Understanding the many moderate Oregon (USA) seaquakes

Last update: March 8, 2011 at 9:20 am by By

Since a few months the transform fault zone about 350 km out of the Coos Bay Oregon coast is discharging energy by means of earthquakes of magnitude 5.x
The Blanco Transform Fault as it is called, has become the most intensely studied ocean transform fault in the world.

Oregon State University scientists have completed a analysis of an earthquake fault line that extends some 200 miles off the southern and central Oregon coast that they say is more active than the San Andreas Fault in California.

The Blanco Transform Fault Zone likely won’t produce the huge earthquake many have predicted for the Pacific Northwest because it isn’t a subduction zone fault. But the scientists say an earthquake of magnitude 6.5 to 7.0 is possible, if not probable in the near future, and their analysis suggests that the region may be under some tectonic stress that potentially could affect the Cascadia Subduction Zone.

The risk of a major tsunami from an earthquake in this transform fault is slim, because the plates move sideways past each other.
You need quite a bit of vertical displacement on the ocean floor to generate a tsunami,” Braunmiller said, “and earthquakes along the Blanco fault don’t generate it.

During the past 40 years, there have been some 1,500 earthquakes of magnitude 4.0 or greater along the Blanco Transform Fault Zone, and many thousands of smaller quakes.

March 7 magnitude 5.1 epicenter location along the Blanco fracture zone

The Blanco fault is the boundary between the Juan de Fuca and the Pacific plates.
As the Juan de Fuca plate moves to the east, it is subducted beneath the North American plate at the rate of about 1.5 inches per year. But as it moves, it must break free of the adjacent Pacific plate.
This slippage causes the numerous earthquakes, according to John Nabelek, an associate professor in OSU’s College of Oceanic and Atmospheric Sciences and one of the authors of the study. When the earthquakes that relieve stress do not account for predicted motion rates, he added, it raises questions.
“The eastern portion of the fault has moved at a predictable rate and the earthquake activity associated with it has been what we would expect,” Nabelek said. “But the western part of the fault has been lagging in terms of the number and size of earthquakes. It seems to be straining, absorbing the motion.

It could mean that the fault is getting ready for a large earthquake, or it could mean that the movement has been so gradual that we couldn’t detect it,” he added

In April 2008, a swarm of 600 earthquakes in 10 days hit the fault region, including magnitude 5.4 and 5.0 events.

This is partly an excerpt of the article hereunder.
Credits : sciencedaily.com and the Oregon State University.
We encourage our readers to read the complete article
Images : courtesy USGS

Comments

  1. John Berbatis says:

    In the past ten years, there has been an exponential melting of the ice sheets and a noticeable disintegration of the ice shelves, owing to ‘global warming’. The loss of mass from the underlying Tectonics Plates causes them to ascend (iso-static rebound), and this results in an increase in the intensification and frequency of global seismological activity. The seismic data of the past ten years confirm this conjecture. Furthermore, the ice shelves impede the flow of glaciers and ice sheets into to the oceans; and when the ‘polar regions’ are subjected to unprecedented seismic upheavals, these events will then cause the ice sheets and glaciers to be dislodged en masse into the ocean. This occurrence will then instantly destabilize the earth’s crust weight distribution (isostasy), and so precipitate a ‘crust displacement’ (Mag. 12), that is, an axis change. The previous subterranean extraction of fossil fuels will greatly exacerbate this impending Apocalypse. Currently, the excessive amount of carbon and methane gasses in the atmosphere is causing catastrophic weather conditions, globally – and this situation will rapidly deteriorate into ‘a runaway climate’.

    The result of the Western Antarctic Ice Sheet dislodging.

    “In a polar region there is a continual deposition of ice, which is not symmetrically distributed about the pole. The earth’s rotation acts on these asymmetrically deposited masses [of ice], and produces centrifugal momentum that is transmitted to the rigid crust of the earth. The constantly increasing centrifugal momentum produced in this way will, when it has reached a certain point, produce a movement of the earth’s crust over the rest of the earth’s body, and this will displace the polar regions toward the equator.”
    Albert Einstein foreward in The Path of the Pole by Prof Charles Hapgood.
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