Monday, May 9, 2011

Japan Sunk Coast


Normally, when there is subduction, you might think that the coast might rise up.  The subduction does raise the volcanoes in the back of Japan, but apparently drags down this part of the coast.  The mere fact that it is productive lowland shows that this has been going on for millions of years.  That's how the land changes, a metre at a time with big earthquakes.  They will have to fill in the land and rebuild, thus creating a hazard for another  earthquake.

It's the same when you look at the lowlands around Hamilton, and you can predict what will happen with the next earthquake.


Anonymous said...

I think your comparison between Hamilton and Japan is a bit of a stretch. I love your blog but don't comments like that question your credability? Don't we require a "first" major earthquake before we have a "next" earthquake.

Harold Asmis said...

That's interesting, and I love the comments! I'm saying that we have about 10 times less strain rate under Hamilton than Japan. So, we have some sizeable earthquakes in our history, but the records are fuzzy. Our twin zone in Penn. has recently had 2 M5+ earthquakes. If we plot the earthquakes, we get a standard frequency plot that is about a factor of 10 off in energy, but still gives us M6+ in the 500 year range.

When we have a big earthquake in the world, such as Northridge, we can see the sudden rise of 3 m that matches the hills. With Hamilton, my expected motions match the topography, but we will have to wait for confirmation. :)

Should we ignore the 500 year event for nuclear plants? For emergency planning?

Anonymous said...

Interesting, but stats just don't support an M6 every 500 years in Hamilton. Europeans have been in North America for over 400 years and outside of Quebec, South Carolina, and New Madrid, we have never seen anything larger than M6. This means that for almost all of eastern North America, the 500 year event may be an M6 but certainly not for a small zone like Hamilton. I think the largest recorded quake in Hamilton approached M4. If we take this as the 250 year earthquake, an M5 could be expected once every 2500 years and an M6 every 25,000 years.

Your thoughts???

Harold Asmis said...

I'm going by the fault mechanics, which concentrates the seismic hazard in these zones. An M6 is entirely reasonable here, and who knows when the last one happened?

Anonymous said...

I don't disagree that an M6 is possible, just that I don't think stats support one every 500 years. Love the blog!!

Harold Asmis said...

Well, it would be 50 years for California, 500 for an active eastern zone, and 5000 for Moose Jaw. The factor of 10 is the uncertainty, so I wouldn't kill myself arguing whether it is actually 1000. As well, we have a factor of 10 uncertainty on ground amplification, and another factor of 10 on seismic capacity.