Fracture systems in granite pavements of the eastern Pilbara Craton, Western Australia: indicators of neotectonic activity?
Titel:
Fracture systems in granite pavements of the eastern Pilbara Craton, Western Australia: indicators of neotectonic activity?
Auteur:
Clark, D. J. Bodorkos, S.
Verschenen in:
Australian journal of earth sciences
Paginering:
Jaargang 51 (2004) nr. 6 pagina's 831-846
Jaar:
2004-12
Inhoud:
Continental Australia is characterised by high levels of seismic activity in comparison with intracratonic areas worldwide. However, the link between earthquake events and earthquake-related geomorphology in Australia remains poorly understood for all except the largest events, because landscape impact unambiguously attributable to seismic activity is difficult to recognise. In this context, we describe several unusual fracture systems of possible tectonic origin that transect granite pavements in the Archaean eastern Pilbara Craton of Western Australia. Occurring at four localities (Gallery Hill, North Shaw, Mulgandinnah Hill and Muccan) separated by up to 150 km, the fracture systems typically range up to 100 m in length and 20 m in width, locally offset pavement surfaces by up to 15 cm vertically, and expose uniformly fresh-looking rock. At one locality (Muccan), the fractures cross-cut two out of three generations of aboriginal petroglyphs etched into the pavement surface, which suggests that fracture formation occurred both recently and rapidly. All four localities are characterised by extensional structures (tension fractures and dilated joints) striking 020-040°, and three preserve compressional structures (steeply dipping reverse faults at Gallery Hill and North Shaw; A-tent crestal fractures at Mulgandinnah Hill) trending 100-135°. The strongly correlated alignments of the fracture systems militate against a purely weathering-controlled origin, and the observed pattern is compatible with fracture formation in a single East Pilbara-wide stress field, dominated by pure shear and characterised by northeast-southwest- to north-northeast-south-southwest-directed horizontal compression. This orientation is consistent with that derived by spatial averaging of existing stress orientation data from northwest Australia. These preliminary results have exciting implications for the inexpensive field-based determination of regional stress orientation, and for the use of granitic landforms in probabilistic seismic hazard assessment and the identification of earthquake-prone areas.
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