Sunday, November 19, 2006


The Northwest Coast of the US is earthquake prone. Unlike frequently shaken California, here the tectonic forces build up over the centuries until very large quakes occur. Small and medium quakes do occur, but rarely and the stress and strain keeps accumulating. The major quakes may be as large as any on Earth.

The last major quake offshore occurred January 26th 1700, dated by tsunami records fron Japan and tree rings here. The Japanese records of the time state that the waves kept arriving for 18 hours and were up to 10 ft. (3 M.) high. On the Northern California to British Columbia Coasts, blocks of land dropped 15 ft. (4.5m) and more, drowning forests and marshes, which were then covered in coarse sand brought in by a tsunami which took only a few minutes to arrive.

Line of stumps along ocean's edge, likely on downdropped block from 1700 quake at Neskowin Oregon

It is thought that the entire length of the Cascadia Subduction Zone lurched in this event - a length up to 685 miles (1100 km.)! Entire Native American villages were rubbed out, and Native tales of the event survived and have been recorded.

Damage nowadays from such a quake could range from California to Canada and would be in the many billions.

A magnitute 5.6 earthquake occurred January 11th 2006 near the Blanco Fracture Trasverse Fault edge of the Juan de Fuca plate 143 miles off the Oregon Coast. Depth of the quake was 6.2 miles (10 km). No tsunami or damage resulted due to the location and size of the quake. This one was small compared to the really big ones of the more distant past.

No comments: