A very interesting quake off of Sumatra today. At 7.3 it is a large quake and at a depth of only 29 km is relatively shallow but it didn’t cause a lot of damage and no damaging tsunami, and here is why.
First location, location, location. It was 400 km from land. A 7+ quake is certainly capable to make a tsunami but that far from land it would have dissipated and been a small wave at landfall. Plus on top of that it was on the wrong side of the subduction zone to cause the up thrust of ocean floor that quakes like the 2004 Sumatra quake did or the 2011 Japan quake. In the location this quake happened it was probably more of a sideways motion rather than an up or down motion. This is where the crust is bending trying to go down to the subduction zone, not release pressure from a stuck zone.
And depth did play a part in it not being so devastating. Most of the violent quakes at the surface are shallower than this one was. Now in the region a lot of people were shaken from their sleep and the shaking continued for 30 seconds by most accounts so this was a very sizable quake but little damage and no loss of life has more to do with where the quake was then how big it was. Move this same quake 400 km North East and things would have been much different.
The real question on everyone’s mind though is does this mean another quake is coming? Or is this the release of energy that quiets the fault for a while. There will be aftershocks from this quake. This is in a zone where there have been quakes in the past that have been followed buy other quakes. This one is on the side of the fault that is moving toward the subduction zone and this is adding stress to the fault not subtracting from it. Movement here means movement toward the fault and so means the fault is being given more stress.
enough stress has built up to cause inequities of the pressure on the rock and here it can only mean that that pressure is building. But is it enough to cause the fault to rupture and set off a larger fault or a similar sized fault closer to shore and closer to the surface. We can’t say that it won’t so the thing to do is remember if you live near a shore line that has faults, if you feel the earth shack move to high ground, the higher the better, some of these tsunami waves can run up 30 to 60 meters depending on topography.
- Large earthquake hits off Sumatra (smh.com.au)
- Offshore 7.3 quake hits near Sumatra in Indonesia (marketwatch.com)
- Indonesia lifts tsunami warning after Sumatra quake | World | Reuters (worldwright.wordpress.com)