Sumatra: quake series no surprise?

Geological structures favor the appearance of strong earth

Research area Sumatra - Java with data on the strongest recorded quakes in the area of ​​the deep - sea ditch off the Indonesian coast. © I. Grevemeyer, IFM-GEOMAR
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Seven strong earthquakes shook the Indonesian island of Sumatra within 48 hours in the last week. But why was there such an unusual seismic series there? For geophysicists of the Leibniz Institute of Marine Sciences (IFM-GEOMAR) this is no surprise. You already answered this question in 2006. In one study, they pointed to the increased risk potential compared to more southern and eastern regions of Indonesia.


The researchers see their results presented last year confirmed by the recent severe earthquake off the coast of Sumatra (Indonesia). "In our work, we investigated why large earthquakes are more likely to occur in front of Sumatra and not in front of the more southeastern island of Java, " explains the lead author of the study, Ingo Grevemeyer from IFM-GEOMAR.

"The investigations have shown that geological structures off northern and central Sumatra favor the occurrence of strong earthquakes over those off the island of Java. In this respect, the situation of the recent earthquakes was to be expected, "continued Grevemeyer. "Since very large earthquakes always have a certain repetition time, the next quake could not actually take place in northern Sumatra, but only in central or southern Sumatra."

Why were not there tsunamis?

Why did the quakes trigger tsunamis in December 2004 and quakes and in March 2005, but the current earthquake does not matter much? There are, according to Grevemeyer, two reasons: On the one hand, the energy of the earlier earthquakes was significantly greater. On the other hand, the coupling zone, where the subsiding oceanic plate is connected to the upper plate - Indonesia, so to speak - is closer to the deep-sea trench (or lesser depth) in northern Sumatra than to the south. As a result, the uplift of the ocean floor, which is particularly critical for the release of tsunamis, was probably lower in the south. display

(idw - Leibniz Institute for Marine Sciences, 17.09.2007 - DLO)