The 2018 Lake Muir Earthquakes: Australia’s Ninth Surface Rupturing Earthquake Sequence in 50 Years

Date: 4/25/2019

Time: 03:45 PM

Room: Pike

A shallow M_W 5.3 earthquake near Lake Muir in southwest Western Australia on the 16 September 2018 was followed on the 8 November by a co-located M_W 5.2 event in the same region. Sentinel-1 synthetic aperture radar interferograms (InSAR) allowed for the timely identification and mapping of the surface deformation relating to both earthquakes. Field mapping, guided by the InSAR observations, revealed that the first event produced an approximately 3 km-long and up to 0.4 m-high west-facing surface rupture. Five seismic rapid deployment kits (RDKs) were installed in the epicentral region within three days of the 16 September event. These data, telemetered to Geoscience Australia’s National Earthquake Alerts Centre, have enabled the detection and location of more than 750 dependent events up to M_L 4.6. Preliminary joint hypocentre relocation of aftershocks using data from RDKs confirms an easterly dipping rupture plane for the first M_W 5.3 event.

The main shocks were recorded throughout the Australian National Seismic Network, in addition to a local broadband network in the Perth Basin operated by University of Texas at Dallas and the University of Western Australia. These data indicate large long-period ground-motions due to Rg phases and basin amplification. The two main shocks were widely felt within the region, including the Perth metro region (300 km away), with over 2400 online felt reports for the 8 November event.

The Lake Muir sequence represents the ninth recorded surface rupturing earthquake in Australia in the past 50 years. All of these events have occurred in the Precambrian cratonic terranes of western and central Australia, in unanticipated locations. Paleoseismic studies of these ruptures found no evidence for regular recurrence of large events on the underlying faults. The events might therefore be considered “one-offs” at timescales of significance to typical probabilistic seismic hazard studies.

Presenting Author: Trevor Allen

Authors