The Blanco Fracture Zone is one of several seismically active transform faults off the coast of Oregon. The Blanco FZ offsets the Juan de Fuca (JDF) Ridge from the Gorda Ridge (ridges are spreading centers where new ocean floor is created).
Although earthquakes occur frequently along the Blanco Fracture Zone, they are rarely felt. Generally, the transform motion of these earthquakes
does not produce tsunamis because the plates slide by each other without
changing the shape of the ocean floor.
Seismicity, Magnitude 4 and greater, 1990 - August. 2002
List of quakes on this map
Locations and magnitudes for Blanco Fracture Zone area earthquakes are provided by NEIC. These quakes are outside the PNSN network, and not well located by PNSN instrumentation.
On this map, red squares show quakes of magnitude 4.0 or greater located in the area since 1990.
Double lines with arrows pointing in opposite directions represent oceanic spreading centers, which are seismically quiet except for occasional swarms of small earthquakes associated with volcanic eruptions near the Axial Seamount on the JDF spreading center (monitored by the NOAA Vents program).
Many earthquakes are located along the north-west trending Blanco Fracture Zone. Seismicity also occurs along a transform fault south of the Blanco F.Z., and along the east-west trending Mendocino Fracture Zone near the bottom of the figure.
Although the distribution of seismograph stations makes it hard to calculate precise locations, all earthquakes in the area most likely originate on the transform faults.
Over the past 20 years, a magnitude 6.0-7.0 earthquake has occurred on the Blanco Fracture Zone every 5 years or so. Each year, there are several earthquakes in the magnitude 5.0 to 6.0 range.
IRIS Page on
Fault Motions - Tranform faults produce strike-slip earthquakes
NOAA "Vents" Program Acoustic Monitoring of Ocean Seismicity
