Bedrock structural controls on the propagation of multi-fault earthquake ruptures and their environmental effects

Tamarah King, Mark C. Quigley, & Dan Clark

Published August 14, 2019, SCEC Contribution #9642, 2019 SCEC Annual Meeting Poster #124

Analyses of geological and geophysical data from ten moderate magnitude (Mw 4.7 – 6.6) historical surface-rupturing earthquakes in cratonic Australia indicate that bedrock structure controlled the orientation and geometry of their seismogenic rupture sources. Nine of ten earthquakes have surface-rupture traces that align with prevailing linear anomalies in geophysical (gravity and magnetic) data and bedrock structure (foliations ± quartz veins ± intrusive boundaries ± pre-existing faults). Six of seven Mw 5.7 to 6.6 events show evidence of multi-fault rupture across 2 to 6 discrete faults of ≥ 1 km length, placing these events as some of the most structurally complex earthquake ruptures identified globally for this magnitude. No unambiguous geological evidence for preceding surface-rupturing earthquakes is present, and five earthquakes contain evidence of absence of preceding ruptures since the late Pleistocene, collectively highlighting the importance of including background floating seismic sources with active fault catalogues for seismic hazard analysis.

The mapping of 570 coseismically displaced rock fragments identified following the 2016 Mw 6.1 Petermann earthquake enables geological analysis of rupture directivity and fling effects proximal (< 10 km) to the surface rupture trace. This highlights an additional opportunity for geological studies of bedrock to contribute to seismic source analysis, and estimation of ground shaking intensity in sparsely instrumented areas.

Key Words
Multi-fault earthquake; reverse fault; seismic source analysis; rupture directivity; intraplate; earthquake geology

Citation
King, T., Quigley, M. C., & Clark, D. (2019, 08). Bedrock structural controls on the propagation of multi-fault earthquake ruptures and their environmental effects. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology