Saturday, April 2, 2011

Fault Geology of Hamilton, Ontario

Although the seismic hazard is about an order of magnitude less than the more active parts of the world, the seismic risk is not that far off, due to high population density, and a lack of 'earthquake living memory'.

Although we must always keep perspective, compared to very active zone, for Eastern North America (ENA) one significantly large fault whips down through Toronto and Hamilton. Now it happens in my many travels and fishing trips, that the most dramatic scenery is associated with earthquakes.

This fault appears to be most active at Hamilton, and the spectacular topography is a result.

The city of Hamiton is located at the west end of Lake Ontario. It is noted for its aromatic steel mills, and less noted for the swamps everywhere. In fact, I was told these swamps are extremely deep, and have blocked decent railroad access for years.

I have been playing around with Digital Elevation Models (DEM's), and viewers. I was using 3DEM to great success. Here a shaded relief view of Hamilton.

That great big gash in the Niagara Escarpment is the Dundas Valley, which was also a major glacial lake drainage outlet, and affects the sediments in Lake Ontario for a great distance. Nobody has really wondered why it is there.

The real fun with 3DEM is taking oblique views. Here's one, shooting down the fault.

The view would be much more spectacular if we could remove the soft sediments. Then you would see some scenery! Over the course of my career, we did a lot of geophysics out in the lake, where you can get an idea of the depths of the swamps.

Why do we even care about Hamilton? First off, the scenery is nice. Second, all those swamps are formed by an active fault, somewhat like sag ponds, but over a much longer time. They are doing a lot of house building in those ponds, and I think it is somewhat dangerous.

The next big earthquake in that area will be a high-speed thrust, much like some of the more destructive earthquakes that hit Japan recently.  (I have dubbed them 'Fist of God' earthquakes!) The damage intensity will have a very narrow zone with a high Peak Ground Velocity (PGV). The deep swamps will amplify this ground motion 10 to 100 times. The damage will have unknown consequences. This earthquake will blow out the electricity and natural gas for most of Southern Ontario.

Yet, we merrily go on, ignoring this threat, not doing the slightest little thing to mitigate the disaster. Such is the power of living memory! We remember Hurricane Hazel, because it happened, yet this earthquake has the same general odds of happening. and has been ignored!

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