Dipping Thrust Research Articles

Numerical study on the dynamic process of ramjet/scramjet mode transition in the integrated RBCC full flow path through multistage fuel injection strategies

The rocket-based combined-cycle (RBCC) engine usually completes the transition process from ramjet to scramjet mode under the Ma∞ = 5.5–6.0. The dual-mode (ramjet/scramjet) transient process is an important technology for engine operation. CFD modeling based on Reynolds average Navier-Stokes was for studying the influence of fuel injection position, high-temperature rocket jet and fuel throttling time on the combustion flow structure and transient characteristics of RBCC engine during the mode transiton . The results showed that whether RBCC engine could successfully achieve stable mode transition was mainly influenced by flame stability in the combustor. When the rocket shuts down, it was more suitable to choose the fuel injection arrangement which distributed downstream of the combustor to realize relatively smooth mode transition. The analysis shows that in the mode transition process, using the synergistic combustion-supporting effect of the cavity and the strut is beneficial to improve the fuel combustion efficiency and reduce the thrust fluctuation. Although the high temperature rocket jet with low mass flow rate cannot maintain the fuel combustion in the isolator at high Mach number, it can expand the high temperature combustion area width in the central flow of RBCC engine and increase the secondary fuel combustion efficiency. Therefore, keeping the rocket running at low mass flow rate can reduce the thrust drop caused by insufficient fuel heat release. When adopting a mode transition strategy that throttles the fuel linearly over time, the engine can go through the thrust dip more smoothly, but this correspondingly increases the time required for the internal flow field to stabilize.

Seismic reflection imaging of crustal deformation within the eastern Yarlung-Zangbo suture zone

Various models have been proposed to explain formational mechanisms for the Himalayan orogeny but uncertainties remain concerning uplift processes and deeper crustal structure of the orogen. Imaging of the orogen's deep structure can help resolve these uncertainties. This paper describes one migrated deep seismic reflection profile across the eastern Yarlung-zangbo suture (YZS) at 92° E, which provides a high resolution image of crustal structure that reveals (1) Yarlhashampo dome is divided into upper, middle and lower tectonic units by two detachments from rim, mantle to the core of dome, (2) one blind north-dipping reverse fault that offsets the South Tibet detachment (STD) developed along the northern flank of the Yarlhashampo dome, (3) a shift of the Main Himalayan thrust (MHT) dip angle from 18° into relatively gentle dips (6°) in the central part of the profile (18–20 s, t.w.t). Meantime, further inferring that (4) North-south compression event happened after ca.10 Ma in North Himalayas, (5) multi-stage duplexing as the primary mechanism for crustal thickening in the eastern YZS based on interpreted structures.

Constraining the Dip of Shallow, Shallowly Dipping Thrust Events Using Long‐Period Love Wave Radiation Patterns: Applications to the 25 October 2010 Mentawai, Indonesia, and 4 May 2018 Hawaii Island Earthquakes

AbstractConstraining precise faulting geometry for shallow, shallowly dipping thrust earthquakes is a common challenge. Plate boundary megathrust faults near the trench and décollement faults beneath volcanic islands and nappes may dip only a few degrees. Long‐period point source moment tensor waveform inversions provide limited resolution of shallow fault dip angle. The possibility of splay faulting requires precise dip estimation. High sensitivity to dip is provided by long‐period Love wave amplitude azimuthal radiation patterns, which undergo rapid change from four lobed to two lobed as dip decreases from 10° to 0°. Modeling variability in Love wave nodal amplitudes allows the dip to be determined to within a few degrees. This is demonstrated for the 25 October 2010 Mentawai (MWW 7.8) tsunami earthquake, which ruptured the 2.0–5.0° dipping megathrust beneath the shallow sedimentary wedge offshore of Indonesia, and the 4 May 2018 Hawaii Island (MWW 6.9) thrust earthquake, which ruptured the 2.5–7.5° dipping décollement under the island flank.

Active tectonics of Erçek Lake Basin and lithostratigraphy of basin deposits (Van, Turkey)

The Erçek Lake Basin
 (ELB) is located in the eastern part of Van Lake and has an area of approximately
 100 km2. The eastern section presents gully morphology towards
 Özalp. Oligo-Miocene and Plio-Quaternary units cover the basement rocks of the
 study area. Oligo-Miocene units are folded on both the southern and northern
 parts of ELB. However, in the north of the basin, northward dipping thrust
 faults generally developed along E-W. In the south, the fold axes differ by a
 maximum of 30 ° from the E-W to the north. The distribution of the structural
 elements within the Plio-Quaternary units is rather limited, and these are more
 prominent in the north of the Erçek Lake. There are a few normal faults in
 these structural elements. The development of these normal faults occurred as a
 consequence of the N-S compression in the region and developed in the active
 tectonic evolution of the region. The Kozluca left lateral strike-slip fault,
 which also deforms the western margin of Lake Erçek and the intra-lake
 morphology, is one of the other intra-plate structural elements within the
 contracted continental crust.

A Neotectonic based Geomorphic Analysis using Remote Sensing Data to Delineate Potential Areas of Hydrocarbon Exploration: Cachar Area, Assam

Abstract: The Assam Arakan fold thrust belt has highly deformed folded units of Tertiary sediments bounded by eastward dipping thrust slices with a convexity towards west. In the Tripura-Cachar region, this folded belt is characterized by the occurrence of wide synclines and narrow anticlines that hosts a number of hydrocarbon producing fields. In the Cachar area of Assam, most of these fields occur in the culmination of anticlinal structures. Other wells drilled in analogous structural settings are found to be dry. In this paper a neotectonic based geomorphic analysis is carried out to delineate a fault network and geomorphic highs in Cachar area as expressions of sub-surface structures which had subsequently been validated by available geophysical data. Of these geomorphic highs, those that are in the synclinal areas are believed to represent subtle sub-surface structural highs. Synclinal structures associated with NNE-SSW faults might be considered interesting for hydrocarbon exploration and are subsequently categorized following their degree of confidence for exploration of hydrocarbon. Additionally, a genetic model of the structures in the region is also proposed.

Evidences of inclined transpression at the contact between Vinjamuru group and Udayagiri group of Nellore Schist Belt, Andhra Pradesh, India

The Nellore Schist Belt (NSB) is a curvilinear Archaean schist belt, approximately 350 km long and 8–50 km wide. The Nellore Schist Belt is considered to be Neoarchean in age and stratigraphically NSB is classified as the western Udayagiri group (dominated by metasediments) and underlying eastern Vinjamuru group (dominated by metabasalts). There is a long controversy regarding the contact relationship between Udayagiri and Vinjamuru groups. Earlier researchers regarded the contact between two groups as tectonic on the basis of metamorphism. A shear zone and a possible thrust contact between the two groups have also been reported. On the basis of present study, an NNW–SSE trending, westerly dipping inclined transpressional zone is found at the contact between Udayagiri and Vinjamuru groups in the central western part of the NSB. Kinematic analysis of both the hanging wall and foot wall of the westerly dipping thrust zone shows presence of strong S1 schistosity, shear bands and S-C fabric in both strike and dip section along with east-verging overturned fold, westerly dipping inverted beds, suggesting partitioning of non-coaxial deformation in strike-slip and dip-slip component along with a pure shear component. Strike-slip is more prominent in the northern part of the contact than the southern part. The presence of steep to moderate northerly plunging non-orthogonal stretching/mineral elongation lineation all along the contact and clockwise shift of plot of the same in stereo net from its orthogonal position and presence of other kinematic indicators in plan suggests a right lateral strike-slip component. As a whole, it is suggested that Udayagiri group is thrusted over Vinjamuru group along a westerly dipping thrust plane with a right lateral strike-slip motion and simultaneous E–W contraction.

Exhumation history of the Tatry Mountains, Western Carpathians, constrained by low‐temperature thermochronology

AbstractThis study tests alternative models for the growth of the Tatry Mountains (Central Western Carpathians) by the application of low‐temperature thermochronology. Zircon (U + Th)/He ages from the north of the range are mostly between 48 and 37 Ma and indicate cooling prior to the onset of fore‐arc sedimentation in the region (42–39 Ma). In contrast, zircon (U + Th)/He ages in the south of the range are around 22 Ma. Apatite fission track ages across the sampled sites range from 20 to 15 Ma. Apatite (U + Th)/He ages range from 18 to 14 Ma with little variation with elevation or horizontal location. Based on thermal modeling and tectonic reconstructions, these Miocene ages are interpreted as cooling in the hanging wall of a northward dipping thrust ramp in the current location of the sub‐Tatric fault with cooling rates of ~20°C/Myr at ~22–14 Ma. Modeled cooling histories require an abrupt deceleration in cooling after ~14 Ma to <5°C/Myr. This is associated with termination of deformation in the Outer Carpathians and is synchronous with the transition of the Pannonian Basin from a syn‐rift to a postrift stage and with termination of N‐S compression in the northern part of the Central Western Carpathians. Overall, the timing of shortening and exhumation is synchronous with the formation of the Outer Carpathian orogen and so the Miocene exhumation of the Tatry records retrovergent thrusting at the northern margin of the Alcapa microplate.

Intrinsic versus extrinsic variability of analogue sand-box experiments – Insights from statistical analysis of repeated accretionary sand wedge experiments

Analogue models are not perfectly reproducible even under controlled boundary conditions which make their interpretation and application not always straight forward. As any scientific experiment they include some random component which can be influenced both by intrinsic (inherent processes) and extrinsic (boundary conditions, material properties) sources. In order to help in the assessment of analogue model results, we discriminate and quantify the intrinsic versus extrinsic variability of results from “sandbox” models of accretionary wedges that were repeated in a controlled environment. The extrinsic source of variability, i.e. the parameter varied is the nature of the décollement (material, friction and thickness). Experiment observables include geometric properties of the faults (lifetime, spacing, dip) as well as wedge geometry (height, slope, length).For each variable we calculated the coefficient of variance (CV) and quantified the variability as a symmetric distribution (Normal, Laplacian) or asymmetric distribution (Gamma) using a Chi squared test (χ2). Observables like fault dip/back thrust dip (CV = 0.6–0.7/0.2–0.6) are less variable and decrease in magnitude with decreasing basal friction. Variables that are time dependent like fault lifetime (CV = 0.19–0.56) and fault spacing (CV = 0.12 – 0.36) have a higher CV consequently affecting the variability of wedge slope (CV = 0.12–0.33). These observables also increase in magnitude with increasing basal friction. As the mechanical complexity of the evolving wedge increases over time so does the CV and asymmetry of the distribution. In addition, we confirm the repeatability of experiments using an ANOVA test. Through the statistical analysis of results from repeated experiments we present a tool to quantify variability and an alternative method to gaining better insights into the dynamic mechanics of deformation in analogue sand wedges.

Faulted craters as indicators for thrust motions on Mercury

Abstract Craters cross-cut by faults are used as markers to obtain fault geometric and kinematic properties. Assuming that the shape of these craters was originally circular, it is possible to measure the horizontal and vertical components of fault displacement as well as the slip trend. By applying trigonometric relations, slip plunge, displacement magnitude, fault true dip and fault rake can be derived from the observed values. An example application of this method on craters faulted by lobate scarps on Mercury shows that most of these inferred reverse faults have moderate oblique-slip trends. Moreover, the derived dips of thrusts vary over a wide range of angles. Some preliminary results in terms of fault rake compared with fault dip, strike and latitude are presented together with a pilot study to test and discriminate global tectonic models suggested for the evolution of Mercury. The possibility of estimating quantitative fault parameters through remotely sensed data provides significant assistance in the structural characterization of faults on planetary surfaces.

Global correlations between maximum magnitudes of subduction zone interface thrust earthquakes and physical parameters of subduction zones

The maximum earthquake magnitude recorded for subduction zone plate boundaries varies considerably on Earth, with some subduction zone segments producing giant subduction zone thrust earthquakes (e.g. Chile, Alaska, Sumatra–Andaman, Japan) and others producing relatively small earthquakes (e.g. Mariana, Scotia). Here we show how such variability might depend on various subduction zone parameters. We present 24 physical parameters that characterize these subduction zones in terms of their geometry, kinematics, geology and dynamics. We have investigated correlations between these parameters and the maximum recorded moment magnitude (MW) for subduction zone segments in the period 1900–June 2012. The investigations were done for one dataset using a geological subduction zone segmentation (44 segments) and for two datasets (rupture zone dataset and epicenter dataset) using a 200km segmentation (241 segments). All linear correlations for the rupture zone dataset and the epicenter dataset (|R|=0.00–0.30) and for the geological dataset (|R|=0.02–0.51) are negligible-low, indicating that even for the highest correlation the best-fit regression line can only explain 26% of the variance. A comparative investigation of the observed ranges of the physical parameters for subduction segments with MW>8.5 and the observed ranges for all subduction segments gives more useful insight into the spatial distribution of giant subduction thrust earthquakes. For segments with MW>8.5 distinct (narrow) ranges are observed for several parameters, most notably the trench-normal overriding plate deformation rate (vOPD⊥, i.e. the relative velocity between forearc and stable far-field backarc), trench-normal absolute trench rollback velocity (vT⊥), subduction partitioning ratio (vSP⊥/vS⊥, the fraction of the subduction velocity that is accommodated by subducting plate motion), subduction thrust dip angle (δST), subduction thrust curvature (CST), and trench curvature angle (αT). The results indicate that MW>8.5 subduction earthquakes occur for rapidly shortening to slowly extending overriding plates (−3.0⩽vOPD⊥⩽2.3cm/yr), slow trench velocities (−2.9⩽vT⊥⩽2.8cm/yr), moderate to high subduction partitioning ratios (vSP⊥/vS⊥⩽0.3–1.4), low subduction thrust dip angles (δST⩽30°), low subduction thrust curvature (CST⩽2.0×10−13m−2) and low trench curvature angles (−6.3°⩽αT⩽9.8°). Epicenters of giant earthquakes with MW>8.5 only occur at trench segments bordering overriding plates that experience shortening or are neutral (vOPD⊥⩽0), suggesting that such earthquakes initiate at mechanically highly coupled segments of the subduction zone interface that have a relatively high normal stress (deviatoric compression) on the interface (i.e. a normal stress asperity). Notably, for the three largest recorded earthquakes (Chile 1960, Alaska 1964, Sumatra–Andaman 2004) the earthquake rupture propagated from a zone of compressive deviatoric normal stress on the subduction zone interface to a region of lower normal stress (neutral or deviatoric tension). Stress asperities should be seen separately from frictional asperities that result from a variation in friction coefficient along the subduction zone interface. We have developed a global map in which individual subduction zone segments have been ranked in terms of their predicted capability of generating a giant subduction zone earthquake (MW>8.5) using the six most indicative subduction zone parameters (vOPD⊥, vT⊥, vSP⊥/vS⊥, δST, CST and αT). We identify a number of subduction zones and segments that rank highly, which implies a capability to generate MW>8.5 earthquakes. These include Sunda, North Sulawesi, Hikurangi, Nankai-northern Ryukyu, Kamchatka-Kuril-Japan, Aleutians-Alaska, Cascadia, Mexico-Central America, South America, Lesser Antilles, western Hellenic and Makran. Several subduction segments have a low score, most notably Scotia, New Hebrides and Mariana.

Major role of shear heating in intracontinental inverted metamorphism: Inference from a thermo-kinematic parametric study

Inverted metamorphism corresponds to the stacking of high-temperature metamorphic units structurally on top of lower-temperature units and is commonly observed along main thrusts in major orogens. Yet, in spite of many existing models, the origin and preservation of the metamorphic inversion in intracontinental collision belts are still debated. In this study, we use a crustal-scale 2D thermo-kinematic model in order to investigate the key parameters controlling the inversion of the geothermal gradient at crustal scale. Our results confirm that the kinematic framework strongly impacts the thermal evolution around the thrust. Erosion velocity and thermal conductivity of rocks are two parameters that control the spatial location of the thermal perturbation and the intensity of inversion, respectively. However, even in extreme kinematic configurations, i.e., convergence velocities > 3 cm ∙ yr− 1 and relatively high thrust dip angles ~ 30°, the thermal inversion is fleeting and thrust temperatures cannot reach the high temperature peak values characteristic of natural occurrences (> 600 °C) if shear heating is not taken into account. Conversion of mechanical energy into heat represents a main contribution to the thermal budget along main crustal shear zones. It leads to high temperature conditions in the thrust zone and our results attest that it is the only process that allows the preservation through time of an intense thermal inversion. Our quantification shows that shear heating is much more efficient than other processes such as accretion and surface denudation and is compatible with the observations of inverted metamorphism in the Himalayan or Variscan belts, for example. This comparison with natural occurrences suggests that the formation and preservation of intracontinental inverted metamorphism require shear zone viscosity values of the order of 1020–1021 Pa ∙ s for convergence velocities between 1 and 3 cm ∙ yr− 1.

Paleoearthquakes of the past 30,000 years along the North Tehran Fault (Iran)

The North Tehran Fault (NTF) is located at the southernmost piedmont of Central Alborz and crosses the northern suburbs of the Tehran metropolis and adjacent cities, where ∼15 million people live. Extending over a length of about 110 km, the NTF stands out as a major active fault and represents an important seismic hazard for the Iranian capital after historical seismicity. In order to characterize the activity of the NTF in terms of kinematics, magnitude and recurrence intervals of earthquakes, we carried out a first paleoseismological study of the fault within its central part between Tehran and Karaj cities. We opened a trench across a 3 m‐high fault scarp affecting Quaternary deposits. Our study shows that the scarp is the result of repeated events along a main N115°E trending shallow dipping thrust fault, associated with secondary ruptures. From the trench analysis and Infrared Stimulated Luminescence (IRSL) dating of fault‐related sediments, we interpreted between 6 and 7 surface‐rupturing events that occurred during the past 30 kyrs. Their magnitudes (estimated from the displacements along the faults) are comprised between 6.1 and 7.2. The two last events – the largest ‐ occurred during the past 7.9 ± 1.2 ka, which yields a Holocene slip rate of ∼0.3 mm/yr. The 7 earthquakes scenario suggests a regular periodicity with a mean recurrence interval of ∼3.8 kyrs. However, the two most recent events could correspond to the two largest historical earthquakes recorded in the area (in 312–280 B.C. and 1177 A.D.), and therefore suggest that the NTF activity is not regular.

Control of Operation Mode Transition in Dual-Bell Nozzles with Film Cooling

In addition to aspiration drag, the advantages gained by dual-bell nozzle utilization in practice are circumvented with a dip of thrust during operation mode transitions that occur outside of the optimal conditions. Practical transition from lowto high-altitude operationmode occurs at lower nozzle pressure ratios (NPRs) than the optimum transition point. The influence of the film-cooling flow on nozzle operationmode transition is investigated. It is found that the operationmode transitionNPR is increased, and the thrust dip during the transition is decreased through the injection of the film-cooling flow with an appropriate inlet pressure and flow rate.

Slip distribution from the 1 April 2007 Solomon Islands earthquake: A unique image of near‐trench rupture

We estimate the slip distribution from the MW 8.1 Solomon Islands earthquake in 2007, from two post‐seismic surveys measuring uplifted coral and submerged coastal features. The occurrence of islands extremely proximal to the trench and nucleation of rupture allowed for the collection of unprecedented coseismic deformation dataset along a large megathrust earthquake. Using data from the two surveys along the southeastern half of the slip zone within five weeks of the event, we model the elastic dislocation to identify the optimal (29°), and alternate (20°), dip and distribution of thrust along the southern rupture. The vertical deformation, which includes both coseismic and early postseismic deformation, has highly variable and large slip within 25 km of the trench and straddling Ranongga Island. The shallow focus of slip in the near‐trench area may explain the locally high tsunami run‐up on portions of Simbo Island, however the aseismic contribution of afterslip remains unknown.

Sensitivity of shear zones in orogenic wedges to surface processes and strain softening

We investigate the internal deformation of orogenic wedges growing by frontal accretion with a two-dimensional numerical model. Our models are limited to crustal deformation and assume a horizontal detachment as observed for various natural orogens (e.g. Alaska and Costa Rica). The model wedges develop as a result of convergence of a brittle sediment layer in front of a strong backstop. We find that our reference model develops in-sequence forward-thrusts which propagate upward from the basal detachment. For this reference model we investigate the sensitivity of shear zone activity to surface processes and strain softening. Model results show that diffusive or slope dependent erosion enhances material transport across the wedge and slows down forward propagation of the deformation front. Frictional strain softening focuses deformation into narrow shear zones and enhances displacement along them. This has also been postulated for natural thrusts such as the Glarus thrust in the Swiss Alps and the Moine thrust in the Scottish Caledonides. A second series of models investigates the effects of regularly spaced weak inclusions within the sediment layer which simulate remnants of previous deformation phases. These inclusions facilitate and focus internal deformation, influence the thrust dip and thrust vergence and enable thrust reactivation in the internal part of the wedge. Our results show that inactive thrusts in the internal part of the wedges may be reactivated in models with diffusive surface processes, strain softening or weak inclusions. Thrust reactivation occurs as models seek to maintain their critical taper angle. First order characteristics of our numerical models agree well with natural orogenic wedges and results from other numerical and analogue models.

Constraints on friction coefficients by an inverse analysis of sand box thrust dips

We measured the dips of thrusts forming in a uniform sand layer under horizontal shortening by a rigid emerging ramp in conditions of full erosion. Various ramp dips and four types of ramp material were used throughout the 12 experiments. In three experiments, the ramp was shortcut by a less steep thrust forming a spontaneous ramp in the sand. The forward modelling proposed to predict these observations involves (i) computing the total dissipation in the structure by using global force equilibrium and a parameterised kinematic framework including the possibility of shortcut development, and (ii) minimising the total dissipation of mechanical work with respect to the kinematic parameters (i.e., the thrust dips), for which two analytic solutions are found. The inverse problem involves computing probability densities over the parametric space of friction coefficients, including the internal friction angle of the sand, and friction angles of the four materials used on the rigid ramps. Practically, this involves computing a misfit (using the L2 norm) between the observed and predicted thrust dips for every possible value of the friction angles. The resulting probability density provides all the quantitative information that can be retrieved from the experiments in the light of our forward modelling. Ramp friction angles exhibit sharp probability changes at values that trigger the occurrence of shortcuts, thus yielding non-trivial bounds on the ramp friction values that are directly related to the observations of ramp and back thrust geometry. Also, the probability distribution of the internal sand friction, and those of the ramp frictions, is in good agreement with independent measurements. This approach is designed to be applicable to field studies of brittle deformation where geometries are observed and rheological parameters are sought.

Crustal deformations associated with the great Sumatra-Andaman earthquake deduced from continuous GPS observation

Abstract We analyzed continuous GPS data from more than 20 sites in Asia, Australia and islands in Indian Ocean in order to detect crustal deformations associated with the Sumatra-Andaman earthquake of December 26, 2004. Coseismic steps can be recognized at sites about 3,000 km away from the epicenter such as Kunming in south China, Quezon in Philippines, and Diego Garcia Island in central Indian Ocean. The largest displacement of about 26 cm is found at Phuket in Thailand about 600 km away from the epicenter, about twice as large as that at Sampari, the nearest site in northern Sumatra. These observations suggest that as large slip as 14 m occurred beneath the Nicobar Islands. Large postseismic displacements are observed at Phuket and Sampari after the mainshock, but the former is three times larger than the latter. This suggests that the spatial distribution of afterslip is different from the coseismic slip distribution. The temporal variation of postseismic displacements can be explained by a logarithmic function derived from rate-state dependent friction law with short characteristic time. The area where coseismic displacements from the Nias earthquake of March 28, 2005 are detected is much smaller than that from the December mainshock, but displacement at Sampari is larger than that during the mainshock. These displacements suggest less than 4 m slip on a shallow dipping thrust fault and resultant moment release is smaller than that estimated from seismological data. Finally, total moment released by afterslip amounts to 3.83 × 1022 Nm which is equivalent to Mw 8.99 for about five months, including the afterslip for the Nias earthquake.

Thrust dip and thrust refraction in fault-bend folds: analogue models and theoretical predictions

Analogue models made of two layers of loose sand separated by a thin layer of micro glass beads were shortened by a rigid emerging ramp dipping at either 30° or 45° and possessing a high, intermediate, or null surface friction. Shortening resulted in formation of closely spaced back thrusts in the sand layers. The dips of the back thrusts vary within a range of 30° depending on the ramp friction, and 7° depending on its dip. An increase in ramp friction, or, to a lesser extent, in ramp dip, decreases the thrust dips in the model. The second important observation is that, when friction is greater along the ramp than along the layer of glass beads, then the glass beads layer acts as a separate upper ramp above which the back thrusts steepen. The theory proposed to explain these observations predicts the thrust dips through a two-step procedure: first, global equilibrium of forces in the two layers is required to yield the mean forces at stake along the ramps and thrusts, second, the total dissipation is minimized with respect to the dips of the back thrusts. The relevant frictional properties of our analogue materials have been measured in stress conditions as close as possible to the experimental ones (below 1 kPa), and used with the theory to yield optimal back thrust dips that are all within 3° of the measured dips. This is a surprisingly good fit when considering that we did not take into account geometric changes, strain-softening, and dilatancy or compaction, due to slip on the thrusts. We conclude that this general two-step theoretical procedure is validated in the context of analogue frictional materials. We also propose a possible mechanism for thrust refraction and top-to-the-foreland sense of shear observed in the hanging walls of lower-flat to ramp transition in sedimentary piles that is based on the triggering of secondary upper ramps. Finally, this mechanical approach can also be seen as complementary to the kinematic models of fold-thrust structures which, by definition, cannot grasp the strong effects of friction on the kinematics.

Geodynamic evolution of the northern Molucca Sea area (Eastern Indonesia) constrained by 3-D gravity field inversion

In order to better understand the tectonic framework of the Northern Molucca Sea area, we inverted satellite and sea-surface gravity data into an iterative scheme including a priori seismological and geological data. The resulting 3-D density model images the various tectonic units from the surface down to 40 km. We proceed to various tests to assess the stability and robustness of our inversion. In particular, we performed an offset and average smoothing method to properly refine our results. The resulting model shows a striking vertical regularity of the structures through the different layers, whereas the density contrasts appear strongly uneven in the horizontal direction. The density model emphasizes the complexity of the upper lithospheric structure in the northern Molucca Sea, which is clearly dominated by the interaction between ophiolitic ridges, sedimentary wedges and rigid blocks of the Philippine Sea Plate. It also provides new, hard information that can be used in discussion of the evolution of the region. Large density variations are concentrated in the central part of northern Molucca Sea and dominate the upper lithospheric. North–south trending density structures along the Central Ridge and west dipping thrust faults on the western side of the region are clearly imaged. In the eastern part of the region, we distinguish several blocks, especially the Snellius Plateau which seems to be split into two parts. We interpret this as an oceanic plateau associated with thicker crust that previously belonged to the Philippine Sea Plate. This crust is now trapped between the Molucca Sea complex collision zone and the Philippine Trench, due to the development of a new subduction zone in its eastern side.

Surface expression of thrust faulting in eastern Iran: source parameters and surface deformation of the 1978 Tabas and 1968 Ferdows earthquake sequences

SUMMARY Previously unrecognised thrust faults in eastern Iran were responsible for a destructive earthquake at Tabas (1978, September 16), which produced over 80 km of distributed and discontinuous surface ruptures above a series of low anticlinal hills to the west of a major range-front. Analysis of long-period body-wave seismograms shows a simple rupture on a gently dipping (∼16 ◦ ) thrust, with a slight right-lateral component. This is compatible with the locally recorded aftershock distribution. Body wave analysis of two later, smaller events show similar source orientations. Several indicators of long-term active folding at Tabas can be recognised in the geomorphology, and surface ruptures from 1978 are consistent with co-seismic fold growth. Drainage incision also indicates uplift at depth on thrust faults dipping eastwards beneath the folds. Body-wave seismograms for two earthquakes near Ferdows, 150 km east of Tabas, in September 1968 also show thrust faulting at depths of ∼10 km. Again, the surface geomorphology indicates a region of folding above an eastward-dipping thrust fault, which is ∼10 km west of a fault bounded range-front. In both Tabas and Ferdows, the active faulting appears to show Quaternary migration away from the range-front, possibly in response to stresses produced by the elevated topography. The identification of zones of active fault-related folding is important for earthquake hazard assessment and also for an understanding of the local tectonics. We conclude that the structures which gave rise to the 1968 and 1978 earthquakes could have been recognised beforehand from the clear signals in the geomorphology, had we known what to look for at that time.