In recent times, there has been an ongoing swarm of small earthquakes in the Puget Sound region. This swarm of quakes is mainly concentrated in the area between Bremerton, Washington and Bainbridge Island.
A news article about this quake swarm, from early Thursday (5-11-2017), linked here, notes that "There have been 18 temblors in the last 24 hours, and the Pacific Northwest Seismic Network has recorded 42 tiny quakes since May 3." The article notes that this quake swarm is occurring on "the western edge of the Seattle fault." The article states further that "Seismologists believe the quakes are being caused by fluid moving underneath the earth’s crust."
The concentration of ongoing earthquakes in this swarm, being in one area of the Puget Sound region, does get the writer's attention. His research over the years has located information about a number of unique geologic occurrences in the waters of northwest Washington and southwest British Columbia. These rather strange occurrences are things of which the public should possibly be aware.
Now, once again looking at first paragraph, the seismologists "believe the quakes are being caused by fluid moving underneath the earth’s crust." Moving fluid means something beneath the fractured and faulted area surrounding the Kitsap Peninsula is not truly solid. This fluid which is moving is most likely extremely hot, molten magma --- yes, the stuff that comes out of volcanoes. At this point, there is something to consider.
Fluid, or molten magma, which is moving below the surface of the earth can potentially increase or decrease in pressure. Depending on the geologic structure surrounding or above a fluid of changing pressure, things potentially can move. Landmasses, islands or seabed can potentially sink or rise. It is a matter of simple hydraulics.
With the above information in mind, it is now time to consider just a couple of the rather strange geologic events which have occurred in these waters of northwest Washington and southwest British Columbia.
A web page, linked here, contains the following information. "During a magnitude 7.3 earthquake in the Strait of Georgia off British Columbia in June 1946, the seabed sunk nearly 85 feet in some places." This quake was also called the 1946 Vancouver Island earthquake. A Wikipedia entry linked on the page states that "The tectonics that caused the 1946 Vancouver Island earthquake are poorly known." But, there is more to this story.
The linked Wikipedia entry also states: "Land subsidence resulted from the earthquake, most commonly around shorelines on the Strait of Georgia. This included the bottom of Deep Bay which sank between 2.7 m (9 ft) and 25.6 m (84 ft)."
Deep Bay is shaped somewhat like an open-ended, irregular oval, as the following links illustrate: (1) (2) (3) (4). This radical sinking is something to take seriously, especially when considering the possibility of major earthquakes in the Puget Sound region.
There is even a more strange geologic occurrence which happened in the San Juan Islands at the same time as the 1906 San Francisco earthquake. At the time of the California quake, an island in the San Juans sank, and very strangely, later rose again. This particular island was called Denver Island.
A web page, linked here, contains links to articles from 1907 and 1908 which present some very interesting information about this very unusual geologic event at Denver Island. This event was likely caused by moving fluids, or molten magmas, below the earth's crust.
It appears that Denver Island may have been supported by pressurized magma. It appears that during the 1906 San Francisco earthquake, this supporting magma lost some of its pressure. This loss of pressure allowed the island to sink beneath its surrounding waters. Later, the pressure appears to have increased in the molten magma beneath the island and it was then, once again, raised above the waters of the region. This is just simple hydraulics in action.
So, what unusual or potentially catastrophic geologic events lie ahead for the Puget Sound region? Well, only time will tell. But, I can say one thing for sure. I am not in any hurry to move to the Puget Sound region.
For further reading:
Current Expectations for a Cascadia Mega-Quake
https://cascadian.neocities.org/cascadiaquake.htm
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