By Ashleigh Fielding | posted on September 20, 2018
TECHNICAL field officers from Geoscience Australia are in Frankland River until at least the end of this week to deploy earthquake recording equipment in the wake of WA’s largest earthquake this year, which occurred there on Sunday.
A 5.7 magnitude earthquake was recorded north-east of Lake Muir near Frankland River, 120km north-west of Albany on Sunday at 12.56pm.
It was the biggest out of 15 earthquakes recorded in the Great Southern this year and surpassed the size of 175 other earthquakes recorded this year across the state.
A magnitude 2.6 earthquake was documented at 7.07am on the same day, and a smaller 2.1 magnitude earthquake followed the large earthquake at 1.11pm.
A Geoscience Australia spokesperson stated the earthquake activity seen this month in WA was “not particularly unusual”, as WA consistently had the most number of recorded earthquakes in Australia each year.
“Earthquake activity is known to vary with time, so it is not unusual to experience six or more earthquakes in WA in any one month,” the spokesperson said.
“Every few years, we record ‘earthquake swarms’ in the south west WA region, which may have 100 or more small earthquakes within any given month.
“There have been 190 earthquakes recorded in Western Australia since the beginning of the year, ranging in magnitude between 1.5 and the 5.7 near Frankland River, and the distribution of these earthquakes covers most of the state, with a concentration in the South West Seismic Zone.”
The spokesperson said the exact location of the Sunday earthquake was yet to be determined.
“The technical field officers are deploying earthquake recording equipment to enable Geoscience Australia to better locate the small but ongoing aftershocks following Sunday’s magnitude 5.7 earthquake,” they said.
“There is still some uncertainty on the actual location of the earthquake – approximately 10 km in any direction – so this deployment will enable us to pin-point the location of the main shock, based on the locations of aftershocks, much more accurately.
“The visit will also enable the technical field officers to deploy GPS sensors to measure if there has been any ground surface deformation as a consequence of the earthquake.”
The spokesperson stated the Frankland River visit would also help scientists develop more accurate models on how earthquake ground shaking propagates from the earthquake source located on a fault line through the earth beneath south-west WA.
“This data is critical to informing national building codes and standards,” they said.
Plate tectonics and structural geology expert Professor Chris Elders from Curtin University’s School of Earth and Planetary Sciences said earthquakes similar in size to the one felt on Sunday occur every three to five years in WA.
He reassured residents that Sunday’s earthquake would not have the potential to impact tides or generate a tsunami because it occurred onshore.
“Earthquakes are caused by stress generated at the boundaries of tectonic plates which is transmitted into the continent and builds up on faults until they fail, causing an earthquake,” Professor Elders said.
“They are unrelated to weather events.”
Professor Elders said a lot of earthquakes in WA are often very small and are barely felt, unless “we were right on top of where they happened”.
The Geoscience Australia spokesperson said the organisation is expecting to record aftershocks following Sunday’s event.
They said aftershocks often follow a general pattern which sees events reduce in frequency and magnitude over time; however, not all sequences follow the same pattern.
“It is important to note that earthquakes are unpredictable,” the spokesperson said.
“While we are expecting to see aftershocks in the Frankland River area over the coming weeks, we cannot discount the possibility of another significant earthquake in the area.”
