Earthquakes, Tsunamis and Eruptions in Indonesia

By Erik Klemetti | October 3, 2018 8:38 am
Landsat 8 image showing the damage to Palu from the M7.5 earthquake and tsunami. NASA Earth Observatory.

Landsat 8 image showing the damage to Palu from the M7.5 earthquake and tsunami. NASA Earth Observatory.

The earthquake and tsunami that happened last week on Sulawesi in Indonesia has been more devastating than anyone expected. The number of deaths in and around Palu has topped 1,400 and aid has been slow to reach the survivors due to the damage to infrastructure in the area. It is still unclear exactly what triggered the tsunami that followed the M7.5 earthquake — there is speculation it was an undersea landslide that followed the temblor. What is known is that this earthquake ruptured a long stretch of the island with displacement of over 5 meters along the strike-slip (side by side) fault (see below). We also know that Indonesia’s early warning system for tsunamis, built mainly after the 2004 Boxing Day tsunami, did not appear to operate as planned.

USGS Shape Map for the Palu earthquake. Soputan is located on the far eastern portion of Sulawesi near Manado. USGS.

USGS Shape Map for the Palu earthquake. Soputan is located on the far eastern portion of Sulawesi near Manado. USGS.

Now, with any big natural disaster, there is the tendency for people (and the media) to start jumping to conclusions about connections and correlations. Case in point: the eruption of Soputan (see below), also on Sulawesi, that happened yesterday. This Indonesian volcano is one of the more active volcanoes in a country that is filled with them. Sulawesi itself has at least 10 potentially active volcanoes. However, although the earthquake and eruption happened on the same island, they are almost 1000 kilometers apart. If you need a comparison, that is almost the distance between Seattle and San Francisco! If you check out the shake map related to the Palu earthquake, very little shaking was felt that far east near Soputan.

Adding in the fact that Soputan has been restless for months and erupts frequently, I think what we have here is correlation that isn’t causation. Indonesia is one of the most geologically-active countries in the world, with 6-10 volcanoes erupting at any given time and dozens of M5+ earthquakes each year. Although the timing might be coincidental, the earthquake and volcano are not particularly close and there is little evidence of this sort of long-distance triggering of eruptions due to earthquakes.

So, the short here is that Sulawesi has just seen a stretch of terrible luck, with a major earthquake and tsunami, along with a more vigorous eruption from Soputan. That’s what happens sometimes when you live in a country surrounded by subduction zones that generate earthquakes and eruptions.

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  • http://www.mazepath.com/uncleal/EquivPrinFail.pdf Uncle Al

    Indonesia’s early warning system for tsunamis, built mainly after the 2004 Boxing Day tsunami, did not appear to operate as planned.

    It was created to be funded, constructed, maintained, and managed. As with the Soviet of California’s “early” warning earthquake network (we can give you up to 60 seconds’ advanced notice to save your life!), failure is insulated against criticism by demands for more funding.

    • 7eggert

      60 seconds is as much as you get when being 60 seconds away from the source, not counting the “you are living on a fault line” warning.

      You can do a lot in 60 seconds, elevators can stop at the next floor, subways and trains will halt, too, traffic lights turn red and a lot of lives will be saved, each worth $10 000 000 on average.

      But I guess there is a lot of money spent on that system. Much more than necessary.

      • OWilson

        “Up to 60 seconds” !

        Helpful if you happen not to be in an elevator, subway or anyplace with no strong cell signal, or if you are politically correct and turn off your phone in the car, or the restaurant! :)

        • 7eggert

          If you are in an elevator, it shall stop at the next floor, so you can get out. If you are in a subway car, it shall stop instead of crashing against a pillar. If you are in a car, you shall stop at the next red light instead of leaving the road and hitting pillars or pedestrians. If you are at the coast, a siren might warn you to get to higher ground.

          That’s how japan does it (according to TV).

          • OWilson

            Let’s hope that things like elevators, subway cars and traffic lights, and even roads, function like they are supposed to in an earthquake.

            Most families are engaged in many activities, in and outside the home and are not sitting watching their phone.

            But up to 60 seconds is better than nothing! :)

          • 7eggert

            They work in these up to 60 seconds before an earthquake, that’s when a warning system helps.

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Rocky Planet covers all the geologic events that made and will continue to shape our planet. From volcanoes to earthquakes to gold to oceans to other solar systems, I discuss what is intriguing and illuminating about the rocks beneath our feet and above our heads. Ever wonder what volcanoes are erupting? How tsunamis form and where? What rocks can tell us about ancient environments? How the Earth might change in the future? You'll find these answers and more on Rocky Planet.
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