Aeromagnetic mapping of Precambrian geological structures that controlled the 1968 Meckering earthquake (Ms 6.8): Implications for intraplate seismicity in Western Australia

Abstract

The 1968 Meckering earthquake (MS 6.8) resulted in the formation of an extensive surface rupture complex comprising faults with a range of orientations and demonstrating reverse and dextral lateral offsets. The rupture extended for approximately 37 km and scarps reached up to 2.5 m high near to the centre of the complex. Modeling of the seismological characteristics of the source show reverse failure occurred on a north-south striking, east-dipping, surface, but how this is related to the local Precambrian bedrock geology is not clear.Interpretation of new aeromagnetic data, together with subsequent ground-truthing, has allowed concealed bedrock lithology and structure to be mapped in previously unachievable detail. These data show that the surface faulting correlates closely with linear magnetic anomalies, interpreted as dykes/faults and lithological contacts. The apparent arcuate form of the fault complex is explained in terms of the reactivation of northeasterly (dykes and faults) and northwesterly (stratigraphic) trending features in a stress regime with an east-west oriented maximum principal stress. Space problems created where these two trends converge led to the creation/reactivation of a linking north-south trending thrust fault which accommodated the greatest displacements recorded for the 1968 event. This interpretation is consistent with previous research on the source parameters of Meckering event, which invoked one or more easterly dipping failure surfaces and reverse slip.