Earthquake news from Scientific American:
• The Japan quake has been upgraded to at least a magnitude 9.0.
• The quake therefore “released around 8,000 times more energy” than the 6.3 Christchurch quake last month.
• The Japan quake is the biggest one ever recorded by instruments there, and “one of the biggest ever detected.”
• “Very little of the devastation resulting from this earthquake was from the initial shaking.” The 10-meter tsunami was the culprit, but:
The real destructive power of tsunamis lies not in excessive height, but in their wavelength. A normal wave rises, breaks on the beach, and is done within seconds. A tsunami wave rises, breaks, and continues to break for several minutes or more. It is a wave that just keeps on coming…and coming, and if it is higher than beach (or seawall) level, it will encroach inland for kilometres, sweeping all before it.
• The tsunami wave heights of 1 to 2 meters that hit the western United States did less damage because they arrived close to low tide. “However there was more serious damage – and some casualties – in northern California and southern Oregon, where the tsunami and the shape of the coast conspired to produce larger waves.”
• “Friday’s earthquake strongly registered on seismometers around the world, with seismic waves rippling across the North America and maxing out instruments as far away as the United Kingdom.”
• “There have been more than 250 aftershocks of greater than magnitude 5, and around 30 of greater than magnitude 6.”
• “Foreshocks” of the Friday quake included a 7.2 magnitude quake last Wednesday “in the same region as today’s earthquake, followed by a number of smaller magnitude 5 quakes, and three magnitude 6-6.1 events.”
THE WARNING for the western U.S. and Canada:
North of the San Andreas Fault, the plate boundary that runs along the west coast is a subduction zone very similar to the ones that run along the coast of Japan, and just as capable of generating large earthquakes. The last time the Cascadia subduction zone ruptured in earnest was around 300 years ago, and geological evidence suggests that the quake itself (probably more than a magnitude 8.5) and the tsunami it generated were very similar in scope and scale to what struck Japan last Friday.