Principal stress orientations from multiple focal-plane solutions: new insight into the Australian intraplate stress field*
D. CLARK, M. LEONARD, 2003. "Principal stress orientations from multiple focal-plane solutions: new insight into the Australian intraplate stress field", Evolution and Dynamics of the Australian Plate, R.R. Hillis, R.D. Müller
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Stress tensor reconstructions are presented for seven domains within the Australian crust based on the formal inversion of four or more earthquake focal mechanisms in close geographic proximity. The data for inversion was sourced from a set of 70 independent quality-ranked focal mechanisms forming part of the recently compiled Geoscience Australia focal mechanism database. When analysed in conjunction with in situ stress data held by the Australian Stress Map Project, the new data make possible for the first time a rigourous comparison of the Australian continental stress field at near-surface and seismogenic depths. A more complete picture of the character of the Australian intraplate stress field is thereby made available. The tensor data agrees well with In situ determinations in western, northern and far-southeastern Australia suggesting that the continental stress field is homogeneous between shallow and seismogenic depth in these areas. Plate-boundary forces are considered to be the dominant source of stress. In contrast, the results for the Sydney Basin and Flinders Ranges imply significant heterogeneity and influence by more localised sources of stress. An apparent persistent northeast stress orientation in the Sydney Basin contrasts with the variable orientations displayed by in situ data, suggesting that the shallow stress field is dominated by near-surface effects, such as those generated by deeply incised topography. Uniformity in orientation of the seismogenic stress field is interpreted in terms of the influence of linear topographic sources of stress (the continental margin and the elevated topography of the Great Dividing Range) superimposed onto a regional stress field of low horizontal anisotropy. In the Flinders Ranges, an anomalous tensor result is interpreted in terms of perturbation of the regional stress field by a locally enhanced geotherm.