December 29, 2012 – SEATTLE– Tiny tremors, smaller than earthquakes, are shaking the Cascadia subduction zone deep beneath the Pacific Northwest. The Cascadia subduction zone is where two of Earth’s tectonic plates meet in an epic collision and one haltingly slides below the other. The Cascadia Fault stretches for almost 700 miles (1,100 kilometers) from Northern California up to Canada. The force required to shove a piece of ocean crust into Earth’s mantle can produce mega-earthquakes along the zone, as in Japan and Sumatra. But unlike its western Pacific cousins, the Cascadia subduction zone has not experienced a major earthquake since 1700, when an estimated 9.0-magnitude earthquake generated an enormous tsunami that killed trees in Puget Sound and traveled across the ocean to Japan. The slow-slip and tremors observed in the area are periodic, coming about every 15 months, said Stanford geophysics professor Paul Segall, and were first spotted…