Earthquake monitoring in the Southwest Seismic Zone, Western Australia

Five new seismic monitoring stations have been added to the Australian National Seismograph Network (ANSN) in Western Australia with the aim of better locating the small earthquakes of the Southwest Seismic Zone of southwest Western Australia. The Southwest Seismic Zone, one of the most seismically active onshore areas in Australia, is an area known for its seismicity by the local people who regularly experience small cupboard rattlers. These often occur in swarms as documented by Dent (e.g. 2009, 2014, 2017, 2019, 2020). It is more widely known for the M6.5 Meckering earthquake of 1968 which destroyed many houses in Meckering, produced a 37 km long and 2 m high fault scarp and dramatically bent the railway line. There is no obvious tectonic reason for PREVIEW AUGUST 2021 earthquakes to be occurring in this area as it is in the middle of an Archean cratonic region although the scarps from surface rupturing events, such as the Meckering event, mainly trend approximately north-south and appear to lie along trends in the magnetic data (Dentith et al 2009). Until mid-2020 the ANSN had a fairly sparse coverage of the area. A secondary Public Seismic Network (PSN) is also monitoring in the area. Inclusion of the PSN data has quite an effect on the calculated locations, as exampled by the tighter clustering of the Beacon swarm of 2009 (Dent, 2009) rather than the linear trend from just using the ANSN data. In mid-2020 four more semi-permanent stations were installed in the area and one in the Goldfields and added to the data streaming into the National Earthquake Alerts Centre (NEAC) and incorporated into the location algorithm. This presentation looks at seismicity of the area, the small swarms that have been detected since then and the relationship of the seismicity to the geology. Presented at the 2021 Australasian Exploration Geoscience Conference (AEGC)