"Nature Guide Journal"

27 July 2000

To most people, "earthquake" conjures up "California." In fact, earthquakes are common throughout the west coast of North America.

The surface of our planet is made up of plates that jostle with one another as they travel slowly about, drifting on the currents of the molten rock beneath. The North American plate is moving west 1½ to 2 inches a year, spawning earthquakes as it moves.

As North America drifts west, it overruns low-lying ocean plates. The shapes and relative movements of the plates involved cause different kinds of earthquakes. The most renown earthquake zone on this leading edge, the San Andreas Fault, is a shear line where two land masses move along side each other.

Oregon currently heads pretty much straight on over the sea plates. The ocean bottom is forced beneath our continent where heat and pressure remelt it. Some of the reliquefied rock eventually finds its way back to the surface as volcanic peaks (such as Mt. St. Helens) and lava flows (such as the lava beds near Bend).

This is not a smooth journey. Our continental land mass tends to snag in places on the ocean plates as they grind underneath. Where the continent is caught it tends to bulge upward, rather as the front edge of a table cloth bows up as you try to push it across a table. Our current rise is about 8 inches per century–a little faster than the rising sea level.

But the snag doesn't last long. Eventually, it will give way and slip, suddenly dropping the land and causing one heck of an earthquake. Geologic records show that very large magnitude earthquakes usually occur in this region about every 300 to 600 years.

Geologic and human records indicate that the last such earthquake off the Oregon coast occurred on a January night in 1700. That quake, far stronger than the famous San Francisco quake of 1906, dropped some coastal areas several feet and generated a seismic sea wave ("tsunami") that scoured the shoreline and removed coastal communities here and as far away as Japan.

Though we can't predict when it will occur, the next big earthquake is in the making.

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Wavecrest Discoveries can craft your personal discovery of this delightful part of our world by customizing one of our distinctive guided excursions.   Our walks, tours, and special activities are wonderful ways to explore this fascinating region—and are the perfect entertainment for guests.