Conjugate Fault System Research Articles

The 2015 Mw 6.4 Pishan earthquake, China: geodetic modelling inferred from Sentinel-1A TOPS interferometry

This study investigates the 3 July 2015 (Mw=6.4) earthquake that affected Pishan County in Xinjiang, China. Using Synthetic Aperture Radar interferometry (InSAR), we mapped the near-field surface displacement of this event to better characterize the seismic source parameters. The inverted results suggest that a conjugate fault system could produce very similar deformation patterns as those observed in both ascending and descending InSAR observations, and the south-dipping fault is selected as the optimal fault responsible for the event. The selected fault was concentrated on a thrust fault with a strike of 112°, a dip of 25° and an average rake angle of 89°. The InSAR analysis reveals a fragmentation of the Western Kunlun north margin fault, and the overall deformation of the seismogenic fault is characterized by thrust motion, which is consistent with the transpressional tectonic characteristics of the major faults in this region.

A Slip Gap of the 2016Mw 6.6 Muji, Xinjiang, China, Earthquake Inferred from Sentinel‐1 TOPS Interferometry

ABSTRACT We use Sentinel‐1A/1B Terrain Observation with Progressive Scans (TOPS) data to map coseismic and postseismic displacements for the 25 November 2016 M w 6.6 Muji earthquake in southwestern Xinjiang, China. Two tracks (T27 and T107) of the TOPS data captured the coseismic deformation area with a maximum line‐of‐sight deformation of ∼0.25 m in the descending track (T107). The inverted best‐fitting coseismic slip model in this study shows that the mainshock was a right‐lateral strike‐slip rupture on the western segment of the Muji fault, with an optimal dip angle of 80°±4°. Two separated slip zones exist in the coseismic slip model, with the maximum slip of 1.6 m located in the western slip zone. The total geodetic moment is 9.87×10 18 N·m, equivalent to an earthquake of M w 6.6. Our model shows that a patch between the two slip zones remained unruptured during the mainshock, indicating a potential future seismic risk. Aftershocks recorded in the first 45 days after the mainshock delineate the modeled rupture patches well. The components of the regional Global Positioning System velocities parallel to the Muji fault have been inverted to obtain an interseismic slip rate of ∼10 mm/yr on this structure. The recent large strike‐slip earthquakes in this area, that is, the 2015 M w 7.2 Tajikistan earthquake (left‐lateral) and 2016 M w 6.6 Muji earthquake (right‐lateral), may be an indicator of conjugate fault systems at the west boundary between the Indian and Eurasian plates in response to north–south convergence produced by the collision of the two plates.

Coulomb Stress Interactions during theMw 5.8 Pawnee Sequence

ABSTRACT We investigate the stress interaction between the Watchorn, Labette, and Sooner Lake fault systems and the effect of precursory activities on the 3 September 2016 M w 5.8 Pawnee earthquake. We obtain fault‐plane solutions for earthquakes with sufficient azimuthal coverage using the HASH algorithm, and then perform coulomb stress analysis on both seismogenic faults and individual nodal planes. Our results found that the three M w ≥3.0 foreshocks exerted a cumulative coulomb stress change increase of 0.68–1.98 bars at the mainshock hypocenter and also promoted failure for most aftershocks within 2 km of the mainshock. The coulomb stress change of 5 bars exerted by the mainshock also promoted failure for most aftershocks within the conjugate fault system. The results suggest that earthquake interaction should be fully considered in hazard assessment for induced seismicity.

Dynamic faulting on a conjugate fault system detected by near-fault tilt measurements

There have been reports of conjugate faults that have ruptured during earthquakes. However, it is still unclear whether or not these conjugate faults ruptured coseismically during earthquakes. In this paper, we investigated near-fault ground tilt motions observed at the IWTH25 station during the 2008 Iwate-Miyagi Nairiku earthquake (M w 6.9). Since near-fault tilt motion is very sensitive to the fault geometry on which the slip occurs during an earthquake, these data make it possible to distinguish between the main fault rupture and a rupture on the conjugate fault. We examined several fault models that have already been proposed and confirmed that only the models with a conjugated fault could explain the tilt data observed at IWTH25. The results support the existence of simultaneous conjugate faulting during the main rupture. This will contribute to the understanding of earthquake rupture dynamics because the conjugate rupture releases the same shear strain as that released on the main fault, and thus it has been considered quite difficult for both ruptures to accelerate simultaneously.

Fault reconstructions using aeromagnetic data in the Great Bear magmatic zone, Northwest Territories, Canada

The Great Bear magmatic zone, located in Wopmay orogen, is a 1.875–1.84 Ga belt, 450 km long by 100 km wide of volcanic and allied plutonic rocks interpreted as a Paleoproterozoic magmatic arc. The belt, which contains economically important mineralization, was folded and subsequently cut by a swarm of northeast-striking transcurrent faults, which are part of a regional conjugate fault system interpreted to result from terminal collision of the Nahanni – Fort Simpson terrane. Fault reconstructions based on the interpretation of aeromagnetic data and geological maps provide first-order models of deformation mechanisms associated with, and the configuration of the Great Bear magmatic zone prior to, its dissection by northeast-striking transcurrent faults. The models show that vertical axis block rotation (plane strain) of ∼4.5° can explain fault offsets in the south, but that greater rotation is required to explain many of the displacements in the north. However, offsets on transcurrent faults that border the Camsell River district are greater than can be explained by vertical axis block rotation model alone and may include a component of Mesoproterozoic contractional deformation associated with the Racklan–Forward orogeny. Following reconstruction, iron oxide alkali alteration and associated mineralization, which pre-date transcurrent faulting, form a pair of northerly trending zones on the east and west margins of the belt. We suggest that these zones, whose exposure is related to broad synclinal folding of some of the oldest rocks in the Great Bear magmatic zone, are where iron oxide copper–gold (IOCG)-targeted exploration efforts should be focused on these areas in both outcrop and subcrop.

Source parameters of the 2005–2008 Balâ–Sırapınar (central Turkey) earthquakes: Implications for the internal deformation of the Anatolian plate

Active tectonics of central Anatolia is mainly governed by the collision of the African, Arabian and Anatolian plates, which causes westward escape of Anatolia along the North and East Anatolian Fault zones, and the counterclockwise rotation of the Kırşehir block with insignificant internal deformation. The formation of the present-day tectonic processes in this region can be deduced from geophysical prospecting and seismological data. Although the seismicity in central Anatolia is distinctively lower than that in the northern and eastern parts of the Anatolian plate, small and moderate earthquakes (2.5≤Mw≤6.0) mostly occurred in the region in the past decades or so. For example, intense earthquake activity was observed in the Balâ–Afşar–Sırapınar (Ankara, central Anatolia) region in the period of 2005 to 2008 with destructive earthquakes of July 30, 2005 (Mw=5.2); December 20, 2007 (Mw=5.7) and December 26, 2007 (Mw=5.6). Therefore, these earthquakes are crucial to analyze the shallow crustal deformation in the central Anatolian block. In the present study, we obtained source parameters of 2005–2008 earthquake sequence using the regional moment tensor (RMT) inversion method. We analyzed complete broad-band waveforms recorded at near-field distances (0.45°≤Δ≤3.6°). Our results reveal NW–SE directed right-lateral strike-slip faulting and NE–SW directed left-lateral strike-slip faulting mechanisms, which are clearly correlated with the conjugate fault systems in the Balâ–Afşar–Sırapınar region. However, some earthquakes also have E–W directed normal faulting components. We suggest that the major characteristics of 2005–2006 and 2007–2008 earthquake activity could have been dominantly associated with left-lateral and right-lateral strike-slip faulting mechanisms, respectively. The seismogenic depth is found to be about 8–10km. This result implies that earthquakes in the study region occurred mostly in the upper crust, which accommodates the strain by brittle deformation. Furthermore, our results are consistent with neotectonic features and available geophysical data (e.g., gravity, aeromagnetic and paleomagnetic) reported by previous studies. It may be envisioned that the joint interpretation of earthquake source parameters with those observations will shed light into the complex deformation processes for future studies.

Structural Geologic Evolution of the Butte District, Montana

The Butte district contains two porphyry Cu-Mo deposits and the younger zoned Main stage base metal lode deposits that formed in the period from 66 to 62 Ma, synchronous with Laramide compressional thrust faulting and folding in southwest Montana. New geologic mapping of the Butte district reveals three distinct episodes of deformation: 1. Gentle (20° ± 10°) NE tilting produced during Laramide compressional deformation, uplift, and exhumation during and after ore formation in the Late Cretaceous to Paleocene (~66–~53 Ma); 2. Moderate (10°–50°) NW tilting of Eocene age produced by NE-striking normal faults that are limited to the northwest part of the district and synchronous with the eruption of the Lowland Creek Volcanics; and 3. Miocene to present gentle (15°) ESE tilting in the hanging walls of the Continental, East Ridge, and Rocker normal faults. Stratigraphic relationships, isotopic ages, hornblende barometry, and fluid inclusion data indicate that exposures of the Butte Granite, which hosts mineralization, crystallized at ~6- to 9-km depth and that early porphyry Cu-Mo deposits formed at similar depths of 5 to 9 km. A period of rapid uplift and erosion removed about 7 km of rock from above the ore deposit between 66 to 64 Ma and 53 Ma, but was mostly completed by 59 Ma. Estimated exhumation rates range from 0.5 to 2 mm/yr, and uplift was likely most rapid between ~63.5 and 62 Ma during Main stage mineralization, which occurred at depths of 2 to 6 km. The Butte Granite and Boulder batholith were emplaced at 79 to 76 Ma into thrust fault ramps, which later became inactive near Butte as Laramide crustal shortening moved eastward in the Helena salient. The accelerated period of uplift and unroofing is attributed to renewed deformation along the Montana disturbed belt south of Butte that uplifted the south end of the Boulder batholith and produced ~20° of gentle NE tilting (episode I) in the district. The exhumation history of the deposit is therefore broadly contemporaneous with ore formation, and is consistent with the general transition from lithostatic to hydrostatic conditions that is evident from the telescoping of early porphyry Cu-Mo ores cut by the Main stage lode veins. Within a 5-m.y. period, the Laramide compressional regime near Butte evolved into an extensional environment characterized by normal faulting. The normal faults were synchronous with eruption of the 53 to 48 Ma Lowland Creek Volcanics, which directly overlie the Main stage veins in the northwest part of the district. Structural reconstruction of the district at the time of mineralization produces orientations of quartz porphyry dikes, porphyry Cu-Mo veinlets, Main stage veins, and alteration zonal patterns that are steeply dipping and symmetrical, similar to observations from other upright or restored porphyry copper deposits. Early porphyry Cu-Mo veins and dikes are oriented E-W and likely originated as tensile hydrofractures above a ductile magma carapace during Laramide shortening. Additionally, during the Laramide compressional phase, two conjugate fault systems occupied by Main stage veins are normal oblique-slip faults that record minor E-W and vertical shortening and N-S extension. These normal faults with minor offset likely resulted from brittle failure caused by doming above a volatile-rich and buoyant granitic magma chamber and cupola at depth. The structural evolution of the Butte district therefore reflects the interaction of a far-field compressive stress regime with local buoyant magmatic forces.

Multi‐fault rupture and successive triggering during the 2012 Mw 8.6 Sumatra offshore earthquake

On April 11, 2012 a Mw 8.6 strike‐slip earthquake struck the northern Sumatra offshore region, and became the largest intraplate event ever recorded there. Preliminary study results show a remarkably complex rupture pattern, on a fault system manifested by north‐south trending paleo‐transform faults and east‐west striking abyssal hill fabric. To image the rupture pattern of the earthquake, we back‐projected teleseismic P wave recordings observed at three regional seismic networks (EU, AU, and F‐net). Our results indicate that the earthquake ruptured on a conjugate fault system, composed of two subparallel WNW‐ESE trending faults, and a NNE‐SSW striking fault in between, for a duration of at least 120 s. The rupture started at the WNW end of the first WNW‐ESE trending fault located at the east of the conjugate fault system, and propagated toward ESE. It then jumped to the second NNE‐SSW trending fault located west of the first fault, and first extended SSWward and 15 s later NNEward. After its end on the second fault, the rupture jumped onto the third WNW‐ESE trending fault and continued WNWward. The static Coulomb stress changes calculated from the rupture of the first and then the second faults, based on simplified uniform slip models, suggest that initiation of the rupture on the second fault could be statically and dynamically triggered by the first fault. However, the third fault was primarily dynamically triggered by S or even Love waves radiated from the southern branch of the second fault.

Mountain front migration and drainage captures related to fault segment linkage and growth: The Polopos transpressive fault zone (southeastern Betics, SE Spain)

The Polopos E–W- to ESE–WNW-oriented dextral-reverse fault zone is formed by the North Alhamilla reverse fault and the North and South Gafarillos dextral faults. It is a conjugate fault system of the sinistral NNE–SSW Palomares fault zone, active from the late most Tortonian (≈7 Ma) up to the late Pleistocene (≥70 ky) in the southeastern Betics. The helicoidal geometry of the fault zone permits to shift SE-directed movement along the South Cabrera reverse fault to NW-directed shortening along the North Alhamilla reverse fault via vertical Gafarillos fault segments, in between. Since the Messinian, fault activity migrated southwards forming the South Gafarillos fault and displacing the active fault-related mountain-front from the north to the south of Sierra de Polopos; whilst recent activity of the North Alhamilla reverse fault migrated westwards. The Polopos fault zone determined the differential uplift between the Sierra Alhamilla and the Tabernas-Sorbas basin promoting the middle Pleistocene capture that occurred in the southern margin of the Sorbas basin. Continued tectonic uplift of the Sierra Alhamilla-Polopos and Cabrera anticlinoria and local subsidence associated to the Palomares fault zone in the Vera basin promoted the headward erosion of the Aguas river drainage that captured the Sorbas basin during the late Pleistocene.

Mid Silurian–Carboniferous tectonic and depositional history of the Darling Basin Conjugate Fault System, western New South Wales: Overview

Mid Silurian–Late Devonian sandstone-rich strata, largely fluvial and several kilometres thick, were deposited in the Darling Basin while the strata were deformed largely by strike-slip and thrust faulting within and adjacent to the basin. This study describes the history of strata exposed in eight areas where strata were mostly deposited from braided streams on braid-plains and streams flowing on alluvial fans, with minor lacustrine and marine deposition. At the centre of the basin, the 1000 km-long, northeast-trending, slightly convex to the northwest Darling Lineament (Fault), intersects the south-southeast-trending ∼80 km-long Lake Wintlow Line (Fault) and the ∼300 km-long north-northwest-trending Koonenberry Fault (which is partly exposed in the study area for ∼50 km). Together these faults form the Darling Basin Conjugate Fault System. The history of the basin suggests that principal stresses switched twice from north-northeast–south-southwest to west-northwest–east-southeast and then back to north-northeast–south-southwest during Mid Silurian–Late Devonian time. Sectors of the DBCFS under greater compression during these orogenic phases tended to be uplifted and eroded, whereas sectors with less compression tended to subside, to accumulate fluvial and shallow marine sediments. The model's recognition indicates that there has been little deformation in the Darling Basin since Mid Carboniferous time.

Relocation of the 10 March 2011 Yingjiang, China, earthquake sequence and its tectonic implications

An earthquake with MS5.8 occurred on 10 March 2011 in Yingjiang county, western Yunnan, China. This earthquake caused 25 deaths and over 250 injuries. In order to better understand the seismotectonics in the region, we collected the arrival time data from the Yunnan seismic observational bulletins during 1 January to 25 March 2011, and precisely hand-picked the arrival times from high-quality seismograms that were recorded by the temporary seismic stations deployed by our Institute of Crustal Dynamics, China Earthquake Administration. Using these arrival times, we relocated all the earthquakes including the Yingjiang mainshock and its aftershocks using the double-difference relocation algorithm. Our results show that the relocated earthquakes dominantly occurred along the ENE direction and formed an upside-down bow-shaped structure in depth. It is also observed that after the Yingjiang mainshock, some aftershocks extended toward the SSE over about 10 km. These results may indicate that the Yingjiang mainshock ruptured a conjugate fault system consisting of the ENE trending Da Yingjiang fault and a SSE trending blind fault. Such structural features could contribute to severely seismic hazards during the moderate-size Yingjiang earthquake.

Evolution of the hourglass structures in the Laminaria High, Timor Sea: Implications for hydrocarbon traps

In cross-section, an hourglass structure can be visualized as an older horst block and superimposed, younger graben. Bounding faults of the horst and graben blocks represent separate conjugate fault systems formed by two distinct episodes of extension in the Timor Sea during Late Jurassic–Early Cretaceous (1st-phase) and Middle Miocene – Pliocene (2nd-phase); with an ∼120My hiatus of limited or no fault activity in-between. Horst blocks were formed by the 1st-phase of extension and buried post-deformation. With the onset of the 2nd-phase of extension, the hourglass geometry began to form by nucleation of the graben-bounding faults in the shallow sedimentary section, in isolation from the horst-bounding faults. Location of the graben is biased by the buried horst block and graben-bounding faults grew down-dip from the shallow locus of nucleation toward the underlying horst block on which only minor reactivation occurred. Detachment of the two systems in this way was predominantly controlled by the first-order mechanical layering. A thick, shale-rich, ductile layer separates the horst- and graben-bounding fault systems and acts as a barrier to vertical fault propagation. Confinement of the graben-bounding faults into the shallow section was also facilitated by outer-arc style extension due to lithospheric flexure controlling the 2nd-phase strain in the region. The complex evolution history and the composite nature of the hourglass structures resulted in systematic along-dip variation of displacement. This variation predominantly relates to syn-kinematic deposition and location of fault tips that are controlled by the ductile layer. The presented evolution model of the hourglass structures concentrates fault tips and related stress perturbation onto the top seal and is likely to be detrimental to top-seal integrity.

Young, active conjugate strike–slip deformation in West Sichuan: evidence for the stress–strain pattern of the southeastern Tibetan Plateau

The active kinematics of the eastern Tibetan Plateau are characterized by the southeastward movement of a major tectonic unit, the Chuan-Dian crustal fragment, bounded by the left-lateral Xianshuihe–Xiaojiang fault in the northeast and the right-lateral Red River–Ailao Shan shear zone in the southwest. Our field structural and geomorphic observations define two sets of young, active strike–slip faults within the northern part of the fragment that lie within the SE Tibetan Plateau. One set trends NE–SW with right-lateral displacement and includes the Jiulong, Batang, and Derong faults. The second set trends NW–SE with left-lateral displacement and includes the Xianshuihe, Litang, Xiangcheng, Zhongdian, and Xuebo faults. Strike–slip displacements along these faults were established by the deflection and offset of streams and various lithologic units; these offsets yield an average magnitude of right- and left-lateral displacements of ∼15–35 km. Using 5.7–3.5 Ma as the time of onset of the late-stage evolution of the Xianshuihe fault and the regional stream incision within this part of the plateau as a proxy for the initiation age of conjugate strike–slip faulting, we have determined an average slip rate of ∼2.6–9.4 mm/year. These two sets of strike–slip faults intersect at an obtuse angle that ranges from 100° to 140° facing east and west; the fault sets define a conjugate strike–slip pattern that expresses internal E–W shortening in the northern part of the Chuan-Dian crustal fragment. These conjugate faults are interpreted to have experienced clockwise and counterclockwise rotations of up to 20°. The presence of this conjugate fault system demonstrates that this part of the Tibetan Plateau is undergoing not only southward movement, but also E–W shortening and N–S lengthening due to convergence between the Sichuan Basin and the eastern Himalayan syntaxis.

Late Devonian–Early Carboniferous structure and tectonics of part of the northeast sector of the Darling Basin Conjugate Fault System, western New South Wales

The Darling Basin, located in the northern part of the Lachlan Orogen, is cut by the 1000 km long east-northeast-trending Darling Lineament (Fault) which intersects the Koonenberry Fault to the north and the Mt Wintlow High (fault) to the south. During the Lachlan Orogeny these faults formed the Darling Basin Conjugate Fault System (DBCFS) in which the four sectors (NW, NE, SE, SW) showed alternate compression/uplift, and tension/subsidence. The DBCFS underwent five phases of development. During orogenic Phase 5, the northeast sector was in compression, and thick distal braidplains, deposited during orogenic Phase 4, when the sector was in tension, and underlying the older strata, were deformed. The study area has a 4–10 km wide concave northeast-facing fault zone, largely comprising, dextral faults, which is consistent with some tectonic transport of the fault blocks of the zone, largely to the southwest. Faulting followed an earlier period of east–west and southeast–northwest folding. This structure overprints unexposed strata deposited during orogenic phases 1, 2 and 4 in the Lachlan Orogeny as well as pre-Late Ordovician structure (Delamerian Orogeny).

Seismic imaging of the Naga thrust using multiscale waveform inversion

This case study images the structural features related to the Naga thrust fault (northeast India) using a combination of multiscale waveform inversion and prestack depth migration (PSDM). The waveform model and the PSDM image complement each other: the former provides a physical-property map (P-wave velocity model) and the latter provides a structural image. The velocity model encompassing the starting model for waveform inversion is constructed using joint inversion of first and reflected traveltimes. The [Formula: see text] data are inverted consecutively in [Formula: see text] bandwidths to yield the final waveform model, which in turn is used for PSDM. The PSDM image and the waveform model are consistent with the lithological interpretation of an inline exploratory well. When interpreted jointly, the PSDM image and the waveform model reveal the presence of a conjugate fault system in the Naga thrust and fold belt.

Middle to Late Devonian distal braidplain deposition in the northeast sector of the Darling Basin Conjugate Fault System, near White Cliffs settlement, western New South Wales

Sandstone-rich, 6 km-thick, Eifelian–Frasnian strata of the northeast sector of the Darling Basin Conjugate Fault System, lie north of the Darling River Lineament, east of the Koonenberry Fault, and south of the Olepeloko Fault. Fossils are very rare in the study area: exceptions are in the Skolithos-rich beds of the Paroo National Park, and the early Eifelian fish-fragment horizon near Mt Jack Station. Four marker horizons are known southeast of the Paroo National Park: (i) the Mt Jack fish-fragment horizon; (ii) a Skolithos-rich belt at Momba Station; (iii) the mid-Givetian Keginni Conglomerate Member; and (iv) a ∼20 m-thick vein quartz clast-rich unit that crops out near the base of the Frasnian strata. Four braidplains are mapped: (i) White Cliffs (largest); (ii) Mt Jack; (iii) Bullocky Bore; and (iv) the distal part of the Keginni Conglomerate Member. Sediment derivation was from west of the Koonenberry Fault (White Cliffs Braidplain) from the northwest (Mt Jack Braidplain), from the north (Bullocky Bore Braidplain) and from the southeast (Keginni Conglomerate Braidplain). The braided streams/rivers depositing the sheet braidplains were very shallow, and sheet-flood deposition on the braidplains was widespread.

Stress Partitioning: a Practical Concept for Analysing Boundary Conditions of Brittle Deformation

Although conjugate fault systems cannot accommodate three-dimensional strain, the notion of stress-driven fracturing based upon Mohr-Coulomb's failure criterium can be reconciled with any kinematic boundary condition if a non-static scenario is considered. The concept of stress partitioning is proposed as a tool for understanding the mechanisms allowing such compatibility. It describes stress changes that occur in response to failure events, giving the appearance that the total stress field is decoupled into distinct, independent components. It can be mainly applied to biaxial horizontal loading conditions (e.g. multidirectional tension or multidirectional compression in intraplate regions). Swapping of horizontal stress axes, caused by stress drop subsequent to failure, can result in two distinct stress events and two, either tensile or shear fracture systems with nearly orthogonal strikes. Each fracture event develops according to Mohr-Coulomb's and Griffith's failure criteria, but the resulting overall deformation is three-dimensional.

Duplex architecture and late‐orogenic backthrusting in Foredeep Units of the Northern Apennines (Italy)

AbstractThe Northern Apennines of Italy is a fold and thrust belt that resulted from the NE‐ward progressive overthrusting of a Mesoalpine stacking (the ocean‐derived Ligurian Units) onto the detached sedimentary cover of the Adria plate continental margin (Foredeep Units). The Futa Pass area represents a key sector for the reconstruction of the deformation history of two Foredeep Units (Acquerino and Carigiola Units). The tectonic evolution of this sector is characterized by the superposition of three main deformation stages, with a constant NNE–SSW compression direction. The oldest structure is represented by the NNE‐verging Acquerino Unit duplex structure, the roof thrust of which is represented by the Ligurian stacking basal thrust. The interpretation of this structure as a large‐scale duplex is supported by the presence in the outer sectors of the Northern Apennines belt of Ligurian Units directly overthrust on younger Foredeep Units. In the second deformation stage the NNE‐verging Tavaiano Thrust developed. This regionally significant tectonic surface juxtaposes the Acquerino Unit (already developed as a duplex) and the overlying Ligurian Units, onto the Carigiola Unit. During this stage the fault pattern of the Carigiola Unit was also developed, characterized by two conjugate fault systems, coherent with a NNE–SSW maximum compression direction. During the last deformation stage, a backthrusting with a top‐to‐the SSW sense of movement (the Marcoiano Backthrust) brings the Carigiola Unit and its tectonic cover over the Acquerino and Ligurian Units, with the development of a large footwall syncline. The deformation history presented here differs from previous studies, and so provides a contribution to the debate on Northern Apennines tectonic evolution. Copyright © 2008 John Wiley & Sons, Ltd.

Early Devonian synorogenic alluvial-fan deposits of the Maccullochs Range, western New South Wales

The Early Devonian, Maccullochs Range beds (new) of the Winduck Interval largely comprise non-marine fine-grained sheet-flood-deposited sandstones which lie in the southeast sector of the Darling Basin Conjugate Fault System. Deposition of the >2.5 km-thick sequence occurred on the Wilcannia, Towers and Coolabah Bore alluvial fans, that were sourced largely from lightly indurated sandstone caps overlying a large basement high lying north of the Darling River Lineament, and also from west of Maccullochs Range (Coolabah Bore Fan). Four lithofacies are recognised. Lithofacies 1, massive sandstone, is proximal and was deposited from hyperconcentrated sheet floods. The more distal lithofacies 2 is partly massive, partly laminated and partly affected by soft sediment slumping during its deposition. It contains 1.3 – 3.5 m-thick sheet-flood successions that rarely show cross-bedding. Lithofacies 3 and 4 are minor: lithofacies 3, stream-flood deposited, comprises coarse-grained, pebbly sandstone and lithofacies 4, transient playa lake deposits that are locally intercalated with lithofacies 2. In lithofacies 2, thick massive fine-grained sandstone is commonly overlain by laminated sandstone that was deformed when soft. Incised channel deposits in lithofacies 2 deposits are rare and palaeosols were not discovered. Permanency of the positions of two of the alluvial fans, and by inference their feeder streams, remained unchanged for ∼9 million years. The fans overlie probable floodplain deposits observed in a quarry in the easternmost part of the study area. Marine fossils are very minor in the range—the brachiopod Howellella jaqueti at one locality indicates an Early Devonian age for one of the brief marine incursions into what was normally an alluvial-fan environment. Very brief marine incursions elsewhere in the group are deduced from the presence of very rare fossil gastropods.

Current slip rates on conjugate strike‐slip faults in central Tibet using synthetic aperture radar interferometry

We estimate the current slip rates on active conjugate strike‐slip faults in central Tibet using repeat‐pass synthetic aperture radar interferometry (InSAR). The conjugate fault systems are centered along the east trending Late Jurassic–Early Cretaceous Bangong‐Nujiang suture zone and are composed of NE striking left‐slip faults to the north and NW striking right‐slip faults to the south. The surface displacement field obtained from InSAR data show 30‐ to 60‐km‐wide zones of concentrated shear that coincide with active fault traces observed in the field. The radar data indicate that, within a 200‐ to 300‐km‐wide belt, the deformation regime defined by the conjugate strike‐slip faults is accommodating ∼5 mm yr−1 of pure shear contraction oriented in the N10°E direction and ∼6 mm yr−1 of right‐lateral simple shear in the N110°E direction. The observation of localized strain along faults indicates that faulting is the dominant mode of deformation in central Tibet with seismogenic depths extending down to ∼25 km. Furthermore, extrapolating the current slip rates estimated for the central Tibet faults, the total magnitude of fault slip based on geological observations would only require the faults to have initiated sometime in the past 2–3 Myr. This appears to contradict the few geochronologic constraints on fault initiation at 8 Ma or even earlier. This discrepancy suggests that the fault slip rates may not have remained constant through time but have accelerated in the recent period. With the exception of the slip rate on the Gyaring Co fault, the slip rates that we determined on the conjugate strike‐slip faults in central Tibet are significantly slower than the rates on faults that bound the Tibetan Plateau, such as the left‐slip Altyn Tagh fault to the north. This observation suggests that although deformation is active within central Tibet, plateau‐bounding structures are dominant in absorbing Indo‐Asian convergence.