By Hannah Jose, ABC
Workers wearing hazmat suit spray disinfectant to sterilise the rubble of a collapsed building in Mandalay on 2 April, 2025, five days after a major earthquake struck central Myanmar. Photo: AFP
Myanmar's catastrophic earthquake last month came amid a flurry of smaller earthquakes across the Asia Pacific.
The magnitude-7.7 quake near Mandalay on 28 March left more than 3600 people dead and shook the Thai capital of Bangkok, more than 1000 kilometres away.
Days before that on 25 March, a magnitude-6.8 earthquake hit off New Zealand's South Island.
On 2 April, Japan was hit with a magnitude-6 quake, on 4 April, a magnitude-7 earthquake struck Tonga, and on 5 April Papua New Guinea felt another magnitude-6.9 quake.
On Wednesday, Taiwan was hit by a magnitude-5.8 quake.
None of these smaller quakes resulted in deaths or significant damage.
But how unusual is it to have a cluster of quakes like this, and do people in the Asia Pacific need to be worried?
The ABC spoke to seismologists to find out.
'Within the normal range'
Brian Kennett is emeritus professor of seismology at the Australian National University's Research School of Earth Sciences.
He said earthquakes often arrived in bunches.
It was understandable that people might be concerned, he said, because there had been quite a few recently over a short span of time.
"The activity we've had in the region would normally be spread over months rather than days," Dr Kennett said.
However, he said they were mostly "within the range you would expect".
"The Myanmar quake was an outlier because it's in a much more infrequent class.
"Up to magnitude-6 is not surprising, it's when you get over 7 that you start worrying," he said.
Dee Ninis, an earthquake geologist at the Seismology Research Centre in Melbourne, similarly said there was no cause for concern at the large number of quakes so close together was a coincidence.
"On average across the globe we see about 18 major earthquakes - magnitude-7 to 7.9 - every year," she said.
"Most of these will occur at or near to plate boundaries, which is precisely where we have seen this activity in the last few weeks, in NZ, Tonga, PNG and Myanmar," Dr Ninis said.
"But these earthquakes are not equally spaced out over any period of time; they often tend to cluster just as a result of their randomness," she said.
Ninis said earthquakes were caused by a "build-up and sudden release of stress in the earth's crust".
"Larger-sized earthquakes often produce aftershocks - an increase in earthquake activity which can last for days, weeks, months, or years afterwards," Ninis said.
But the quakes across the Asia Pacific were too distant from each other to be aftershocks of the Myanmar quake, she said.
Although the recent earthquakes fell along the India-Australia plate boundary, Ninis said they were likely unrelated, "responding to local plate boundary tectonic forces generating stress within the crust".
"When there is pressure built up in the crust, even a large earthquake may not be enough to release it," she said.
The pressure would then find a weak point somewhere else to burst through, but pinpointing where that had happened was difficult.
Seismologists are improving rapidly in terms of forecasting ability, but Kennett said advancements were only useful if the information was put into practice.
"The biggest problem we have is persuading people that they ought to build to standards where they'll stand up in the event of an earthquake, especially in poor countries," Kennett said.
- ABC
