EGU2020-12723
https://doi.org/10.5194/egusphere-egu2020-12723
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

The 2016 Mw 6.1 Petermann Ranges earthquake rupture, Australia: another “one-off” stable continental region earthquake

Mark Quigley1, Tamarah King1, and Dan Clark2
Mark Quigley et al.
  • 1University of Melbourne, School of Earth Sciences, Australia
  • 2Geoscience Australia, Canberra, Australia

The 20th May 2016 moment magnitude (MW) 6.1 Petermann earthquake was the 2nd longest single-event historic Australian surface rupture (21 km) and largest MW on-shore earthquake in 28 years. Trench logs from two hand-dug trenches show no evidence of penultimate rupture of surface eolian sediments or underlying calcrete. Available dating of eolian dunes 140 to 500 km away from the Petermann fault indicated eolian deposition during either the last glacial maximum (approximately 20 ka) or a period of aridification at approximately 180 - 200 ka. Ten 10Be cosmogenic nuclide erosion rates of bedrock outcrops at 0 to 50 km from the surface rupture trace are within error of each other between 1.4 to 2.6 mMyr-1. These samples have approximate averaging times between 208 to 419 ka. Bedrock erosion rates, trenching results and interpretation of the landscape history suggest the 2016 event is the only surface rupturing earthquake on the Petermann fault in the last 200 to 400 kyrs, and possibly the first ever on this fault. This finding is consistent with a lack of evidence for penultimate rupture for all eleven historic Australian surface rupturing events, as described by either trenching and/or landscape analysis and bedrock erosion rates. These ‘one-off’ events within Precambrian cratonic Australian crust are not consistent with trenching results and geomorphology of paleo-scarps within the Flinders Ranges and Eastern Australia which indicate multiple recurrent fault offset. Variable fault recurrence behaviour highlights that uniform seismic hazard modelling approaches are not applicable across Stable Continental Regions.

How to cite: Quigley, M., King, T., and Clark, D.: The 2016 Mw 6.1 Petermann Ranges earthquake rupture, Australia: another “one-off” stable continental region earthquake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12723, https://doi.org/10.5194/egusphere-egu2020-12723, 2020

Comments on the presentation

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Presentation version 1 – uploaded on 06 May 2020
  • CC1: Comment on EGU2020-12723, Christoph Grützner, 08 May 2020

    Thanks for the great poster. This is really worrying from a hazard perspective, of course...
    It also seems to be at odds with anything we believed to know about how faults grow, that is, increasing fault length with increasing displacement. I guess you don't have much data to backup a comment on that, but anyway: Would you think there's an upper magnitude limit for such events?  Would you think there's any reason these new faults can only rupture in M6-ish events or could they get much stronger?
    Thanks!

    • AC1: Reply to CC1, Dan Clark, 08 May 2020

      >This is really worrying from a hazard perspective, of course...
      Indeed it is! We are moving in the central and western cratonic parts of Australia to using the faults to estimate Mmax only and not include them explicitly as sources in the future iterations of the national hazard maps. I discuss this distinction a little more in my presentation materials. https://meetingorganizer.copernicus.org/EGU2020/EGU2020-6279.html

       

      >It also seems to be at odds with anything we believed to know about how faults grow, that is, >increasing fault length with increasing displacement.

      We find no evidence in the Australian continent for the formation of new faults. The historic and pre-historic fault scarps predominantly overlie lineaments that can be seen in aeromagnetic data, suggesting that ancient faults (sometimes Proterozoic and Archaean) are breaking.

      >I guess you don't have much data to backup a comment on that, but anyway: Would you think there's an upper magnitude limit for such events?  Would you think there's any reason these new faults can only rupture in M6-ish events or could they get much stronger?

      Because of very low rates of erosion we have a very good record of fault scarps. I maintain a database of neotectonic faults across Australia (http://www.ga.gov.au/neotectonic-feature-distribution/home). In the west and central parts of Australia these relate often to single events (or 1-3 events), so we can get a good idea of the magnitude of the causative earthquakes from scaling relations. In my EGU poster I present a contour map of the total neotectonics throw of faults across Australia. This gives an idea of the recurrence (very little in the west, and more in the east and NW, in younger crust with thinner lithosphere):

       

       

      Below I have contoured the scarp length data, which can be thought of as a proxy for Mmax. These are minimum estimates as I’ve taken the mean value from each 1.5 degree square. I’ve then coloured it so it saturates at Mw6.8, though the maximum is Mw7.4.

      I hope the above answers your questions and sparks further conversation!


      Cheers,

      Dan.

       

       

      • CC2: Reply to AC1, Christoph Grützner, 08 May 2020

        Thanks Dan!

        "We find no evidence in the Australian continent for the formation of new faults." --> I missed this and thought that in the Peterman case there was no hint for a pre-existing fault at all. At least it seems that the very old structures are sufficiently well-oriented to be activated every now and then. I wonder what the EQ pattern would like if those inherited structures were striking differently...

        I'll move over to your poster with another comment on your presentation.

        Thanks,
        Christoph

        • AC2: Reply to CC2, Tamarah King, 08 May 2020

          I enjoy your enthusiasm Christoph! 

          Just to clarify Dan's comment as well: "The historic and pre-historic fault scarps predominantly overlie lineaments that can be seen in aeromagnetic data, suggesting that ancient faults (sometimes Proterozoic and Archaean) are breaking"

          These lineaments are, as far as we can tell, ancient planar structural features (not just ancient faults). So, bedrock foliation planes, dike intrusions, faults, lithological boundaries, etc. It's a bit complicated to say that they are all aligned with the current stress field (because some ruptures involve multiple structures slightly oblique to each other, creating arcuate / complex surface ruptures). But in nearly all cases the section of rupture with maximum offset, and focal mechanisms, are aligned pretty much perpendicular to the stress field (the exception is the Mw 4.7, ~1.5km long Katanning rupture - but that's another story). In the case of the Petermann, rupture seems to have propagated along NE dipping foliation planes within the mylonitic bedrock which are perpendicular to the stress field (from bore-hole breakouts and focal mechanisms)

          Dan's replied well to your other comments, but I might also come back to them once I've had some time to ponder!