Stress and faulting in southeast Australia as derived from the strongest earthquakes in the region

Spassov, Edelvays

doi:10.1016/s1367-9120(99)00022-x

Cited by 3 publications

(2 citation statements)

References 7 publications

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“…Similarly, an explanation for mechanical anisotropy elsewhere could be sought in relation to the contemporaneous intraplate stress field. However, regional stress indicators for Australia (e.g., borehole breakouts [Hillis et al, 1998[Hillis et al, , 1999 or focal mechanisms [Lambeck et al, 1984;Spassov, 1998;Spassov and Kennett, 2000]) are poorly consistent with each other, and Australia has very low seismicity. In addition to the difficulty of identifying a representative stress direction responsible for anisotropic isostatic compensation, there is no a priori causal relationship between them.…”

Section: Mechanical Anisotropy and Lithospheric Stressmentioning

confidence: 99%

Spatiospectral localization of isostatic coherence anisotropy in Australia and its relation to seismic anisotropy: Implications for lithospheric deformation

2003

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[1] We investigate the two-dimensional (2-D) nature of the coherence between Bouguer gravity anomalies and topography on the Australian continent. The coherence function or isostatic response is commonly assumed to be isotropic. However, the fossilized strain field recorded by gravity anomalies and their relation to topography is manifest in a degree of isostatic compensation or coherence which does depend on direction. We have developed a method that enables a robust and unbiased estimation of spatially, directionally, and wavelength-dependent coherence functions between two 2-D fields in a computationally efficient way. Our new multispectrogram method uses orthonormalized Hermite functions as data tapers, which are optimal for spectral localization of nonstationary, spatially dependent processes, and do not require solving an eigenvalue problem. We discuss the properties and advantages of this method with respect to other techniques. We identify regions on the continent marked by preferential directions of isostatic compensation in two wavelength regimes. With few exceptions, the short-wavelength coherence anisotropy is nearly perpendicular to the major trends of the suture zones between stable continental domains, supporting the geological observation that such zones are mechanically weak. Mechanical anisotropy reflects lithospheric strain accumulation, and its presence must be related to the deformational processes affecting the lithosphere integrated over time. Threedimensional models of seismic anisotropy obtained from surface wave inversions provide an independent estimate of the lithospheric fossil strain field, and simple models have been proposed to relate seismic anisotropy to continental deformation. We compare our measurements of mechanical anisotropy with our own model of the azimuthally anisotropic seismic wave speed structure of the Australian lithosphere. The correlation of isostatic anisotropy with directions of fast wave propagation gleaned from the azimuthal anisotropy of surface waves decays with depth. This may support claims that above $200 km, internally coherent deformation of the entire lithosphere is responsible for the anisotropy present in surface wave speeds or split shear waves.

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Section: Mechanical Anisotropy and Lithospheric Stressmentioning

confidence: 99%

Spatiospectral localization of isostatic coherence anisotropy in Australia and its relation to seismic anisotropy: Implications for lithospheric deformation

2003

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“…[4] For a continent located within a plate interior, Australia shows a surprising level of earthquake activity (Figure 1). Some 7000 earthquakes were recorded in the southeastern portion of Australia in the interval 1958-1999 [Spassov and Kennett, 2000]. The most notable of these being the Richter magnitude (M L ) = 5.6 Newcastle earthquake in December 1989, the first since European settlement in which lives were lost.…”

Section: Introductionmentioning

confidence: 99%

Modes of active intraplate deformation, Flinders Ranges, Australia

Célérier¹,

Sandiford

Hansen³

et al. 2005

Tectonics

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[1] The Flinders Ranges form one of the most seismically active zones within the Australian continent with seismogenic strain rates over the last 30 years of $10 À16 s À1 . Active deformation in the region reflects late Neogene increases in stress levels in the Indo-Australian plate as a response to increased plate boundary forcing from collision zones with the neighboring Asian and Pacific plates. Geological and geophysical observations suggest two modes of active deformation in operation in the Flinders Ranges over the last several million years: (1) . Numerical models are developed to explore the contribution of each of these deformation modes to the observed geophysical signals. An elastic mode of deformation is suggested by a distinctive longwavelength positive correlation between gravity and topography in which the Flinders Ranges are bordered by anomalous topographic and gravity lows, now occupied by playa-lake systems, centered some 50 km outboard of range-bounding faults. Numerical models show that flexural instabilities localized by vertical loads arising from older tectonic structuring produce a first-order match with observed topography and gravity. Numerical models are also used to illustrate how the localized failure evident in the contemporary seismicity and Quaternary faulting record within the Flinders Ranges reflects thermal weakening associated with extraordinary concentrations of heat producing elements in the crust, as reflected in modern-day heat flows of $90 mW m À2 .

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Enhanced intraplate seismicity along continental margins: Some causes and consequences

Sandiford

Egholm

2008

Tectonophysics

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Stress and faulting in southeast Australia as derived from the strongest earthquakes in the region

Cited by 3 publications

References 7 publications

Spatiospectral localization of isostatic coherence anisotropy in Australia and its relation to seismic anisotropy: Implications for lithospheric deformation

Spatiospectral localization of isostatic coherence anisotropy in Australia and its relation to seismic anisotropy: Implications for lithospheric deformation

Modes of active intraplate deformation, Flinders Ranges, Australia

Enhanced intraplate seismicity along continental margins: Some causes and consequences

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