Commentary: Cause of Bali upheaval can furnish even bigger …

SINGAPORE: A moderate-sized trembler of bulk 5.5 shook a southern seashore of Bali on Mar 22.

Naturally, it caused amazement to those who felt it, though did really tiny damage. By now, it is yesterday’s news. But there is a really critical doctrine to be learnt from this quake.

Bali does not mostly have earthquakes, and so it stays different to many that sneaking sensitively underneath this traveller island of Indonesia is a slumbering tectonic dragon.

This dragon comes in a form of a subducting chunk – a enormous chunk of oceanic lithosphere (also famous as a Australian plate) that slopes northward underneath Java.


A cross-section of a subduction section underneath Java. (Source: Earth Observatory of Singapore/Yves Rene Descatoire Jamie McCaughey)

Occasionally, this subduction section produces earthquakes, like a bulk 5.5 upheaval that struck Bali. As a image army a approach down into a layer of a earth, it deforms, and infrequently that deformation leads to a small, remarkable snap within a plate.

And that is what happened on Mar 22.

In fact, interjection to seismology, we can establish a accurate plcae of a snap that resulted in a quake. 

Initial reports by a United States Geological Survey, formed on research of seismogrammes from around a world, settled that it occurred about 118 kilometres underneath southern Bali.

Seismologists during a Earth Observatory of Singapore (EOS) after polished that dimensions to a some-more accurate abyss of about 106 kilometres.

That is approximately how distant underneath a review communities of southern Bali a chunk of oceanic membrane entrance off of a Australian image is. Just for reference, that’s about 20 km deeper than a north-to-south camber of a island.

It would be satisfactory to contend that all this is of tiny some-more than educational interest. Except for a fact that other tools of a forward chunk can furnish giant, lethal earthquakes and ensuing tsunamis.

Shallower tools of a forward slab, south of Bali, are closer to a aspect of a Earth and to a sea floor. Those tools of a subducting Australian image are so cold that a overlying image sticks to it as it solemnly descends.

No one nonetheless knows how frequently, though maybe each few hundred years, a attrition that binds a dual cold plates together yields and a good slippage occurs.  

That remarkable trip underneath a seafloor creates a good trembler and tsunami.

In a entirety of available history, such a good trembler and tsunami has never struck Bali.

One competence so be tempted to breathe a whine of relief. But that was also a prevalent view in Aceh, in a years and decades before to a Boxing Day trembler and tsunami that killed a scarcely entertain million people there in 2004.

Since that trembler and unusually harmful tsunami, scientists from EOS have schooled that a predecessors were some-more than 500 years in a past and not remarkable in a ancient chronicles of a traders plying a Indian Ocean during a time. 

The orange star indicates a plcae of a epicentre of a Bali upheaval that took place on Mar 22. Since a 1960s, there has been really tiny trembler activity, represented by dots, nearby Bali island. (Source: Earth Observatory of Singapore/Wang Yu)

Although no one has nonetheless proven it, we consider that a good subduction section offshore and underneath southern Java and Bali could good beget a bulk 8.5 to 9.0 quake, or maybe a array of them.

So a new upheaval that softly shook Bali is an critical sign to us that this “sleeping tectonic dragon” fibbing underneath will many expected some day furnish one or several vast earthquakes and tsunamis that could impact a southern coasts of Java and Bali.

Professor Kerry Sieh is Director of a Earth Observatory of Singapore.

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