Maximum Principal Compressive Stress Research Articles

Cretaceous‐Early Eocene Tectonic Stress Field in China1

Abstract The Cretaceous‐early Eocene tectonic stress field in China was reconstructed using the data of 369 large‐and medium‐scale flexural folds and 157 joint sets. It was found that the maximum compressive principal stress axis in eastern China dips 32 ° NE (nearly horizontal), and strikes SW 212 °, whereas that in western China dips 15 ° NE (also nearly horizontal) and trends SW 195 °. The estimation of the dip angles of fold limbs and the palaeotectonic stress values indicates that there was a tendency of gradual weakening of tectonism from southwestern to northeastern China in the Cretaceous‐early Eocene. At the depth of 2‐3 km, the differential stress value changes from 183 MPa in Tibet to 100 MPa in North and East China.The authors consider that the tectonic stress of this period was related to the north‐northeastward movement and push of the Indian‐Australian plate.

High-angle reverse faulting in northern New Brunswick, Canada, and its implications for fluid pressure levels

The 1982 Miramichi earthquake sequence in northern New Brunswick included four shocks in the magnitude range, 5.7 > m, > 5.0, and extensive aftershock activity. Rupturing occurred within granitic terrain on a pair of NNE—SSW-striking, opposite-facing, high-angle reverse faults which converge at the mainshock focal depth of ≈7 km. It seems probable that the earthquake sequence involved the reactivation under horizontal compression of an existing set of steep normal faults, perhaps derived from Mesozoic rifting of the Atlantic continental margin. The symmetry of the V-shaped profile of faults in WNW—ESE section suggests that the maximum principal compressive stress (σ 1) during reactivation was subhorizontal and the least principal stress (σ 3) was subvertical, so that the reactivation angle between σ 1 and the faults corresponded to the 50–65° dip of the faults. Stress analysis of the conditions for frictional reactivation of existing cohesionless faults shows that pore-fluid pressures approaching or exceeding lithostatic values are required for reshear at such high reactivation angles, with the implication that the earthquake sequence was triggered by locally elevated fluid pressure. While the source and composition of the inferred high pressure fluids are uncertain, a mixed H 2O—CO 2 fluid of mantle origin seems most likely.

Some characteristics of the seismicity and the stress field in the Panxi rift zone

Some characteristics of the horizontal distribution of the earthquakes, the focus depth distribution, distribution of the earthquakes with time, b-values, fault slip rates and stress field in the Panxi rift zone have been investigated. The results are as follows: 1. (1) Earthquakes with M ⩾ 4.7 occurred mainly along the major faults in the Panxi rift zone. Earthquake activity is greater along the sides of the Panxi rift zone than along its axis. Earthquakes with M ⩾ 6 occurred along the bounding faults of the Panxi rift zone. The small earthquakes exhibit a random distribution. 2. (2) The focal depths along the axis of the Panxi rift zone are shallow (5–20 km), but the focal depths outside the rift zone are deeper (6–40 km). 3. (3) The b-values in the Panxi rift zone are 0.58–0.75. 4. (4) The correlation of the seismicity between the Panxi rift zone and the eastern India-Eurasian collision zone is high. 5. (5) The fault planes in the Panxi rift zone are nearly vertical and strike-slip. The fault slip rates in the Panxi rift zone are 0.13–0.19 cm/yr. 6. (6) The maximum principal compressive stress axis in the Panxi rift zone is nearly horizontal, NNW-SSE in direction. According to the above results, a dynamic model for the aborting process of the Panxi rift zone is suggested.

Rupture characteristics of normal faults: an example from the Wasatch fault zone, Utah

Summary The Salt Lake fault segment is one of several independent rupture segments in the Wasatch normal fault zone, Utah. The segment is about 35 km long and consists of several, approximately linear fault sections that intersect in geometrical barriers defined by bends and branching of the fault trace. The dips of these fault sections vary based on a preliminary model of the fault zone, with estimated dips ranging from 45 to 90°. The palaeo-stress tensor was characterized by sub-vertical maximum principal compressive stress, a minimum principal stress axis trending about 050° and φ ≈ 0.2−0.5. The average slip direction across the fault segment was ≈240°. Three large, non-conservative barriers occur within the fault segment—at the northern and southern ends of the segment, and a branch point in the centre of the segment. Bifurcation of the rupture zone into two primary fault systems has presumably increased the fracture toughness of the northern part of the segment due to the overlap of secondary faulting adjacent to the primary fault planes. Two large historic earthquakes in the eastern Basin and Range and Rocky Mountain transition region have ruptured bifurcated fault zones similar in structure to the Salt Lake segment; the Hebgen Lake, Montana earthquake ( M = 7.5) in 1959 and the Borah Peak, Idaho earthquake ( M = 7.3) in 1983. The earthquake foci were located at depths of 12–18 km and the ruptures propagated towards the regions of fault-zone bifurcation in both cases. A characteristic earthquake ( M ≈ 7−7.5) may initiate at either the centre or the southern end of the Salt Lake segment. In the first case, the rupture would propagate bilaterally, but in the latter case the rupture would propagate unilaterally to the N. A unilateral propagation direction is preferred based on inferences drawn from the structural geology of the segment and direct comparison with the rupture traces of the Borah Peak and Hebgen Lake earthquakes.

4. In situ stress measurements in the Japanese islands: Over-coring results from a multi-element gauge used at 23 sites

The authors have developed a new over-coring stress relief method with a multi-element strain gauge. The new gauge has been used to estimate in situ stress at more than 20 sites for electric power stations in Japan. The results of in situ stress measurements obtained by the method exhibit a general tendency that the maximum compressive principal stress acts horizontally and the horizontal to vertical stress ratio exceeds 1.0. The directions of maximum horizontal compressive in situ stress obtained by the method seem to be consistent with those of the geodetic strains calculated from first order triangulation survey data, and with those estimated from the distribution of tectonic zones which have become active in the Quaternary period. The Japanese islands are located in a tectonically active region, i.e. they are situated near the eastern boundary of the Asian plate towards which both the Philippine Sea plate and the Pacific plate advance. For further detailed discussion a more refined analysis would be required; however, the in situ stress in the Japanese islands is likely to have been significantly affected by these crustal movements.

Basement diapirism associated with the emplacement of major ophiolite nappes: Some constraints

The association of basement uplifts with major ophiolite nappes in some Phanerozoic orogenic belts suggests that gravitational instability results in the local diapiric uplift of the basement following ophiolite emplacement. In previous analyses of diapirism in crustal silicate rocks, viscous behaviour of rocks has been assumed. It is argued that this assumption is not valid. An alternative analysis is offered to determine whether or not the stress would be sufficient for diapirism to occur. The negative buoyancy stress resulting from the emplacement of an ophiolite nappe 5–15 km thick onto continental basement may be in the range 10–50 MPa. If the horizontal deviatoric stress is zero, this will be the maximum principal compressive stress. After ophiolite emplacement the thermal profile through the ophiolite and the basement will relax from a saw-tooth form to an equilibrium profile. If the ophiolite is young and thick there will be a zone of ductile strain in the lower part of the ophiolite and in the upper part of the continental basement. Results from steady-state creep experiments suggest that temperatures in this zone may be high enough for a short time after ophiolite emplacement (3 Ma or more) for the rocks in this zone to deform at geologically significant strain rates (10 −14 or greater) in response to the negative buoyancy stress. A thin ophiolite or rapid erosion will result in this ductile zone being absent or too short-lived for significant strain. Aquaeous fluids may reduce the strength of brittle rocks by decreasing the effective normal stress or by encouraging pressure solution creep. Evidence suggests that the deviatoric stress across presently active faults may be as low at 10 MPa. Thus diapirism in response to ophiolite emplacement may occur through brittle strain. Gravity spreading within the ophiolite is an alternative mechanism for accommodating the gravitational instability. The critical evidence lies in the field.

PRESENT STRESS STATE NEAR MEILING ARCUATE FAULTS

In this paper an analysis of the present stress field near the Meiling arcuate faults in Beijing area is made. Based on the in situ stress measurements, petrofabric analysis and model experiments, it has been found that this local stress field is a rotational shear stress field. It has been active from the late Yenshanian up to the present with the outer side rotating clockwise. The features of the local stress field are different from those of the present regional stress field characteristic of the Neocathaysian system. The trajectories of the maximum principal compressive stresses of the former show an arcuate pattern converging towards SE and diverging towards NW. However, those of the latter extend approximately in the NWW direction.

Anisotropic growth in the olivine-spinel transformation of Mg 2GeO 4 under nonhydrostatic stress

The olivine-spinel phase transformation in Mg 2GeO 4 does not occur by a martensitic mechanism. The evidence, from samples transformed in a Griggs-type solid medium deformation apparatus, are: 1. (1) lack of microstructural features in the olivine phase which can be specifically associated with a martensitic mechanism 2. (2) the orientation relationship between the two phases that is predicted by the martensitic mechanism does not occur nor is there any apparent consistency of relative orientations 3. (3) application of a differential stress to the transforming sample resulted in an anisotropic growth rate for the spinel phase indicating that growth was externally controlled rather than crystallographically controlled. Anisotropic growth of the spinel phase results in elongation of the residual olivine phase grains in the plane normal to the direction of maximum principal compressive stress. A velocity ratio of 1.7 −0.7 +5.4 has been determined for the growth rate of the spinel from measurements on residual olivine grains. The interphase grain boundary in samples transformed under stress has cusp-shaped fingers of spinel with a blunt end separated by thin spikes of olivine. Samples transformed isostatically do not exhibit this feature providing further confirmation of anisotropic growth of the spinel. The preferred growth of the spinel is consistent with a theory of phase transformation under nonhydrostatic stress. The predicted spinel finger shape based on this theory is generally consistent with observed shapes except for the blunt end. The discrepancy may be due to surface energy which has not been considered here, or to local deviations of the applied macroscopic stress.

Changing stress field in the middle segment of the Tan-Lu fault zone, eastern China

The Tan-Lu active fault zone is an important tectonic boundary in east China. Minor structures associated with the fault show that the nature of displacement on the middle segment of the fault zone has changed in consecutive episodes since the Cretaceous: normal faulting during the Cretaceous, sinistral strike-slip and reverse faulting at the end of the Cretaceous or in the early Tertiary, and dextral strike-slip and reverse faulting from the late Tertiary to the present. The regional orientation of the maximum principal compressive stress, based upon the statistical study of minor shear fracture orientation, is 6°, S52°W in the late Tertiary to Quaternary. This stress field may be related to the collision between India and Tibet and the microspreading of the Japan Sea.

Deformation of single‐crystal clinopyroxenes: 2. Dislocation‐controlled flow processes in Hedenbergite

Laboratory deformation experiments were carried out on two single‐crystal clinopyroxenes: chrome diopside and hedenbergite. The tests were made in a Griggs solid‐medium, triaxial, not creep tester. A confining pressure of 1000 MPa was applied in all the experiments. The crystals were deformed at strain rates from 10−4 s−1 to 10−8 s−1 and at temperatures from 400°C to 1200°C. Two orientations of the crystals with respect to the maximum principal compressive stress were tested. The first orientation subjects the (100), [001] and (001), [100] mechanical twinning systems in clinopyroxene to a high, resolved shear stress appropriate for mechanical twinning to occur. The second orientation subjects these systems to an equal resolved shear stress, but in a way that mechanical twinning is not possible. The effects of temperature and strain rate on the flow stress were observed for the two clinopyroxene compositions. Mechanical twinning on the system (100), [001] was observed to be the primary deformation mechanism in crystals oriented favorably for twinning. Above 850°C, deformation occurs by dislocation glide and is strongly temperature and strain‐rate dependent. In the orientation for which mechanical twinning is not possible, crystals deformed by two different dislocation glide mechanisms, depending on temperature. From 400°C to 900°C, deformation in hedenbergite occurs by dislocation glide controlled by lattice resistance. This thermally activated mechanism has an activation energy of 285 kJ/mol (68 kcal/mol) and an activation area that expresses the effect of the applied stress on the total activation energy. This mechanism only operates at stresses above 520 MPa. At temperatures above 900°C and applied stresses less than 520 MPa, flow in hedenbergite occurs by climb‐controlled dislocation glide. This leads to a thermally activated power law flow equation. The activation energy is 523kJ/mol (125 kcal/mol). Strain rate depends on the stress raised to the power 3.6. The flow law derived for hedenbergite at high temperatures and low stresses may be extrapolated to a strain rate of 10−14 s−1, thought to be appropriate for flow in the mantle. This flow law predicts an equivalent viscosity of hedenbergite of 1021 poise at 800°C and 1019 poise at 1200°C.

Compressive failure and kinking in uniaxially aligned glass-resin composite under superposed hydrostatic pressure

The failure process in uniaxially-aligned 60% fibre volume fraction glass fibre-epoxide compressive specimens strained parallel to the fibre axis was investigated at atmospheric and superposed hydrostatic pressures up to 300 MN m−2. The atmospheric strength was about 1.15 GN m−2 (about 20% less than the tensile) and strongly pressure dependent, rising to over 2.2 GN m−2 at 300 MM m−2 pressure, i.e. by about 30% per 100 MN m−2 of superposed pressure. The corresponding figure is 22% if the maximum shear stress and not the maximum principal compressive stress is considered. This is incompatible with atmospheric compressive failure mechanisms controlled by weakly dependent or pressure independent processes, e.g. shear of the fibres. The results also could not be satisfactorily interpreted in terms of microbuckling of individual fibres. Kinking, involving buckling of fibre bundles was proposed as the mechanism of failure propagation, but the critical stage (for this glass reinforced plastic) is suggested as being yielding of the matrix, which initially restrains surface bundles from buckling. A strong pressure dependent failure criterion, about 25% increase per 100 MN m−2, was derived by modifying the Swift-Piggott analysis of deformation of initially curved fibres. It is postulated that it is the axial compression that causes bundle curvature. Other systems, particularly carbon fibre-reinforced plastic, in which there appears to be a transition in the critical stage of failure from bundle buckling to matrix yielding with increasing superposed pressure, are also considered.

Deformation of single‐crystal clinopyroxenes: 1. Mechanical twinning in diopside and hedenbergite

Laboratory deformation experiments were carried out on two single‐crystal clinopyroxenes: chrome diopside and hedenbergite. Tests were made in a Griggs solid medium, triaxial, hot creep tester. A confining pressure of 1000 MPa was applied in all experiments. Crystals were deformed at strain rates from 10−4 to 10−8 s−1 and at temperatures from 400°C to 1200°C. Two orientations of the crystals with respect to the maximum principal compressive stress were tested. The first orientation subjects the (100), [001] and (001), [100] mechanical twinning systems in clinopyroxene to a high resolved shear stress in the sense appropriate for mechanical twinning to occur. The second orientation subjects these systems to an equal resolved shear stress but in the opposite sense so that mechanical twinning is not possible. Effects of temperature and strain rate on the flow stress are observed for the two clinopyroxene compositions. Mechanical twinning on the system (100), [001] is observed to be the primary deformation mechanism in crystals oriented favorably for twinning. The resolved shear stress required for mechanical twinning on this system is 140 MPa for hedenbergite and 100 MPa for chrome diopside. The smaller twinning stresses for diopside are considered to be due to abundant inclusions in the crystals. The mechanical twinning stress is nearly independent of temperature from 400°C to 850°C and strain rate from 10−4 to 10−8 s−1. Above 850°–1000°C for diopside and 1000°C for hedenbergite, deformation occurs by dislocation glide and is strongly temperature and strain rate dependent. Crystals tested in the orientation for which mechanical twinning is not possible deform by two different dislocation glide mechanisms depending on temperature. Details of these experiments are reported in part 2. Results for mechanical twinning predict that this is not an important deformation mechanism in the earth unless resolved shear stress on the twinning system exceeds 140 MPa. Lack of dependence of twinning stress on strain rate implies that large, rapid strains will occur in this mineral if the twinning stress is reached. Independence of twinning stress in clinopyroxenes from temperature, strain rate, or composition allows use of this mineral as a geopiezometer. At plate margins where stresses are high, presence of mechanically twinned clinopyroxene grains allows determination of the orientation and magnitude of stresses responsible for the deformation.

Non-coaxial experimental deformation of olivine

Dunite samples have been deformed non-coaxially at high temperatures and pressures. In samples which were deformed by translation glide on {Okl}[100], olivine [100] = Z-axes rotated toward the maximum extensile-strain axis. In samples which were partly or completely recrystallized syntectonically the new olivine grains attained preferred orientations with [010] = X and [100] = Z parallel to the maximum and least principal compressive stress axes, respectively. These results may be used for kinematic and dynamic analysis of naturally deformed dunites and peridotites.

Progressive Neogene Deformation of Southern Hedil, Tunisian Atlas: GEOLOGIC NOTES

Detailed structural mapping in the southern Hedil region of the northern Tunisian Atlas suggests that the area is characterized by multiple-faulted folds, facing southeast, rather than by the nappes and imbricate thrusts of previous interpretations. Our structural analysis shows that major deformation occurred during the middle Miocene (Langhian-Serravallian). This deformation was progressive and occurred in two discrete phases. In the first phase, shelf-type rocks of Late Cretaceous-early Miocene age were involved in kink-style folding which developed above a gliding surface in Triassic evaporites to form northeast-trending structures. The second phase produced conjugate strike-slip and extensional faulting in these structures. The acute bisectrix of the strike-slip faults, at right angles to the major trends of folding and parallel with the extensional faults, suggests that the maximum principal compressive stress (^sgr1) was directed S38°E and was constant during middle Miocene deformation. This faulted-fold co cept contrasts with that suggested in other studies in which the sequence of events is envisioned as faulting followed by folding.

Neogene deformation in northern Tunisia: Origin of the eastern Atlas by microplate—continental margin collision

Detailed structural analysis in the southern Hedil region, northern Tunisia, suggests that the area is characterized by normal faulted, southeast-vergent and upright, box- to close-style folds. Fold nappes and imbricate thrust sheets postulated previously are absent in the Hedil, although thrust sheets do occur farther north in the Mogods and Kroumerie regions. A two-stage tectonic model is proposed: (1) middle Miocene progressive deformation involving initial buckle folding and later shear faulting in the Hedil, and southeast-directed thrusting in the Mogods and Kroumerie; and (2) postdeformation extensional faulting parallel to regional fold trends, bimodal (basalt-rhyolite) volcanism, and molasse deposition. Minor, post-Messinian southeast-vergent thrust faulting followed this extensional regime and continues to the present. Maximum principal compressive stress (σ1), horizontal and striking S38°E, is inferred for the middle Miocene deformation. The middle Miocene fold and thrust structures are related to the collision of the counterclockwise-rotating Corsica-Sardinia-Petit Kabylie plate with the Tunisian continental margin. Following this collision, in the Tortonian, the development of a sphenochasm spreading system to the west of the present-day Straits of Sardinia produced the extensional regime that prevailed in northern Tunisia. As spreading continued, the Petit Kabylie rotated clockwise away from Sardinia. Movement ceased when the Petit Kabylie collided with the Algerian continental margin.

Fracture processes of concrete under generalised stress states

Based on previous investigations of the behaviour of concrete under multiaxial stress, it is found that the fracture processes of concrete can be categorised into (a) those which are caused by the deviatoric component of a stress state and occur in the direction of the “applied” maximum principal compressive stress, and (b) those which are caused by the hydrostatic component and are of “random” orientation.

Progressive deformation and orogenic uplift at the southern extremity of the Andes

The Middle to Upper Jurassic and Lower Cretaceous silicic volcanic and sedimentary rocks of Isla de los Estados, Argentina, at the southern extremity of the Andean Cordillera, have been interpreted to lie on the rear (continental) side of an Early Cretaceous marginal basin. The basin floor was uplifted, together with the magmatic arc on its Pacific side, in mid-Cretaceous time. Uplift was accompanied by inhomogeneous deformation of the rocks of the magmatic arc, of the basin floor, and particularly of those on the continental side of the basin. Detailed structural analysis shows that the rocks of Isla de los Estados are disposed in a major asymmetric, noncylindrical syncline. The island, nearly 1,000 m high, lies in the core of this fold. A strong slaty cleavage developed prior to the large-scale folding. Both bedding and early slaty cleavage were reoriented by this folding. A new foliation axial planar to the large syncline is present only on the inverted limb in the more strongly compressed eastern area. Late, flat-lying cleavages are also most strongly developed in the east, but in the lower limb of the fold. The structures are all interpreted to be the result of progressive deformation of the rocks during a single period of regional compression. The sequence of strains correlates closely with that deduced from theoretical and experimental studies of buckling. The early cleavage is thought to have developed during initial shortening of the layering of the rocks. Subsequent buckling of the thick multilayer of competent silicic volcanics produced the syncline. The late, flat-lying cleavages are considered to have resulted from gravitationally induced vertical shortening produced by the greatly increased overburden of the tectonically thickened rock pile. The dominant northward vergence of the structures undoubtedly reflects the uplift of the Pacific margin of the continent, but the initial layer-parallel shortening indicates the operation of a stress system with maximum compressive principal stress subhorizontal and at right angles to the Pacific margin. The crustal thickening resulting from the horizontal shortening and the buckling seems to have played a major role in the mid-Cretaceous orogenic uplift of the southernmost part of the Andean Cordillera.

Structural Development of the Hanover-Fierro Pluton, Southwestern New Mexico

Structures associated with the forcibly emplaced Hanover-Fierro pluton were studied to determine its mechanisms of intrusion. The pluton has been extensively examined, and good three-dimensional information is available from drill holes and mines. The funnel-shaped body plunges northward, and approximately 700 m of structural relief appears along the length of the present outcrop. At higher structural levels around the southern end, the country rocks were deformed by folding and thrusting; at deeper levels near the center and north end, the country rocks were deformed largely by rotation and tectonic thinning. Joints in the pluton indicate that maximum principal compressive stress (σ 1 ) rotated from a vertical orientation at depth to a horizontal east-west orientation near the surface, forming a pair of vertical conjugate shear (transverse) joints of moderate dihedral angle (36°). Along the main axis of the pluton, a set of vertical north-trending (longitudinal) joints formed; plumose structure on the joints indicates that they propagated upward . Apparently, upward-directed maximum principal compressive stress governed the direction of fracture propagation, and tensile stresses caused by outward rotation of σ 1 governed their orientation . The intermediate principal compressive stress (σ 2 ) rotated with σ 1 , forming a set of joints dipping gently inward toward the center of the pluton with dip progressively decreasing from the center to the margins. Structures around the pluton indicate that the early stage of injection produced arching and deformation by simple shear in the sedimentary overburden. With continued intrusion, an entire plug of overburden was uplifted, and lateral pressure of the magma locally exceeded the coefficient of friction along pre-existing regional joints causing minor shearing. Strata near the pluton were significantly thinned tectonically. During the final stage, lithostatic pressure of 200 to 640 m of overburden was no longer sufficient to prevent large-scale deformation, and folds and thrusts developed around the pluton.

Cataclasis and the Generation of Fault Gouge

Cataclasis, a friction-dependent mechanism of deformation involving fracture and rigid-body rotation, occurs during faulting of sandstone in the upper crust. Two stages of cataclasis of a sandstone are represented by (1) mildly deformed cataclastic sandstone that is shattered but contains many original grains that have not been fragmented and (2) gouge so severely deformed that the few surviving grains are almost surrounded by a fine-grained matrix of crushed grains. Gouge is restricted to shear fractures and larger slip planes within the natural fault zones, whereas cataclastic sandstone usually pervades the fault zone. Grain size and sorting of gouge decrease as a function of increasing confining pressure and increasing displacement along a shear fracture. In cataclastic sandstone associated with gouge, microfractures ate strongly oriented parallel to the maximum principal compressive stress. These microfractures, which are extension fractures, may be used to determine the orientation of the stress field during faulting. Rigid-body rotation is important during Cataclasis, and grains rotate in a manner that agrees with the sense of shear on the fault plane.

Antithetic Faults in Upthrusting: GEOLOGICAL NOTES

Antithetic Faults in Upthrusting: GEOLOGICAL NOTES