Tamarah King, Mark Quigley, Dan Clark

The 14th October 1968 MW 6.6 Meckering earthquake surface rupture is comprised of a main 37 km long concave Meckering scarp (with a 1.5 km wide dextral step-over along the Burges en-echelon rupture complex) and a minor 9 km long rupture on the Meckering scarp foot-wall (the Splinter scarp, also with a 1.5 km dextral step-over). We recommend a total surface rupture length of 44.4 km for implementation into magnitude-length scaling relationships based on a reassessment of primary rupture lengths. High resolution aeromagnetic data show the arcuate limbs of the Meckering scarp are controlled by basement structures, with supportive evidence from surface outcrops. No definitive evidence exists to support any rupture along these structures between their Archean - Proterozoic formation and Tertiary to Quaternary sedimentation. The rupture is characterised by near-surface bedrock along most of its length, and available trenching shows only the historical offsets. We find that available seismological, geological and surface rupture data support a model in which rupture intiates on the Splinter fault as a sub-event 3.5 sec before the mainshock, propagating to the surface and downwards to an intersection with the main Meckering fault at 2.8 km depth (consistent with centroid depth estimates of 2.3 – 3.0 km). Rupture then propagates bi-laterally from the fault intersection across the Meckering faults to produce the mainshock. Further modelling would be required to test the strength of this model. This earthquake is one of the most structurally complex (as proxied by the number of discrete faults) for its magnitude, as evidenced by comparison with a global compilation.