Continental Rifting and Eastern Washington

An article in the Spokane Daily Chronicle of December 17, 1981, linked here, speaks about a giant rift which extends across the continental United States. It extends from north central Georgia, on its eastern end, to at least the Spokane, Washington area, on its western end. The article notes that this potential split in the continent "might end near Spokane." But, there appears to be much more to this story.

The 1981 article, linked above, states that there will need to be more research to prove whether or not this giant rift, "just discovered with space-age technology, actually extends into Washington." Regarding this giant rift and other fault systems from Idaho, it appears that geologists are having trouble tracing them into the state of Washington, "although they may exist." Why are they having this problem tracing fault systems into Washington? It is "because of alluvial deposits and the basalt covering over older rocks west of Spokane." In other words, the fault systems are deeply buried, with possibly no clear signs of their existence on the surface.

At this point, there is a comment to make. Look at the map in the linked news article. It shows the general location of this major rift system. Look where the western end is shown in Washington. Now, let us note a particular statement in the article. Regarding this rift, one geologist stated that "it apparently hasn't caused any trouble." A USGS geologist indicated that this giant continental rift "could be associated with earthquake disturbances in some parts of the country, [but] apparently hasn't affected Spokane that way."

At this point, there is a thought to keep in the back of our minds. What about that large, unexplained earthquake which occurred in Washington in 1872? Yes, just hang onto that thought. Getting back to the article, it notes that this giant rift "is 90 miles across at its widest and extends deep into the earth's crust, but poses no danger." Note the statement about posing "no danger." We will, further down in this discussion, see how thinking has changed somewhat over the years.

Another article from 1981, this one from the Nevada Daily Mail of December 16, linked here, speaks about this cross-continent rift as being a "rift, or series or [sic] rifts." A correction of the preceding sentence may be a "rift, or series of rifts." There is something to note at this time in the article. This rift system "lines up perfectly with other topographical features." And, what are some of these other topographical features?

A PDF document from the NASA website, linked here, speaks about this rift system (a linear gravity low), which is "aligned with the Lewis and Clark lineament (Montana to Washington), forming a linear feature of approximately 2800 km in length." Of the cross-continent "gravity low," the linked document states: "The origin of the linear gravity feature is problematical - it may be a rift, a transcurrent fault, or some combination." The document also states: "Perhaps the most plausible explanation is that the gravity low may be as part of an extensive transcurrent fault system or a failed continental rift."

A July 2016 webpage, linked here, contains some interesting information. It declares: "In Nov 1981, a study was published that rocked the scientific world, and sparked concern in FEMA circles..." That report turns out to be the NASA document linked in the preceding paragraph. The linked page then states: "New discoveries, from more recent research, has extended this 'Crack' anomaly in where it combines with a MegaShear zone to the middle of Washington State and possibly with the Olympic-Wallowa Lineament (OWL) – which reaches to the Pacific Ocean near Port Angeles Washington. Thus the total length may total nearly 2,200 miles."

It is now time to consider a particular statement made in 1981 news articles, linked further above, about the giant rift posing no danger. The page linked in the preceding paragraph declares: "What is known, is that these linear rift zones have exhibited the ability to unleash very large earthquakes." It also appears that "scientists are unable to identify if any section of these linear rift zones may be at risk of a sudden large earthquake." The information presented thus far in this discussion should now give us some food for thought.

This ancient, cross-continent rift system, on its Washington end, appears to reside in older rocks which presently are buried deeply beneath thick alluvial deposits and thick layers of basalt in areas to the west of Spokane, Washington. The NASA document indicates that this deeply buried rift system may be associated with the Lewis and Clark lineament. The page linked in the preceding paragraph talks about "more recent research" which links the cross-continent rift "with a Megashear zone to the middle of Washington State and possibly with the Olympic-Wallowa Lineament..." It is now time for a question. Could this deeply buried rift system have been instrumental in Washington's largest recorded earthquake, in 1872?



For further reading:

Current Expectations for a Cascadia Mega-Quake
https://cascadian.neocities.org/cascadiaquake.htm