The Cascadia fault, a 600-mile-long collision between two chunks
of the earth's crust off the Pacific Northwest coast, has been
quiet for a long time, and that is not a comforting fact.  Major
earthquakes occur somewhere in the world every year or two.
Catastrophic tsunamis -- giant waves generated by undersea
earthquakes or landslides -- strike less often, and some of the
largest of tsunamis originate in places that do not, at first
glance, appear particularly treacherous.  The devastating
tsunamis created Dec. 26 by a magnitude 9.0 earthquake that
killed as many as 150,000 people on the shores of the Indian
Ocean caught the world off guard, including most tsunami
experts.  ''Here is something that we didn't foresee,'' said Dr.
Costas E. Synolakis, a professor of civil engineering at the
University of Southern California.  Dr. Synolakis said that
experts would now take a closer look at the Indian Ocean and
that he expected that they would find geological evidence of
earlier tsunamis, which would allow scient