Rotation Of Stress Axes Research Articles

Anatomy of an escape tectonic zone: Western Irian Jaya (Indonesia)

The western fold‐and‐thrust belt of New Guinea in Irian Jaya is presently a complex boundary, dominated by the Bird's Head block escape from the collision between the Australian plate and the remnants of volcanic belts carried by the Pacific plate. The escape rate given by geodetic measurements is of the order of 7 cm/yr, and movement is accommodated by a broad shear zone. We analyze this shear pattern using fault slip analyses performed in the field from 1992 to 1996, combined with focal mechanism inversions, moment tensors summations, and surface trace of structures inferred from radar and multispectral satellite images. Time control of the deformation is attained by isotope dating of the recent syntectonic intrusives. The geometry of the macro and microstructures occurred in two stages from the early Pliocene to the Present. The first stage (5 to 2 Ma) is marked by flat‐and‐ramps structures guided by N60°E lateral ramps associated with a N60°E cleavage, affecting the whole of western Irian Jaya. The second stage (2 Ma to Present) shows the collapse of the western fold‐and‐thrust belt and the escape of the Bird's Head and the Lengguru belts along N60°E transtensile faults. In the latter stage, the strike‐slip offset is distributed on the N60°E schistosity zone along which some fracture planes are reactivated as left‐lateral transtensile faults. Shallow earthquakes moment tensors have been inverted for stress and summed to get strain rates to define contrasting structural provinces. The spatial variations in both stress and strain fields from earthquakes and microtectonics show that (1) they are consistent and are assumed to be coeval, (2) they reveal that oblique convergence is partitioned, and (3) they are influenced by the existence of a free boundary. We see no significant rotation of stress axes laterally along the escape zone. Instead, stresses change according to the different orientations of basement structures and thus undergo rapid spatial variations or principal axes permutations. Eastward, in front of the Australian craton, the oblique convergence is partly distributed on reverse and strike‐slip faults. Westward, along the NW part of the craton, we infer the Seram trench is a free boundary which allows material to escape. These results show that the evolution of the escape zone depends on the importance of the geometry of the former margin of Australia (e.g., tilted blocks), which controls the style deformation relative to the regional stress, and the boundary conditions, which control the variation of the state of stress through time.

Analysis of wave-induced liquefaction of sand beds

This paper describes finite element analyses of wave-induced liquefaction of sand beds. The authors were motivated by previous experimental results in which a series of centrifuge wave tank tests were performed on loosely packed fresh deposits of sand with viscous scaling introduced. The principal finding was that the resistance to liquefaction under progressive waves was considerably smaller than the resistance exhibited under standing waves. An important factor for this marked difference was suggested to be the rotation of the principal stress axes that occurs under progressive wave loading. The present study extends an existing cyclic-plasticity constitutive model to account for the effect of stress axis rotation of sands. This model was incorporated into a finite element analysis procedure, which was applied to soil responses to progressive wave and standing wave loading. The predicted results compare well with observed soil behaviour. The predicted effective stress paths and associated stress–strain curves for the representative soil element are discussed, illustrating how the effects of rotations of the principal stress axes manifest themselves in the course of liquefaction under progressive wave loading. The prediction of the propagation of the liquefied zone is also discussed as a subject for future study.

Analysis of wave-induced liquefaction of sand beds

This paper describes finite element analyses of wave-induced liquefaction of sand beds. The authors were motivated by previous experimental results in which a series of centrifuge wave tank tests were performed on loosely packed fresh deposits of sand with viscous scaling introduced. The principal finding was that the resistance to liquefaction under progressive waves was considerably smaller than the resistance exhibited under standing waves. An important factor for this marked difference was suggested to be the rotation of the principal stress axes that occurs under progressive wave loading. The present study extends an existing cyclic-plasticity constitutive model to account for the effect of stress axis rotation of sands. This model was incorporated into a finite element analysis procedure, which was applied to soil responses to progressive wave and standing wave loading. The predicted results compare well with observed soil behaviour. The predicted effective stress paths and associated stress–strain curves for the representative soil element are discussed, illustrating how the effects of rotations of the principal stress axes manifest themselves in the course of liquefaction under progressive wave loading. The prediction of the propagation of the liquefied zone is also discussed as a subject for future study.

Effective Stress Analyses of Port Structures

ABSTRACT Effective stress analyses are performed on the seismic response of port structures during the 1995 Hyogoken-Nambu earthquake. The structures analyzed include: caisson type quay walls which moved up to 5 m maximum toward the sea; pneumatic caisson type bridge foundations which moved toward the sea, reducing the distance between the bridge foundations across a sea channel by a total of 0.8 m; and composite breakwaters which settled 2 m. Although these structures were all a rigid concrete type and shaken by the same earthquake, the mode and extent of deformation/failure were different depending on the backfill and embedment conditions of the structures. The constitutive model of soil used for the seismic analyses is a multiple mechanism model defined in strain space. The model can take the effect of principal stress axis rotation into account, which is known to play an important role in the cyclic behavior of sand under anisotropic stress conditions. The model parameters are calibrated based on in-situ and laboratory investigations, including in-situ freeze sampling. The results of the effective stress analyses are consistent with those measured, including the mode and extent of deformation/failure, suggesting that the cyclic behavior of soil, idealized through the effective stress model, can explain the variety of seismic response of the port structures in a unified manner.

Response of a Dense Sand Deposit During 1993 Kushiro-Oki Earthquake

In the 1993 Kushiro-oki Earthquake of Richter magnitude 7.8, simultaneous recording of earthquake motions was successfully made at the ground surface and at a depth of 77 meters in a dense saturated sand deposit. The peak horizontal acceleration was 0.47 g on the ground surface and 0.21 g at a depth of 77 meters. The acceleration record at the ground surface showed a distinctive ground response, which consisted of a cyclic motion having a period of about 1.5 seconds overlain by a spike at each peak of the motion. In order to study the mechanism of this peculiar ground response, effective stress analysis was conducted on the dense saturated sand deposit. The model used for this study was a strain space multiple mechanism model, which takes into account the effect of principal stress axis rotation. The recorded earthquake motion at a depth of 77 meters was used as the input earthquake motion for the analysis. Sampling after in-situ freezing was done in order to evaluate the properties of the sand. The results of the analysis indicated that the observed ground response was due to the effect of dilatancy of sand, which plays a significant role in the response of the dense saturated sand deposits during strong earthquake motions.

Yielding and flow of sand under principal stress axes rotation : Pradel, D; Ishihara, K; Gutierrez, M Soils FoundV30, N1, March 1990, P87–99

Yielding and flow of sand under principal stress axes rotation : Pradel, D; Ishihara, K; Gutierrez, M Soils FoundV30, N1, March 1990, P87–99

Yielding and Flow of Sand Under Principal Stress Axes Rotation

ABSTRACT In order to investigate the influence of inherent anisotropy on the yielding and plastic flow of loose and dense sand, a series of experiments involving a wide range of principal stress axes directions were carried out on hollow cylindrical specimens of Toyoura sand using a torsional shear test apparatus. Stress paths involving cycles of stress reversal and stress axis rotation were performed in order to identify the states of stress at which plastic flow begins to take place. The test results revealed well-defined families of yield loci having identical shapes in the stress space independent of the density of sand. Experimental evidence presented here shows that the direction of the plastic strains for different stress increments is not uniquely established indicating the non-existence of a unique plastic potential. Consequently, within the framework of conventional theory of plasticity, the yielding and flow of sand can only be explained with the concept of multiple yield surfaces.

Sand behavior under principal stress axes rotation : Toki, S; Miura, S; Miura, K Proc Eighth Asian Regional Conference on Soil Mechanics and Foundation Engineering, Kyoto, 20–24 July 1987V1, P113–116. Publ Japan: Japanese Society for Soil Mechanics and Foundations Engineering, 1987

Sand behavior under principal stress axes rotation : Toki, S; Miura, S; Miura, K Proc Eighth Asian Regional Conference on Soil Mechanics and Foundation Engineering, Kyoto, 20–24 July 1987V1, P113–116. Publ Japan: Japanese Society for Soil Mechanics and Foundations Engineering, 1987

Modelling soil behaviour under principal stress axis rotation : Towhata, I; Ishihara, K Proc 5th International Conference on Numerical Methods in Geomechanics, Nagoya, 1–5 April 1985V1, P523–530. Publ Rotterdam: A. A. Balkema, 1985

Modelling soil behaviour under principal stress axis rotation : Towhata, I; Ishihara, K Proc 5th International Conference on Numerical Methods in Geomechanics, Nagoya, 1–5 April 1985V1, P523–530. Publ Rotterdam: A. A. Balkema, 1985

Deformation behaviour of anisotropic dense sand under principal stress axes rotation : Miura, K; Miura, S; Toki, S Soils Found V26, N1, March 1986, P36–52

Deformation behaviour of anisotropic dense sand under principal stress axes rotation : Miura, K; Miura, S; Toki, S Soils Found V26, N1, March 1986, P36–52

Deformation Behavior of Anisotropic Dense Sand Under Principal Stress Axes Rotation

In order to investigate the fundamental deformation behavior of sand under the more general stress condition involving the rotation of principal stress axes, a series of drained tests was carried out on a dense anisotropic sand using a hollow cylinder torsional shear apparatus. The hollow cylindrical specimens have an anisotropic fabric formed by the parallel alignment of particles induced during deposition, and are tested under the principal stress axes rotation keeping the values of three principal stresses constant. The experimental results showed that the shear deformation of sand due to the rotation of principal stress axes are not negligible as compared with that due to the shear with fixed principal stress axes and the effects of inherent anisotropic fabric on the shear deformation and volume change behavior are considerably large. The mode of anisotropic effects on the deformation characteristics depends strongly on whether the rotation of principal stress axes are involved or not. It was also indicated that the anisotropic deformation characteristics under the principal stress rotation can be explained by taking account of the predominant sliding occurring on the bedding plane, irrespective of whether the principal stress axes rotate or not. This consideration is supported by the fact that the bedding plane has the lowest value of the resistance against shear stress according to the horizontal alignment of subelongated sand particles.

Earthquake Swarm Along the San Andreas Fault near Palmdale, Southern California, 1976 to 1977

Between November 1976 and November 1977 a swarm of small earthquakes (local magnitude </= 3) occurred on or near the San Andreas fault near Palmdale, California. This swarm was the first observed along this section of the San Andreas since cataloging of instrumental data began in 1932. The activity followed partial subsidence of the 35-centimeter vertical crustal uplift known as the Palmdale bulge along this "locked" section of the San Andreas, which last broke in the great (surface-wave magnitude = 8(1/4)+) 1857 Fort Tejon earthquake. The swarm events exhibit characteristics previously observed for some foreshock sequences, such as tight clustering of hypocenters and time-dependent rotations of stress axes inferred from focal mechanisms. However, because of our present lack of understanding of the processes that precede earthquake faulting, the implications of the swarm for future large earthquakes on the San Andreas fault are unknown.

Theory of earthquakes

The scale independent inclusion theory of rock failure developed in Part I is applied to the problem of crustal earthquakes and, in particular, to the problem of premonitory phenomena reported to precede such earthquakes. Several well-known premonitory effects such as anomalous variation in the ratio of longitudinal (V p ) and shear (V s ) seismic velocities, V P /V S , tilt, regional and local crustal movements and stress axis rotation, to mention a few, are shown to be a natural consequence of the physical processes leading to failure in dry rock. The effects of fluids on failure in the focal region of a potential earthquake are considered in terms of the scale independent inclusion theory.

Effect of rotating secondary principal axes in scattered-light photoelasticity

A set of equations is presented and the effect of rotation of the secondary principal stress axes is discussed. The equations, general and relatively simple, adequately describe observed results. In studying the equations, a better understanding of the rotational effect can be achieved, and a technique is suggested which can eliminate any error resulting from rotation. This technique and the concepts involved are substantiated with experimental evidence and reported in this paper.