A series of overdue high magnitude earthquakes is expected to strike at any moment along some of Earth's major fault lines, an expert says.
UTS Geotechnical and Earthquake Engineering senior lecturer Dr Behzad Fatahi said "no one in the world is safe" from the looming natural disasters of potentially apocalyptic proportions.
"There are a lot of magnitude 6-plus earthquakes overdue in the Middle East, India, China, Japan and the US," Dr Fatahi told news.com.au.
"There are some fault lines that have not released their energy for a while.
"There are at least 5-10 that are overdue, but we don't know when they're going to happen.
"The question is not will they be activated. The question is when."
Dr Fatahi said there was a "return period" for earthquakes and those that didn't strike within the expected time frame only came back stronger. He said an example of this was the 7.8 magnitude earthquake in Nepal that left more than 8000 people dead in April last year.
"You expect a particular fault line will be activated every 100 years or 500 years," he said.
"If the period is longer we expect higher magnitude earthquakes ... looking at the history of some of those major fault lines, some are very overdue.
"The return period has passed but the earthquakes haven't happened.
"So we are just waiting for them to happen."
THE COLLISION COURSE
Earthquakes claim tens of thousands of lives all over the world each year.
But the places most often rocked by them are those closest to major fault lines, where different tectonic plates meet.
"The crust has several pieces," Dr Fatahi said.
"The line between each of these pieces is called a 'fault line'.
"The most dangerous fault lines are those where two tectonic plates collide."
That was the case in central Italy, when a 6.2 magnitude earthquake struck the region on Wednesday. More than 257 people died and many more were injured. Rescue workers are racing against the clock to find people trapped under rubble, but hope is diminishing as reports of voices from under collapsed buildings drift off.
"The Eurasian Plate and African Plate both have a very big fault line where they meet somewhere under Italy ... this is what caused the earthquake (on Wednesday)," Dr Fatahi said.
"Below that plate you have got magma... if the fault opens there's a chance magma will come up."
Tectonic plates are giant slabs of rock that make up the earth's upper crust (lithosphere) and move, float, and sometimes fracture, causing continental drift, earthquakes, volcanoes, mountains, and oceanic trenches.
Seismic activity is most common around the edge of the Pacific Plate, which takes in New Zealand, Vanuatu, the Solomon Islands, Papua New Guinea, Japan and the Americas, and in Indonesia, where the Indo-Australian Plate collides with the Eurasian Plate.
THE RING OF FIRE
The San Andreas fault line in California is the longest in the world. It sits between the Pacific and North American plates and measures 1300kms. The depths of these collision zones can range from 0-700km.
Some countries, including Japan, Chile, Mexico and New Zealand, lie on the 'Ring of Fire' - a horseshoe-shaped band of fault lines that circles the Pacific Basin and is prone to frequent earthquakes and volcanic eruptions.
"The earthquake in Japan in 2011 was above a magnitude 8 and caused a tsunami and the melting down of the nuclear power plant and so on," Dr Fatahi said.
"If something of that scale happens it's really devastating."
There is an earthquake every minute, according to Dr Fatahi. But it's mostly those stronger than a magnitude 6 that tend to cause significant destruction and loss of life. For every numberhigher, the earthquake is 30 times stronger, he said.
Peru, also on the 'Ring of Fire', was struck by a magnitude 7.9 earthquake on August 15, 2007. Its epicentre was on the central coast, just west of the major city of Pisco. It killed 595 people.
Earlier this month, a moderate 5.3-magnitude earthquake in Peru killed at least four people including a US tourist and left 68 injured, crushing villagers under rubble and blocking roads. The quake knocked down about 50 homes and cut off roads and power in the southern Arequipa region.
"It was tragic. They got wounded people out as best they could," said John Rivera, a resident of Yanque, a hard-hit rural village of mud huts.
New Zealand has endured more than its fair share of earthquakes. New fault lines emerged there as recently as September 2010 when Christchurch was struck by a powerful 7.1-magnitude earthquake. The quake smashed buildings, cracked roads, twisted rail lines and ripped a new 3.5 metre wide fault line in the earth's surface.
Italy sits on two fault lines, making it one of the most seismically active countries in Europe.
This week's 6.2 magnitude earthquake in central Italy killed at least 247 people and injured many more. It occurred 1,937 years to the day since Mt Vesuvius erupted in 79AD and destroyed Pompeii and Herculaneum - one of the most catastrophic volcanic eruptions in European history.
The most deadly since the start of the 20th century came in 1908, when an earthquake followed by a tsunami killed an estimated 80,000 people in the southern regions of Reggio Calabria and Sicily.
More recently, a 2009, 6.3-magnitude earthquake in the Aquila region, about 90km south of the latest quake, which was felt in the Italian capital, left more than 300 dead.
That disaster led to lengthy recriminations over lax building controls and the failure of authorities to warn residents that a quake could be imminent.
Another quake hit the northern Emilia Romagna region in May 2012, when two violent shocks 10 days apart left 23 people dead and 14,000 others homeless.
Associate Professor of Earthquake Science in the School of Earth Sciences at the University of Melbourne, Mark Quigley said central Italy was experiencing "crustal extension".
"Eastern central Italy is moving to the NE relative to Rome," Mr Quigley said.
"As a result, this region experiences normal faulting earthquakes as the land is torn apart. The fault systems are short and structurally complex, so the earthquakes are not overly large by global standards (almost always < magnitude 6.8 to 7).
"But because the earthquakes are shallow and structurally complex, and because many of the local towns and cities contain vulnerable buildings, strong shaking from these earthquakes has the potential to inflict major damage and loss of life in urban areas."
The highly active tectonic plate boundary passing through middle of Myanmar - known as the Sagaing Fault - has induced many deadly earthquakes in the small country, as recently as this week.
Rescue workers are surveying the damage after a powerful earthquake shook Myanmar on Wednesday, killing at least four people and damaging 185 ancient Buddhist pagodas in the former capital of Bagan, a major tourist site.
The US Geological Survey said the magnitude 6.8 quake was centred about 25 kilometres west of Chauk, a town south of Bagan.
It was located fairly far below the Earth's surface at a depth of about 84 kilometres, it said.
"Since this is a deep earthquake very few aftershocks are expected," Dr Fatahi said.
Deep earthquakes generally cause less surface damage because the energy dissipates before it gets there. At least 185 brick pagodas in Bagan were damaged, the state newspaper reported. Bagan, also known as Pagan, has more than 2,200 structures, including pagodas and temples constructed from the 10th to the 14th centuries. Many are in disrepair while others have been restored in recent years, aided by the UN cultural agency UNESCO. The "major strike slip fault in (Myanmar) moves about 18mm per year", according to Dr Fatahi. In April 2016, a magnitude 6.9 earthquake hit the country, causing two deaths and dozens more injuries.
While Australia is not on the edge of a plate, the continent experiences earthquakes because the Indo-Australian Plate is being pushed north and is colliding with the Eurasian, Philippine and Pacific plates, according to Geoscience Australia. This causes the build up of mainly compressive stress in the interior of the Indo-Australian Plate which is released during earthquakes.
"Australia is right in the middle of a plate and it's not sitting on a major fault line," Dr Fatahi said.
"Everywhere you have minor faults, which are measured in terms of being only 100m or so long. Activity that cause earthquakes happens around the sides of plate, where one plate meets the other plate. Australia is sitting in the middle of a relatively stable plate, and that's why we don't have huge tectonic activity."
There are on average 80 earthquakes of magnitude 3.0 or more in Australia each year. Adelaide has the highest earthquake hazard of any Australian capital. It has experienced more medium-sized earthquakes in the past 50 years than any capital because South Australia is being slowly squeezed in an east-west direction by about 0.1mm/yr, according to Geoscience Australia.
Australia's largest recorded earthquake was in 1988 at Tennant Creek in the Northern Territory with an estimated magnitude of 6.6, but it occurred in a sparsely populated area. A magnitude 6.5 earthquake at Meckering in 1968 caused extensive damage to buildings and was felt over most of southern Western Australia. Earthquakes of magnitude 4.0 or more are relatively common in Western Australia with one occurring about every five years in the Meckering region.
PREDICTING WHEN AND WHERE MAJOR QUAKES WILL STRIKE
Dr Fatahi said it was impossible to accurately predict the exact timing, place or scale of an earthquake.
"Usually with earthquakes you can only measure them around one minute before they happen, as the activity happens kilometres below ground," he said.