Australia is the continent least affected by seismic forces. It lacks volcanoes, glaciers, and earthquakes are infrequent. This is because it is situated on the ancient Australian platform, formed during the Precambrian era. 87% of its territory lies below sea level, mountain formation ceased long ago, and natural erosion processes have resulted in the formation of vast flat plains across the continent’s terrain.
However, in the northwest, the continent is connected to another geological structure – the Indian Oceanic Subcontinent, which is drifting northeast at a speed of 7 mm/year and has recently shown an increased drift intensity. The relatively calm seismic situation is due to Australia being located in the middle of a lithospheric formation, away from faults – potential earthquake hazards.
Indo-Australian Fault – The Beginning of Rift Processes in the North
The Indonesian and Australian platforms merged during the Cenozoic era and have since been slowly moving towards Asia. A powerful earthquake in the Northern Sumatra region with a magnitude of 8.6 occurred on April 11, 2012, altering the structure of the Indo-Australian lithospheric plate, splitting it into two parts. Both parts, the Indian and Australian, are still moving together northeast. The Indian part collides with the Asian continental plate, forming the Himalayas, while the Australian part subducts beneath Sumatra, creating a dangerous subduction zone where the most destructive earthquakes and tsunamis occur.
The 2012 earthquake caught the attention of scientists because its epicenter was not on a traditional tectonic plate boundary, but within the Indo-Australian formation. In the epicenter, four massive new faults were discovered, each several hundred kilometers long. This led to the conclusion that the Indo-Australian Plate has split into two parts, and the areas of new fractures are potential sites for destructive earthquakes, which may occur in regions previously considered seismically stable. During the plate’s splitting, rock formations shifted by 35-40 meters, and its effects were felt throughout the Pacific region, causing earthquakes with magnitudes greater than 7.0 in Indonesia, Japan, and the western coast of the United States.
New Continent Zealandia
Thanks to extensive geophysical and geological research data in the 21st century, a new continent named Zealandia was discovered, located off the eastern coast of Australia. Over 94% of its territory is submerged underwater, with only certain islands like New Zealand and New Caledonia protruding above the surface of the Pacific Ocean. The continental block covers an area equivalent to two-thirds of Australia, and its subduction onto the ocean floor is the reason behind the formation of the Pacific Ring of Fire.
Zealandia, like Australia, separated from the supercontinent Gondwana more than 80 million years ago through the process of rifting. Unlike Australia, the boundaries of Zealandia became extremely thin, causing the continent to submerge underwater. It is believed that rifting processes may have caused the continental plate to periodically rise and fall. New Zealand, which formed due to the intense subduction of the Australian and Pacific Plates, experiences frequent earthquakes and volcanic activity.
Approximately 30 million years ago, powerful seismic processes pushed New Caledonia and New Zealand to the surface. The ongoing processes in this region continue to cause significant volcanic eruptions and earthquakes within the Pacific Ring of Fire.
Earthquakes in Eastern Australia
Although Australia is considered one of the most seismically stable regions, in recent years, its southeastern coast has started to experience relatively strong earthquakes regularly (once every 10-12 years). For instance:
- In 1989, Newcastle experienced a 5.7 magnitude earthquake, resulting in 13 fatalities;
- In 2012, seismic tremors in Thorpdale reached a magnitude of 6.0;
- In 2021, an earthquake with a magnitude of 6.0 occurred. A magnitude 5 earthquake disturbed the peace in Melbourne. With the epicenter located just 10 km below the surface, residents of neighboring states could feel the tremors.
What does the increased seismic activity in the southeastern part of Australia indicate? Accelerating tectonic processes are occurring here, which geophysicists and seismologists have only just begun to study. Considering that around 80% of Australia’s population lives in major cities along the eastern coast of the continent, an increase in seismic activity in this region will significantly heighten the risk of natural disasters.