-CBC
HOW BIG IS REALLY BIG ON RICHTER’S SCALE?
by William Thomas
“Every fault line has an upper limit to its potency, determined by its length and width, and by how far it can slip,” writes Ms. Schulz. “For the San Andreas, one of the most extensively studied and best understood fault lines in the world, that upper limit is roughly an 8.2.”
And because Richter’s earthquake scale is logarithmic, a magnitude 9.0 is 707-times more powerful than a structure-damaging 7.1!
The powerful 8.2 your mother warned you about is just 6% as strong as a 9.2!
Best guess is that when the overdue Cascadia Subduction Zone seriously slips, we’ll be in for a 9.0 - 9.2 “megathrust” quake. At the risk of inviting loud groans and catcalls, let’s see how Richter’s deceptively numbered scale actually shakes out…
6.7 – 6.9
SoCal’s “minor” 6.7 earthquake in 1994, killed 57 people and caused $42 billion damage. The 1989 “World Series Quake” scored a 6.9 on Richter's scale, causing 69 deaths, nearly 4,000 injuries, and more than $6 billion in property damage.
8.2
This epic-scale seismic event anywhere on the Pacific west coast will demolish older buildings, and knock down towns and communities up to 100 miles from its epicentre.
9.2
“You can start to see the dragon,” comments Tim Melbourne, director of the Northwest Geodetic Array. “And it’s a big dragon.”
In 2004, the 9.3 magnitude rupture between the Burma and Indian plates sloshed 100-foot waves over Sumatra, shifting this planet on its axis and killing nearly a quarter-million people.
Japan’s 9.1 Great Tōhoku Quake on March 11, 2011 was centred on the seafloor 45 miles offshore at a depth of 15 miles and lasted about six minutes. The consequent series of tsunamis wrecked the north-central Honshu coast for miles inland, before washing 6.6-foot waves ashore in Chile, 11,000 miles distant.
More than 18,000 people were killed – most of them within the first hour. The damage to northeastern Japan – not counting Dai-Ichi’s ongoing triple meltdowns – has been estimated at $220 billion. A low-ball number if there ever was one.
Nearly 250 miles of northern Honshu coastline dropped 2 feet as the jolts moved Japan's main island eastward 8 feet. The Pacific Plate – largest of Earth's seven major tectonic plates – was shoved west 79 feet, and the megaquake’s low-frequency rumble was picked up by an orbiting satellite as its outward-radiating tsunami snapped icebergs off Antarctica’s Sulzberger Ice Shelf.
NUKED
The subsequent meltdown of three nuclear reactors at Fukushima Dai-Ichi and massive outflows of radioactive cooling water are still poisoning the Pacific, bioaccumulating in fish and shellfish – and anyone who eats them. How long before “very low level” contamination becomes “too much” for all manner of creatures whose health, immunity and body mass vary widely?
Most nuclear reactors in North America are designed to withstand a 6.1 shaker. If locked-in liquefaction does not occur. Even then, at least 10 U.S. reactors are at “critical” quake risk from broken cooling pipes, downed powerlines, and subsequent “criticalities”.
MISSING TIME
Earthquakes can shift hundreds of kilometers of rock by several meters, changing the distribution of mass on this planet. This displacement affects the Earth’s rotation, says Richard Gross, a geophysicist at NASA’s Jet Propulsion Laboratory in Pasadena, California. Subsequent days have become 1.26 microseconds (millionths of a second) shorter.
How does that work?
“As the ice skater’s going around in a circle, and she pulls her arms in, she gets faster and faster,” explains David Kerridge, head of Earth Hazards and Systems at the British Geological Survey. “With the Earth going around if you change the distribution of mass, the rotation rate changes.”
Tōhoku's “megathrust” shifted Earth on its axis and shortened all subsequent days by more than one-millionth of a second.
The magnitude 9.1 Sumatran megathrust shortened the day by 6.8 microseconds (millionths of a second) and caused “the wobbling motion of the planet to change by about an inch,” calculates Richard Gross, a geophysicist at NASA's Jet Propulsion Laboratory studying Earth's rotation.
While killing more than 700 people and causing nearly $30 billion damage, the 6.7 aftershock from Chile's earthquake similarly shifted the Earth’s axis and shortened the day.
All those lost microseconds are starting to add up!
SIDEBARS:
Waiting For The Really Big One On The BC Coast
If You’re In The Gulf Islands During A Megaquake
Earthquake Highlights 2018 & July 2019
How To Deal With An Earthquake