b'Rapid deployment for aftershock monitoringFeatureRapid deployment for earthquake aftershock monitoring in southwest Western Australiathe Arthur River swarm 2022Ruth Murdie1, Huaiyu Yuan2, Meghan S Miller3, Robert Pickle3,for Exploration Targeting at the University of Western Australia, Michelle Salmon3 and Justin Whitney4 was recently equipped with a new set of Smartsolo IGU-BD3c-5 1Geological Survey of Western Australia seismometers sitting under his desk and would be perfect for this purpose. This looked like a good opportunity to test them 2Macquarie University and University of Western Australia out. DFES were also interested in what could be done in such an event. GSWA and Dr. Yuan used the DFES regional network 3The Australian National University to gain contacts in the Arthur River area as first points where 4Department of Fire and Emergency Services, Western Australia seismometers could be deployed.ruth.murdie@dmirs.wa.gov.au Five days after the initial shock, on 10 January, six additional On 5 January 2022, the residents in Western Australias Southernseismometers were installed in the immediate area of the Wheatbelt were in for a shockquite literally. They experiencedswarm to bolster the pre-existing SWAN network (Figure1). a magnitude 4.0 earthquake. Reports from the area tell of cracksRetired seismologists from the Seismologists Association of in masonry and pictures falling off the walls. Although the StatesAustralia also deployed an instrument in the area.southwest is known as the southwest seismic zone, (Doyle,These instruments were initially left for three weeks. During 1971), one of the most seismically active regions in Australiathis time, the largest event in the sequence so far - an ML 4.8 - (Leonard, 2008, Dentith and Featherstone 2003), this eventoccurred on 24 January and was felt across southwest Australia came as a surprise to many and there was more in store for thisincluding Perth, Albany and Margaret River (Figure 2). This event normally quiet community. Aftershocks continued to register onwas again followed by many aftershocks over the next two the Earthquakes@GA website at a rate of several per day. weeks; so many that the local community became quite used to The initial measurements by Geoscience Australia estimatedthem. Data was collected on 1 February. A local farmer reckoned this event to have occurred close to the community of Arthurthe swarm was over as he hadnt felt any events for a couple River at a depth of approximately 7 km. However, theseof days, but as the team were driving away from the area that measurements relied on data from stations located mainlyevening, a third main shock of ML 4.3 occurred. The swarm was to the north of the event with the nearest being locatednot over yet!at Narroginapproximately 50 km away. The depths ofData was passed to ANU and was run through a machine-earthquakes in the southwest seismic zone have always beenlearning detection algorithm which has been trained to identify uncertain, as although large surface-wave phases observed inthe phase arrivals of very small earthquakes with high precision. the seismic signal demonstrate the earthquake sources are veryThe initial earthquake locations from the period between the shallow, the low density of the earthquake monitoring networkfirst main shock to the start of swarm deployment included two makes it challenging to resolve the earthquake depth with anySWAN sites plus the Australian National Seismograph Network accuracy. (ANSN; managed by GA) and the Seismometers in Schools (managed by the ANU) stations. Unfortunately, the SWAN This earthquake alerted the South West Australia seismicinstruments situated just south of the swarm had failed to Network (SWAN) team (ARC linkage grant LP180101118)record anything during this initial period. Based on the available consisting of scientists from Australian National Universityinstruments, the events were estimated to have occurred just (ANU), Geoscience Australia (GA), Macquarie University, Geological Survey of Western Australia (GSWA) and the Western Australian Department of Fire and Emergency Services (DFES) (Murdie etal., 2020) who are in their second year of monitoring the earthquakes of southwest Western Australia. The current SWAN deployment has three stations within 60 km of the epicentre, but additional closer instruments would be critical to characterise the ongoing earthquake sequence. With Western Australias border still closed, and GAs aftershock monitoring instruments still deployed following the M W5.9 22 September 2021 Woods Point earthquake in the Victorian Highlands (Ninis etal., 2021; Quigley and La Greca, 2021), the question was put to the Western Australian contingent of SWAN could we get seismometers on the ground to monitor any aftershocks? The enhanced understanding gained from recording the seismicity of Western Australia thanks to the deployment of monitoring equipment following the Lake Muir earthquakes of 2018 demonstrates the importance of such initiatives (Clark etal., 2020).Up until now, however, Western Australia has had no rapidFigure 1.A typical installation includes a seismometer (front) and an deployment capabilities. But as luck would have it, Dr. Huaiyuaccelerometer (back) to accurately record seismic vibrations caused by the Yuan of Macquarie University, who is based out of the CentreArthur River earthquake swarm.39 PREVIEW APRIL 2022'