Mentawai Earthquake & Tsunami – Better To Be On a Boat Than Land Based Surf Resort?

by Glenn Reeves

A fanciful view of the lineup after an 8.7 magnitude quake, smack bang in the middle of the channel separating the Mentawai islands from Sumatra, sends one or more walls of water over the top of Playgrounds or into Katiet to wipe it from the face of the earth. Can you imagine what’s left of Katiet decorating the lineup at HTs?

If you’ve been keeping any sort of an eye on natural events since the massive Indonesian quake in December 2004, you’d have been aware that there have been quite a few since. They have certainly not been as catastrophic as the the 2004 event which caused the death of around a quarter of a million people; this may be just around the corner.

Since that initial calamity there has been the March 2005 (8.6 magnitude), September 2007(8.4 magnitude), September 2009 (7.6 magnitude)and the April 2012 double (8.6 and 8.2 magnitude) shocks, all within 1000km of each other.

If you had any suspicions that these are connected then you’d be right.

The documentary People-Coral-Mentawai produced by the Earth Observatory of Singapore  gives a nice account of research into these events. What is most disturbing is that one of the worst quakes is yet to come.

sequence of recent earthquakes reveal the weakest spot

The researchers have identified the channel between the Mentawai Islands and the mainland as the most likely point at which the quake will strike. And as the cliche goes, it is not a matter of if but when.

How do we know? Well it would seem that tectonic events occur in waves. The pressure builds and builds. Then the release, which is rolled out over several years or decades.

a model of the most recent earthquake sequence

Dr. Kerry Sieh explains that during the quiet times in between these episodes of letting off steam, the islands slowly subside. During a quake they spring upwards as the pressure is released. Surfers who know the Mentawai breaks well are aware that the profiles of some breaks have changed noticeably due to this.

The story of this rise in pressure/fall in island height above sea level and the sudden release and uplift is written in the corals around the islands. In this case the researchers were investigating Parak Batu, South Pagai. Cutting up chunks of coral and then X-raying them in the lab reveals the annual growth patterns.

The truth is not in the tea leaves, but the coral bands.

This particular video was made in 2009. The prediction was that there would be an earthquake in the region within 30 minutes to 30 years. The guarantee was that it would happen in the lifetime of children living in the area. Waddaya know. Around a month after this, Padang gets a fair smack in the chops from one.

Was this the one? It was near to the indicated area. Maybe it was. Maybe it wasn’t. The thing is we’ve had more since,  including, of course, fairly substantial tsunami impacts on the Mentawais.

What to do about it? Not much. It’s more a matter of how likely is it that you will be in the area at the time that it hits. The odds would have to be enormously in your favor that you would not be. Random events strike when they strike and because of that make all the difference. The odds would be mind-bogglingly hugely in your favor if you’re on a boat and not on land, unless of course some other boat gets picked up and lands on yours.

The local people aren’t getting out their statistical calculators for reassurance. Nor do they or the government authorities seem to be very concerned. There’s a bit behind this, but the most common rationale is that it’s in the hands of God so it will be all for the best whatever happens.

Right at the end of the video you’ll see the Director of Kogami, an NGO that has been working in and around Padang to raise people’s awareness, explaining this issue.  “Do you think you are more powerful than God? Do you want to invite the Tsunami to Padang? Get out of here!” is the attitude she has to deal with from the locals.

Now if you’re a trekker just arrived in Siberut, or just departing,  you can breathe easy; you’ve got even less chance of being impacted. It would have to hit in that brief time early in the morning before the motor boat whisks you away from the Muara Siberut harbor where you disembark after the overnight trip to the interior on the Siberut river. Or having just arrived back in Muara Siberut in transit to the boat back to Padang which anchors just offshore.

With the recent tsunami action in the area it would be tempting to think the adage about lightening striking twice is relevant. The area dodged a bullet with the 2004 mega event. It has had its tsunami since then.

The key point of this video is that lightening does strike the same place repeatedly. All you’ve got on your side is God or statistics, whichever you prefer.

Either should suffice…maybe.

People–Coral–Mentawai from Isaac Kerlow on Vimeo.

Leave a Comment

{ 2 comments… read them below or add one }

Christie August 31, 2012 at 10:47 am

Hi there,
hard to not get my hackles up at the title of the piece. Your comment, “The odds would be mind-bogglingly hugely in your favor if you’re on a boat and not on land” is also frightening. Have you seen what happened to the boat in this video: http://www.youtube.com/watch?v=5-zfCBCq-8I relative to those that shot the video on land? A tsunami event is a hugely complex event that is unpredictable in its scale, location, direction and consequences. If you really want to calculate the odds of safety, you might want to hire some statisticians to start with, instead of blanket assumptions. At least on land we can feel the earthquake that creates the tsunami. Oh yeah, and we have 24/7 internet with email-based reports from USGS, so we know where the earthquake was, when it happened, and if a tsunami was likely generatred. Did you put those variables into your calculator of safety?

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Glenn August 31, 2012 at 12:07 pm

Thanks for the comment Christie. It’s a valid point you make. I make no blanket assumptions here, just a few thoughts. And I do point out that the likelihood of any particular person being affected is very slim. I really doubt that yours or any other land-based business will be affected by my musings in this tiny corner of the matrix. Hope you had a great season this year and wishing you even better for next year 🙂

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