(s):  
Bridget Garnier ◽  
Basil Tikoff ◽  
Omar Flores ◽  
Brian Jicha ◽  
Charles DeMets ◽  
...  
Keyword(s):  
El Salvador ◽  
Global Positioning System ◽  
Slip Rate ◽  
Fault Analysis ◽  
Fault System ◽  
Normal Faults ◽  
Central Section ◽  
Global Positioning ◽  
Major Fault ◽  
Fault Trace

The Jalpatagua fault in Guatemala accommodates dextral movement of the Central America forearc. We present new global positioning system (GPS) data, minor fault analysis, geochronological analyses, and analysis of lineaments to characterize deformation along the fault and near its terminations. Our data indicate that the Jalpatagua fault terminates at both ends into extensional regions. The western termination occurs near the Amatitlan caldera and the southern extension of the Guatemala City graben, as no through-going structures were observed to continue west into the active volcanic arc. Along the Jalpatagua fault, new and updated GPS site velocities are consistent with a slip rate of 7.1 ± 1.8 mm yr–1. Minor faulting along the central section of the fault includes: (1) N-S–striking normal faults accommodating E-W elongation; and (2) four sets of strike-slip faults (oriented 330°, 020°, 055°, and 295°, parallel to the Jalpatagua fault trace). Minor fault arrays support dextral movement along a major fault in the orientation of the Jalpatagua fault. GPS and fault data indicate that the Jalpatagua fault terminates to the east near the Guatemala–El Salvador border. Data delineate a pull-apart basin southeast of the fault termination, which is undergoing transtension as the Jalpatagua fault transitions into the El Salvador fault system to the east. Within the basin, minor faulting and lineations trend to the NW and accommodate NE-directed elongation. This faulting differs from E-W elongation observed along the Jalpatagua fault and is more similar to minor faults within the El Salvador fault system.

scholarly journals Evolution of a Normal Fault System, northern Graben, Taranaki Basin, New Zealand

2021 ◽  
Author(s):  
◽  
Hamish Cameron
Keyword(s):  
New Zealand ◽  
Seismic Reflection ◽  
Normal Fault ◽  
Growth Patterns ◽  
Fault System ◽  
Normal Faults ◽  
3D Seismic ◽  
Fault Evolution ◽  
Migration Pathways ◽  
Insight Into

<p>This study investigates the evolution (from initiation to inactivity) of a normal fault system in proximity to active petroleum systems within the Taranaki Basin, New Zealand. The aim of this research is to understand the evolution, interaction, and in some cases, death of normal faults in a region undergoing progressive regional extension. This research provides insight into the geometry, development, and displacement history of new and reactivated normal fault evolution through interpretation of industry standard seismic reflection data at high spatial and temporal resolution. Insight into normal fault evolution provides information on subsidence rates and potential hydrocarbon migration pathways.  Twelve time horizons between 1.2 and 35 Ma have been mapped throughout 1670 square kilometres of the Parihaka and Toro 3D seismic reflection surveys. Fault displacement analysis and backstripping have been used to determine the main phases of fault activity, fault growth patterns, and maximum Displacement/Length ratios. The timing, geometry, and displacement patterns for 110 normal faults with displacements >20 m have been interpreted and analysed using Paradigm SeisEarth and TrapTester 6 seismic interpretation and fault analysis software platforms.  Normal faults within the Parihaka and Toro 3D seismic surveys began developing at ˜11 Ma, with the largest faults accruing up to 1500 m of displacement in <10 Myr (mean throw displacement rate of 0.15mm/yr). Approximately 50% of the 110 mapped faults are associated with pre-existing normal faults and have typical cumulative displacements of ˜20 – 1000 m, with strike parallel lengths of <1 – 23 km. In contrast, new faults have typically greater displacements of 20 – 1400 m, and are generally longer with, with strike parallel lengths of ˜1 – 33 km.   New faults were the first faults within the system to become inactive when strain rates decreased from 0.06 – 0.03 between 3.6 and 3.0 Ma. Eight of the largest faults with > 1000 m cumulative displacement reach the seafloor and are potentially active at present day. An earthquake on one of these faults could be expected to produce MW 2.2 based on the maximum strike-parallel length of the fault plane.</p>

Geological fissures: linking sub-surface structures to surface processes

2021 ◽  
Author(s):  
Bob Holdsworth ◽  
Kit Hardman ◽  
Rich Walker ◽  
Alodie Bubeck ◽  
Cat Greenfield ◽  
...  
Keyword(s):  
Sedimentary Basins ◽  
Wall Rock ◽  
Surface Processes ◽  
Major Influence ◽  
Normal Faults ◽  
High Porosity ◽  
Block Rotation ◽  
Geothermal Resources ◽  
Diverse Range ◽  
Near Surface

&lt;p&gt;Dilatant fissures are a common feature at the Earth&amp;#8217;s surface in active rift systems where faults cut mechanically-strong rocks, such as igneous rocks, metamorphic basement or carbonates. Much attention has focused on modern examples of large-aperture fissures in basaltic rocks, where in most cases, only the near-surface-expression is accessible to depths of ~100 m. Numerous mechanisms have been proposed for the formation of such dilatant fractures, including near-surface tensile fracturing along active normal faults at depth, geometric mismatch along faults, and fault-block rotation. However, fissure system architecture and connectivity in the subsurface, and the depth to which dilatant sections can grow are less well understood, as are the ways in which such structures may interact with surface processes.&lt;/p&gt;&lt;p&gt;In this presentation, we focus on dilatant faults and fractures from the ancient rock record, including examples hosted in rocks below regional erosional unconformities, commonly on the upfaulted flanks of nearby sedimentary basins. Such fissures are typically sub-vertical Mode I fractures that can be kilometres long, tens of metres wide and can extend to depths of 1 km or more below the palaeosurface. They are filled with a remarkably diverse range of high porosity, high permeability fills which act as natural proppants holding fractures open for tens to hundreds of million years. Fills include: wall rock collapse breccias; clastic or carbonate sediment; fossiliferous materials, and a variety of epithermal mineral deposits with characteristically vuggy forms and cockade-like textures. Alteration related to weathering and/or near-surface epithermal mineralization may extend down fissure systems to depths of many hundreds of metres. The subterranean clastic fills are commonly water-lain and preserve a unique record of the stratigraphic or fossil record that may be missing due to erosion at the overlying unconformity. Fissures can form along active normal faults at depth, as later-stage reactivations of pre-existing exhumed fault zones and along regional joint sets associated with folds. Some fissures form along the margins or interior of pre-existing mafic dykes or may act as sites of subsequent dyke emplacement &amp;#8211; or both. Sub-unconformity fissure systems and their associated fills are likely to be a major influence on both the fluid storage capacity and flow behaviour in subsurface reservoirs including those hosting hydrocarbons, geothermal resources, and in aquifers worldwide.&lt;/p&gt;

scholarly journals Evolution of a Normal Fault System, northern Graben, Taranaki Basin, New Zealand

2021 ◽  
Author(s):  
◽  
Hamish Cameron
Keyword(s):  
New Zealand ◽  
Seismic Reflection ◽  
Normal Fault ◽  
Growth Patterns ◽  
Fault System ◽  
Normal Faults ◽  
3D Seismic ◽  
Fault Evolution ◽  
Migration Pathways ◽  
Insight Into

<p>This study investigates the evolution (from initiation to inactivity) of a normal fault system in proximity to active petroleum systems within the Taranaki Basin, New Zealand. The aim of this research is to understand the evolution, interaction, and in some cases, death of normal faults in a region undergoing progressive regional extension. This research provides insight into the geometry, development, and displacement history of new and reactivated normal fault evolution through interpretation of industry standard seismic reflection data at high spatial and temporal resolution. Insight into normal fault evolution provides information on subsidence rates and potential hydrocarbon migration pathways.  Twelve time horizons between 1.2 and 35 Ma have been mapped throughout 1670 square kilometres of the Parihaka and Toro 3D seismic reflection surveys. Fault displacement analysis and backstripping have been used to determine the main phases of fault activity, fault growth patterns, and maximum Displacement/Length ratios. The timing, geometry, and displacement patterns for 110 normal faults with displacements >20 m have been interpreted and analysed using Paradigm SeisEarth and TrapTester 6 seismic interpretation and fault analysis software platforms.  Normal faults within the Parihaka and Toro 3D seismic surveys began developing at ˜11 Ma, with the largest faults accruing up to 1500 m of displacement in <10 Myr (mean throw displacement rate of 0.15mm/yr). Approximately 50% of the 110 mapped faults are associated with pre-existing normal faults and have typical cumulative displacements of ˜20 – 1000 m, with strike parallel lengths of <1 – 23 km. In contrast, new faults have typically greater displacements of 20 – 1400 m, and are generally longer with, with strike parallel lengths of ˜1 – 33 km.   New faults were the first faults within the system to become inactive when strain rates decreased from 0.06 – 0.03 between 3.6 and 3.0 Ma. Eight of the largest faults with > 1000 m cumulative displacement reach the seafloor and are potentially active at present day. An earthquake on one of these faults could be expected to produce MW 2.2 based on the maximum strike-parallel length of the fault plane.</p>

scholarly journals A new model for the growth of normal faults developed above pre-existing structures

Geology ◽  
2021 ◽  
Author(s):  
Emma K. Bramham ◽  
Tim J. Wright ◽  
Douglas A. Paton ◽  
David M. Hodgson
Keyword(s):  
Early Period ◽  
Normal Fault ◽  
Sedimentary Basins ◽  
Vertical Displacement ◽  
Wide Distribution ◽  
Airborne Lidar ◽  
Normal Faults ◽  
Constant Length ◽  
Existing Structures ◽  
Fault Growth

Constraining the mechanisms of normal fault growth is essential for understanding extensional tectonics. Fault growth kinematics remain debated, mainly because the very earliest phase of deformation through recent syn-kinematic deposits is rarely documented. To understand how underlying structures influence surface faulting, we examined fault growth in a 10 ka magmatically resurfaced region of the Krafla fissure swarm, Iceland. We used a high-resolution (0.5 m) digital elevation model derived from airborne lidar to measure 775 fault profiles with lengths ranging from 0.015 to 2 km. For each fault, we measured the ratio of maximum vertical displacement to length (Dmax/L) and any nondisplaced portions of the fault. We observe that many shorter faults (&lt;200 m) retain fissure-like features, with no vertical displacement for substantial parts of their displacement profiles. Typically, longer faults (&gt;200 m) are vertically displaced along most of their surface length and have Dmax/L at the upper end of the global population for comparable lengths. We hypothesize that faults initiate at the surface as fissure-like fractures in resurfaced material as a result of flexural stresses caused by displacements on underlying faults. Faults then accrue vertical displacement following a constant-length model, and grow by dip and strike linkage or lengthening when they reach a bell-shaped displacement-length profile. This hybrid growth mechanism is repeated with deposition of each subsequent syn-kinematic layer, resulting in a remarkably wide distribution of Dmax/L. Our results capture a specific early period in the fault slip-deposition cycle in a volcanic setting that may be applicable to fault growth in sedimentary basins.

scholarly journals Seismic characteristics of polygonal fault systems in the Great South Basin, New Zealand

2020 ◽  
Vol 12 (1) ◽  
pp. 851-865
Author(s):  
Sukonmeth Jitmahantakul ◽  
Piyaphong Chenrai ◽  
Pitsanupong Kanjanapayont ◽  
Waruntorn Kanitpanyacharoen
Keyword(s):  
Three Dimensional ◽  
Late Eocene ◽  
Seismic Survey ◽  
Fault System ◽  
Normal Faults ◽  
Tier 2 ◽  
South Basin ◽  
Fault Systems ◽  
Tier 1 ◽  
Polygonal Fault

AbstractA well-developed multi-tier polygonal fault system is located in the Great South Basin offshore New Zealand’s South Island. The system has been characterised using a high-quality three-dimensional seismic survey tied to available exploration boreholes using regional two-dimensional seismic data. In this study area, two polygonal fault intervals are identified and analysed, Tier 1 and Tier 2. Tier 1 coincides with the Tucker Cove Formation (Late Eocene) with small polygonal faults. Tier 2 is restricted to the Paleocene-to-Late Eocene interval with a great number of large faults. In map view, polygonal fault cells are outlined by a series of conjugate pairs of normal faults. The polygonal faults are demonstrated to be controlled by depositional facies, specifically offshore bathyal deposits characterised by fine-grained clays, marls and muds. Fault throw analysis is used to understand the propagation history of the polygonal faults in this area. Tier 1 and Tier 2 initiate at about Late Eocene and Early Eocene, respectively, based on their maximum fault throws. A set of three-dimensional fault throw images within Tier 2 shows that maximum fault throws of the inner polygonal fault cell occurs at the same age, while the outer polygonal fault cell exhibits maximum fault throws at shallower levels of different ages. The polygonal fault systems are believed to be related to the dewatering of sedimentary formation during the diagenesis process. Interpretation of the polygonal fault in this area is useful in assessing the migration pathway and seal ability of the Eocene mudstone sequence in the Great South Basin.

How Chosen Seismic Fault Picking Strategy Influences Subsequent Fault Analyses: A Case Study from the Horda Platform, with Implications for CO2 storage

2021 ◽  
Author(s):  
Emma Michie ◽  
Mark Mulrooney ◽  
Alvar Braathen
Keyword(s):  
Fluid Flow ◽  
Co2 Storage ◽  
Fault Analysis ◽  
Surface Generation ◽  
Storage Site ◽  
Seismic Line ◽  
Fault Stability ◽  
Line Spacing ◽  
Fault Growth

&lt;p&gt;Significant uncertainties occur through varying methodologies when interpreting faults using seismic data.&amp;#160; These uncertainties are carried through to the interpretation of how faults may act as baffles/barriers or increase fluid flow.&amp;#160; Seismic line spacing chosen by the interpreter when picking fault segments, as well as the chosen surface generation algorithm used, will dictate how detailed or smoothed the surface is, and hence will impact any further interpretation such as fault seal, fault stability and fault growth analyses.&lt;/p&gt;&lt;p&gt;This contribution is a case study showing how picking strategies influence analysis of a bounding fault in terms of CO&lt;sub&gt;2&lt;/sub&gt; storage assessment.&amp;#160; This example utilizes data from the Smeaheia potential storage site within the Horda Platform, 20 km East of Troll East.&amp;#160; This is a fault bound prospect, known as the Alpha prospect, and hence the bounding fault is required to have a high seal potential and low chance of reactivation upon CO&lt;sub&gt;2&lt;/sub&gt; injection.&lt;/p&gt;&lt;p&gt;We can observe that an optimum spacing for fault interpretation for this case study is set at approximately 100 m.&amp;#160; It appears that any additional detail through interpretation with a line spacing of &amp;#8804;50 m simply adds further complexities, associated with sensitivities by the individual interpreter.&amp;#160; Hence, interpreting at a finer scale may not necessarily improve the subsurface model and any related analysis, but in fact lead to the production of highly irregular surfaces, which impacts any further fault analysis.&amp;#160; Interpreting on spacing greater than 100 m often leads to overly smoothed fault surfaces that miss details that could be crucial, both for fault seal / stability as well as for fault growth models.&lt;/p&gt;&lt;p&gt;Uncertainty associated with the chosen seismic interpretation methodology will follow through to subsequent fault seal analysis, such as analysis of whether in situ stresses, combined with increased pore pressure through CO&lt;sub&gt;2&lt;/sub&gt; injection, will act to reactivate the faults, leading to up-fault fluid flow / seep.&amp;#160; We have shown that changing picking strategies significantly alters the interpreted stability of the fault, where picking with an increased line spacing has shown to increase the overall fault stability, and picking using every line leads to the interpretation of a critically stressed fault.&amp;#160; Alternatively, it is important to note that differences in picking strategy show little influence on the overall predicted fault membrane seal (i.e. shale gouge ratio) of the fault, used when interpreting the fault seal capacity for a fault bound CO&lt;sub&gt;2&lt;/sub&gt; storage site.&lt;/p&gt;

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