What is going on?
A magnitude 8.3 earthquake strikes the south of Samoa on Tuesday, triggering a tsunami. Then, 16 hours later, a magnitude 7.6 quake occurs 30 miles off the east coast of the Indonesian island of Sumatra.
Why has there been a large amount of seismic activity in the Asia-Pacific region over the past few weeks? Clive Collins, Senior Seismologist for GeoScience Australia, gives us some answers:
Samoa and Indonesia are just over 6,000km apart. Are these earthquakes, only 16 hours apart, linked?
The short answer, says Collins is that “we don’t know, we don’t think they are linked directly”. Although there is “some evidence that sometimes large earthquakes can cause distant earthquakes to occur some time later”, Collins says that there is “no proved cause and effect”.
While it is unlikely that the earthquake near Samoa caused the earthquake in Indonesia, “in the big picture they are linked as they are both on same tectonic plate”. In layman’s terms, both earthquakes are “due to the movement of the Australian plate”.
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Over the last few weeks there has been considerable activity around the Australian plate, in Java, Maluku and even the south-eastern suburbs of Melbourne. What’s going on?
“The earth’s plates are always moving,” says Collins. “The Australian plate is drifting north whilst the South Pacific plate is moving westwards” and when these plates meet, seismic activity is triggered.
More specifically, in the case of the earthquake in Samoa, “the Pacific plate is being pushed underneath the Australian plate” and this activity causes “breakages and build-up of pressure which causes earthquakes”.
Is it possible that this seismic activity could cause any volcanic activity?
Yes. As the plates meet and crash, says Collins, “debris from the crash heats up and melts”. Then, as it moves down deeper under the plate “it eventually has nowhere to go and gets pushed upwards”. The result: a volcanic eruption.
Are more earthquakes expected?
Lots of aftershocks and small earthquakes are expected, says Collins. However, “we don’t know if there will be another large one in the same place in the near future. [However] areas to the south and the north of the breakages may break and cause more earthquakes.” [After this interview was conducted reports started coming in that another major earthquake had hit Sumatra]
There has been an increase in seismic activity in the Indonesian fault line since the 2004 Asian tsunami. What causes such an upswing in earthquakes?
According to Collins, “this was such a big event and caused a whole lot of the boundary to break which puts pressure and stress on the rocks and surrounding areas”. Yet, while “earthquakes occur in clusters, if you look at a long enough time span, on average, the rate of earthquakes doesn’t change”.
Could this be at all related to the effects of climate change?
“Not directly, not these ones, this will happen regardless,” assures Collins. Other earthquakes though “may be related [to climate change]. If, for example, the polar ice caps melt you get more water in oceans or more weight in some places or pressure released in some places” which can cause plates to shift and earthquakes to occur.
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