Strains developed in the hangingwalls of thrusts due to their slip/propagation rate: a dislocation model: reply

Folding related to the propagation of thrusts is common in thrust belts, including the Rocky Mountains. The rare development of such folds in the southern Rockies, due to lithological control, is a special case of the dislocation/ductile bead model, which, it is argued, is of general applicability.     

Strains developed in the hangingwalls of thrusts due to their slip/propagation rate: a dislocation model: discussion

Modern seismic data indicate that the sole fault of the Turner Valley thrust sheet does not lose displacement in an up-dip direction and that it does not crop out but rather flattens into the triangle zone on the eastern edge of the Rocky Mountain Foothills Belt. Well constrained balanced cross-sections drawn through this part of the belt do not incorporate significant folding related to the propagation of thrust faults.     

A dislocation model of aseismic fault slip under nonuniform friction

A model is proposed for studying the mechanical behaviour of faults during their interseismic periods. The model considers a plane fault surface in an elastic medium, subject to a uniform shear stress which increases slowly with time. A1-D friction distribution is assumed on the fault, characterized by asperities and a weaker zone. The traction vector on the fault plane has an arbitrary orientation: in particular, it can be nonperpendicular to the asperity borders. Aseismic fault slip takes place when the applied stress exceeds the frictional resistance: slip starts in weak zones and is confined by asperities, where it propagates at increasing velocity. Propagation into asperities is characterized by a dislocation front, advancing perpendicularly to the asperity border. Fault slip does not take prate in the direction of traction, except when traction is perpendicular or parallel to the asperity border. The propagation of such aseismic dislocations produces a stress redistribution along the fault and can play a key role in determining the conditions which give rise to earthquakes.     

A three‐phase soil model for simulating stress wave propagation due to blast loading

A three‐phase soil model is proposed to simulate stress wave propagation in soil mass to blast loading. The soil is modelled as a three‐phase mass that includes the solid particles, water and air. It is considered as a structure that the solid particles form a skeleton and their voids are filled with water and air. The equation of state (EOS) of the soil is derived. The elastic–plastic theory is adopted to model the constitutive relation of the soil skeleton. The damage of the soil skeleton is also modelled. The Drucker–Prager strength model including the strain rate effect is used to describe the strength of the soil skeleton. The model is implemented into a hydrocode Autodyn. The recorded results obtained by explosion tests in soil are used to validate the proposed model. Copyright © 2004 John Wiley & Sons, Ltd.     

Static elastic deformation in an orthotropic half-space with rigid boundary model due to non-uniform long strike slip fault

The solution of static elastic deformation of a homogeneous, orthotropic elastic uniform half-space with rigid boundary due to a non-uniform slip along a vertical strike-slip fault of infinite length and finite width has been studied. The results obtained here are the generalisation of the results for an isotropic medium having rigid boundary in the sense that medium of the present work is orthotropic with rigid boundary which is more realistic than isotropic and the results for an isotropic case can be derived from our results. The variations of displacement with distance from the fault due to various slip profiles have been studied to examine the effect of anisotropy on the deformation. Numerically it has been found that for parabolic slip profile, the displacement in magnitude for isotropic elastic medium is greater than that for an orthotropic elastic half-space, but, in case of linear slip, the displacements in magnitude for an orthotropic medium is greater than that for the isotropic medium.     

Stress triggering of normal aftershocks due to strike slip earthquakes in compressive regime

A few cases of occurrence of normal aftershocks after strike slip earthquakes in compressive regime have been reported in the literature. Occurrence of such aftershocks is intriguing as they occurred despite the apparent stabilizing influence of compressive plate tectonic stresses on the normal faults. To investigate the occurrence processes of such earthquakes, we calculate change in static stress on optimally oriented normal and reverse faults in the dilational and compressional step over zones, respectively, due to slip on a vertical strike slip fault under compressive regime. We find that change in static stress is much more pronounced on normal faults as compared to that on reverse faults, for all values of fault friction. Change in static stress on reverse fault is marginally positive only when the fault friction is low, whereas for normal faults it is positive for all values of fault friction, and is maximum for high fault friction. We suggest that strike slip faulting in compressive regime creates a localized tensile environment in the dilational step over zone, which causes normal faulting in that region. The aftershocks on such normal faults are considered to have occurred as an almost instantaneous response of stress transfer due to strike slip motion.     

Stress triggering of normal aftershocks due to strike slip earthquakes in compressive regime

A few cases of occurrence of normal aftershocks after strike slip earthquakes in compressive regime have been reported in the literature. Occurrence of such aftershocks is intriguing as they occurred despite the apparent stabilizing influence of compressive plate tectonic stresses on the normal faults. To investigate the occurrence processes of such earthquakes, we calculate change in static stress on optimally oriented normal and reverse faults in the dilational and compressional step over zones, respectively, due to slip on a vertical strike slip fault under compressive regime. We find that change in static stress is much more pronounced on normal faults as compared to that on reverse faults, for all values of fault friction. Change in static stress on reverse fault is marginally positive only when the fault friction is low, whereas for normal faults it is positive for all values of fault friction, and is maximum for high fault friction. We suggest that strike slip faulting in compressive regime creates a localized tensile environment in the dilational step over zone, which causes normal faulting in that region. The aftershocks on such normal faults are considered to have occurred as an almost instantaneous response of stress transfer due to strike slip motion.     

Asymmetric slip partitioning in the Sea of Marmara pull‐apart: a clue to propagation processes of the North Anatolian Fault?

Between 1939 and 1999 the North Anatolian fault (NAF) experienced a westward progression of eight large earthquakes over 800 km of its morphological trace. The 2000-km-long North Anatolian transform fault has also grown by westward propagation through continental lithosphere over a much longer timescale (∼10 Myr). The Sea of Marmara is a large pull-apart that appears to have been a geometrical/mechanical obstacle encountered by the NAF during its propagation. The present paper focuses on new high-resolution data on the submarine fault system that forms a smaller pull-apart beneath the Northern Sea of Marmara, between two well-known strike-slip faults on land (Izmit and Ganos faults). The outstandingly clear submarine morphology reveals a segmented fault system including pull-apart features at a range of scales, which indicate a dominant transtensional tectonic regime. There is no evidence for a single, continuous, purely strike-slip fault. This result is critical to understanding of the seismic behaviour of this region of the NAF, close to Istanbul. Additionally, morphological and geological evidence is found for a stable kinematics consistent both with the long-term displacement field determined for the past 5 Myr and with present-day Anatolia/Eurasia motion determined with GPS. However, within the Sea of Marmara region the fault kinematics involves asymmetric slip partitioning that appears to have extended throughout the evolution of the pull-apart. The loading associated with the westward propagation process of the NAF may have provided a favourable initial geometry for such a slip separation.     

Quasistatic propagation of a normal fault: A fracture mechanics model

We have carried out boundary element calculations to simulate quasistatic propagation of a normal fault in the earth's crust under a horizontal tensile loading. Byerlee's frictional law is employed to describe the mechanical behavior of the fault surface. We hypothesize that in order for a normal fault to grow quasistatically, the mixed-mode effective shear stress intensity factor must exceed a threshold value (fracture toughness), a crustal material property. We suggest that the fault grows in a direction of local maximum shear stress. The direction of fault propagation thus depends on the ratio of tensile and shear stress intensity factors. A listric normal fault is likely to form in crustal material with a small shear fracture toughness. A listric normal fault is also more likely to form in crustal material with a high degree of plasticity.The propagation trajectory of an incrementally growing normal fault is examined. As the normal fault extends to a greater depth, the shear stress intensity factor drops, owing to an increase in fault surface friction. The equilibrium depth to which a normal fault will grow is controlled by the far field loading and the fracture mechanical property of the crustal material. The decrease of shear stress intensity with fault length also stabilizes the fault growth.     

A new geological slip rate estimate for the Calico Fault,eastern California: implications for geodetic versus geologic rate estimates in the Eastern California Shear Zone

ABSTRACT

Accurate estimation of fault slip rate is fundamental to seismic hazard assessment. Previous work suggested a discrepancy between short-term geodetic and long-term geologic slip rates in the Mojave Desert section of the Eastern California Shear Zone (ECSZ). Understanding the origin of this discrepancy can improve understanding of earthquake hazard and fault evolution. We measured offsets in alluvial fans along the Calico Fault near Newberry Springs, California, and used several techniques to date the offset landforms and determine a slip rate. Our preferred slip rate estimate is 3.2 ± 0.4 mm/yr, representing an average over the last few hundred thousand years, faster than previous estimates. Seismic hazard associated with this fault may therefore be higher than previously assumed. We discuss possible biases in the various slip rate estimates and discuss possible reasons for the rate discrepancy. We suggest that the ECSZ discrepancy is an artefact of limited data, and represents a combination of faster slip on the Calico Fault, off-fault deformation, unmapped fault strands, and uncertainties in the geologic rates that have been underestimated. Assuming our new rate estimate is correct and a fair amount (40%) of off-fault deformation occurs on major ECSZ faults, the summed geologic rate estimate across the Mojave section of the ECSZ is 10.5 ± 3.1 mm/yr, which is equivalent within uncertainties to the geodetic rate estimate.     

A model with rigid rotations and slip deficits for the GPS-derived velocity field in Southwest Japan

We interpret the GPS-derived velocity field in southwest Japan by a superposition of the elastic deformation caused by fault interactions (slips or slip deficits) on the rigid motion of tectonic blocks (or plates). Based on the strain rate field and crustal seismicity, we apply a model with three blocks (Inner Arc, Outer Arc, and the northern Ryukyu block) and slip deficits along the block boundaries.Several characteristics of the synthesized contributions are found:

(1) Westward motion of the outer arc relative to the Amurian plate and the inner arc,

(2) southeastward motion of the northern Ryukyu block relative to the Amurian plate,

(3) 2−4 mm/yr deficits of left lateral slip rates along the boundary at 32°N in southern Kyushu,

(4) 0−8 mm/yr deficits of right lateral slip rates along the Median Tectonic Line and the Beppu-Shimabara Graben,

(5) slip deficit rates on the plate interface smaller than those in the case without any consideration for rigid block motions,

(6) clockwise deflection of slip deficit rate vector on the plate interface from that estimated when not taking rigid block motions into consideration.

Variation of infiltration rate through karstic surfaces due to land use changes: A case study in Murgia (SE-Italy)

Groundwaters of the Murgia carbonate aquifer represent the main groundwater resource of the Apulia region (SE Italy). In the highlands (Alta Murgia) karst crops out in different forms and textures which have been preserved up to the 1970s: little evolved agriculture and sheep rearing produced only a marginal modification of the epikarst while a high degree of division into parcels by drystone walls helped in preserving soils from erosion. In the last years the original scenery of the Alta Murgia changed due to widespread transformations of surface karstic textures for agricultural purposes, with undeniable negative consequences on the hydrogeological balance, concerning both the infiltration and the runoff terms. Stone shattering led to flattening and deep alteration of a large part of the original karstic landscape and to demolition of drystone walls.In a study area of about 139 km² located in the Alta Murgia, the comparison of aerial photos related to the period 1950–2001 indicated that stone shattering had occurred for about 42% of the area.The hydrological behaviour of the first soil layer of experimental parcels representing both shattered stone and natural karstic surface textures was analysed by using the numerical model Hydrus-2D with the aim of estimating the variation on infiltration rate due to stone shattering. Intensive field and laboratory measurements concerned soil texture, soil water content, pressure head, saturated hydraulic conductivity, pan evaporation and meteorological parameters.     

抽水地面沉降预计的随机介质模型

本文视抽水引起的地面沉降为一随机过程,应用随机介质理论和土力学基本原理,建立了随机介质模型,对抽水地面沉降及变形分布进行了分析预测,计算实例表明,该模型是有铲的。     

利用拉分盆地和错断河流阶地定量评估康西瓦断裂晚第四纪平均左旋走滑速率

康西瓦断裂为青藏高原西北缘的一条大型左旋走滑断裂。目前,不同学者对康西瓦断裂晚第四纪的平均走滑速率仍存在较大争议。文章以青藏高原西北缘喀拉喀什河谷段一处冲洪积扇上发育的一个小型拉分盆地以及该冲洪积扇上发育的一个错断河流阶地为研究对象,基于拉分盆地演化的两种简单模式,分别利用拉分盆地的长边和斜边限定对应冲洪积扇的水平位错位量和错位量的上限值,而通过光释光定年技术约束该冲洪积扇的形成年代,结合相关数据,分别估算出康西瓦断裂晚第四纪以来的平均左旋走滑速率为小于或等于8.6±1.0 mm/a和小于约12.4 mm/a。与此同时,利用该冲洪积扇上发育的错断河流阶地的水平位错和对应阶地的放弃年龄,估算出康西瓦断裂晚第四纪以来的平均左旋走滑速率为8.4±1.0 mm/a。

     

Thrust tectonics,thin skinned or thick skinned,and the continuation of thrusts to deep in the crust

The paper analyses the geometry of thin-skinned thrust zones, where the thrusts shallow out at depth and of thicker-skinned fault zones where much of the crust is involved and where the thrusts are frequently observed to become steeper downwards. In the interiors of many orogenic belts the steep dip of faults is not original but due to the folding above lower decoupling zones. The energy involved in the internal deformation of hanging-wall rocks may prohibit many faults becoming more shallow upwards. Such shallowing-upwards faults may occur in more ductile rocks to maintain compatibility between zones which have experienced different deformation intensities, but displacements on the faults are unlikely to be large.Another mechanism for producing faults which steepen downwards is proposed for the major thrusts which form the southern margin to the Himalayas. These carry large thicknesses (30 to 100 km) of crustal and upper mantle rocks to the south, causing flexuring and isostatic depression of the Indian plate. The steeply dipping thrusts are not footwall ramps; these may be some distance behind the steepened zone. This thrust-induced isostatic bending of the crust has important implications when considering regional seismic interpretations as well as thrust mechanics and kinematics.     

Deformation of an elastic layer coupling in different ways to a base due to a very long vertical strike-slip dislocation

The closed-form analytic expressions for the displacement and stresses at any point of an elastic layer lying over a base due to a very long vertical strike-slip dislocation are obtained. The interface between the layer and the base is assumed to be either ‘smooth-rigid’ or ‘rough-rigid’ or ‘welded’. The variations of displacement and stresses with the horizontal distance from the fault for different types of coupling of the layer with the base have been studied. It is found that the displacement for ‘welded interface’ lies between the displacements due to ‘smooth rigid’ and ‘rough-rigid’ interfaces for different positions of the observer and different values of the ratio of rigidities of the layer and half-space.     

Modeling hydrologic responses of the Zwalm catchment using the REW approach: propagation of uncertainty in soil properties to model output

The research presented in this paper focuses on the application of a newly developed physically based watershed modeling approach, which is called representative elementary watershed approach. The study stressed the effects of uncertainty of input parameters on the watershed responses (i.e., simulated discharges). The approach was applied to the Zwalm catchment, which is an agriculture-dominated watershed with a drainage area of 114 km² located in East Flanders, Belgium. Uncertainty analysis of the model parameters is limited to the saturated hydraulic conductivity because of its high influence on the watershed hydrologic behavior and availability of the data. The assessment of output uncertainty is performed using the Monte Carlo method. The ensemble statistical watershed responses and their uncertainties are calculated and compared with measurements. The results show that the measured discharges fall within the 95% confidence interval of the modeled discharge. This provides the uncertainty bounds of the discharges that account for the uncertainty in saturated hydraulic conductivity. The methodology can be extended to address other uncertain parameters as far as the probability density function of the parameter is defined.     

A tectonic model for the Tertiary evolution of strike–slip faults and rift basins in SE Asia

Models for the Tertiary evolution of SE Asia fall into two main types: a pure escape tectonics model with no proto-South China Sea, and subduction of proto-South China Sea oceanic crust beneath Borneo. A related problem is which, if any, of the main strike–slip faults (Mae Ping, Three Pagodas and Aliao Shan–Red River (ASRR)) cross Sundaland to the NW Borneo margin to facilitate continental extrusion? Recent results investigating strike–slip faults, rift basins, and metamorphic core complexes are reviewed and a revised tectonic model for SE Asia proposed. Key points of the new model include: (1) The ASRR shear zone was mainly active in the Eocene–Oligocene in order to link with extension in the South China Sea. The ASRR was less active during the Miocene (tens of kilometres of sinistral displacement), with minor amounts of South China Sea spreading centre extension transferred to the ASRR shear zone. (2) At least three important regions of metamorphic core complex development affected Indochina from the Oligocene–Miocene (Mogok gneiss belt; Doi Inthanon and Doi Suthep; around the ASRR shear zone). Hence, Paleogene crustal thickening, buoyancy-driven crustal collapse, and lower crustal flow are important elements of the Tertiary evolution of Indochina. (3) Subduction of a proto-South China Sea oceanic crust during the Eocene–Early Miocene is necessary to explain the geological evolution of NW Borneo and must be built into any model for the region. (4) The Eocene–Oligocene collision of NE India with Burma activated extrusion tectonics along the Three Pagodas, Mae Ping, Ranong and Klong Marui faults and right lateral motion along the Sumatran subduction zone. (5) The only strike–slip fault link to the NW Borneo margin occurred along the trend of the ASRR fault system, which passes along strike into a right lateral transform system including the Baram line.     

A grid-search inversion method looking for the best classification of polyphase fault/slip data

A novel, grid search-based stress inversion method is developed in this paper to find the global minima in the solution region for the classification of fault/slip data into many single-phase subsets. Exhaustively repetitious grid searches are taken to deal with possible local minima, in a departure from existing grid search-based inversion methods. Two stopping rules, to stop at the abrupt change of the objective function or at the least change of the classification, are adopted in the method to look for the best classification. Much calculation time is saved by using a modified version of conventional grid search. The feasibility of this proposed method is demonstrated by applying it to two artificial examples and two real examples. However, enormous time in calculation is still needed in the case of a data set either with a large number of data or for a large number of assigned subsets.