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  • 1
    Call number: SR 90.0002(1202)
    In: Professional paper
    Type of Medium: Series available for loan
    Pages: IV, 61 S. + 1 pl.
    Series Statement: U.S. Geological Survey professional paper 1202
    Language: English
    Location: Lower compact magazine
    Branch Library: GFZ Library
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  • 2
    Monograph available for loan
    Monograph available for loan
    Cambridge [u.a.] : Cambridge Univ. Press
    Call number: 9/M 06.0017
    Description / Table of Contents: Motivations and Opportunities. - Structural Mapping Techniques and Tools. - Characterizing Structures Using Differential Geometry. - Physical Quantities, Fields, Dimensions, and Scaling. - Deformation and Flow. - Force, Traction, and Stress. - Conservation of Mass and Momentum. - Elastic Deformation. - Brittle Behavior. - Viscous Flow. - Rheological Behavior. - Model Development and Methodology.
    Type of Medium: Monograph available for loan
    Pages: XII, 500 S. , Ill., graph. Darst., Kt.
    ISBN: 0521839270
    Classification: A.3.4.
    Location: Reading room
    Branch Library: GFZ Library
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  • 3
    ISSN: 1420-9136
    Keywords: Stress field regional ; Volcanic dike pattern ; Paleopiezometer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The radial pattern of syenite and syenodiorite dikes of the Spanish Peaks region is analysed using theories of elasticity and dike emplacement. The three basic components of Odé's model for the dike pattern (a pressurized, circular hole; a rigid, planar boundary; and uniform regional stresses) are adopted, but modified to free the regional stresses from the constraint of being orthogonal to the rigid boundary. Dike areal density, the White Peaks intrusion, the strike of the upturned Mesozoic strata, and the contact between these strata and the intensely folded and faulted Paleozoic rocks are used to brient the rigid boundary along a north-south line. The line of dike terminations locates the rigid boundary about 8 km west of West Peak. The location of a circular plug, Goemmer Butte, is chosen as a point of isotropic stress. A map correlating the location of isotropic stress points with regional stress parameters is derived from the theory and used to determine a regional stress orientation (N82E) and a normalized stress magnitude. The stress trajectory map constructed using these parameters mimics the dike pattern exceptionally well. The model indicates that the regional principal stress difference was less than 0.05 times the driving pressure in the West Peak intrusion. The regional stress difference probably did not exced 5 MN/m2.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1420-9136
    Keywords: Strike-slip faults ; kink bands ; Sierra Nevada ; stress orientation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Small left-lateral strike-slip faults and right-lateral monoclinal kink bands with subvertical fold axes may be related to the formation of a very large right-lateral kink band (Bear Creek kink band), about 8 km wide and at least 15 km long, trending N27W along Bear Creek Valley in the Mt. Abbot quadrangle, Sierra Nevada, California. A foliation within Bear Creek Valley is defined by vertical slabs of granodiorite bounded by joints and faults. Small strike-slip faults and larger fault zones have nucleated along preëxisting joints and accommodated shearing between granodiorite slabs. The orientations of small cracks that occur near the tips of faults or connect adjacent fault segments indicate that the direction of maximum compression was about 20° counterclockwise from traces of joints at the time the faults nucleated. In some places where faults are closely spaced there are small, right-lateral kink bands with widths of 1 to 20 m. The slabs of granodiorite are gently curved through the kink bands, and analysis of the orientations of slabs in the limbs of the small kink bands indicates that the direction of maximum compression during kink-band formation was 15° to 20° counterclockwise from the traces of faults outside the kink bands. The orientation of the maximum compression for the formation of the small cracks at tips of many strike-slip faults and for the formation of the small kink bands, relative to the orientation of the maximum compression inferred from the joints on the limb of Bear Creek kink band, suggests that the foliation within the Bear Creek Valley has reoriented a maximum of 40° to 60° clockwise. Although the various orientations of joints, faults, and kink bands could be explained in terms of different regional compression directions at different places and at different times in the Mt. Abbot quadrangle, a much simpler interpretation, based on analysis of large and small structures in the granodiorite in Bear Creek Valley, is that they all formed in response to one maximum regional compression in the direction N25E.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Recent K-Ar dating of eruptions at Pantelleria, a peralkaline volcanic island in the Strait of Sicily, shows a correlation between eruption of pantellerite lavas from caldera ring fractures and low stands of sea level as determined fromδ 18O stratigraphy. Post-caldera pantellerite lavas associated with an ∼ 114-ky-old caldera erupted along the ring-fracture zone during a major low stand of sea level at about 67 Ka. The most recent episode of lava-flow emplacement began about 20 ky ago during the last glacial maximum. Magma vented along the ring fault of a 45-ky-old caldera, from fractures radial to the caldera, and along faults formed by intracaldera trapdoor uplift. Two mechanical models based on elasticity theory are presented to explain the correlation of post-caldera ring-fracture eruptions at Pantelleria with lowering of sea level. A simple analysis of a bending circular plate of thickness,T r, and radius,R, representing the magma-chamber roof block, shows that tensile stress is concentrated by a factor of 0.75R 2/T r 2 at the lower perimeter of the plate when sea level drops. Stress changes may be even greater ifT r is effectively less than the stratigraphic thickness due to layering of rocks in the roof block. Calculated stress changes due to a 100-m drawdown of sea level are similar in magnitude to stresses associated with dike propagation. More realistic model geometries, including different chamber shapes, a conical volcanic edifice, and sea-level drawdown beyond the surface projection of the magma chamber, were tested using the boundary-element method. Lowering sea level generates a horizontal tensile stress above the chamber, even when sea water is removed outboard of the magma chamber. For some chamber geometries the magnitude of the tensile stress maximum is greater than the ∼ 1 MPa pressure of the 100 m of removed water and is of the right order of magnitude for dike propagation. Dikes initiated by the change of the stress field may originate and propagate along fractures inboard of the chamber margin. The magnitudes of tensile maxima along the top of the chamber decrease as original sea level is moved outboard of the chamber margin and as the chamber thickness decreases. When the depth to the top of the magma chamber reaches a critical value, dependent on chamber geometry, the propagation of dikes to the surface is inhibited.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-8868
    Keywords: mathematics ; structural geology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract A mechanical model based upon elasticity theory for the deformation around a pressurized elliptical hole in an homogeneous, isotropic solid has found application in many areas of engineering, rock mechanics, and structural geology. The explicit equations for stress and displacement around such a hole are given. An apl computer program for calculating these stresses and displacements also is presented. These equations and this program should ease future usage of this model by engineers and geologists.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-2673
    Keywords: Critical fracture spacing to layer thickness ratio ; edge fractures ; finite element modeling ; layered materials ; stability of fracture propagation ; stress state transition.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Opening-mode fractures developed from a free surface in a layered material often terminate at the interface that divides the fractured layer and the underlying layer. They also display regular spacing that is of the same order of magnitude as the thickness of the fractured layer. We have investigated the stress distribution between two adjacent edge fractures as a function of the ratio of fracture spacing to thickness of the fractured layer using a two-layer elastic model with a fractured top layer. The results show that when the ratio of fracture spacing to the layer thickness changes from greater than to less than a critical value the normal stress acting perpendicular to the fractures near the free surface changes from tensile to compressive. This stress state transition precludes further infilling of fractures unless they are driven by mechanisms other than a pure extension, or there are flaws that significantly perturb the local stress field between the fractures. Hence, the critical fracture spacing to layer thickness ratio defines a lower limit for fractures driven by extension, which also defines the condition of fracture saturation. The critical value of the fracture spacing to layer thickness ratio is independent of the average strain of the fractured layer, and it increases with increasing ratio of Young's modulus of the fractured layer to that of the underlying layer. The critical value increases with increasing Poisson's ratio of the fractured layer, but it decreases with increasing Poisson's ratio of the underlying layer. For the case with the same elastic constants for the fractured layer and the underlying layer, the critical spacing to layer thickness ratio is about 3.1. Delamination between the fractured layer and the underlying layer makes the critical spacing to layer thickness ratio much greater. Infilling fractures grow more easily from flaws located near the bottom of the fractured layer than from those located near the free surface when the spacing to layer thickness ratio is less than the critical value. The propagation of an edge flaw between adjacent edge fractures is unstable, but for the flaw to propagate to the interface, its height has to be greater than a critical size, that decreases with increasing fracture spacing to layer thickness ratio. The propagation behavior of an internal flaw with its lower tip at the interface depends on the edge fracture spacing to layer thickness ratio. The propagation is unstable, when the fracture spacing to layer thickness ratio is greater than a critical value; stable, when the fracture spacing to layer thickness ratio is less than another critical value; and first unstable, then stable, and/or unstable again, when the fracture spacing to layer thickness ratio is between these two critical values.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Using a three-layer model with a fractured central layer, and with a top layer and a bottom layer of the same thickness, we study the change of the critical fracture spacing to layer thickness ratio (i.e., the ratio at fracture saturation) as a function of the thickness of the top and bottom layers. Results show that, with increasing thickness of these layers, the critical spacing to layer thickness ratio decreases rapidly from infinity to a constant value, corresponding to that for very thick top and bottom layers. Also, we study the change of the critical spacing ratio as a function of the thickness of the top layer where the bottom layer is much thicker (5 times) than the fractured layer. In this case, the critical spacing to layer thickness ratio decreases rapidly from the value for edge fractures to the same constant value as the thickness of the top layer increases. These results imply that if the adjacent layers are thicker than 1.5 times the thickness of the fractured layer, the multilayer can be treated approximately as a system with infinitely thick top and bottom layers in terms of spacing at fracture saturation.
    Type of Medium: Electronic Resource
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  • 9
    Publication Date: 2012-02-01
    Description: Investigation of the mechanics of complex earthquakes requires insight into fault geometry. We use linear-elastic, quasi-static mechanical models of faults involved in the M 7.3 Landers earthquake to test the influence of fault continuity, dip, and strike on fault slip and the perturbed stress field in regions of complex surface deformation and dense aftershock activity. Subsurface fault structure is constrained with both geological and geophysical data by comparing observed right-lateral surface slip with slip along model faults and by comparing focal mechanisms with model Coulomb planes at the locations of large aftershocks. The refined structure of major faults at Landers includes a southward extension of the Johnson Valley fault (JVF) at depth, beyond the mapped fault trace, a 75 degrees W dip along the central Johnson Valley fault, and a near-surface discontinuity along the southern Homestead Valley fault (HVF). The final model better captures observed slip deficits along the Johnson Valley and Homestead Valley faults, improves quantitative fit to the observed offset data, and captures the local stress state in 9 of 12 locations studied. Relating aftershock orientations to local stresses resulting from mainshock fault slip provides a mechanical basis for deciphering between the two nodal planes provided by each focal mechanism. Slip along nonplanar faults with friction of 0.6 produces model failure planes in a variety of orientations, indicating that heterogeneous aftershocks do not necessarily result from low fault friction. Mechanical selection of nodal planes suggests that aftershocks do not consistently reflect the orientation of their cluster or the orientation and slip direction of mainshock faults.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences
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  • 10
    Publication Date: 1988-09-01
    Description: Recent K-Ar dating of eruptions at Pantelleria, a peralkaline volcanic island in the Strait of Sicily, shows a correlation between eruption of pantellerite lavas from caldera ring fractures and low stands of sea level as determined from δ 18O stratigraphy. Post-caldera pantellerite lavas associated with an ∼ 114-ky-old caldera erupted along the ring-fracture zone during a major low stand of sea level at about 67 Ka. The most recent episode of lava-flow emplacement began about 20 ky ago during the last glacial maximum. Magma vented along the ring fault of a 45-ky-old caldera, from fractures radial to the caldera, and along faults formed by intracaldera trapdoor uplift. Two mechanical models based on elasticity theory are presented to explain the correlation of post-caldera ring-fracture eruptions at Pantelleria with lowering of sea level. A simple analysis of a bending circular plate of thickness, T _r, and radius, R , representing the magma-chamber roof block, shows that tensile stress is concentrated by a factor of 0.75 R 2/ T _ r 2 at the lower perimeter of the plate when sea level drops. Stress changes may be even greater if T _r is effectively less than the stratigraphic thickness due to layering of rocks in the roof block. Calculated stress changes due to a 100-m drawdown of sea level are similar in magnitude to stresses associated with dike propagation. More realistic model geometries, including different chamber shapes, a conical volcanic edifice, and sea-level drawdown beyond the surface projection of the magma chamber, were tested using the boundary-element method. Lowering sea level generates a horizontal tensile stress above the chamber, even when sea water is removed outboard of the magma chamber. For some chamber geometries the magnitude of the tensile stress maximum is greater than the ∼ 1 MPa pressure of the 100 m of removed water and is of the right order of magnitude for dike propagation. Dikes initiated by the change of the stress field may originate and propagate along fractures inboard of the chamber margin. The magnitudes of tensile maxima along the top of the chamber decrease as original sea level is moved outboard of the chamber margin and as the chamber thickness decreases. When the depth to the top of the magma chamber reaches a critical value, dependent on chamber geometry, the propagation of dikes to the surface is inhibited. ©1988 Springer-Verlag
    Print ISSN: 0258-8900
    Electronic ISSN: 1432-0819
    Topics: Geosciences
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