Researchers warn of earthquake

Wednesday, June 23, 2010 , Posted by TJ at 11:56 AM

Researchers warn Southern Ontario may face earthquakes

WATERLOO, Ont. -- If a controversial theory put forth by a team of researchers studying seismic activity in Lake Ontario proves correct, Southern Ontario is more earthquake- prone than was previously believed.

"It's a fairly highly populated area, so it introduces an element of risk which didn't exist before in the minds of people," says Prof. Richard Thomas, head of the research team and director of the Waterloo Centre for Groundwater Research based at the University of Waterloo.

Scans of the bottom of Lake Ontario conducted during searches for downed aircraft revealed three previously undocumented features. Using that data and studies of their own, the research team identified the features as the result of tectonic activity due to a fault line.

The three features, known as pop-ups, plumose structures and dark linear patterns, are located in western Lake Ontario. A pop-up is a ridge with a crack at the top, formed when the bedrock fractures because of compressional forces in the crust. A plumose structure is several kilometres long and looks like a feather etched into the lake bottom. The dark linear patterns are believed to be due to natural gas coming up through the rocks into the bottom sediments.

Interestingly enough, says Thomas, the features all occur on the same line going through Burlington to Toronto. "In 1987 and 1988, there were two earthquakes recorded right on that line, which were about magnitude 3.5 (on the Richter scale). So there is earthquake evidence to suggest that the interpretation of these features is correct.

"This indicates a major fault structure occurring in that part of the lake. . . . What it indicates is that there is a greater likelihood of a significant earthquake taking place than was originally believed."

Earthquakes occurring in the Great Lakes region were thought to be in response to crustal rebound caused by the removal of ice from the last ice age. "Now, crustal rebound is taking place, but if you look at the pattern, it's not random," Thomas says. "The pattern would suggest that it's following a quite distinct orientation."

Additional work has revealed faulting in the south- eastern part of Lake Ontario. The scientists are coming to believe that Lake Ontario and possibly Lake Erie lie on an extension of the well-known St. Lawrence fault system.

The growing realization that fault lines could occur in the middle of a continent has led to a new science called intra-plate tectonics. "These are (earthquake) areas occurring in the middle of plates. The traditional belief was that all activity occurred on (continental) plate margins, where they collide or are in motion. They (mid- continental faults) are basically resulting from the various pressures induced on the plate because they're in motion, and these are lines of weakness which are currently being re- activated."

More work is needed before the team is completely satisfied that its theory is correct, Thomas adds. "What we need to do is do a lot more investigative work, using marine geo-physical systems to map the structures and make sure that they follow the concepts that we currently have."

In the scientific domain, this has been battled over since 1987, he says. "The actual release to the public, and the public debate, has only just begun. And not all scientists subscribe to this. It's still in the process of being verified. What they say is that Southern Ontario is in a stable area. It's in the middle of a continent, and it's stable, that the minor earthquakes are related to crustal rebound from removal of the ice masses, and that the Great Lakes originated by ice scrapping. The hypothesis challenges that paradigm totally.

"If you accept that it (the increased possibility of earthquakes) exists, it gives you a whole new way of looking at things."

If the theory is true, Thomas says, it may have some ramifications in the location of waste disposal sites and building construction.

He says this should be getting a bit more attention from scientists than it is receiving at present, because of the possibility of a large earthquake re-occurring in the area. The features indicate that the Great Lakes region experienced a large earthquake at some time in the past. But without knowing the "return frequency," scientists are in the dark about when it will recur.

"The return frequency is a statistical evaluation of how often an earthquake at one location will return with a certain level of magnitude," Thomas explains. "What is the return frequency of the San Francisco earthquake? It hasn't come back yet. But it will happen again. What it means is that stress is building up and releasing. Large earthquakes have a long return frequency. And the trouble is we don't know when the last large earthquake occurred in this area (the Great Lakes)."

This is a article from 1994

Currently have 1 comments:

  1. justin says:

    once the earthquake is done in brantford there is really older places in the new world

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