Footwall Block Research Articles

Numerical modeling of brittle tectonic deformation in poorly consolidated sandstones

This work presents the results of a study about the effects of brittle deformation on the distribution of porosity and permeability in poorly consolidated sandstones. The study was carried out in an outcrop of the Resende Formation, located in the Volta Redonda Basin (State of Rio de Janeiro, Brazil), which has been described by other authors as a geomechanical analog of poorly consolidated Maastrichtian sandstone reservoirs in the Campos Basin. This outcrop is composed of fluvial deposits of poorly consolidated sandstones interlayered with green siltstones, characteristics of the Resende Formation. According to previous works on the outcrop, the deformation that operated in these deposits results from the superposition of three of the tectonic events that occurred in the Volta Redonda Basin – a right-lateral strike-slip deformational event (TD), a left-lateral strike-slip deformational event (TS), and finally a Holocene extensional event (E2). These events produced a graben structure, several minor secondary faults and deformation band zones. To better understand how the evolving process of those structures affected the distribution of the original porosity and permeability through the outcrop, a series of finite element numerical models were done in this study, based on the continuum mechanics. In these models, only the final extensional tectonic event in the Volta Redonda Basin, E2, was considered. Results showed a higher volumetric loss caused by deformational compaction in the hanging wall of the main outcrop structures. These models are consistent with the permeability distribution measured in the outcrop and with the observed rock-staining patterns derived from the iron-precipitation process associated with zones of restricted fluid flow, and reveal notable differences concerning tectonic strain distribution between the hanging wall and footwall blocks. Although the uncertainty in the geomechanical parameters is a challenge, the technique can improve geological modeling of reservoirs for exploratory purposes, especially in poorly consolidated and fractured sandstones related to the extensional structural style of Brazilian offshore basins.

The Miocene stratigraphy of the Laberinto area (Río Ica Valley) and its bearing on the geological history of the East Pisco Basin (south-central Peru)

Global sea-level changes and substantial vertical displacement along the Monte Grande Fault (MGF) in the lower Río Ica Valley of south-central Peru influenced the accumulation of bioclast-bearing and diatom-bearing Miocene siliciclastic sediments in an area of the East Pisco forearc basin (EPB) colloquially known as Laberinto. Two depositional hiatuses in the Laberinto area (~17–14 Ma, ~12.5–10 Ma) manifest as sediment-filled erosional depressions a few kilometers in breadth. Erosion of the older depression was preceded by an ~18-Ma massive debris flow, possibly triggered by motion on the MGF causing lower Miocene lithoclastic olistoliths of up to two hundred meters length to spill off the footwall block. Sediment shed from the same footwall block may have formed previously recognized early Miocene deltas. From 14 to 13 Ma, the older depression filled with sediments herein assigned to the provisionally named Laberinto, Pampa, and Naranja members of the Pisco Formation, the latter member being characterized by marine delta foreset beds. The three members are at least partly correlative with the Pisco-0 sequence of the Pisco Formation. The younger depression was overrun at 10 Ma by debris flows of lithoclastic and granitic cobbles and boulders, then filled with diatomaceous silty sand with 5-m-sized lithoclastic olistoliths. The two lithologies constitute the provisionally named Mature Formation. Radiometric and newly revised biochronological data from throughout the EPB coupled with new diatom data from the Laberinto area have provided new insights into the correlation of sequences within the Chilcatay and Pisco formations and the interaction of local and basin-wide tectonism and global eustatic sea-level events across the basin.

Morphometric properties of river basins as indicators of relative tectonic activity – Problems of data handling and interpretation

Morphometric properties of drainage basins, expressed as indices related to their shapes, altitude variability, river networks and stream profiles, are frequently used as proxy information concerning the relative intensity of uplift. Research procedures lead towards division of an area into classes of relative tectonic activity (various rates of surface uplift) and are typically based on compound indices that jointly consider various individual parameters. Given that index approaches are quantitative in nature and comprise large sets of data, their statistical treatment should become an inherent component of the workflow, whereby the results of the statistical analyses should guide the conclusions. However, various data handling issues seem to be seldom addressed or are given inadequate attention. They include selection of variables, correlation analysis, principles of classification in terms of relative tectonic activity, validity of classifications, and criteria for using specific statistical procedures. In this paper we demonstrate the need for rigorous statistical data analysis in a morphometric study, focused on an intraplate mountainous terrain in Central Europe (Orlickie-Bystrzyckie Mountains Block), subject to low or moderate uplift. We analysed 56 drainage basins within the footwall blocks of several prominent fault-generated escarpments. Following literature guidance, the hypsometric and shape characteristics of the drainage basins were considered, whereas clustering and pure-rank based approaches were tested to distinguish classes of relative tectonic activity. The results were compared with indicators of tectonic activity calculated for the escarpments themselves and using DEM-derived terrain attributes indicating enhanced erosion. In addition, we used statistical tests to identify possible lithological influence on the variability of morphometric parameters, which in this study was found to be of secondary importance. Statistical considerations neither allowed for unequivocal classification of drainage basins in terms of relative tectonic activity, nor did they reveal a clear spatial distribution pattern of drainage basins with different morphometric characteristics, typically considered to reflect tectonic forcing. Thus, statistics-based analysis is recommended to avoid the risk of over-interpretation. It is also possible that the likely morphometric signature of tectonically less active settings comprises spatially inconsistent information rather than it is typified by consistently low values of various morphometric parameters.

Fault motion reversals predating the M w 6.3 2009 L'Aquila earthquake: insights from synthetic aperture radar data

The millimetre accuracy of Synthetic Aperture Radar (SAR) measurements and related multi-temporal data analyses provide fundamental information on surface displacements caused by strong earthquakes. The multi-temporal analysis of SAR interferometry data allows for the geometry, kinematics and temporal behaviour of earthquake-generating faults to be better constrained, and is being acknowledged as a promising technique in the field of earthquake precursors. We used SAR data obtained by multi-temporal interferometric techniques such as Permanent Scatterers (PS) interferometry for the investigation of pre- to post-seismic ground displacements in the region struck by the M w 6.3, 2009 L'Aquila earthquake. We analysed Europen Remote Sensing (ERS) and Envisat PS-datasets from ascending and descending orbits, and COSMO-SkyMed PS-datasets from descending orbit, collectively covering a > 20 year long time span. On a yearly scale, a reversal of motions that affected the hanging-wall and footwall blocks of the earthquake-generating fault is detected. In particular, the hanging-wall block is characterized by pre-seismic uplift – which we document as being independent of any hydrological control – and eastward horizontal motion for about six years, followed by subsidence and westward motion (starting six to eight months prior to the earthquake). We suggest that such a ground displacement pattern may represent an earthquake precursor signal. Supplementary material: Figures showing SAR satellites viewing geometry, examples of raw PS time series of obtained from ERS ascending and descending orbits and maps of LoS-oriented mean velocities obtained from PS datasets from the Envisat ascending and descending orbits and a Table reporting detailed numerical results of the performed statistical analysis are available at https://doi.org/10.6084/m9.figshare.c.5289357

Fault-controlled contourite drifts in the southern South China Sea: Tectonic, oceanographic, and conceptual implications

Over the past decades, contourite drifts have been widely identified in the deep ocean with their classification constantly being improved. Some contourite drift types, however, are not yet well constrained. The present study investigates contourite drifts in the southern South China Sea for the first time based on high-resolution reflection seismic profiles and bathymetric data, thereby determining the common occurrence of a lesser-known type: the “fault-controlled drift.” In this area, normal fault movements have been active during the Quaternary, associated with the formation of sea-floor irregularities and highs that represented obstacles to Deep Water circulation. Six fault-controlled drifts are generated in the study area due to interactions between regional faulting/fault-generated topography and bottom currents. They are divided into two major types depending on their shapes, locations, and relative faulting movements: Type-1) drifts deposited coeval to the fault movement and are situated over the footwall block top or along the fault scarp, and Type-2) drifts deposited after the fault movement and are located along the fault scarp base. Spatial distribution of these drifts is a result of variations on bottom currents dynamics associated with the South China Sea Deep Water. The South China Sea Deep Water settling depth, 200–300 m shallower than that of the northern South China Sea, tentatively indicates upwelling which may have, in turn, contributed to the South China Sea meridional overturning circulation. The present study demonstrates new types of contourite drifts that are not well-constrained in the literature and require more detailed studies. The types of fault-controlled drift are described based on the relative movement of normal faults. However, future research should be conducted in other active tectonic settings for evaluating fault effects on the sedimentary stacking patterns, geometries, and evolution of contourite drifts.

Micropalaeontological analysis and palaeoenvironmental interpretation of the upper sedimentary sequence of Corinth Marl (Corinth Isthmus, Greece)

The current study performs a detailed micropalaeontological analysis, in terms of ostracods, benthic foraminifera and calcareous nannoplankton, in order to reconstruct the palaeoenvironmental history of the sedimentary sequence exposed in the central part of Corinth Isthmus. Twenty one samples from two lateral sections were studied, on both sides of a westwards dipping normal fault at the west end of the central horst, which are part of the same stratigraphical sequence. The calcareous nannofossil analysis provided for the first time dating evidence for the upper Corinth Marl sequence, revealing that Section A (at the footwall block of the fault/the upper part of the Corinth Marl) is attributed to the Early Pleistocene /Calabrian (nannofossil biozone MNN19f) and that Section B (at the hanging wall of the fault) is assigned to the Middle Pleistocene /Chibanian (MNN20). Both parts of the studied sequence not only differentiate in age but bear notably separated species composition of the main ostracod assemblages as well. The combined study of ostracod and benthic foraminiferal microfaunas indicated that at least since Early Pleistocene the Corinth Marl deposits at the central part of Corinth Isthmus corresponded to a shallow, restricted, oligohaline lagoon with salinity alternations expressed as layers enriched in nannofossil content. Towards Middle Pleistocene the lagoon presented increased salinity and signs of shoaling. The studied sequence closes upwards with a bed of Middle Pleistocene age, rich in marine molluscs and corals indicating a radical environmental change: the opening of the lagoon and the establishment of a shallow marine coastal environment.

Structural Complexity and Mechanics of a Shallow Crustal Seismogenic Source (Vado di Corno Fault Zone, Italy)

AbstractThe mechanics and seismogenic behavior of fault zones are strongly influenced by their internal structure. In this perspective, the internal structure of the extensional seismically active Vado di Corno Fault Zone (VCFZ, Central Apennines, Italy) was quantified by combining high‐resolution structural mapping with 3‐D fault network analysis over ∼2 km along fault strike. The fault zone was exhumed from ∼2 km depth in carbonate rocks, accommodated 1.5–2 km of extensional throw since Early Pleistocene, and cuts through the Pliocene Omo Morto Thrust Zone (OMTZ) with partial reactivation in extension. The exceptional exposure of the footwall block allowed us to reconstruct in detail the geometry of the OMTZ and quantify the spatial arrangement of master/subsidiary faults and fault zone rocks within the extensional VCFZ. The combination of the structural map and the 3‐D fault network with kinematic and topological analyses pointed out the crucial role of the older thrust geometry (i.e., lateral ramps) in controlling the along‐strike segmentation and slip distribution of the VCFZ. These observations were discussed in the framework of regional extension through a slip tendency analysis and a simplified mechanical model, which suggest the activation of oblique inherited structures during the lateral propagation of the VCFZ segments. The interaction of the VCFZ with the OMTZ generated along strike and possibly downdip mechanical asperities. Considering the exhumed VCFZ as an analog for the shallow structure of other seismic sources in the Central Apennines, similar settings could play first‐order control on the spatio‐temporal evolution and rupture heterogeneity of earthquakes in the region.

A three-dimensional (3D) structural model for an oil-producing basin of the Brazilian equatorial margin

Hydrocarbon discoveries in Equatorial Brazil, Equatorial Africa and French Guiana-Suriname-Guyana have recently confirmed their importance as new exploration frontiers. The Mundaú sub-basin, located on the Brazilian Equatorial Margin, comprises four producing fields in shallow waters: Xaréu, Atum, Espada e Curimã. In order to understand the structural and seismic-stratigraphic frameworks of an oil-producing region in Equatorial Brazil, this work addresses the 3D geometry and spatial distribution of main faults in the Curimã and Espada fields. The occurrence of hydrocarbons in the Mundaú sub-basin is compared with fields in other parts of the Brazilian Equatorial Margin and Equatorial Africa. Data from 12 wells and a 3D post-stack time-migrated multichannel seismic volume are used to define nine (9) seismic-stratigraphic units: the syn-rift Mundaú Formation (Units 1, 2, 3 and 4); the transitional Paracuru Formation (Unit 5); and the drift Ubarana (Uruburetama and Itapagé Members, Units 6 and 7), Tibau and Guamaré Formations (Units 8 and 9). The study area is dominated by NW-SE planar normal faults, basinward-dipping, that form multiple half-grabens, and tilted blocks with small anticlines and synclines genetically related to a transtensional system. Three types of plays are recognised in the Mundaú sub-basins: structural, combined (structural-stratigraphic) and stratigraphic (turbiditic). In the eastern part of the study area, where the basement is shallow, no oil was found. Conversely, oil was discovered in an anticlinal trap formed over a hanging-wall block analogous to fields on the Côte D'Ivoire-Ghana transform margin. This work shows that combined traps on footwall blocks are successful plays near the shelf break of the Mundaú sub-basin, in similarity with the Espoir and Baobab fields in Ivory Coast. Furthermore, turbiditic reservoirs in drift units are analogous to the Stabroek block in Guyana and prospects in the Gulf of Guinea. The structural and petroleum-play analyses in this work are therefore crucial to understand the multiple geological processes leading to the trapping of hydrocarbons in the larger Equatorial Atlantic Ocean.

Abutting faults: a case study of the evolution of strain at Courthouse branch point, Moab Fault, Utah

Abstract. Slip planes and slip directions of subsequent generations of faults were measured and analysed in the interaction damage zone of two abutting faults in porous sandstones in order to understand the palaeostress/palaeostrain evolution. The Courthouse branch point of the Moab Fault in SE Utah (USA) is a much-studied, spectacular outcrop of two abutting faults, located in the footwall block of the main fault and in the hanging wall block of the abutting fault. The abutting fault is synthetic to the main fault. The outcrop shows a wide range of deformation structures and fault-related diagenesis such as striated slip planes, deformation bands, veins, Liesegang bands and copper-rich mineralization. By combining our own measurements with published data on the relative age of these structures, we classified the data in four sets. Using a Numeric Dynamic Analysis (NDA) to calculate the orientation of the kinematic axes we found three different palaeo-extension directions in the four sets, recording the evolution of stress/strain axes during the abutting process. The first phase of deformation is regional extension in the NE–SW direction. As the second fault approached the main fault from its footwall side and the two faults started to become kinematically linked, the extension direction changed so that the overall extension became perpendicular to the approaching fault (NW–SE). Finally, the extension direction changed back to being perpendicular to the first segment (NE–SW) when the two faults became geometrically linked and regional extension became dominant again.

Exhumation history of the north-central Shanxi Rift, North China, revealed by low-temperature thermochronology

We present new apatite U-Th-Sm/He (AHe; n = 51), apatite fission track data (AFT; n = 12), and zircon U-Th/He (ZHe; n = 8) data for two elevation transects in the north-central Shanxi Rift, North China. Low-temperature thermochronologic data combined with forward and inverse time-temperature history models reveal a Precambrian to Quaternary thermal history characterized by: (1) cooling to <∼50°C during the Proterozoic, consistent with the development of a regional unconformity above Neoarchean–Paleoproterozoic cratonic basement rocks; (2) reheating to <∼180°C due to sediment burial during the Paleozoic to Mesozoic; (3) cooling at a rate >3.5°C/Ma during the Late Jurassic to earliest Cretaceous Yanshanian orogeny; (4) a possible ca. 120-90 Ma reheating event due to elevated geothermal gradients and/or local sediment burial; (5) Late Cretaceous (ca. 110-65 Ma) cooling contemporaneous with regional extension in eastern Asia and denudation of the paleo-Taihangshan highlands; and finally, (6) post ca. 10 Ma cooling associated with extension in the Shanxi Rift. AFT dates from the deepest exhumed structural positions of the sampled footwall blocks are mostly >65 Ma and AHe dates tend to be highly dispersed within samples. AFT inverse and AHe forward model results indicate that samples were at temperatures of <∼75°C by ca. 70 Ma. Despite the early Cenozoic and older AFT and AHe dates, metamict zircon grains with high effective uranium (eU >∼750 ppm) yield young ZHe dates of ca. 13-9 Ma, consistent with Late Miocene exhumation. We argue for the onset of latest cooling by ca. 10 Ma based on these ZHe dates; however, the precise timing for the onset of rifting remains uncertain. The results further suggest that Late Miocene–Quaternary extension in the north-central Shanxi Rift is responsible for ≤∼2.5 km of exhumation, such that published Quaternary extension and fault throw rates are significantly (>100%) higher than long-term rates inferred from the thermochronologic data.

A study of the relationship between the pressuremeter modulus and the preconsolidation pressure around a thrust fault

The study area is in a zone under the influence of the Lake Van water changes and the Van fault, which caused a destructive earthquake in 2011. Due to the level changes of Lake Van, sediments with different thicknesses as well as grain sizes were deposited in this region and the characteristics of these sediments were significantly affected by the morphology and lake water fluctuations in the past. A total of six boreholes were drilled along a 3-km line within the study area to determine the preconsolidation pressure (σpc) and the pressuremeter test values of the clayey levels of old lake deposits—which are known to have different physical and mechanical properties—with hopes to gain an insight on how they influence the mechanical tests performed in the field and in laboratory conditions. The relationship between these values was also statistically evaluated. When both datasets were evaluated together, it was determined that the stresses in the area close to the Van Thrust Fault plane caused deformations in the soil, which in turn affected the hanging-wall block of the thrust fault in particular. The inspection of EM and σpc values for the area within the primary compression zone of the Van Fault revealed that both values of the boreholes on the footwall block were higher compared to other boreholes close to the lake (southwest). This finding indicates that the fault stresses at the footwall block of the fault plane enhance the mechanical characteristics of the soil. The data obtained were also evaluated using regression analysis. Relationships between all available data were investigated and a high coefficient of determination was derived between the Menard deformation modulus (EM) and the preconsolidation (σpc) pressure.

Evolution of Low-Angle Normal Faults in the Enping Sag, the Northern South China Sea: Lateral Growth and Vertical Rotation

Low-angle normal faults (dip <30°, LANFs) are widespread in the northern margin of the South China Sea where the maximum crust thickness is approximately 30.0 km. Based on 3D seismic survey data and drilling wells in the Enping sag, evidences for LANFs that initially formed at high-angles are discussed. After a detailed investigation of extensional fault system and description of 3D fault geometry, the initial fault dips under the model of distributed vertical simple shear are also calculated. The results indicate that the present-day dip angles of the LANFs are in the range of 12° to 29°, and the initial fault dip angles are in the range of 39° to 49°. Deep seismic imaging suggests that the upper crust in the footwall block of the LANFs was tilted at an angle of ~14° to 22° due to the isostatic rebound during rifting. Moreover, the temporal and spatial sequences of the lateral growth of the LANFs have been investigated by the seismic interpretation of four isochronous stratigraphic interfaces, which demonstrates that two individual fault segments propagated towards each other and subsequently, were hard-linked during the Early Eocene.

Hidden Holocene Slip Along the Coastal El Yolki Fault in Central Chile and Its Possible Link With Megathrust Earthquakes

AbstractMegathrust earthquakes are commonly accompanied by increased upper‐plate seismicity and occasionally triggered fault slip. In Chile, crustal faults slipped during and after the 2010 Maule (M8.8) earthquake. We studied the El Yolki fault (EYOF), a transtensional structure midways the Maule rupture not triggered in 2010. We mapped a Holocene coastal plain using light detection and ranging, which did not reveal surface ruptures. However, the inner‐edge and shoreline angles along the coastal plain as well as 4.3‐ to 4.0‐ka intertidal sediments are back‐tilted on the EYOF footwall block, documenting 10 m of vertical displacement. These deformed markers imply ~2‐mm/year throw rate, and dislocation models a slip rate of 5.6 mm/year for the EYOF. In a 5‐m‐deep trench, the Holocene intertidal sediments onlap to five erosive steps, interpreted as staircase wave‐cut landforms formed by discrete events of relative sea level drop. We tentatively associated these steps with coseismic uplift during EYOF earthquakes between 4.3 and 4.0 ka. The Maule earthquake rupture may be subdivided into three subsegments based on coseismic slip and gravity anomalies. Coulomb stress transfer models predict neutral stress changes at the EYOF during the Maule earthquake but positive changes for a synthetic slip distribution at the central subsegment. If EYOF earthquakes were triggered by megathrust events, their slip distribution was probably focused in the central subsegment. Our study highlights the millennial variability of crustal faulting and the megathrust earthquake cycle in Chile, with global implications for assessing the hazards posed by hidden but potentially seismogenic coastal faults along subduction zones.

Seismic analysis of the gas hydrate system at Pointer Ridge offshore SW Taiwan

Pointer Ridge is a gas hydrate prospect on the South China Sea continental slope offshore SW Taiwan. It is characterized by densely distributed bottom simulating reflections (BSRs), active gas seepage, and potential sandy gas hydrate reservoirs. To understand how the fluids have migrated toward the seafloor, and the role of geological processes in the gas hydrate system, we have collected and analyzed high-quality 2D and 3D reflection seismic data. We first mapped the spatial distribution of the BSRs, and interpreted a major normal fault, Pointer Ridge Fault (PR Fault). The NE-SW trending fault dips to the east, and separates the erosional regime to the west from the depositional regime to the east. One active vent site was identified directly above the PR Fault, while another is located on a topographic high to the west of the fault. On the hanging block of the fault we found at least one major unconformity. The seismic data indicate refilled channels with coarser-grained sediments in the hanging wall of the normal fault. Seismic attribute analysis shows subsurface fluid conduits and potential gas hydrate reservoirs. We propose two types of gas chimneys, which are separated by the fault. Gas plumes derived from hydroacoustic data are mostly from the footwall block of the fault. We infer that fluid flow is more active in the erosional environment compared to the depositional one, and that this is the result of reduced overburden. The methane-bearing fluids migrate upward along the PR Fault and chimneys and form hydrates above the base of the gas hydrate stability zone. Based on seismic interpretation and seismic attribute analysis, we postulate that the channel infill constitutes the most promising hydrate reservoirs in this geological setting. In the surveyed area of Pointer Ridge these channels occur mainly below the gas hydrate stability zone.

Modelling reservoir deliverability within the Northern Beagle Sub-basin, Western Australia

Reservoir deliverability is a critical component affecting the viability of petroleum systems within a sedimentary basin. Deliverability can be described as the ability of a given rock to flow hydrocarbons to the surface. Calculating deliverability relies on estimates of reservoir pressure, permeability and thickness as well as fluid viscosity, all of which are difficult to predict in a frontier basin. Burial and erosional processes exert a fundamental control on these rock and fluid properties. If this erosion is not uniformly distributed across an area then complex variations in deliverability may result. This paper presents a novel approach to quantifying predictions of reservoir deliverability within the Northern Beagle Sub-basin of Western Australia, via the use of a 3D basin-scale model that provides spatial and temporal estimates of variations in rock and fluid properties.Active extension began in the Northern Beagle Sub-basin during the Early Jurassic and resulted in deposition of proposed source and reservoir intervals. A thick (>5km) succession of progradational Middle Jurassic deltaics overlies the early Jurassic petroleum system. During the Late Jurassic, the basin underwent a complex phase of erosion (attributed to rift flank uplift), which resulted in upwards of 3km of sediment being locally removed on footwall blocks of active faults, as well as over structural highs. In other areas, however, such as contemporaneous structural lows, amounts of erosion are minimal. This complex spatial pattern of erosion has implications for both the thermal history (affecting fluid viscosity), as well as reservoir quality (permeability).The final product generated from this workflow was an integrated, basin-scale 3D model of reservoir deliverability for the Northern Beagle Sub-basin.

Controls on Mesozoic rift-related uplift and syn-extensional sedimentation in the Exmouth Plateau

The Exmouth Plateau, part of the Northern Carnarvon Basin, has experienced a multi-phase extensional history, which is associated with regional-scale uplift, as well the uplift and erosion of individual footwall blocks. Detailed interpretation of 3D seismic surveys over the area shows that fault activity began in in the latest Triassic, mainly on NNE-SSW and NE-SW trending faults. Rotation of Triassic fault blocks initiated in the Upper Triassic and continued during the Jurassic. Erosion of pre-rift Triassic sediment occurred during the latest Triassic and the Jurassic. In the latest Jurassic deposition infilled half-grabens and deposition onto highs was limited in the west as the area was starved of sediment. A significant change in sediment supply in the early Cretaceous associated with progradation of the Barrow Delta resulted in the infilling of previously starved half-grabens. Fault activity had decreased by the mid-Cretaceous, with limited activity confined to major faults. Later Cretaceous sediment distribution in the study area was largely controlled by remnant topography. High-quality 3D seismic data allows a detailed examination of the way in which rift-related fault activity affects sediment distribution. In addition to creating fault block traps in pre-rift Triassic sediments, understanding syn-extensional sediment patterns and fault reactivation has implications for syn-rift plays and seal integrity.

Ground Deformation and Source Geometry of the 30 October 2016 Mw 6.5 Norcia Earthquake (Central Italy) Investigated Through Seismological Data, DInSAR Measurements, and Numerical Modelling

We investigate the Mw 6.5 Norcia (Central Italy) earthquake by exploiting seismological data, DInSAR measurements, and a numerical modelling approach. In particular, we first retrieve the vertical component (uplift and subsidence) of the displacements affecting the hangingwall and the footwall blocks of the seismogenic faults identified, at depth, through the hypocenters distribution analysis. To do this, we combine the DInSAR measurements obtained from coseismic SAR data pairs collected by the ALOS-2 sensor from ascending and descending orbits. The achieved vertical deformation map displays three main deformation patterns: (i) a major subsidence that reaches the maximum value of about 98 cm near the epicentral zones nearby the town of Norcia; (ii) two smaller uplift lobes that affect both the hangingwall (reaching maximum values of about 14 cm) and the footwall blocks (reaching maximum values of about 10 cm). Starting from this evidence, we compute the rock volumes affected by uplift and subsidence phenomena, highlighting that those involved by the retrieved subsidence are characterized by significantly higher deformation values than those affected by uplift (about 14 times). In order to provide a possible interpretation of this volumetric asymmetry, we extend our analysis by applying a 2D numerical modelling approach based on the finite element method, implemented in a structural-mechanic framework, and exploiting the available geological and seismological data, and the ground deformation measurements retrieved from the multi-orbit ALOS-2 DInSAR analysis. In this case, we consider two different scenarios: the first one based on a single SW-dipping fault, the latter on a main SW-dipping fault and an antithetic zone. In this context, the model characterized by the occurrence of an antithetic zone presents the retrieved best fit coseismic surface deformation pattern. This result allows us to interpret the subsidence and uplift phenomena caused by the Mw 6.5 Norcia earthquake as the result of the gravitational sliding of the hangingwall along the main fault plane and the frictional force acting in the opposite direction, consistently with the double couple fault plane mechanism.

Morphotectonics and neotectonic activity of the Schuppen Belt of Mokokchung, Nagaland, India

A stretch of the schuppen belt, trending NE-SW in the western sector of the Indo-Myanmar Ranges, represents a tectonically active zone. Deformed Quaternary deposits and various geomorphic features lend evidence for the same. In a portion of the footwall block of the Sanis-Chongliyimsen Thrust, the Nazira Sandstone of the Tipam Group of Mio-Pliocene age is thrust over tilted Quaternary fluvial deposits near Tzudikong, with a displacement of more than 2 m along the plane of the thrust fault. Deformed Quaternary deposits such as tilted terraces and faulted Quaternary sediments are indicative of ongoing tectonic activity in the area. The sediments are tilted towards the southeast by varying degrees (21°–39°) similar to the trend of stream migrations observed at four locations in and around Tuli. In some sections, faulting has not only affected the underlying bedrock but also deformed the overlying fluvial sediments. An important morphotectonic feature representing tectonic movement along the Kongan Thrust is evident from drainage migration in the hanging wall block of the thrust. The stream has migrated towards the southeast as a result of NW verging along the Kongan Thrust, which has left behind a trail of palaeochannels. Numerous palaeochannels, mostly linear in nature, associated with the scarp of the terrace, are indicative of migration of the river. Stream migrations suggest that the two anticlines noted in the study area are possibly growing in the present tectonic regime. Multiple levels of strath terraces lend evidence to tectonic pulses in the study area, each strath representing a tectonic phase. Lineaments have been extensively mapped in the area, out of which, around 70% are parallel to the regional NE-SW trend and the other 30% are approximately perpendicular to this trend. Any movement along the NW-SE plane may be normal faults. The mountain front sinuosity index of the emerging mountain front is close to 1, which is indicative of a relatively active mountain front. Steam length gradient index and steepness index correspond with each other, with high values in the thrust zones, which is indicative of a neotectonically active region.

Neotectonic activity along the Churachandpur-Mao Fault in and around Karong, Manipur, India: based on morphotectonics and morphometric analyses

The Churachandpur-Mao Fault (CMF), trending NNE-SSW, is morphogenic in nature and can be traced for ~ 300 km. It is defined by straight valleys; most prominent being between Kangpokpi and Maram. The fault takes a north-easterly trend from Maram where the fault zone is characterized by active landslides during the monsoon. At Puni Pfosemai, which represents the hanging wall of the fault, extensional tectonics of local extent is observed. This is designated the Puni Pfosemai Fault that trends NNE-SSW and is about 2.5 km in length. The downthrown block is characterized by single-order streams with steep gradients. In the downstream, the fault scarp facing SE developed in the footwall block is more than 100 m in height. The upper portion of the Barak River is tectonically controlled. The SW flowing Barak River takes an almost 360° turn at Karong to flow NNE, before changing course again towards the northwest near Maram. The immediate hanging wall of the CMF is characterized by a narrow valley with relatively high stream-gradient index and steepness index values. A strath terrace of 11 m height is observed on the hanging wall block of the CMF. The straight river valley and concavity (θ) of 0.64 for the Barak River are indicative of active tectonics.

Structural and depositional controls on Plio‐Pleistocene submarine channel geometry (Taranaki Basin, New Zealand)

AbstractHigh‐quality 3D seismic data are used to investigate the effect of the Parihaka Fault on the geometry of submarine channels in Northern Graben of the Taranaki Basin, New Zealand. The Parihaka Fault comprises of four segments (S1–S4) with variable displacements. As part of the Plio‐Pleistocene Giant Foresets Formation, the older Channel Complex Systems 1 and 2 reveal a two‐stage evolution: (a) a syn‐tectonic depositional stage with channels incising the slope during early fault growth (ca. 4.5 Ma) and (b) a stage of sediment bypass (ca. 3 Ma) leading to the infill of hanging‐wall depocentres. The Channel Complex System 3 is syn‐tectonic relative to segment S3 and was formed at ca. 2.5 Ma. We show that the successive generation of new fault segments towards the north controlled the formation of depocentres in the study area. This occurred in association to rotation and uplift of the footwall block of the Parihaka Fault and subsidence of its hanging‐wall block, with fault activity controlling the orientation of channel systems. As a result, we observe three drainage types in the study area: oblique, transverse and parallel to the Parihaka Fault. This work is important as it shows that relay zones separating the Parihaka Fault segments had limited influence on the geometry and location of channel systems. Submarine channels were diverted from their original courses close to the Parihaka Fault and flowed transversally to fault segments instead of running through relay ramps, contrasting to what is often recorded in the literature. A plausible explanation for such a discrepancy relates to rapid progradation of the Giant Foresets Formation during the Plio‐Pleistocene, with channel complexes becoming less confined, favouring footwall incision and basinward deposition of submarine fans.