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Yes, Canada will get a BIG quake

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Cascadia's Fault

The Deadly Earthquake That Will Devastate North America

By Jerry Thompson

HarperCollins, 329 pages, $33

Is Canada safe from earthquakes? Will it get a "Big One"? Should I retire to Victoria?

These questions are answered in an informative and comprehensive examination of earthquakes on the west coast of North America by a B.C. writer, director and journalist who has covered earthquakes and tsunamis for 25 years.

Jerry Thompson's focus is on megathrust earthquakes, the type of destructive earthquake that occurred recently in Japan, and their impact on the west coast of North America.

He makes the compelling case that this area is definitely not safe -- from earthquakes or tsunamis. The question is no longer whether these events will occur, it's when.

The Earth is a dynamic planet. Its outermost, rigid part is made up of lithospheric plates that move at the rate fingernails grow. Geological faults occur at the boundaries between plates, and sometimes these faults lock up. Strain energy accumulates and is released in earthquakes.

Megathrust earthquakes occur where ocean plates are pushed, or, in scientific terms, subducted beneath continents. The Ring of Fire, the belt of earthquakes and volcanoes rimming the Pacific, is caused mainly by ocean plates being subducted beneath Asia, South America and Central America.

In a megathrust quake, release of strain can cause the sea floor to snap upwards, causing a tsunami. The larger the rupture on the fault, the larger the earthquake, and the bigger the tsunami.

U.S. Geological Survey studies show the recent Japan earthquake resulted from 35 metres of movement on the fault over a rupture length of 300 kilometres, and the sea floor moved upwards by five to eight metres.

What about Canada? An ocean plate called the Juan de Fuca plate is being subducted beneath B.C., Washington and Oregon forming part of the 1,300-kilometre-long Cascadia Fault.

Thompson shows the Cascadia Fault is part of the Ring of Fire -- and when it ruptures, it ruptures big. The last Big One occurred at 9 p.m. on Jan. 26, 1700. The fault ruptured along its whole length, producing a magnitude 9 earthquake.

Thompson outlines the geological and historical evidence in North America for the quake and how the resulting tsunami damaged farms and buildings in Japan.

He describes the geology and social impact of related earthquakes, tsunamis and volcanoes, including the Alaska earthquake of 1964 and its impact in Port Alberni, B.C., the 1980 eruption of Mount St. Helens, the 1985 Mexico City earthquake, and the 2004 Sumatra earthquake and tsunami.

He relates these events to the growing understanding of the Cascadia Fault and supporting geological evidence. How do tree rings and sediments drilled on the ocean floor provide evidence of earthquakes? How do repeated surveys of highways record the buildup of strain?

He examines whether we're properly prepared for a magnitude 9 earthquake and its accompanying tsunami? Do cities have adequate emergency plans? What can families do to be ready?

Thompson uses a narrative style, weaving between individuals, disasters and scientific details. He gives personality to scientists and officials and everyday people affected by the earthquakes and tsunamis. Some readers may prefer a more direct, scientific, style and an occasional explanatory figure.

Thompson is careful. His facts are accurate and information is presented in a balanced way. This is unlike parts of the foreword by popular British historian Simon Winchester that are overly sensationalized.

Will Canada get a Big One? Yes. There have been 19 megathrust earthquakes of magnitude 9 or above on the west coast of the continent in the last 10,000 years. On average, this is about one every 500 years -- and the last one was 311 years ago.

Should you retire to Victoria? Yes, but read this book first.

Ian Ferguson teaches geophysics in the department of geological sciences at the University of Manitoba in one of the most earthquake-safe cities in the world.

Republished from the Winnipeg Free Press print edition April 16, 2011 J8

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