The 1987 to 2019 Tennant Creek, Australia, earthquake sequence: a protracted intraplate multi-mainshock sequence

Abstract

The 1987 to 2019 Tennant Creek earthquake sequence comprises three 1988 surface-rupturing mainshocks (moment magnitude (Mw 6.2, 6.3, and 6.5) that occurred within a 12-hour period, a preceding foreshock sequence commencing in 1987, and a prolonged aftershock sequence including a Mw 5.0 earthquake on the 1st August 2019. Each surface rupturing event produced a distinct scarp; the south-dipping Kunayungku scarp, north-dipping Lake Surprise west scarp and south-dipping Lake Surprise east scarp. Fault geometries were confirmed by trenches across the rupture traces, levelling surveys across the rupture traces, newly acquired satellite-derived high-resolution elevation data, and well-located aftershocks. Focal mechanisms and modelling using available seismic data support the hypothesis that the first mainshock ruptured the Kunayungku fault, the second mainshock ruptured the Lake Surprise west fault (and potentially rupturing across multiple other blind faults), and the third mainshock ruptured the Lake Surprise east fault. Trenching across all three ruptures found no evidence of prior rupture along the Lake Surprise east and Kunayungku faults. Potential evidence of prior rupture on the Lake Surprise west scarp has been reported. However, we consider this evidence to be circumstantial and to equally support an alternative interpretation; that the pre-1988 topography relates to a paleo-channel along underlying bedrock topography. Surface rupture locations and orientations are strongly aligned to underlying linear geophysical anomalies, suggesting strong control of bedrock structure on contemporary seismicity. Almost 31 years after the initial sequence, a Mw 5.0 aftershock was recorded near the western tip of the West Lake Surprise rupture. InSAR fault modelling suggests this occurred on a shallow blind fault (< 2 km depth to top of fault). This structure is also aligned with linear geophysical anomalies, providing further support that pre-existing basement structures are providing strong controls on the location and geometry of faulting in this intraplate stable continental region.

Surface-Rupturing Historical Earthquakes in Australia and Their Environmental Effects: New Insights from Re-Analyses of Observational Data

“…Detailed summaries of the geology, seismology, surface rupture and palaeoseismology for the eleven considered historical surface ruptures from 1968 to 2016 are available as seven EarthArXiv reports ( [120][121][122][123][124][125][126]). Figures and data in these reports include available geological maps, geophysical maps, borehole data, surface rupture maps, displacement data, and available palaeoseismic trench logs.…”

“…The Marryat Creek, Pukatja and Petermann events occurred within the Mesoproterozoic Musgrave Block (Figure 1) within 0-10 km of major terrane boundaries. The Tennant Creek ruptures extend across the boundary of the Proterozoic Warramunga Province and Neoproterozoic-Cambrian Wiso Basin (Figure 1) (summary of all regional geology in Table 3, comprehensive details in EarthArXiv reports [120][121][122][123][124][125][126]). Granitic gneiss, migmatite, mylonite, granulite, and/or amphibolite basement rock is observed in trenches or outcrop at <1 m depth at multiple locations along the Petermann (Figure 2), Pukatja, Marryat Creek (Figure 2), Cadoux and Meckering ruptures.…”

“…This may relate to dip measurement difficulties for heavily weathered bedrock. (Summary of basement/bedrock in Table 4, comprehensive details in EarthArXiv reports [120][121][122][123][124][125][126]).…”

“…Uncertainties listed in Table 5 include published uncertainties or an assigned value of ± 10 km where no uncertainties are available [102]. Epicenters with lower uncertainties are derived using a variety of relocation methods including extra analysis (e.g., InSAR slip distributions, joint hypocenter determination) or extra data (e.g., surface rupture location, aftershocks from temporary seismometer arrays) (comprehensive details in EarthArXiv reports [120][121][122][123][124][125][126]). The epistemic uncertainty relating to the quality of velocity models used to locate epicenters is unconstrainted but appears to be one of the major sources of inaccurate locations where instrumentation is particularly sparse.…”

“…3 Centroid moment tensor depth, preferred value from publication. 4 Earthquake within 6 months and 50 km of epicenter (affected by catalogue completeness for very remote events, see EarthArXiv reports ( [120][121][122][123][124][125][126]) for details). 5 Earthquakes (n > 5) within 10 years and 50 km of the epicenter (affected by catalogue completeness for very remote events, see EarthArXiv reports for details).…”