Faulting (Structural Geology)

SUMMARY Numerical simulations of long-term crustal deformation reveal the important role that damage healing (ie fault-zone strengthening) plays in the structural evolution of strike-slip fault systems. We explore the sensitivity of simulated fault zone structure and evolution patterns to reasonable variations in the healing-rate parameters in a continuum damage rheology model. Healing effectiveness, defined herein as a function of the healing rate parameters, describes the post-seismic healing process in terms of the characteristic inter- ...

This paper examines the geology of the Lagrasse area, southern France. The stratigraphy in the area ranges in age from 72ma-52ma with recent Quaternary superficial deposits noted. All the strata in the region are calcite bearing, this along with tectonic influences in the area forms the rugged valley filled landscape around Lagrasse. The area is located in the Pyrenean foothills and has noticeable deformation throughout many units especially the Ribaute Limestone, likely deformed during the Eocene. The tectonic processes before the Eocene that led to the formation of the Pyrenees are also responsible for the depositional environments of the strata. The depositional settings are controlled by related processes such as foreland basin formation. The rugged landscape created makes the region prone to flooding with narrow valleys that have to share waterways and roads making natural disasters ever present in the area such as disastrous floods in 1999 and 2014.

Paleostress Inversion Techniques: Methods and Applications for Tectonics is an ideal reference for both academic and industry researchers in the Earth Sciences. The book introduces the methodologies developed to reconstruct (paleo) stress tensors from geological data. The interest and potential outcomes of the methods are illustrated by practical examples and supplementary electronic material and an overview on future research directions. As paleostress inversion methods are particularly useful in tectonic analyses at regional and local scales and their outcomes are relevant when trying to predict the orientations of fracture sets and potential fluid flow paths and associated mineralizations, this book provides an ideal resource.

Doğu Anadolu Fay Sistemi (DAFS) Alp-Himalaya sistemi içerisinde Arabistan ve Afrika
levhalarının Anadolu levhası ile çarpışmalarıyla ilişkili olarak gelişmiş kıta içi doğrultu atımlı bir
fay sistemidir. Bu çalışmada DAFS üzerinde kuzeyde Palu‟dan başlayıp güneyde Pütürge‟ye
kadar uzanan yaklaşık 120 km uzunluğundaki bir alan çalışılmıştır. Çalışma alanındaki fayların
geometrileri uzaktan algılama yöntemleri ve arazi çalışmaları yardımıyla haritalanmıştır.
Bölgedeki çizgisellikler, Landsat ETM+ uydu görüntüsünden otomatik yöntemler kullanılarak
çıkartılmış ve çalışma alanında toplam 101 jeolojik çizgisellik tanımlanarak alana ait çizgisellik
haritası oluşturulmuştur. Çizgiselliklerin yorumlanması için hazırlanan gül diyagramına göre,
ana yönelimler K75D olarak saptanmıştır. Çalışma alanında bulunan fay düzlemlerinden
ölçülen fay kayma verilerin Angelier (1994) yöntemi ile kinematik analizi yapılmış ve bölgede
en az iki farklı tektonik fazın (gerilme sisteminin) varlığı tespit edilmiştir. İlk deformasyon fazı
bölgede KB-GD doğrultulu sıkışma ile karakterize edilir. Bu fazın Üst Miyosen-Pliyosen
zamanında bölgede etkili olan çarpışma sonrası sıkışma ile ilişkili olduğu düşünülmektedir.
İkinci deformasyon fazı ise günümüzde etkin olan KD-GB doğrultulu sıkışma ile karakterize
edilir. Geç Pliyosen‟den itibaren etkin olan bu dönem DAFS ve birçok doğrultu atımlı fayların
aktif hale geçmeleri ile ilişkilidir. Arazi ve uzaktan algılama çalışmaları sonucunda elde edilen
veriler bölgede etkin olan gerilme eksenleri hakkında önemli ve birbirlerini destekleyici bilgiler
sunmaktadır.

A B S T R A C T Although extension in the high Andes vs. compression in the lowlands has already been widely discussed in the literature, for the first time we recognized both extensional and contractional structures that developed con-temporaneously during late Pliocene-Quaternary times in a wide area of the central Andean chain (about 90,000 km 2), where crustal earthquake data are missing. This area comprises northeastern Chile, southwestern Bolivia and northwestern Argentina, and extends from the Puna Plateau to the Altiplano-volcanic belt. Late Pliocene-Quaternary folds, with hinge lines trending NNE-SSW to N-S, are mostly located along the westernmost part of the volcanic belt and the eastern part of the Western Cordillera. Locally, there are coeval reverse faults, parallel to the folds, which reach up to the surface; particularly, the Miscanti Ridge, Tolocha Fault and La Casualidad Ridge may be the morphostructural expression of tens-km-long fault-propagation folds, which locally show topographic scarps hundreds of meters high. North and east of the contractional structures, we found evidence of late Pliocene-Quaternary normal faults striking N-S in the southern part of the study area, and NW-SE in the northern part. Well-developed grabens are present in the higher areas of the volcanic belt and in the transition zone with the Puna Plateau. The surface rupture zones of normal fault swarms range 8–24 km in length, with single fault strands up to 18 km long, which are typical of tectonic structures. The distribution in space and time of the studied contractional and extensional structures indicates that they originated in the same time period; we thus address the challenging question regarding the possible origin of the stress sources, by analysing possible causes such as volcanotectonics, high topography, orogeny collapse, and gravitational spreading of the orogen, in relation also with the role played by inherited structures. We finally analyse the relations between the different structures and magma upwelling, and the potential for seismic hazard.

GOLD IN LIGURIAN OPHIOLITES (Italy)
In the Ligurian Alpine-Apenninic arc, from west to south-east, there are three ophiolite complexes, known as "Gruppo di Voltri", "Zona Sestri-Voltaggio" and "Ofioliti della Liguria orientale".
The Voltri Group is an Alpine-type ophiolite association, which have been affected by the Alpine orogenesis and the consequent metamorphism, that completely canceled  the stratigraphic relationships and gave rise to important green schist facies modifications which often make it difficult to recognize the original nature of the rocks.  The most important forming lithotypes are: lherzolites, serpentine schists, metagabbros, prasinites, amphibolites, quartzites, shales: acid crystalline schists are  present along the western  margin.
The Sestri-Voltaggio and the East Ligurian ophiolites have similar petrographic and structural characteristics: in each complex it is possible to observe a normal ophiolite suite, composed of serpentinized lherzolites, gabbros, basalts, cherts, limestones and shales.  Sestri-Voltaggio is a real tectonic-shared “zone”, directed North-South, which represents the geological contact between Alps and Apennines. A vast flyschoid sedimentary sequence, from the Cretaceous-Paleocene age, separates the Sestri-Voltaggio Zone from the complex of eastern Liguria: this is composed of more or less extended ophiolithe bodies, elongated in the NNW-SSE direction, emerging from the flysch.
Gold presence in the Ligurian ophiolites has been known for a long time. The most ancient records date back to the 15th century, but the most important works were carried out during the last century, mostly in the Voltri Group, where placers, eluvial soils and quartz veins were exploited. A certain amount of gold has been recognized in the most important lithotypes. Gold traces are present in pyrite and marcasite which are contained in limestone, schist, flint, gabbros, serpentinite, basalts, as well as in the contacts among them. In the copper mine of Monte Loreto, East Ligury, large native specimens of gold have occasionally been found in altered veins.
Recent studies dealing with the Voltri Group ophiolite complex, have shown that gold is unevenly distributed in the ultramafic rocks, where the average gold content ranges from 0.1 to 2.0 gr/ton. However, the most interesting mineralizations are the hydrothermal quartz veins in alterated serpentinites, that form small deposits know in ancient Italian literature as “ydrothermalites”, to day better know as “listwaenites” and similar, derived from Russian word.  These are stock-work type deposits, mainly composed by quartz and Ca-Mg carbonates with gold, chalcopyrite, sphalerite, tetrahedrite, pyrrhotite, marcasite, pyrite, galena, and nickel sulphides, cementing crushed breccias near the contact between ultramafics and metabasites, or cutting serpentinites near the above contact.  The single veins are sometimes more than 40 metres thick and several hundred metres in length. Gold is very unevenly distributed; the average content range from 2.0 to 20.0 gr/ton in the most altered veins, but locally the content can be 200 gr/ton and more.

Much of this guide was published originally for the 1976 Annual Meeting of the Geological Society of America:

Matthews, V.; Work, D.F.; LeMasurier, W.; Stearns, D.W., 1976, Mechanism of Laramide deformation along the northeastern flank of the Front Range (Road Log), in Epis, R.C. and Weimer, R.D., ed., Studies in Colorado Field Geology; Colo. Sch. of Mines Prof. Contr. No. 8, p. 386-397.

This version differs in several ways:
1. Color images
2. GPS locations for stops
3. Numerous updates over the four decades in which a wide assortment of groups and associations were taken on this trip by the senior author.  The final trip was led in the summer of 2016 for invited scientists from the USGS, CSM, and CSU.

Sinkholes and other karst structures in settled carbonate lands can be a significant source of hazard for humans
and human works. Acque Albule, the study area of this work, is a Plio-Pleistocene basin near Rome, central Italy,
superficially filled by a large and thick deposit of late Pleistocene thermogene travertine. Human activities blanket
large portions of the flat territory covering most evidence from geological surface processes and potentially
inducing scientists and public officials to underestimate some natural hazards including those connected with
sinkholes. To contribute to the proper assessment of these hazards, a geomorphologic study of the basin was performed
using digital elevation models (DEMs), recent aerial photographs, and field surveys. Historical material
such as old aerial photographs and past geomorphologic studies both pre-dating the most part of quarrying
and village building was also used together with memories of the elderly population. This preliminary study
pointed out the presence of numerous potentially active sinkholes that are at present largely masked by either
quarrying or overbuilding. Where this first study pointed out the apparent absence of sinkholes in areas characterized
by high density of buildings, a detailed subsurface study was performed using properly-calibrated electrical
resistivity tomography (ERT) and dynamic penetration measurements (DPSH), together with some borehole
logs made available from the local municipality. This second study highlighted the presence of sinkholes and
caves that are, this time, substantially hidden to the resolution of standard methods and materials such as aerial
photographs, DEMs, and field surveys. Active sinkhole subsidence in the Acque Albule Basin may explain, at least
in part, the frequent damages that affect numerous buildings in the area. The main conclusion from this study is
that the mitigation of sinkhole hazard in highly populated areas has to pass through a thorough search of (hidden)
sinkholes that can be masked by the Anthropocenic molding and blanketing of the territory. For these purposes,
data from historical (pre-Anthropocene) documents as well as, where possible, subsurface investigations
are fundamental.

The Mw 6.3 Meinong earthquake, which struck southern Taiwan on February 6, 2016, was characterized by an oblique left lateral strike-slip motion with a minor reverse component. The earthquake occurred at approximately 16 km depth on an unknown fault that did not rupture the ground surface, but rather produced a noticeable long period velocity pulse east to west, with the strongest amplitude motions recorded about 30km west of the epicentral region in Tainan City. Within this city, more than 20 multi-story buildings constructed under relatively modern building codes were severely damaged, including seven that suffered complete collapse. In addition, there was widespread damage associated with liquefaction, a substantial portion of which affected residential buildings causing large uniform and differential settlement, the later causing severe tilt to buildings in many cases. In response to this event, local earthquake professionals, faculty members, and students teamed with US NSF-sponsored Geotechnical Extreme Events Reconnaissance (GEER) members visited the affected area to document the geologic/geotechnical effects and to assess seismic performance of infrastructure [1,2]. Unique to past efforts, US-Taiwan reconnaissance team members utilized unmanned aerial vehicles and LiDAR in several areas to guide the field data collection efforts and assist with post-reconnaissance data interpretation. This paper presents important lessons learned from this event, focusing particularly on 1) the impact of marginally liquefiable soils on shallow foundations and in particular foundation detailing aspects which led to good performance and 2) the advantages of using remote sensing tools to offer insight into important features of earthquake performance post-event.

Magnetite-rich iron oxide copper-gold deposits (IOCGs) are geologically and geochemically complex and present major challenges to geophysical investigation. They often sit beneath significant cover, exhibit magnetic remanence, and suffer from self-demagnetization effects. Because remanence in magnetite-bearing drill core samples is commonly overprinted by drilling, in situ natural remanent magnetization is difficult to measure accurately, and thus IOCGs cannot be modeled definitively using geophysics alone. We examined structural controls on a magnetite-rich IOCG in northwest Queensland and the relationships between structure, alteration, Fe oxides, and mineralization at core to deposit scale. Magnetite within the deposit has a multidomain structure, and thus it would commonly have an in situ magnetization parallel to the earth’s field. In contrast, pyrrhotite has a pseudosingle-domain structure and so it is the predominant carrier of stable remanence within the ore system. Geophysical lineament analyses are used to determine structural controls on mineralization, geophysical filters (e.g., analytic signal amplitude) are used to help define structural extent of the deposit, and basement geochemistry is used to map mineral footprints beneath cover. These techniques identified coincident anomalies at the intersection of north and northwest lineaments. Leapfrog™ interpolations of downhole magnetic susceptibility and Cu, Au, and Fe assay data were used to map the distribution of magnetite, copper, gold, and sulfur in 3D. The analysis revealed that Cu and Au mineralization were coupled with the magnetite net-vein architecture, but that Cu was locally enriched in the east–northeast-trending demagnetized zone. The results from this suite of geophysical, petrophysical, and geochemical techniques were integrated to constrain modeling of the Brumby IOCG. Brumby can be described as a breccia pipe sitting at the intersection of north-striking, east-dipping, and northwest-striking, southeast-dipping structures that plunges moderately to the south–southeast. The breccia pipe was overprinted by a relatively late net-vein magnetite breccia and crosscut by a later, magnetite-destructive, east–northeast-striking fault.
Read More: http://library.seg.org/doi/abs/10.1190/INT-2013-0005.1

We present the first evidence of surface rupture along the causative fault of the 14 January 1703 earthquake (Mw 6.9, Italian central Apennines). This event was sourced by the ~30 km-long, Norcia fault system, responsible for another catastrophic event in Roman times, besides several destructive earthquakes in the last millennium. A dozen paleoseismological excavations have already investigated the surface ruptures occurred during the Holocene along the Cascia-Mt Alvagnano segments, as well as along secondary splays close to the Medieval Norcia Walls. Remarkably, the master fault bounding the Norcia-Campi basins have never be proved to rupture at the surface. An antique limekiln that was improvidently set across the main fault scarp provides the amazing evidence of an abrupt offset in the 1703 earthquake, which likely occurred during a liming process of carbonate stones. Obviously, the limekiln became useless, and was progressively buried by slope debris. The amount of the offset and the kinematics indicators surveyed in the site allow the strengthening of our knowledge on the seismogenic potential of the Norcia fault system, on its geomorphic rule, and on its impact on the human activities.

In this study, the structural controls of a high-temperature system (188 to 287 oC) associated with the detachment fault in Gediz Graben generating approximately half of this electricity generation in Turkey which is in the top five of the world in the generation of electricity from geothermal resources are examined. The high-temperature geothermal reservoirs associated with detachment fault in the study area have formed along the normal faults nearly in E-W orientation and in intensely fractured rocks in a structurally complex manner associated with transfer faults approximately in N-S orientation. Generally, it has been determined that the reservoirs are closely located to strike-slip faults intersecting, overlapping, and/or terminated with Quaternary transfer faults.  The same results as this study have also presented in the studies performed in western Anatolia and some regions of the world.  Since the detachment fault and the high-angle normal faults cutting the detachment fault form the paths, this mechanism ensures that the geothermal fluids are drained from the surface to the reservoir rock environment. High-angle normal faults cutting the detachment fault and the transfer faults cutting the detachment-high-angle normal faults constitute the carrier systems. This causes that the fluids heated in the reservoir rock environment at the depths are carried to the surface. Therefore, transfer faults control the position of high-temperature geothermal systems and should be used as the primary guide for geothermal exploration.
Keywords: high-temperature geothermal field, detachment fault, transfer fault, listric faulting, Western Anatolia

This paper describes a training and research tool for learning basic issues related to BIST (Built-In Self-Test) generator. The main didactic aim of the tool is presenting complicated concepts in a comprehensive graphical and analytical way. The paper describes a computer-aided design (CAD) that is used to generate automatically the BIST to any digital circuit. This software technique attempts to reduce the amount of extra hardware and cost of the circuit. In order to make our software being easily available, we used the Java platform, which is supported by most operating systems. The multi-platform JAVA runtime environment allows for easy access and usage of the tool.

In this paper, an enriched finite element technique is presented to simulate the mechanism of interaction between the hydraulic fracturing and frictional natural fault in impermeable media. The technique allows modeling the discontinuities independent of the finite element mesh by introducing additional degrees of freedom. The coupled equilibrium and flow continuity equations are solved using a staggered Newton solution strategy; and an algorithm is proposed on the basis of fixed-point iteration concept to impose the flow condition at the hydro-fracture mouth. The cohesive crack model is employed to introduce the nonlinear fracturing process occurring ahead of the hydro-fracture tip. Frictional contact is modeled along the natural fault using the penalty method within the framework of plasticity theory of friction. Moreover, an experimental investigation is carried out to perform the hydraulic fracturing experimental test in fractured media under plane strain condition. The results of several numerical and experimental simulations are presented to verify the accuracy and robustness of proposed computational algorithm as well as to investigate the mechanisms of interaction between the hydraulically-driven fracture and frictional natural fault.

Structural features in geothermal systems, including fault and fracture networks, can play significant roles in controlling magmatic intrusion and the focusing of hydrothermal fluid flows. These roles have been proven in the exploration programs in well-developed geothermal fields in West Java, Indonesia. Despite the important role of structure in geothermal fields, little is known about this in the abundant, less explored systems of West Java. In this study, we synthesise existing data with the new automated remote sensing analysis in more than 20 geothermal fields in West Java. The structures are analysed using regional datasets including Bouguer Anomaly, which represents deep-seated structures, and the Shuttle Radar Topographic Mission (SRTM 30 m) digital elevation model (DEM) which represents active, thinskinned and surficial deformation. The automatic multi-scale edge detection method is applied to interpret the structural trends.

Quaternary sea-level cycles have caused dramatic depocentre shifts near the mouths of major rivers. The effects of these shifts on fault activity in passive margin settings is poorly known, as no studies have constrained passive margin fault throw-rate variability over 103 to 105 year time scales. Here we present 11 mean throw rates for the Tepetate–Baton Rouge fault zone along the northern Gulf of Mexico coast in southern Louisiana. These data were obtained by optically stimulated luminescence dating over time scales spanning the last interglacial to the late Holocene. The mean throw rate is ca. 0.22 mm year−1 during the late Holocene, ca. 0.03 mm year−1 during the last glacial and at least 0.07 mm year−1 during the last interglacial. Throw rates averaged over the late Pleistocene to present are spatially uniform within our study area. The temporal variability in throw rates suggests that shifts of the Mississippi River depocentre relative to this fault zone, driven by Quaternary sea-level cycles, may have imposed a significant control on fault activity. The late Holocene throw rate is at least in the order of magnitude smaller than the rates of land-surface subsidence in the Mississippi Delta, indicating that this fault zone is not a dominant contributor to subsidence in this region.

Developments in the measurement of surface creep on California  faults are presented. Graphite rods buried obliquely across creeping faults offer advantages over previous methods for measuring creep. LVDT sensors offer limited range (20 mm) with high resolution (10 µm), however a rotary sensor can extend this range to several meters.

The Argentine broken foreland has been the subject of continuous research to determine the uplift and exhumation history of the region. High-elevation mountains are the result of NeS reverse faults that disrupted a WeE Miocene Andean foreland basin. In the Sierra de Ambato (northern Argentine broken foreland) the reverse faults offset Neogene sedimentary rocks (Aconquija Fm., ~9 Ma) and affect the basement comprising Paleozoic metamorphic rocks that have been dated at ~477À470 Ma. In order to establish a chronology of these faults affecting the previous continuous basin we date the formation age of clay minerals associated with fault gouge using the KeAr dating technique. Clay mineral formation is a fundamental process in the evolution of faults under the brittle regime (<<300 C). KeAr ages (9 fractions from 3 samples collected along a transect in the Sierra de Ambato) vary from Late Devonian to Late Triassic (~360e220 Ma). This age distribution can be explained by a long lasting brittle deformation history with a minimum age of ~360 Ma and a last clay minerals forming event at ~220 Ma. Moreover, given the progression of apparent ages decreasing from coarse to fine size fractions (~360À311 Ma for 2À1 mm grain size fraction, ~326À286 Ma for 1e0.2 mm and ~291À219 Ma of <0.2 mm), we modeled discrete deformation events at ~417 Ma (ending of the Famatinian cycle), ~317e326 Ma (end of Gond-wanic orogeny), and ~194e279 Ma (Early Permian-Jurassic deformation). According to our data, the Neogene reactivation would not have affected the KeAr system neither generated a significant clay minerals crystallization in the fault gouge, although an exhumation of more than 2 Km is recorded in this period from stratigraphic data.

3D structural interpretation, well information and dynamic production data are combined to propose a different trapping geometry for the rich condensate gas in the Mirador Reservoir of the northernmost part of the Cupiagua Field.
The proposed model consists of two completely overlapping ramp anticlines separated by east verging partially sigmoidal thrust faults. The lowest thrust fault (Informally Named Base Fault) is the main thrust, and has a detachment along the Upper Guadalupe Mudstone. The upper thrust (Informally Named Core fault), which separates the two anticlines and creates the main trap in Recetor, has a detachment along the shaly Los Cuervos Formation. This duplex structure merges to the north allowing the communication between the two Mirador sections, explaining their dynamic behavior in terms of fluids and pressure through time.
The described ramp anticlines in the Recetor area were buried by the El Morro and the Nunchia folds, which were transported by the Yopal Fault System along the shaly Carbonera C6 unit.
This structural configuration was geometrically restored using dip cross sections, where a maximum shortening of 3.5 Km is interpreted, confirming the feasibility of the model and honoring the depth maps generated for each one of the reservoirs. The proposed structural configuration was also confirmed by the latest results observed during the 2007 drilling campaign.
Although genetically similar to the previous interpretation of this area, the proposed model considers an additional detachment zone along Los Cuervos Formation, creating new opportunities for exploration and production projects.

Proteklih desetljeća geolozi su često koristiti analogne modele kako bi simulirali
ponašanje zemljine kore tijekom djelovanja deformacijskih sila. Analogno modeliranje rasjeda
daje vrijedan uvid u geometriju i kinematiku stvaranja rasjeda, a točna rekonstrukcija stvarnih
geoloških struktura može pružiti ispravna shvaćanja o njihovom nastanku. Također, upotrebom
analognih modela moguće je u laboratoriju promatrati geološke procese kojima je potrebna
značajna količina vremena kako bi se razvili.
Svrha ovog rada bila je upoznati se s aparaturom i metodama analognog modeliranja, a
s ciljem proučavanja geometrije i kinematike struktura koje nastaju tijekom pokusa kako bi se
dobio jasniji uvid u nastanak stvarnih struktura na terenu. 
Eksperiment se sastoji od dvije faze: (1) postavljanje eksperimenta, što uključuje sijanje
pijeska različitih boja u slojeve, te (2) izvođenje eksperimenta primjenom sile na pijesak.
Suština samog pokusa je imati jasno razlučive slojeve u materijalu, te nakon i tokom primjene
sile bilježiti uočene promijene.
U ovom radu napravljena su  četiri pokusa (dva kompresijske tektonike, jedan
ekstenzijske i jedan kombinirani) te su opisane nastale strukture i njihov razvoj kroz pokus. Pri
različitom postavljanju pokusa stvarat će se različite strukture.

Eleven Quaternary fissure ridge travertines from Mammoth Hot Springs (Wyoming) and seventeen ones from Bridgeport (California) were mapped and studied with a morphotectonic approach to understand possible relationships between travertines and active versus passive tectonics. Results are compared with other known geothermal fissure ridges on the Earth. The studied fissure ridges are all located in the hangingwall of normal faults, but the fissure ridges appear as non-dislocated by faults, rather by axial fissures. Both in the two principal study areas and elsewhere, azimuthal analyses of faults and fissure ridges show that the distribution of fissure ridge long axis is rather dispersed around the strike of the local normal faults. No correlation occurs between the fissure ridge length and the angle between the strike of the normal fault and the strike of fissure ridges. The studied fissure ridges are 2 to 360 m long (mean length: 72.1 m), 1 to 15 m wide (mean width: 6.7 m), and 0.5 to 8 m high (mean height: 3.9 m). Fissure ridge aspect ratios show a moderate correlation between the length and both the width and the height of fissure ridges, whereas the correlation between width and height is less marked. The growth in height and width of ridges appears as much more inhibited than in length. A model is proposed in which fissure ridge travertines grow with enhanced elongation along one sub-horizontal direction, which seems moderately controlled by the associated normal fault and the regional extension. Other factors, such as the inherited fracture network and the geothermal and artesian pressure of fluids (fluid discharge) may be important in the development of the studied fissure ridges. Results from this study may contribute to the knowledge of factors that control the long-term geothermal circulation and also the long-term hermetic durability of CO2 subsurface repositories.

"The Palaeoproterozoic Svecofennian crust in southern and central Fennoscandia was established about 1.8 Ga ago after a prolonged history of accretion and intrusion. During late stages of the Svecofennian orogeny, deformation was partitioned into several crustal-scale shear zones in present-day Finland, Sweden and Estonia. One such major ductile deformation zone, ‘the South Finland shear zone’ (SFSZ) extends for almost 200 km through the Aland archipelago in southwestern Finland, and further along the southern and southwestern coast of Finland. This more than a kilometer wide transpressional zone appears to have been repeatedly reactivated. The deformation started with a period of regional, ductile dextral shearing of igneous rocks, producing striped granodioritic and tonalitic gneisses. The ductile phases are locally overprinted and followed by ductile to semi-ductile deformation evidenced by mylonite zones of variable width. The last stage of tectonic activity along the shear zone is recorded by pseudotachylites.

Within this study, we dated zircons (SIMS U–Pb) and titanites (ID-TIMS U–Pb) from eight rock samples, and two pseudotachylite whole-rock samples (40Ar/39Ar) in order to reconstruct the deformation and (re)activation history of the shear zone. The results suggest that the medium-grained gneisses underwent three distinct deformation phases separated by time intervals without regional deformation. The ductile deformation within the study area initiated at ∼1.85 Ga. A second, more intensive deformation phase existed around 1.83 Ga, by which the shear zone was already well developed. Finally, the last ductile event is recorded by ∼1.79 Ga metamorphic titanites in relatively granoblastic granitoid gneisses that nevertheless already display protomylonitic textures, suggesting the initiation of large-scale mylonitisation around or soon after this time. The age of a pseudotachylite sample and, hence, the brittle deformation is bracketed between 1.78 and 1.58 Ga based on the age of pegmatites cut by pseudotachylites as well as 40Ar/39Ar minimum ages for the pseudotachylite, respectively. The data imply that the rocks within the study area entered the ductile–brittle transition zone due to rapid cooling and exhumation of the crust after ∼1.79 Ga."

The objective of this work is to give new insights into the
geometry and kinematics of the tectonic wedge of the
Piedemonte License. The interpretation presented herein
involved and integrated the lately acquired surface and
subsurface data; 470 km2 of pre-stack depth migrated (PSDM)
3D seismic, geological information and production data from
11 wells and detailed surface geology. The main reservoirs,
Mirador, Barco and Guadalupe formations, are involved into
the hanging wall of the thrust sheets of the intercutaneous
wedge.
The structural analysis is based on “backward” modeling
(cross section restoration) and on forward modeling of the area
using the fault parallel flow algorithm. The Forward
Modelling comprises a model divided into 15 stages of
deformation; taking into account the deformation produced
since the Oligocene.
The main structural features are the Monterralo, El Morro,
Floreña, Dele, Pauto and Volcanera anticlines, and the
Nunchia syncline. The anticlines of the wedge could be
divided into two groups. One is characterized by greater
amplitude and been more symmetrical. The second one is
characterized by slightly more elongated back limbs and
shorter front limbs.
The structural analysis of the PTZ is based in the
modification of the Hubbert and Rubey`s (1959) model.
Previous experiments demonstrate that the relative strength
affects the development of active- or passive-roof duplexes.
Based on available surface and subsurface data, is
proposed that the structure of the License is an antiformal
stack duplex instead of the classic triangle zone.
Tectonic wedges remain undrilled along the Foothills of
the Eastern Cordillera. Those areas where is a syncline at
surface, may be a potential tectonic wedge. However, in the
southern part of the Llanos foothills some of the structures
may be pseudo – tectonic wedges.

The only occurrence of monoclines along the eastern flank of the Colorado Front Range is near Llvermore at the northern end of the tten echelonrl fold-and-fault belt (Fig. l). The monocl ines I ie along the Kawuneeche-Livermore Iineament (h/ork and tlatthev,rs, in preparatlon). sedimentary rocks elsewhere along the eastern flank of the Front Range were deformed into either homoclines, anticllnes, or syn-clines during the Laramide orogeny. Erosion has removed the sedlmentary rock cover from the Precambrian basement on the western edge of the area of monoclinal folding. Thus, the area pro-vldes an unusual opportunlty for studying the role of structural basement in the formation of the monocllnes. Our study comblned detalled field work with photo-interpretation of NASA U-2 photography stereo-pa I rs. DESCR I PT ION OF I1ONOCL lNES Northeast of Llvermore, Colorado the Paleozoic and l.lesozoic strata are folded into a series of narrov't linear monoclines (Flgs. 2r3)" The monoctines separate large areas where the strata are planar and lilanuscript received, February 18, 1976; accepted, llarch 3, 1976. fhe Mowttain Geologiet u. 73, no. 2 (Aprti lszol p. 61-66 6]. ABSTMCT: Honoclinal foldlng is the dominant style of deformation in Paleozoic and }lesozolc sedimentary strata northeast of Livermore, Colorado. The markedly llnear monocllnes are narrow and bound large areas of nearly flat-lylng strata. Axes of the monoclines are not parallel, which indlcates that they did not form as a resutt of reglonal horizontal compression. Several mlles to the west, eroslon has stripped the sedimentary cover from the underlylng Precambrian basement. The basement is characterized by brittle deformation in the form of dlfferentlally upllfted fault blocks. The pre-Pennsylvanian erosion surface developed on top of the Precambrlan igneous and metamorphlc rocks Is only sllghtly tilted. Where the faults ln the basement pass under the Paleozoic sedimentary cover to the east, the sedlmentary rocks are folded into unfaulted monoclines. This suggests that the monocllnes in the area are formed by passive draping of sedimentary rocks over dlfferentially uplifted basement blocks. Such an interpretation ls conslstent with the geometrlcal relationships of the monocllnes, with burlal conditlons durlng the Laramlde orogeny, and with experimental results on the behavior of rock materlals.

The mechanics of slip on low-angle normal faults (LANFs) remain an enduring problem in structural geology and fault mechanics. In most cases, new faults should form rather than having slip occur on LANFs, assuming values of fault friction consistent with Byerlee’s Law. We present results of laboratory measurements on the frictional properties of natural clay-rich gouges from low-angle normal faults (LANF) in the American Cordillera, from the Whipple Mts. Detachment, the Panamint range-front detachment, and the Waterman Hills detachment. These clay-rich gouges are dominated by neoformed clay minerals and are an integral part of fault zones in many LANFs, yet their frictional properties under in situ conditions remain relatively unknown. We conducted measurements under saturated and controlled pore pressure conditions at effective normal stresses ranging from 20 to 60MPa (corresponding to depths of 0.9–2.9km), on both powdered and intact wafers of fault rock. For the Whipple Mountains detachment, friction coefficient (μ) varies depending on clast content, with values ranging from 0.40 to 0.58 for clast-rich material, and 0.29–0.30 for clay-rich gouge. Samples from the Panamint range-front detachment were clay-rich, and exhibit friction values of 0.28 to 0.38, significantly lower than reported from previous studies on fault gouges tested under room humidity (nominally dry) conditions, including samples from the same exposure. Samples from the Waterman Hills detachment are slightly stronger, with μranging from 0.38 to 0.43. The neoformed gouge materials from all three localities exhibits velocity-strengthening frictional behaviorunder almost all of the experimental conditions we explored, with values of the friction rate parameter (a −b)ranging from −0.001 to +0.025. Clast-rich samples exhibited frictional healing (strength increases with hold time), whereas clay-rich samples do not. Our results indicate that where clay-rich neoformed gouges are present along LANFs, they provide a mechanically viable explanation for slip on faults with dips <20◦, requiring only moderate (Pf<σ3) overpressures and/or correcting for ∼5◦of footwall tilting. Furthermore, the low rates of frictional strength recovery and velocity-strengthening frictional behavior we observe provide an explanation for the lack of observed seismicity on these structures. We suggest that LANFs in the upper crust (depth <8km) slip via a combination of a) reaction-weakening of initially high-angle fault zones by the formation of neoformed clay-rich gouges, and b) regional tectonic accommodation of rotating fault blocks.

Curved thrust systems are commonly associated to linked frontal, oblique and lateral thrust ramps, which are oriented normal, oblique and parallel, respectively, to the regional compressive tectonic transport direction. Abrupt lateral variations of the thrust architecture usually occur in thrust belts across lateral/oblique ramps and their identification is crucial since they may mark the transition from different structural styles, kinematics of the thrust sheets and stratigraphic domains. Arcuate thrusts systems composed by linkage of frontal, oblique and lateral thrust ramps characterizing curved thrust belts likely indicate that the thrust system architecture has been strongly influenced by the sub-thrust inherited extensional fault pattern. Indeed, in fold-and-thrust belts that suffered an extensional fault heritage the localisation of lateral/oblique thrust ramps is strictly controlled by deep-rooted pre-orogenic normal faults that are transpressively reactivated when favourably oriented. The identification of inversion structures in thrust belts has a direct impact on both the unravelling of the structural style and the hydrocarbon prospectivity of a region, because the inversion processes control the petroleum system elements from the initial extension up through the later compressional deformation. The study of tectonic inversion-related folds in regions where the mechanical stratigraphy is well known is valuable for the development of geometric and kinematic models that may add useful information for unravelling the structural style of thrust belts.
In this contribution, we document the geometrical characteristics of inversion structures (i.e., push-up inversion structures and fault-bend reactivation anticlines) occurring along oblique thrust ramps, by examining some examples of buried Apulian structures in the Central-Southern Apennines (i.e., Setteporte and Mt. Taburno push-ups) and outcropping thrust-related folds in the Central-Northern Apennines of Italy (i.e., Sabini Mts. push-up and OAS hanging-wall fault-bend macro-anticlines). The different geometrical features between push-up inversion structures and fault-bend reactivation anticlines are functionally controlled by: (i) the mechanical characteristics of the involved sedimentary multilayer, (ii) the original architecture of the former extensional basin, and (iii) the amount of thrust displacement. The recognition of such inversion structures is important in understanding the anatomy and structural style of foreland fold-and-thrust belts; in addition, this recognition is critical in interpreting the geometry and types of structural traps that may be expected along oblique thrust ramps. This study reveals that push-up inversion structures and fault-bend reactivation anticlines could coexist along oblique thrust ramps within a unique curved thrust system and may be detected among analogous foreland thrust belts that experienced structural inheritance of extensional basins.

We use interferometric synthetic aperture radar (InSAR), body wave seismology, satellite imagery, and field observations to constrain the fault parameters of the Mw 7.1 2011 Van (Eastern Turkey) reverse-slip earthquake, in the Turkish-Iranian plateau. Distributed slip models from elastic dislocation modeling of the InSAR surface displacements from ENVISAT and COSMO-SkyMed interferograms indicate up to 9 m of reverse and oblique slip on a pair of en echelon NW 40°–54° dipping fault planes which have surface extensions projecting to just 10 km north of the city of Van. The slip remained buried and is relatively deep, with a centroid depth of 14 km, and the rupture reaching only within 8–9 km of the surface, consistent with the lack of significant ground rupture. The up-dip extension of this modeled WSW striking fault plane coincides with field observations of weak ground deformation seen on the western of the two fault segments and has a dip consistent with that seen at the surface in fault gouge exposed in Quaternary sediments. No significant coseismic slip is found in the upper 8 km of the crust above the main slip patches, except for a small region on the eastern segment potentially resulting from the Mw 5.9 aftershock on the same day. We perform extensive resolution tests on the data to confirm the robustness of the observed slip deficit in the shallow crust. We resolve a steep gradient in displacement at the point where the planes of the two fault segments ends are inferred to abut at depth, possibly exerting some structural control on rupture extent.

A contact zone between porphyritic microgranite of the early ring-complex of the Paleocene Slieve Gullion igneous centre and Lower Palaeozoic metasedimentary rocks of the Longford–
Down inlier was exposed along a 300m section excavated during construction of the new M1 motorway. The outcrop displays a thin sliver of Longford–Down metasediment in contact with porphyritic microgranite in a steep, and locally intensely crushed, contact zone that dips away from the ring-complex. This outcrop pattern is reminiscent of a ‘caldera-superfault’. Given the recent discussion on sheet versus ring-dyke emplacement of the early ring-complex at Slieve
Gullion, this new evidence argues in favour of the traditional ring-dyke model with magma ascending along an active ring fracture associated with caldera subsidence.

Monitoring of soil radon gas has been continuously carried out during the last two years around Opak Fault, Yogyakarta, as one of earthquake disaster mitigation efforts. This study aimed to analyze the variations of radon gas and seismic activity, and to explore the emergence of local earthquake precursors that occurred around the Opak Fault. Radon
gas monitoring conducted at two locations:  in Pundong and Piyungan areas. While the earthquake activities around Opak Fault were obtained from BMKG. This radon gas anomaly is studied to see earthquake precursors by applying the correlation method. Radon gas anomaly is determined if the ratio of correlation coefficient deviation (Sk) with
standard deviation (Ds) is smaller than -1. The results showed an increase in emissions of radon gas correlated with the increase in the frequency of seismic events.  The application of correlation method showed the presence of radon gas anomalies as earthquake precursors around Opak Fault. Further researches are needed to see the correlation and consistency of the results of monitoring radon gas anomalies with earthquakes around Opak Fault.