Tamarah King, Mark Quigley, Dan Clark

The 2nd June 1979 moment magnitude (Mw) 6.1 Cadoux earthquake caused a complex, multi-fault surface rupture consisting of six mapped scarps: (from south to north) the 8 km long west dipping Robb scarp, 3 km long south dipping Cumming scarp, the Lone Tree, Carter and Tank scarps (which together define an east-dipping arcuate rupture) and the 2.5 km long southwest-dipping Kalajzic scarp. Surface ruptures are classified as six intersecting faults using kinematic and orientation criteria, with a total simplified surface rupture length of 20.6 km (47% greater than lengths previously published in earthquake scaling relationship analyses). These faults align with structural trends in basement geology as mapped from surface outcrops and geophysical maps. No prior attempts have been made to reconcile seismological data with the geometrically complex surface rupture in order to investigate rupture initiation and propagation. We speculate that this earthquake ruptured unilaterally (from south to north) towards an area of increased structural complexity, within which the rupture eventually terminated. Aftershock locations have large epistemic uncertainties and do not enable accurate constructions of sub-surface fault geometry. Descriptions of shallow trenches across the Carter and Tank scarps suggest no prior rupture along at least some of the Calingiri scarps between the formation of basement structures (Archean – Proterozoic) and Tertiary – Quaternary surface sedimentation. The Cadoux earthquake is one of the most structurally complex earthquakes globally for this moderate (i.e., Mw ≤ 6.1) magnitude.