The post for Friday, August 26, 2016 included the first mention in this blog of the largest earthquake which occurred in the state of Washington. This quake occurred on December 14, 1872 at about 9:40 PM. This quake was again mentioned in posts for Monday, August 29, 2016 and Friday, September 2, 2016. Current estimates for the size of this major quake run as high as M7.5. But there was another big earthquake in 1872, which should be noted. It also was a massive quake in at least the M7.0+ range. This one occurred in southern California at Lone Pine, approximately 9 months before the Washington event. At this point, a question should be asked. Could there be any connection between these two major quakes via transferred stress or some other geologic phenomenon? Keep this question in mind as we explore that other, massive earthquake of 1872.
The Lone Pine earthquake of 1872 (also called the Owens Valley earthquake) struck on March 26 in the north-northwest to south-southeast trending Owens Valley, which lies east of the Sierra Nevada. This quake had an estimated magnitude of 7.4 to 7.9 (link). It was one of the largest quakes California has ever experienced in recorded history. In this quake, the ground also did something strange. It suddenly moved vertically a distance of 15 to 20 feet. Another source, linked here, states: "Vertical displacement was measured at nearly 17 feet." Furthermore, according to the Wikipedia entry (first link above), things to the west of the Lone Pine Fault moved northward for a distance of approximately 35 to 40 feet. In this quake, a good share of the buildings in the local area were utterly destroyed.
A page, linked here, presents information from the April 4, 1872 issue of the Colorado Chieftain of Pueblo, Colorado and an issue of the Sterling Standard of Sterling, Illinois -- of the same date. It declares: "Stage passengers report that several fissures, miles in length and fifty to two hundred feet wide and twenty feet deep, opened along the eastern base of the Sierra Nevada. Near Big Pine Camp, and at other places in the vicinity, the ground was heaved up in great ridges." Further down, the page states: "A chasm was opened extending 85 miles down the valley, and ranging from three inches to forty feet in width." On the second page of the link is something very interesting. It states: "Indians in the vicinity have all left, fearing a recurrence of a general convulsion of nature, which according to tradition, occurred there some hundred years ago, and created what is now known as Owen's River Valley, but what was before a chain of mountains."
What is this which is recorded above? The Indians local to the Owens Valley have a tradition about a massive earthquake somewhere in the not-too-distant past which created the Owen's River Valley out of what was formerly a chain of mountains. What could cause such large-scale faulting and relatively swift sinking of land in the midst of a chain of mountains? Keep these thoughts in the back of your mind as we continue looking at other things.
The 1872 California earthquake was felt from Mexico to Oregon (link). The early morning quake was so powerful that adobe buildings 400 miles north of the epicenter, in Red Bluff, collapsed (link). A page, linked here, states that this "massive earthquake on the fault shook the West from San Diego to Salt Lake City. At the bottom of a USGS page, linked here, is a picture of a 23-foot-high fault scarp in the Owens Valley, which was caused by the ground sinking during the 1872 quake. What caused this rather sudden sinking in the valley?
According to a Live Science webpage, linked here, there is something very unique about the 1872 Owens Valley quake. The page states: "The Owens Valley fault broke along 70 miles (113 kilometers) of fault, less than one-half to one-third of the sections ruptured by the San Andreas Fault's biggest earthquakes." The page continues: "Despite its short length, the Owens Valley quake seemed to have very energetic shaking." The page states that "in Eastern California, big earthquakes seem to link up several smaller faults when they strike, instead of staying on one fault." For those in the Pacific Northwest, this is a phenomenon which is worth keeping in mind regarding the coming Cascadia megaquake event. Faults can "link up" and produce a much bigger quake than is currently expected.
An abstract from a 2009 issue of the Bulletin of the Seismological Society of America (BSSA), linked here, states that the preferred magnitude estimate for the 1872 Owens Valley earthquake is 7.8 to 7.9. The page then states: "The results of our study suggest that either the Owens Valley earthquake was larger than the 1906 San Francisco earthquake or that, by virtue of source properties and/or propagation effects, it produced systematically higher ground motions at regional distances. The latter possibility implies that some large earthquakes in California will generate significantly larger ground motions than San Andreas fault events of comparable magnitude." This gives some food for thought.
In the BSSA abstract, linked above, is something else which should be noted. It declares: "Macroseismic observations thus suggest a magnitude
greater than that of the 1906 San Francisco
earthquake, which appears to be at odds with geological observations." Macroseismic observations take into account more than just the observations of seismologists. Macroseismic observations also take into account the observations of engineers (link).
The seismologists may say, "The geologic evidence shows the quake could only have been this particular size," while the engineers can say, "But it takes this much shaking to destroy this type of structure." So, macroseismic observation could possibly produce a more accurate picture of a quake event than seismology alone. At this point, there is something to consider. In true science, we must look at all the facts.
The BSSA abstract, linked further above, is associated with a much larger study. The complete 42 page study which is associated with the above abstract is linked here. It is a good read for those desiring more detailed information about how scientists have viewed the Owens Valley quake.
The 42 page study, linked above, on PDF page 8 of 42 notes that "the Owens Valley is [a] major structural depression. The study indicates, on PDF page 14 of 42, that the hypocenter depth for the 1872 quake may have been somewhere in a range of 15 km to 25 km below the surface. This appears to be getting down somewhere relatively near to "the basement" of the continental crust in this region. On PDF page 18 of 42 is another piece of information to note. It states that "a more shallow seismogenic zone would of course reduce the maximum magnitude that a given fault could generate." This would tend to indicate that a deeper seismogenic zone would increase the maximum magnitude that a given fault could generate. This is another thing to keep in mind regarding the Cascadia region and its unique network of faults and rifts. Looking further, the study states on PDF page 19 of 42 that earthquake "events with magnitudes approaching 8 are not restricted to the San Andreas fault, but can occur over much if not quite all of California." This does not bode well for Californians.
A 1894 edition of the Annual Publication of the Historical Society of Southern California, linked here, presents some very detailed information about things which happened during the 1872 Owens Valley earthquake. (NOTE - Turn pages via arrows at top or bottom of pages. Six pages total.) The entry begins with a picture of a very peaceful night in 1872. Then it declares: "In an instant, without any warning symptoms from the heavens above or the earth beneath, the mountains were swaying like storm-tossed trees and the valley rolled like the sea." It continues: "About 25 minutes past 2 o'clock in the morning great rumbling and roaring were heard to come from deep in the earth. At the same instant the ground rolled violently; there was also a twisting motion, and this, together with the heaving and rolling, produced great and instant destruction."
The 1894 publication, linked above on page 31 of 32, declares: "That the center of this great disturbance of the earth was deep-seated is evident from the permanent changes on the surface. About twenty-eight miles north from Lone Pine the bed of Owens River sank, making a depression that took the river several hours to fill up. This depression still remains, a lake of some hundreds of acres in extent." The page continues: "About seven miles north of Lone Pine the ground sank toward the west; the river followed this depression and made a new channel, in which it continues to flow. The high banks of the old channel can yet be seen about two miles to the east from the present west bank of the river, at a point four miles north of Lone Pine." This is quite an event to think about. It does present food for though for people in the Cascadia region, especially when considering the coming Cascadia megaquake event. Things can change, geologically, very quickly. Large areas of land can sink and waterways can be changed -- in a moment.
Looking further, an abstract, linked here, declares: "The Owens Valley fault zone apparently accommodates some of the relative motion (dextral shear) between the North American and Pacific plates along a discrete structure. This shear occurs in the Walker Lane belt of strike-slip and normal faults within the mainly extensional Basin and Range Province. In Owens Valley, the displacement is partitioned between the Owens Valley fault zone and the nearby, subparallel, and purely normal range-front faults of the Sierra Nevada."
Look, once again, at what is stated in the paragraph above. The Owens Valley fault zone and the Walker Lane belt of faults appear to be a point of movement between the North American and Pacific plates. Things on the west side of this valley are moving northward, compared to things on the east side of the valley. This movement is said to occur along a "discrete structure." What is this discrete structure?
A Wikipedia entry, linked here, declares: "Owens Valley is a graben -- a downdropped block of land between two vertical faults... It is also part of a trough which extends from Oregon to Death Valley called the Walker Lane." The Wikipedia entry states that "this graben was formed by a long series of earthquakes..." Could this have anything to do with the Indian tradition about "a general convulsion of nature," a massive earthquake event in earlier times which rapidly formed the Owens River Valley in the midst of a chain of mountains? What happened to cause or allow the land to drop such a great distance? What are we truly dealing with here?
A webpage, linked here, states: "Continental rift zones are typically made up by a series of asymmetric graben..." Note, again, the word "graben." A Wikipedia entry, linked here, declares: "Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben with normal faulting and rift-flank uplifts mainly on one side... The axis of the rift area may contain volcanic rocks, and active volcanism is a part of many, but not all active rift systems... Many rifts are the sites of at least minor magmatic activity, particularly in the early stages of rifting." This information does give us some food for thought, especially when considering the volcanic centers in the Owens Valley.
A page on the Caltech website, linked here, declares: "Owens Valley is a nearly perfect rift valley, a divergent boundary in which both sides are moving apart. Many geologic and hydrologic features, which are characteristic of rift valleys, are evident in Owens Valley, including normal faulting, volcanism, and geothermal hot springs, to name a few."
A webpage, linked here, declares: "The Owens Valley is a classic 'graben' formed by extensional forces pulling the western regions of California and Oregon westward away from the interior of North America." So, as extensional forces tug on the landmass, stretching it, things finally crack. When a chain of mountains is pulled apart during this spreading, the unsupported land between the cracks can sink rather suddenly. A scenario like this adds credibility to the tradition of Indians in the Owens Valley area about "a general convulsion of nature," which, in earlier times "created what is now known as Owen's River Valley" out of "what was before a chain of mountains."
A 73-page USGS document titled Structural Geology and Volcanism of Owens Valley Region, California - A Geophysical Study, is linked here. On PDF page 6 of 73 are found the following words: "Owens Valley is a downdropped block, or graben, between the Sierra Nevada and the White and Inyo Mountains." The USGS document states further, on PDF page 6 of 73: "The association of volcanic rocks with the depressions of Long Valley and Mono Basin suggests that these structural features may have been created in part by volcano-tectonic processes." So, we appear to be looking at a combination of volcanic and tectonic processes in the making of this unique region. Yes, the moving of plates, or the rifting of the landmass, with associated volcanism.
The USGS document, linked above, contains even further statements of interest. On PDF page 11 of 73, it states: "Owens Valley is a structural trough that has been dropped down as a graben along normal faults that separate it from the Sierra Nevada on the west and from the White and Inyo Mountains on the east." On PDF page 60 of 73, the document states that the "Owens Valley seems to lie near the crest of a great arch that has been broken by block faulting. As the crest of the arch broke, perhaps during general uplift of the Sierra Nevada and of the extreme western Great Basin, Owens Valley seemingly subsided as a graben."
Wow! Once again, the USGS information above hints a little at the Indian tradition, noted further above, about "a general convulsion of nature." When rifting is being initiated and the land is "stretched," when things suddenly snap, the unsupported land can sink rather suddenly. Nature proves this fact over and over again when areas on steep-sided mountains suddenly break loose and come crashing down. In the case of Owens Valley, it was similar to fractures on steep-sided mountains, except in this case, being fractures going deep into the landmass. When things "snapped," it is possible that the valley was formed rather rapidly, just like Indian tradition indicates.
Once again, noted further above and linked here, is an abstract which declares: "The Owens Valley fault zone apparently accommodates some of the relative motion (dextral shear) between the North American and Pacific plates along a discrete structure. This shear occurs in the Walker Lane belt of strike-slip and normal faults within the mainly extensional Basin and Range Province. Again, a Wikipedia entry, linked here, declares: "Owens Valley is a graben -- a downdropped block of land between two vertical faults... It is also part of a trough which extends from Oregon to Death Valley called the Walker Lane." What is this Walker Lane all about -- this geologic trough which "extends from Oregon to Death Valley?"
A page, linked here, is titled The Walker Lane RIFT SYSTEM: A Natural Laboratory to Study Rift Initiation that Culminated in Seafloor Spreading (in the Gulf of California). PDF page 3 of 25 declares: "Walker Lane rift system - currently accommodates 20-25% of the plate motion between the Pacific and the North American plates..." From what is stated on the page, it appears we are, in the Walker Lane, looking at continental rifting. On PDF page 25 of 25 of the document, it notes "the successful Gulf of CA rift" and the "rift initiation in the Walker Lane," plus an "interface with Cascadia." What, yes once again, WHAT is being dealt with in the coastal states of North America? Hold this thought for a few more moments.
Another page, linked here, is titled Siting of Large Volcanic Centers at Releasing Fault Stepovers, Walker Lane Rift. On PDF page 4 of 54, it speaks of the Walker Lane Belt as being "like [the] Gulf of California, but no sea floor spreading yet." Note very closely, once again, the use of the word "YET," and then finish looking through the document. On PDF page 8 of 54, it is noted that the "Gulf of California rifting was unusually FAST." PDF page 11 of 54 speaks of "large volcanic centers in transtensional pull-aparts along the eastern margin of the Sierra Nevada." In effect, these would be similar to the short spreading centers, sandwiched between the transform faults in the bottom of the Gulf of California.
In the document linked in the preceding paragraph, on PDF page 15 of 54, is noted how "the northern Walker Lane increasingly interacted with the Cascade subduction zone to produce transtensional environments favorable to the development of major volcanic centers." So, it is very clear -- we are dealing with a rift -- a process where the continent is rifting or pulling apart. And this rifting or pulling apart has links to the Cascadia region. So, what kind of seismic activity can we expect from all this in the Cascadia region, in the times ahead?
At this point, let us remember the two major earthquakes in 1872 -- the first in the Owens Valley, and then about 9 months later, the massive earthquake in Washington. Seeing that rifting in the Owens Valley and the Walker Lane is associated geologically with Cascadia, there is a question to ask. When the massive Cascadia megaquake occurs, will it have been preceded by a massive quake somewhere along the trough of the Walker Lane? In other words, will a massive quake in southern California be like an advanced warning system? Will it give the warning so citizens of the Pacific Northwest can then be watching for more localized signs -- signs which may help indicate more closely when the devastating Cascadia event is about to occur?
By the way, what appears to be controlling or associated with this large-scale continental rifting? Once again we must look at the Gulf of California, and the Gulf of California Rift Zone. A Wikipedia entry, linked here, declares: "The Gulf of California Rift Zone (GCRZ) is the northernmost extension of the East Pacific Rise which extends some 1300 km from the mouth of the Gulf of California to the southern terminus of the San Andreas Fault at the Salton Sink." But, after considering all the information presented in this discussion, we now know the rest of the story.
The oceanic rift system, when it burrows into the North American continent, does not follow the San Andreas Fault back out to sea again, north of San Francisco, California. Instead, the ancient oceanic rift (which was over-ridden by the westward moving North American continent) ended up far down at the basement of the continent, somewhere far inland. Generally, it is situated below the Owens Valley graben and the Walker Lane. It extends all the way to the Cascade Mountains in southern Oregon. From there, it appears that this now deeply buried oceanic rift generally follows the line of the Cascade Mountain volcanoes.
Once again, it appears that the ancient, now deeply buried oceanic rift system is that which is controlling the rifting in the continental landmass above it. It appears that this ancient rift system may also be a major initiator of earthquakes in the Pacific states. Now you know more about what is happening, geologically, on the West Coast of the United States. Now you can better understand what the future may hold, even in the Cascadia region. And remember, things can change really fast in life, even in the geology of the Pacific states. The writer wishes you all the best in the times ahead.
For further reading:
Current Expectations for a Cascadia Mega-Quake
https://cascadian.neocities.org/cascadiaquake.htm
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