Where quake struck in Moreton Bay

Researchers have uncovered evidence of an ancient earthquake which struck along a fault line west of Caboolture.

Funded by the City of Moreton Bay, a team from the University of Melbourne has also found the size and scope of the earthquake.

It is believed to have exceeded magnitude 6.5 (6 can be destructive over a restricted area) at some stage in the last 20,000 to 35,000 years.

After the fault was identified by Geoscience Australia, Council initiated a Queensland-first project with researchers using Light Detection and Ranging (LiDAR) mapping.

This enabled the university team to determine the location of large earthquake surface ruptures and through that, the most likely locations of future ruptures.

Excavations took sediment samples at different locations along a break in the ground caused by the earthquake, known as a scarp, late last year.

“Any project like this, where we can get a better understanding of the risks posed by potential disasters, is invaluable,” Mayor Peter Flannery said.

“It means we can not only better plan for the infrastructure needs of our community but also work towards how we respond to a future event.”

Local Disaster Management Group Chair Cr Matt Constance said the data would feed into exercises performed with allied agencies and emergency partners.

“This really detailed and accurate data means we, as a Council, and our partners are better prepared to serve our community in their time of need,” he said.

Unitywater and the Queensland Fire Department also contributed funding to the project.

UoM Professor of Earthquake Science Dr Mark Quigley said using LiDAR allowed the team to laser scan the earth’s surface for evidence of where large earthquakes had ruptured ground.

“What we’re looking for are places where young sedimentary materials are broken by faults or pass across faults unbroken,” he said.

“We can use those to guide studies to determine the timing and the magnitude of past earthquakes.”

Dr Quigley said the second phase of the study involved analysing sediment samples collected from the scarp which are currently being dated by University of Melbourne researchers.

The results will be compared to findings uncovered from the team’s earlier LiDAR mapping data.

“This is effectively geological detective work; we’re uncovering the mysteries of these past earthquakes,” Dr Quigley said.

“We dug a trench perpendicular to the trace of the fault in the landscape, digging down several metres.

“We then mapped what’s been broken by those earthquakes in terms of the faults and what passed through that fault zone unbroken.

“Through dating techniques, we’re then able to get a picture of when this earthquake roughly occurred, how big the magnitude was, and how much displacement occurred at this location.

“From that we can build scenarios around earthquake hazards for all sorts of end users.”

Earthquakes in Queensland are relatively uncommon compared to global standards but are considered the state's ninth natural hazard risk priority.