STRUCTURAL AND SEISMIC DEFORMATIONS ALONG NORMAL FAULTS IN THE EASTERN VENEZUELAN BASIN

Geophysics ◽  
1956 ◽  
Vol 21 (2) ◽  
pp. 368-387 ◽  
Author(s):  
Hans P. Laubscher
Keyword(s):  
Fault Zone ◽  
Normal Fault ◽  
Fault Zones ◽  
Fault Analysis ◽  
Structural Deformation ◽  
Normal Faults ◽  
Seismic Deformations ◽  
Structural Deformations ◽  
Fault Structures ◽  
Seismic Reflections

Seismic reflections in normal fault zones in the Eastern Venezuelan basin usually appear distorted. Studies of reflections over fault structures delineated by drilling indicate that this is due to the similar effects of two entirely different phenomena: 1. True structural deformation of beds on the downthrown side. 2. Purely seismic distortion of reflections from underneath the fault. Analysis indicates that the structural deformations form an integral part of the fault zone; the purely seismic distortion is caused by passage of the wave through this zone of deformation.

scholarly journals The Morphotectono-Volcanic of Menoreh-Gajah-Ijo Volcanic Rock In Western Side of Yogyakarta-Indonesia

2018 ◽  
Vol 3 (3) ◽  
pp. 155
Author(s):  
Asmoro Widagdo ◽  
Subagyo Pramumijoyo ◽  
Agung Harijoko
Keyword(s):  
Volcanic Rocks ◽  
Normal Fault ◽  
Normal Faults ◽  
Body Distribution ◽  
Circular Structure ◽  
Volcanic Processes ◽  
Fault Structures ◽  
Western Side ◽  
Slope Direction ◽  
Volcanic Body

Menoreh-Gajah-Ijo have a very distinctive shape, where there are form of circular structure of volcano that is still intact and the other has not been intact. These morphologies are the morphology of the remaining volcanoes formed by tectonics and certain volcanisms. This study was conducted through a series of interpretations of volcanic body distribution, constructing a Slope Map, constructing a Slope Direction Map, constructing an alignment interpretation on satellite imagery and field mapping work. The formation of Menoreh-Gajah-Ijo morphologies are strongly influenced by tectonics and volcanic processes. The process of tectonism that produces the strike-slip fault structures, the normal faults, and the uplift have formed the lineaments of the valleys and hills with various directions patterns. The Menoreh-Gajah-Ijo volcanisms that have occurred form the structure of volcanic remains. Distribution of Menoreh-Gajah-Ijo volcanic rocks form some semicircle structures because of the normal fault structure that has occurred.

3D geometry of outcrop-scale normal faults from Taranaki, New Zealand

2020 ◽  
Author(s):  
Inbar Vaknin ◽  
Andy Nicol ◽  
Conrad Childs
Keyword(s):  
New Zealand ◽  
Fault Zone ◽  
Slip Surface ◽  
Geometric Model ◽  
Fault Zones ◽  
Normal Faults ◽  
Small Scale ◽  
Fault Geometry ◽  
Fault Rock ◽  
Fault Surface

<p>Fault surfaces and fault zones have been shown to have complex geometries comprising a range of morphologies including, segmentation, tip-line splays and slip-surface corrugations (e.g., Childs et al., 2009*). The three-dimensional (3D) geometries of faults (and fault zones) is difficult to determine from outcrop data which are typically 2D and limited in size. In this poster we examine the small-scale geometries of faults from normal faults cropping out in well bedded parts of the Mount Messenger and Mahakatino formations in Taranaki, New Zealand. We present two main datasets; i) measurements and maps of 2D vertical and horizontal sections for in excess of 200 faults and, ii) 3D fault model of a small-fault (vertical displacement ~1 cm) produced by serial fault-perpendicular sections of a block 10x10x13 cm. The sectioned block contains a single fault that offsets sand and silt layers, and comprises two main dilational bends; in the 3D model we map displacement, bedding and fault geometry for the sectioned fault zone. Faults in the 2D dataset comprise a range of geometries including, vertical segmentation, bends, splays and fault-surface corrugations. Although we have little information on the local magnitudes and orientations of stresses during faulting, geometric analysis of the fault zones provides information on the relationships between bed characteristics (e.g., thickness, induration and composition) and fault-surface orientations. The available data supports the view that the strike and dip of fault surfaces vary by up to 25° producing undulations or corrugations on fault surfaces over a range of scales from millimetres to metres and in both horizontal and vertical directions. Preliminary analysis of the available data suggests that these corrugations appear to reflect fault refractions due to changing bed lithologies (unexpectedly the steepest sections of faults are in mudstone beds), breaching of relays and development of conjugate fault sets. The relative importance of these factors and their importance for fault geometry will be explored further in the poster.</p><p> </p><p>*Childs, C., Walsh, J.J., Manzocchi, T., Bonson, C., Nicol A., Schöpfer, M.P.J. 2009. A geometric model of fault zone and fault rock thickness variations. Journal of Structural Geology 31, 117-127.</p>

scholarly journals Mechanisms of clay smear formation in unconsolidated sediments – insights from 3-D observations of excavated normal faults

Solid Earth ◽  
2016 ◽  
Vol 7 (3) ◽  
pp. 789-815 ◽  
Author(s):  
Michael Kettermann ◽  
Sebastian Thronberens ◽  
Oscar Juarez ◽  
Janos Lajos Urai ◽  
Martin Ziegler ◽  
...  
Keyword(s):  
Microscopic Study ◽  
Thickness Distribution ◽  
Normal Fault ◽  
Fault Zones ◽  
Unconsolidated Sediments ◽  
Normal Faults ◽  
Low Permeability ◽  
Lignite Mine ◽  
Log Normal ◽  
Open Cast

Abstract. Clay smears in normal faults can form seals for hydrocarbons and groundwater, and their prediction in the subsurface is an important problem in applied and basic geoscience. However, neither their complex 3-D structure, nor their processes of formation or destruction are well understood, and outcrop studies to date are mainly 2-D. We present a 3-D study of an excavated normal fault with clay smear, together with both source layers, in unlithified sand and clay of the Hambach open-cast lignite mine in Germany. The faults formed at a depth of 150 m, and have shale gouge ratios between 0.1 and 0.3. The fault zones are layered, with sheared sand, sheared clay and tectonically mixed sand–clay gouge. The thickness of clay smears in two excavated fault zones of 1.8 and 3.8 m2 is approximately log-normal, with values between 5 mm and 5 cm, without holes. The 3-D thickness distribution is heterogeneous. We show that clay smears are strongly affected by R and R' shears, mostly at the footwall side. These shears can locally cross and offset clay smears, forming holes in the clay smear, while thinning of the clay smear by shearing in the fault core is less important. The thinnest parts of the clay smears are often located close to source layer cut-offs. Locally, the clay smear consists of overlapping patches of sheared clay, separated by sheared sand. More commonly, it is one amalgamated zone of sheared sand and clay. A microscopic study of fault-zone samples shows that grain-scale mixing can lead to thickening of the low permeability smears, which may lead to resealing of holes.

scholarly journals Structural characterization of fault damage zones in carbonates (Central Apennines, Italy)

2021 ◽  
Author(s):  
Miriana Chinello ◽  
Michele Fondriest ◽  
Giulio Di Toro
Keyword(s):  
Fault Zone ◽  
Hanging Wall ◽  
Damage Zone ◽  
Normal Fault ◽  
Vertical Displacement ◽  
Fault System ◽  
Normal Faults ◽  
Central Apennines ◽  
Fault Surface ◽  
Fracture Intensity

<p>The Italian Central Apennines are one of the most seismically active areas in the Mediterranean (e.g., L’Aquila 2009, Mw 6.3 earthquake). The mainshocks and the aftershocks of these earthquake sequences propagate and often nucleate in fault zones cutting km-thick limestones and dolostones formations. An impressive feature of these faults is the presence, at their footwall, of few meters to hundreds of meters thick damage zones. However, the mechanism of formation of these damage zones and their role during (1) individual seismic ruptures (e.g., rupture arrest), (2) seismic sequences (e.g., aftershock evolution) and (3) seismic cycle (e.g., long term fault zone healing) are unknown. This limitation is also due to the lack of knowledge regarding the distribution, along strike and with depth, of damage with wall rock lithology, geometrical characteristics (fault length, inherited structures, etc.) and kinematic properties (cumulative displacement, strain rate, etc.) of the associated main faults.</p><p>Previous high-resolution field structural surveys were performed on the Vado di Corno Fault Zone, a segment of the ca. 20 km long Campo Imperatore normal fault system, which accommodated ~ 1500 m of vertical displacement (Fondriest et al., 2020). The damage zone was up to 400 m thick and dominated by intensely fractured (1-2 cm spaced joints) dolomitized limestones with the thickest volumes at fault oversteps and where the fault cuts through an older thrust zone. Here we describe two minor faults located in the same area (Central Apennines), but with shorter length along strike. They both strike NNW-SSE and accommodated a vertical displacement of ~300 m.</p><p>The Subequana Valley Fault is about 9 km long and consists of multiple segments disposed in an en-echelon array. The fault juxtaposes pelagic limestones at the footwall and quaternary deposits at the hanging wall. The damage zone is < 25 m  thick  and comprises fractured (1-2 cm spaced joints) limestones beds with decreasing fracture intensity moving away from the master fault. However, the damage zone thickness increases up to ∼100 m in proximity of subsidiary faults striking NNE-SSW. The latter could be reactivated inherited structures.</p><p>The Monte Capo di Serre Fault is about 8 km long and characterized by a sharp ultra-polished master fault surface which cuts locally dolomitized Jurassic platform limestones. The damage zone is up to 120 m thick and cut by 10-20 cm spaced joints, but it reaches an higher fracture intensity where is cut by subsidiary, possibly inherited, faults striking NNE-SSW.</p><p>Based on these preliminary observations, faults with similar displacement show comparable damage zone thicknesses. The most relevant damage zone thickness variations are related to geometrical complexities rather than changes in lithology (platform vs pelagic carbonates).  In particular, the largest values of damage zone thickness and fracture intensity occur at fault overstep or are associated to inherited structures. The latter, by acting as strong or weak barriers (sensu Das and Aki, 1977) during the propagation of seismic ruptures, have a key role in the formation of damage zones and the growth of normal faults.</p>

Geometrical comparison of outcrop data and discrete element models of extensional fault zones in layered carbonates

2020 ◽  
Author(s):  
Hagen Deckert ◽  
Steffen Abe ◽  
Wolfgang Bauer
Keyword(s):  
Fluid Flow ◽  
Fault Zone ◽  
Seismic Data ◽  
Discrete Element ◽  
Fault Zones ◽  
Normal Faults ◽  
Small Displacement ◽  
Small Scale ◽  
Burial Depth ◽  
Multiple Fault

<p>In the course of hydrocarbon or geothermal exploration the characterisation of fault zone architectures is of interest for fluid flow modelling and geomechanical studies. Seismic data normally offer the best information for the identification of fault zone geometries in sedimentary basins. However, the internal structure or the damage zone of a fault can be hardly resolved with seismic data as displacements along single fault strands or fractures are by far too small. Thus, it is not possible to directly map small scale faults with seismic methods, though these structures might significantly influence fluid flow. We try to examine the architecture of extensional fault zones in carbonate rocks at subseismic scales by using discrete element method (DEM) techniques to numerically simulate the evolution of fault zones including their associated damage zones.</p><p>As a case study we have analysed the geometry, displacement and fault width of normal faults in fine grained jurassic limestones in a quarry in Franconia, Germany. The quarry shows a rather simple set of conjugated 60deg dipping normal faults. Displacement is rather small and varies between c. 5cm up to c. 2m, some faults show almost no offset. The fault thickness varies between 2cm and c. 1m. A closer investigation of the fault geometries reveals, next to planar parts, sometimes complex fault zone structures including restraining and releasing bends, multiple fault strands as well as lenses and associated riedel shears. Analysis of high resolution photogrammetric data revealed a high number of small scale fractures between neighbouring discrete fault surfaces which are interpreted as highly fractured damage zones. Some faults with rather small displacement suggest that the overall inclination of the fault is a result of small subvertical sections which are connected in a staircase like appearance. </p><p>The DEM models simulate normal faulting in a layered marl-limestone sequence driven by the displacement of an underlying basement fault. Different layer geometries and effective vertical stresses in the range of 15-45 MPa, equivalent to an overburden thickness of c. 1000-3000m, have been used in the models. The stress range covers the maximum burial depth of the carbonates, which is assumed to be c. 1500m. Material properties used in the DEM were calibrated based on laboratory data, i.e. results of triaxial deformation tests on the studied limestones.</p><p>Results of the models show fault geometries which resemble those observed in the studied outcrop. In particularly under low stress, small offsets and with strongly decoupled layers we observe steeply dipping faults (>70deg) which also show staircase structures composed of sub-vertical fractures within each of the layers and horizontal offsets along the layer interfaces. We also observe the development of multiple fault strands and associated damage zones. </p><p>Our study shows that the DEM models are capable to reproduce observed fault geometries and damage zones. The results help to understand fault zone architectures and depict highly fractured areas in a sub-seismic scale.</p>

Large near-surface block rotations at normal faults of the Iceland rift: Evolution of tectonic caves and dilatancy

Geology ◽  
2019 ◽  
Vol 47 (8) ◽  
pp. 781-785 ◽  
Author(s):  
Michael Kettermann ◽  
Christopher Weismüller ◽  
Christoph von Hagke ◽  
Klaus Reicherter ◽  
Janos L. Urai
Keyword(s):  
High Resolution ◽  
Plate Boundary ◽  
Normal Fault ◽  
Fault Zones ◽  
Normal Faults ◽  
Failure Zone ◽  
Near Surface ◽  
Modeling Studies ◽  
The Family ◽  
Aerial Vehicle

Abstract Surface ramps in normal fault zones of the Iceland plate boundary have been described in many studies, but their structure and evolution are not well understood. We show that surface ramps are manifestations of large tilted blocks (TBs) formed in dip relays of normal faults. Based on existing modeling studies, we propose three classes of TBs defined by kinematics and location of the hinge of the TB. TBs are considered a member of the family of fault relay structures that form near the surface, commonly, but not exclusively, in columnar basalts with orthotropic strength. We present high-resolution aerial vehicle–based observations of a representative set of normal faults in Iceland and compare these with geometric models we derived from modeling studies. We predict extensive tectonic cave (fluid conduit) systems under the TB, which interact with magma and groundwater flow. The general fault structure is dominated by large, subvertical open fractures reactivating cooling joints that are locally filled by basalt rubble. We propose the existence of a hybrid failure zone at larger depths before the effective vertical stress is sufficient to initiate shear fractures in intact basalt.

Evolution of Faulting Induced by Deep Fluid Injection, Paradox Valley, Colorado

2020 ◽  
Vol 110 (5) ◽  
pp. 2308-2327 ◽  
Author(s):  
Roger P. Denlinger ◽  
Daniel R. H. O’Connell
Keyword(s):  
Fault Zone ◽  
Induced Seismicity ◽  
Fault Zones ◽  
Focal Mechanisms ◽  
Fault System ◽  
Fluid Injection ◽  
Normal Faults ◽  
Failure Condition ◽  
Planar Fault ◽  
Failure Conditions

ABSTRACT High-pressure fluid injection into a subhorizontal confined aquifer at 4.3–4.6 km depth induced >7000 earthquakes between 1991 and 2012 within once seismically quiescent Paradox Valley in Colorado, with magnitudes up to Mw 3.9. Earthquake hypocenters expanded laterally away from the well with time, defining the margins of the aquifer pressurized by injection at the well. Within 5 km of the well, alignment of earthquake hypocenters defines strikes of nine vertical fault zones. Previous studies show that these fault zones predate injection, producing left-stepping offsets in the normal faults of the Wray-Mesa fault system that cradles Paradox Valley. Hypocenters, rakes, and strikes of 2041 well-constrained focal mechanisms show that most injection-related earthquakes occur where these vertical faults intersect the pressurized aquifer. Well-defined focal mechanisms show that this induced seismicity consists of Riedel shear faults at acute angles to the strikes of these fault zones. These small faults develop an anastomosing fault structure of focal planes along each planar fault zone, as fluid injection continues, even as their hypocenters define a single planar fault zone. Failure conditions at each hypocenter are found using a fully coupled poroelastic analysis of stress induced by fluid injection, and this analysis indicates a minimum Coulomb failure condition of 0.1 MPa. This failure condition is primarily a result of aquifer pore-fluid pressurization, as almost all well-located seismicity is within the pressurized aquifer. Reducing the rate of injection and frequent well shutdowns in the second decade nearly eliminated induced seismicity, except very near the well where gradients in pressurization are the largest. Despite these decreases in failure conditions and seismicity, some fault zones continued to produce earthquakes larger than M 3 as injection continued.

Tectonic evolution in the early to Middle Pleistocene off the east coast of the Boso Peninsula, Japan

2020 ◽  
pp. SP505-2019-116
Author(s):  
Seishiro Furuyama ◽  
Tomoyuki Sato ◽  
Kohsaku Arai ◽  
Masanori Ozaki
Keyword(s):  
Fault Zone ◽  
Normal Fault ◽  
Early Pleistocene ◽  
Philippine Sea Plate ◽  
Middle Pleistocene ◽  
Normal Faults ◽  
Shelf Area ◽  
Boso Peninsula ◽  
Kanto Basin ◽  
Uplift Zone

AbstractThe Kanto Basin developed, starting c. 3 Ma, influenced by the subduction of the Philippine Sea plate and the Pacific plate. Sediments in this basin have influenced the geomorphology of the Kanto region. In the Boso Peninsula, located at the eastern edge of the Kanto Basin, uplift continues in what is called the Kashima–Boso uplift zone. Although the development of this uplift after the Late Pleistocene is well understood, there are few data from the Early to Middle Pleistocene. In this study, we investigated the offshore shelf area east of the Boso Peninsula using a high-resolution seismic reflection survey, and report new information on the geological structure and uplift processes in the area from the Early to Middle Pleistocene. We identified the Kujukuri-oki anticline and the Kujukuri-oki normal fault zone. The Kujukuri-oki anticline, more than 47 km long, is north–south striking and deforms the Kujukuri-oki Group. There are numerous normal faults with displacements of less than tens of metres spread widely in the survey area (Kujukuri-oki normal fault zone). These findings reveal that the Kujukuri-oki anticline uplifted during the end of the Early Pleistocene and attenuated during the Middle Pleistocene. This anticline comprised the axis of the Kashima–Boso uplift zone at the Boso Peninsula from the Early to Middle Pleistocene and the Boso Peninsula is located at the western limb of this anticline.

scholarly journals Mechanisms of clay smear formation in unconsolidated sediments – insights from 3D observations of excavated normal faults

2016 ◽  
Author(s):  
Michael Kettermann ◽  
Sebastian Thronberens ◽  
Oscar Juarez ◽  
Janos Lajos Urai ◽  
Martin Ziegler ◽  
...  
Keyword(s):  
Thickness Distribution ◽  
3D Structure ◽  
Normal Fault ◽  
Fault Zones ◽  
Unconsolidated Sediments ◽  
Normal Faults ◽  
Low Permeability ◽  
Lignite Mine ◽  
Log Normal ◽  
Open Cast

Abstract. Clay smears in normal faults can form seals for hydrocarbons and groundwater, and their prediction in the subsurface is an important problem in applied and basic geoscience. However, neither their complex 3D structure, nor their processes of formation or destruction are well understood, and outcrop studies to date are mainly 2D. We present a 3D study of an excavated normal fault with clay smear, together with both source layers, in unlithified sand and clay of the Hambach open cast lignite mine in Germany. The faults formed at a depth of 150 m, and have Shale Gouge Ratios between 0.1 and 0.3. The fault zones are layered, with sheared sand, sheared clay and tectonically mixed sand-clay gouge. Thickness of clay smears in two excavated fault zones of 1.8 and 3.8 m2 is approximately log-normal, with values between 5 mm and 5 cm, without holes. The 3D thickness distribution is heterogeneous. We show that clay smears are strongly affected by R- and R'-shears, mostly at the footwall side. These shears can locally cross and offset clay smears, forming holes in the clay smear, while thinning of the clay smear by shearing in the fault core is less important. Thinnest parts of the clay smears are often located close to source layer cutoffs. Locally, the clay smear consists of overlapping patches of sheared clay, separated by sheared sand. More commonly, it is one amalgamated zone of shared sand and clay. Microscopic study of fault zone samples shows that grain-scale mixing can lead to thickening of the low permeability smears, which may lead to resealing of holes.

scholarly journals SEGMENTATION AND INTERACTION OF NORMAL FAULTS IN CENTRAL GREECE

2017 ◽  
Vol 43 (1) ◽  
pp. 428 ◽  
Author(s):  
S. Kokkalas
Keyword(s):  
Scaling Laws ◽  
Normal Fault ◽  
Fault Zones ◽  
Segment Length ◽  
Normal Faults ◽  
Mechanical Interaction ◽  
Fault Segment ◽  
Central Greece ◽  
Fault Length ◽  
Radial Propagation

The aim of this study is to improve our understanding on the mechanical interaction and linkage process between normal fault segments. Faults grow by the process of radial propagation and the linkage of segments, as strain increases, evolving to large fault systems. For this purpose we conducted a combined field and photogeological study on two major segmented fault zones in Central Greece, the Atalanti and Arkitsa fault zones. This approach includes effects of fault size and spatial distribution, scaling laws and footwall-hanginwall topography. Throw distribution and the geometry of the segmented fault arrays were analyzed in order to investigate the complexity of fault zones, the fault linkage process and the geometric characteristics of the relay zones formed between individual segments. The correlation of fault throw with fault length (D-L) and the ratios of overlap-separation (OL-S), separation-fault segment length (S-L) and relay displacement vs. separation (Dr-S) were examined in order to give an insight for fault segment interaction and linkage .

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