Blanco Fracture Zone

The Blanco Fracture Zone or Blanco Fault Zone (BFZ) is a transform fault zone running northeast off the coast of Oregon in the Pacific Northwest of the United States which runs between the Gorda Ridge to the south and the Juan de Fuca Ridge to the north. The zone varies in width from 20 km to 75 km. The principal feature of the Blanco zone is the Blanco Ridge, a right lateral-moving fault which also incorporates some compression, thus accounting for the uplift expressed in the ridge. The ridge is not an oceanic spreading center, despite its name, whereas the Juan de Fuca and Gorda Ridges to which it is connected are. Similarly confusing, the portion of the Blanco Fracture Zone which lies east of the rift zone spreading center is not technically a true fracture zone, but a transform fault zone. The western part of the fracture zone moves slower than the eastern part, with the whole zone averaging a slip of 20 mm per year.

In March and April 2008, a series or swarm of moderate earthquakes occurred both near and within the Blanco zone. The swarm began on March 30 when over 600 measurable tremors began occurring north of the zone within the Juan de Fuca Plate. On April 23, activity moved to the Blanco fault zone itself, near its junction with the Gorda Ridge.

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