Major Fault Plane Research Articles

Implication of fault seal analysis method to evaluate the sealing conditions of major fault planes at Barapukuria basin, North-West Bangladesh

The Barapukuria coal basin stands as Bangladesh’s sole active underground coal mining site. The geological setting of this basin is marked by two major faults, the Eastern Boundary Fault and FB fault encircling the basin perimeter, alongside several smaller faults and those induced by underground longwall mining activities. A major concerning issue of this mine is the water inrush into the mine area from the extensive groundwater aquifer, Upper DupiTila (UDT). Using the Fault Seal Analysis technique employed by (Yielding et al. in Am Assoc Pet Geol Bull 81:897–917, 1997) algorithm, this analysis attempts to identify susceptible areas and potential unsealed faults that could provide the risk of water invasion into the mine area. Evaluation of Fault Seal Analysis reveals varying Shale Gauge Ratio (SGR) values: 0.08 and 0.13 for the major Eastern Boundary Fault, 0.05 for the second largest FB fault, 0.35 and 0.53 for FB-1, and 5.65, 1.69, and 1.22 for the smaller faults BGP-N-F11, BGP-N-F2, and F-24, respectively. According to SGR values, the Eastern Boundary Fault and the FB fault plane are anticipated to be unsealed and dip westward at an angle of 75°-80°, rendering them vulnerable to water inflow through the fault planes. The analysis also suggests that the Lower DupiTila (LDT) aquiclude which can impede the groundwater flow from the UDT aquifer into the mine area, is very thin or absent in the northern region of the basin making this region highly susceptible to water inundation.

Induced seismicity in the Groningen gas field – arrest of ruptures by fault plane irregularities

AbstractFrom dynamic rupture simulations, we reveal under which conditions a rupture in the Groningen gas field stops along fault dip or along fault strike after it starts on a fault in the reservoir. The simulations focus on the capabilities of fault plane irregularities to arrest ruptures. Such irregularities can be recognised in sandstone outcrops. Fault planes in the Groningen field, extracted from the 3D seismic data by seismic attribute extraction methods, show similar irregularities. A detailed surface of a major fault plane in the field indicates that steps and jogs of tenths of metres are possible. Although these irregularities are close to seismic resolution and could be partially artificial, we investigated their effect on rupture arrest.For typical current stresses in the Groningen field, jogs and steps of this length scale are found to be remarkably effective to stop ruptures in the reservoir. Also, a significant increase in the fault dip along fault strike can stop these ruptures but a kink in the fault under a constant fault dip not.Including non-planar fault features and pressure diffusion in the Carboniferous, the simulations in this paper follow trends of previous simulations in the literature using 2D planar faults. In particular, the horizontal stress in this formation and the strength of the Carboniferous fault zone are important for rupture propagation. If the fault would have been reactivated in the Neogene or Quaternary and poorly healed in clay-rich parts, rupture propagation into the Carboniferous can only be prevented by jogs of sufficient size and lateral continuity under the present estimate of the horizontal field stress.

Active faults, Paleoseismological trenching and seismic hazard assessment in the Northern Mygdonia Basin, Northern Greece: The Assiros-Krithia fault and the Drimos fault zone

The Plio-Quaternary Mygdonia Basin in Northern Greece is bounded by active normal faults that can host significant earthquakes and produce considerable damage to the city of Thessaloniki (the second biggest city in Greece – 1 million population), located only 15–20 km away. In 1978, a damaging M = 6.5 earthquake occurred along a fault in the southern part of the basin, generating primary and secondary surface ruptures. This manuscript offers the results of the first detailed geomorphological and paleoseismological investigations in the northern part of the basin. As a result: i) a new active normal fault has been mapped, the Assiros-Krithia fault (AKF); and ii) another fault zone that has been assessed with probable activity in the literature, the Drimos fault zone (DFZ), has been confirmed active and mapped in detail. Paleoseismological trenching investigations supported by radiometric dating were carried out along both structures. The AKF and DFZ form the northern and northwestern boundaries of the Mygdonia Basin, respectively. The AKF deflects the local drainage network and is expressed as a single north dipping localised fault trace, gently uplifting the northern part of the Mygdonia Basin. The last event produced 48 cm of vertical displacement around 4540 cal. yrs BP, and the fault has an estimated slip rate of ∼0.1 mm/yr. The DFZ is an 8-10 km-long NW-SE trending normal fault that dips and downthrows to the NE (045o-050o). It is characterised by distributed deformation across eight major and secondary fault planes. Four of these planes have been activated over the last 9000 years, therefore the structure is Holocene active. The DFZ has an estimated slip rate of 0.1–0.3 mm/yr and may merged with the Liti-Gerakarou fault zone in multi-segment ruptures. The DFZ highlights that NW-SE trending faults are potentially active in Northern Greece. Their long recurrence intervals justify why they were not activated during the period covered by the historical record and emphasise, once again, the necessity of paleoseismological studies and the implementation of fault specific approaches in seismic hazard assessment.

Active Faulting in Lake Constance (Austria, Germany, Switzerland) Unraveled by Multi-Vintage Reflection Seismic Data

Probabilistic seismic hazard assessments are primarily based on instrumentally recorded and historically documented earthquakes. For the northern part of the European Alpine Arc, slow crustal deformation results in low earthquake recurrence rates and brings up the necessity to extend our perspective beyond the existing earthquake catalog. The overdeepened basin of Lake Constance (Austria, Germany, and Switzerland), located within the North-Alpine Molasse Basin, is investigated as an ideal (neo-) tectonic archive. The lake is surrounded by major tectonic structures and constrained via the North Alpine Front in the South, the Jura fold-and-thrust belt in the West, and the Hegau-Lake Constance Graben System in the North. Several fault zones reach Lake Constance such as the St. Gallen Fault Zone, a reactivated basement-rooted normal fault, active during several phases from the Permo-Carboniferous to the Mesozoic. To extend the catalog of potentially active fault zones, we compiled an extensive 445 km of multi-channel reflection seismic data in 2017, complementing a moderate-size GI-airgun survey from 2016. The two datasets reveal the complete overdeepened Quaternary trough and its sedimentary infill and the upper part of the Miocene Molasse bedrock. They additionally complement existing seismic vintages that investigated the mass-transport deposit chronology and Mesozoic fault structures. The compilation of 2D seismic data allowed investigating the seismic stratigraphy of the Quaternary infill and its underlying bedrock of Lake Constance, shaped by multiple glaciations. The 2D seismic sections revealed 154 fault indications in the Obersee Basin and 39 fault indications in the Untersee Basin. Their interpretative linkage results in 23 and five major fault planes, respectively. One of the major fault planes, traceable to Cenozoic bedrock, is associated with a prominent offset of the lake bottom on the multibeam bathymetric map. Across this area, high-resolution single channel data was acquired and a transect of five short cores was retrieved displaying significant sediment thickness changes across the seismically mapped fault trace with a surface-rupture related turbidite, all indicating repeated activity of a likely seismogenic strike-slip fault with a normal faulting component. We interpret this fault as northward continuation of the St. Gallen Fault Zone, previously described onshore on 3D seismic data.

Rupture process of the 2018 Hokkaido Eastern Iburi earthquake derived from strong motion and geodetic data

The source rupture process of the 2018 Hokkaido Eastern Iburi earthquake was investigated by performing a joint inversion analysis using the strong motion and geodetic data. A fault model that consists of two fault planes was constructed by considering the relocated aftershock distribution and the focal mechanisms. The inversion result showed that the large slip occurred at approximately 22 km depth, which was much shallower than the hypocentral depth. Our results showed that the rupture initiated on the minor fault plane around the hypocenter and the major fault plane started to rupture 4–6 s after the rupture initiation. Although the shape of the minor fault plane has not been clearly determined, the major fault plane appears to be high-angle, east-dipping. An additional inversion with only the major fault plane showed that the strong ground motion near the source was mainly generated from the major fault plane. The total seismic moment estimated by the inversion with the two fault-plane model was 1.1 × 1019 Nm, which yielded an Mw of 6.6. Using the inversion result of the two fault-plane model, we simulated the ground surface and borehole waveforms at strong motion station IBUH03 where the large velocity pulse was observed on the ground surface. The simulations suggest that this large velocity pulse was generated from the combination of the large slip of the source and large site amplification of the velocity structure between the ground surface and borehole seismometers.

Gravity Field Interpretation for Major Fault Depth Detection in a Region Located SW- Qa’im / Iraq

This research deals with the qualitative and quantitative interpretation of Bouguer gravity anomaly data for a region located to the SW of Qa’im City within Anbar province by using 2D- mapping methods. The gravity residual field obtained graphically by subtracting the Regional Gravity values from the values of the total Bouguer anomaly. The residual gravity field processed in order to reduce noise by applying the gradient operator and 1st directional derivatives filtering. This was helpful in assigning the locations of sudden variation in Gravity values. Such variations may be produced by subsurface faults, fractures, cavities or subsurface facies lateral variations limits. A major fault was predicted to extend with the direction NE-SW. This fault is mentioned by previous studies as undefined subsurface fault depth within the sedimentary cover rocks. The results of this research that were obtained by gravity quantitative interpretation find that the depth to this major fault plane center is about 2.4 Km.

Gravity Field Interpretation for Major Fault Depth Detection in a Region Located SW- Qa’im / Iraq

This research deals with the qualitative and quantitative interpretation of Bouguer gravity anomaly data for a region located to the SW of Qa’im City within Anbar province by using 2D- mapping methods. The gravity residual field obtained graphically by subtracting the Regional Gravity values from the values of the total Bouguer anomaly. The residual gravity field processed in order to reduce noise by applying the gradient operator and 1st directional derivatives filtering. This was helpful in assigning the locations of sudden variation in Gravity values. Such variations may be produced by subsurface faults, fractures, cavities or subsurface facies lateral variations limits. A major fault was predicted to extend with the direction NE-SW. This fault is mentioned by previous studies as undefined subsurface fault depth within the sedimentary cover rocks. The results of this research that were obtained by gravity quantitative interpretation find that the depth to this major fault plane center is about 2.4 Km.

Redox-controlled selenide mineralization in the Upper Old Red Sandstone

Synopsis Selenium concentrations occur in organic-rich lithologies such as coal, and as secondary accumulations from the oxidative mobilization, migration and subsequent concentration upon encountering reductants such as organic matter or H 2 S. Here we assess the redox mineralization of copper and lead selenide phases in the cores of reduction spheroids in Devonian sedimentary red beds. We propose that the selenide mineralization occurred as descending meteoric fluids, supplied with selenium from Carboniferous coal seams, migrated through a major fault plane into underlying sandstones where localized, microbially-induced reducing conditions prevailed. These findings and other occurrences of selenide mineralization between Devonian and Carboniferous strata on the British Isles suggest a widespread selenide mineralization system between strata of that age. Supplementary material: Detailed quantitative methodologies and supplementary data are available at http://www.geolsoc.org.uk/SUP18770 .

Specialized mapping of crustal fault zones. Part 1: Basic theoretical concepts and principles

Specialized mapping of crustal fault zones. Part 1: Basic theoretical concepts and principles

The influence of perturbed stresses near faults on drilling strategy: A case study in Blacktip field, North Australia

When in-situ stresses are disturbed around large scale fractures, typically faults, the direction of principal stresses can deviate from the regional trend to a completely new direction. This can have a great impact on engineering design and planning. In a gas field offshore Australia, a number of drilling difficulties and wellbore instability were reported at lower depths of one of three wells, while two wellbores in the field did not encounter similar problems. A detailed geomechanics study performed on the wellbore of interest indicated that it approached one of four major fault planes in the area as it was drilled deeper. This caused large stress anisotropy between the two horizontal stresses at lower depths, leading to a stress regime change from a normal to a strike/slip regime. The large contrast between the minimum and maximum horizontal stresses induced a number of shear failures in the form of breakouts around the wellbore, which we also observed on caliper and image logs. Accordingly, after performing sensitivity analysis on wellbore trajectory, we developed a mechanical earth model (MEM) to examine the planned well trajectories for the development campaign. The results demonstrate that the existence of natural fractures at any scale may have significant influence on in-situ stresses and stresses induced during construction of an opening.

Paleoseismological analysis of an intraplate extensional structure: the Concud fault (Iberian Chain, eastern Spain)

The Concud fault is a 13.5 km long, NW–SE striking normal fault at the eastern Iberian Chain. Its recent (Late Pleistocene) slip history is characterized from mapping and trench analysis and discussed in the context of the accretion/incision history of the Alfambra River. The fault has been active since Late Pliocene times, with slip rates ranging from 0.07 to 0.33 mm/year that are consistent with its present-day geomorphologic expression. The most likely empirical correlation suggests that the associated paleoseisms have potential magnitudes close to 6.8, coseismic displacements of 2.0 m, and recurrence intervals from 6.1 to 28.9 ka. At least six paleoseismic events have been identified between 113 and 32 ka. The first three events (U to W) involved displacement along the major fault plane. The last three events (X to Z) encompassed downthrow and hanging-wall synthetic bending prompting fissure opening. This change is accompanied by a decrease in slip rate (from 0.63 to 0.08–0.17 mm/year) and has been attributed to activation of a synthetic blind fault at the hanging wall. The average coseismic displacement (1.9–2.0 m) and recurrence period (6.7–7.9 ka) inferred from this paleoseismic succession are within the ranges predicted from empirical correlation. Such paleoseismic activity contrasts with the moderate present-day seismicity of the area (maximum instrumental Mb = 4.4), which can be explained by the long recurrence interval that characterizes intraplate regions.

Optimum well trajectory design in a planned well in Blacktip field, Australia: a case study

A geomechanics study carried out in the Blacktip field, offshore Australia led to optimum wellbore deviation and azimuth to minimise drilling-associated instability problems near a major fault in the field. Elastic and strength properties of the formations and magnitude of principal stresses in the field were estimated from a mechanical earth model (MEM) based on offset well data. The direction of the minimum horizontal stresses was predicted from formation microresistivity image (FMI) logs available in offset wells. The MEM results were calibrated using results from laboratory experiments, well tests and drilling incidents from drilling reports. The MEM showed that formations at the lower section of the well are very competent and have high uniaxial strength; however, most of the failures in the form of breakouts observed from calliper and image logs were in this interval. Therefore, obtaining a good match between the model and observed failures required a large stress anisotropy to be considered for the lower section of the wellbore. Further investigations demonstrated that this is because the wellbore trajectory at deeper depth gets closer to the major fault plane, and this large stress anisotropy is due to the stress redistribution near the fault. The data from offset well was mapped into the planned trajectory, and the selection of the optimum trajectory and a stable mud weight window for the appropriate section led to successful drilling of the deviated well.

Fault and fluid interaction in a rifted margin: integrated study of calcite-sealed fault-related structures (southern Corinth margin)

Abstract This work integrates microstructural, petrologic, microthermometric and geochemical analysis of calcite-sealed fault-related structures of the major faults of the southern margin of the Corinth rift (Greece). It draws attention to the main deformational processes and fault–fluid interaction in fault zones along the whole margin. Data analysed come from the compact breccia located immediately adjacent to major fault planes. Samples were collected at different positions alongside different faults juxtaposing synrift continental deposits (hanging wall) against the prerift Pindus limestones (footwall). This implies hectometric fault displacements and that the fault zones have recorded a relatively long evolution of deformation. Our study identifies four main deformation features common to all studied faults: calcite cemented breccia, extensional veins, shear veins and fault slip surfaces. The integrated data analysis shows that deformation structures and fault rocks that coexist in the same outcrop formed at different depths and times. During inferred upward fault propagation, the style of deformation evolved from distributed (brecciation) to localized (slip surfaces) and from a closed system with fluid–rock equilibrium during brecciation to a more open one with limited influx of meteoric water during extensional and shear fracturing. This implies relative uplift of the footwall during fault propagation and fault interaction with different water aquifers as the fault propagates upwards. The results demonstrate similar fault evolution and fault–fluid interaction through the entire rifted margin and during the whole rifting period.

Episodic reactivation of large‐scale push moraines in front of the advancing Taku Glacier, Alaska

Taku Glacier, an advancing former tidewater glacier in Alaska, has been actively pushing its proglacial sediments along part of its terminus over the last 50 years, producing so‐called push moraines. The mobilization of these sediments, which were locally lifted more than 20 m above sea level by 2004, has happened episodically rather than steadily. The last major event of proglacial sediment deformation occurred in 2001, presumably caused by sliding along a basal detachment layer. Since then, most deformation has been localized within a few meters of the terminus, including impressive deformational features of the terminal ice, where slabs of ice, tens of centimeters in thickness, have undercut proglacial sediments and vegetation and lifted them up. Between 2002 and 2004, surface velocities and horizontal displacements were measured across the terminus and in the proglacial push moraine area. Sediment displacement was highest between the end of March and mid‐June. A decrease in displacement with distance from the terminus revealed that the sediments were deforming internally rather than along a basal décollement. We present a simple model which suggests that, under 2004 conditions, reactivation of major movement along this décollement is unlikely to happen, unless some critical factors change. These factors include (1) a steepening of the glacier surface, (2) an increased surface angle of the sediment wedge, and/or (3) higher water pressure in the system, which decreases the effective frictional resistance. An observed wet clay‐rich layer presumably acted as a major fault plane during the 2001 event.

Geophysical Characteristics of the Tow Valley Fault Zone in North-East Ireland

The Tow Valley Fault Zone in north-east Ireland consists of number of ENE–WSW trending major fault segments and shorter N–S ones with different dips, downthrows and geophysical characteristics. The fault zone is associated with high magnetic gradients and a marked north-westerly decrease in gravity. Modelling of gravity data suggests that near Garvagh (south-west) and Ballycastle (north-east) the major fault plane dips to the north-west at about 20°–25° whereas the central section dips at 56° to the north-west. Thick sediments (c. 2.4km), mainly Permo- Triassic in age, occur beneath the Tertiary basalts north-west of the fault zone. Ground-based magnetic profiles across the fault zone yield a range of signatures. At some localities the fault is characterised by a 1km-wide zone of fracturing in the Tertiary basalts. Seismic data indicate that the fault zone continues offshore to the north-east of Rathlin Island.

Thin-skin tectonics in the Essaouira basin (western High Atlas, Morocco): evidence from seismic interpretation and modelling

In the Essaouira basin, detailed re-examination of seismic profiles and the use of modelling computer programs based on widely accepted concepts in fold kinematics has allowed us to set additional kinematic constraints on the geometry of the structures in this area. Forward modelling, conducted with the help of computer programs, was carried out in order to find the best kinematic pathway accounting for the geometry of the folds. We have observed two main geometrical types: fault-bend folds and a fault-propagation fold. Simple fault-bend folds were observed at the Tabelaouart, Oued Tahria, Bouzergoun and N’dark anticlines. All the ramps are located within the Triassic formations and have variable height. However, the ramps in the western structures have a northerly dip, whereas the eastern anticlines have grown upon southerly-dipping ramps. The amount of displacement is variable. Complex fault-bend folds occur at the Amsitten anticline, developed upon three major fault planes. Finally, an example of fault-propagation folding was observed at the Jeer anticline. In conclusion, the cover in the Essaouira basin appears decoupled from its basement in most structures, and its kinematics follows a ramp-flat geometry. From the oil exploration point of view, we believe that the whole tectonics of the Essaouira basin has to be reviewed on the basis of geometrical analysis, in order to improve the knowledge on the potential targets.

Seismic hazard reappraisal from combined structural geology, geomorphology and cosmic ray exposure dating analyses: the Eastern Precordillera thrust system (NW Argentina)

Because earthquakes on large active thrust or reverse faults are not always accompanied with surface rupture, paleoseismological estimation of their associated seismic hazard is a difficult task. To improve the seismic hazard assessments in the Andean foreland of western Argentina (San Juan Province), this paper proposes a novel approach that combines structural geology, geomorphology and exposure age dating. The Eastern Precordillera of San Juan is probably one of the most active zones of thrust tectonics in the world. We concentrated on one major regional active reverse structure, the 145 km long Villic´um-Pedernal thrust, where this methodology allows one to: (1) constrain the Quaternary stress regime by inversion of geologically determined slip vectors on minor or major fault planes; (2) analyse the geometry and the geomorphic characteristics of the Villic´um-Pedernal thrust; and (3) estimate uplift and shortening rates through determination of in situ-produced 1 0 Be cosmic ray exposure (CRE) ages of abandoned and uplifted alluvial terraces. From a structural point of view, the Villic´um-Pedernal thrust can be subdivided into three thrust portions constituting major structural segments separated by oblique N40°E-trending fault branches. Along the three segments, inversion of fault slip data shows that the development of the Eastern Precordillera between 31°S and 32°S latitude is dominated by a pure compressive reverse faulting stress regime characterized by a N110° ′ 10°E-trending compressional stress axis (σ 1 ). A geomorphic study realized along the 18 km long Las Tapias fault segment combined with CRE ages shows that the minimum shortening rate calculated over the previous ∼20 kyr is at least of the order of 1 mm yr - 1 . An earthquake moment tensor sum has also been used to calculate a regional shortening rate caused by seismic deformation. This analysis of the focal solutions available for the last 23 yr shows that the seismic contribution may be three times greater than the shortening rate we determined for the Las Tapias fault (i.e. ∼3 mm yr - 1 ), suggesting that the San Juan region may have experienced a seismic crisis during the 20th century. Moreover, the ramp that controls the development of the Eastern Precordillera appears to be one of the main seismic sources in the San Juan area, particularly the 65 km long Villic´um-Las Tapias segment. A first-order evaluation of the seismic hazard parameters shows that this thrust segment can produce a maximum earthquake characterized by a moment magnitude of ∼7.3 (′0.1) and a recurrence interval of 2.4 (′1.5) kyr. This part of the Villic´um-Pedernal ramp may have ruptured during the Ms =7.4, 1944 San Juan earthquake producing very few surface ruptures and only distributed flexural slip deformation on to the Neogene foreland bedding planes between the Eastern Precordillera and Pie de Palo.

Application of a two-dimensional electrical tomography technique for investigating landslides along the Amman-Dead Sea highway, Jordan

Electrical tomography geophysical surveys were conducted with the SYSCAL-R2 resistivity instrument at the location of instantaneous rock failure of a few 1,000s m3 along the Amman–Dead Sea highway, Jordan, providing a ground image for investigating landslide sites which caused material damage and closed the road. This slide occurred along two major fault planes after heavy rainfall in a rock consisting of a succession of shale, marl and marly limestone layers which were folded, tilted and fractured. Three electrical tomography profiles were performed along the axis of the slope to assess the landslide risk in such potential unstable areas. The results obtained, based on two-dimensional inversion of field data, have allowed mapping of the shale zones at depths which are characterized by a lower resistivity value, and have demonstrated that the rupture was initiated at the contact between the shale mass (black colored) and the massive limestone (white, yellowish-brown colored).

Numerical modeling of Cenozoic stress patterns in the mid‐Norwegian margin and the northern North Sea

Numerical modeling of Cenozoic stress patterns in the northern North Sea and the mid‐Norwegian margin is presented, and the sense of potential slip along major fault planes belonging to the two areas is restored. We assume that the main regional source of stresses is the Atlantic ridge push as demonstrated by previous studies. Furthermore, we also assume a nearly consistent NW‐SE strike for the far‐field stress from continental breakup between Greenland and Norway (earliest Eocene) to present day. First, we applied the commercial two‐dimensional distinct element method (UDEC) to simulate Cenozoic stress and displacement patterns in the study area. Variations in rheology and major fault zones were introduced into the model. The Møre‐Trøndelag Fault Complex and its inferred continuation into the Shetland Platform forms the major mechanical discontinuity in the model. Second, we used the SORTAN method, developed at the University of Paris VI, to predict the sense of potential slip along major fault planes. The input for the SORTAN model was constrained by the geometry of the selected fault planes and local principal stress directions extracted from the UDEC modeling. Our results show that the Møre‐Trøndelag Fault Complex and its inferred continuation into the Shetland Platform act as a weak fault zone. This fault zone divides the study area into two different stress provinces: the continental margin and the northern North Sea. This result agrees well with the observed differences in Cenozoic structural evolution of the two areas. Compressive structures are observed along the continental margin, whereas relative tectonic quiescence characterizes the northern North Sea during the Tertiary. The restored stress patterns in the northern North Sea and the mid‐Norwegian margin also agree well with the observed present‐day stress configuration. Our analysis demonstrates a method to reconstruct the sense of slip on major fault planes by combining two complementary numerical tools (UDEC and SORTAN). As a result, it is demonstrated that oblique‐slip motions are mainly expected, in particular, strike‐slip and reverse dip‐slip faulting are simulated.

Deformation character and palaeo-fluid flow across a wrench fault within a Palaeozoic subduction–accretion system: Waratah Fault Zone, southeastern Australia

Mélange formation, cataclasis, meso- to micro-scale faulting, and veining reflect faulting processes within turbidite and limestone sequences juxtaposed along a steeply dipping, sinistral wrench-fault zone in the Lachlan Orogen, southeastern Australia. Fault damage occurs across a zone up to 600 m wide. Effects of faulting in the turbidites are shown by a 100–150 m wide zone of scaly mudstone-matrix mélange, mud-injection `dykes' and veinlets, and refolding of mélange fabrics, with minor subsidiary brittle-faulting and cataclasis extending up to 500 m from the major fault plane. Veining and cataclastic zones occur in the limestone and are most pronounced up to 100 m from the main brittle fault. Fluid inclusion data from quartz and calcite veins suggest faulting took place at temperatures between 160 and 200°C, whereas folding is inferred to have taken place at temperatures above 300°C. Fluid-assisted, fault zone `weakening' mechanisms (pressure solution/solution transfer) were active over the whole fault zone. Veining, characteristic of fluid-assisted fault zone `strengthening' processes (i.e. rock-mass cementation), is confined to the limestone sequence. Here, calcite precipation led to fault rocks with lower porosity and permeability than in the turbidite sequence. Overprinting between different veins and fractures, and zonation in vein cement suggest cyclic deformation and fluid flow. The repeated change between brittle fracturing and veining/cementation led to a combined conduit–barrier system in the limestone sequence, whereas the mélange zone in the turbidites acted as a fluid conduit only.