Tag: Faults

It’s been an interesting few days here in Southern California, with several large earthquakes and an ensuing aftershock sequence out in the desert near Ridgecrest. Ridgecrest, of course, is at the very southern edge of the Walker Lane—more properly part of the Eastern California Shear Zone—a region of the country that runs broadly northwest along the California/Nevada state border that I covered at length for the May 2019 issue of Wired.

[Image: My own loose sketch of the Walker Lane, using Google Maps].

To make a story short, a handful of geologists have speculated, at least since the late 1980s, that the San Andreas Fault could actually be dying out over time—that the San Andreas is jammed up in a place called the “Big Bend,” near the town of Frazier Park, and that it is thus losing its capacity for large earthquakes.

As a result, all of that unreleased seismic strain has to go somewhere, and there is growing evidence—paleoseismic data, LiDAR surveys, GPS geodesy—that the pent-up strain has been migrating deep inland, looking for a new place to break.

That new route—bypassing the San Andreas Fault altogether—is the Walker Lane (and its southern continuation into the Mojave Desert, known as the Eastern California Shear Zone).

What this might mean—and one of the reasons I’m so fascinated by this idea—is that a new continental margin could be forming in the Eastern Sierra, near the California/Nevada state border, a future line of breakage between the Pacific and North American tectonic plates.

If this is true, the Pacific Ocean will someday flood north from the Gulf of California all the way past Reno—but, importantly, this will happen over the course of many millions of years (not due to one catastrophic earthquake). This means that no humans alive today—in fact, I would guess, no humans at all—will see the final result. If human civilization as we know it is roughly 15,000 years old, then civilization could rise and fall nearly 700 times before we even get to 10 million years, let alone 15 million or 20.

In any case, these recent big quakes out near Ridgecrest do not require that the most extreme Walker Lane scenario be true—that is, they do not require that the Walker Lane is an incipient continental margin. However, they do offer compelling and timely evidence that the Walker Lane region is, at the very least, more seismically active than its residents might want to believe.

I could go on at great length about all this, but, instead, I just want to point out one cool thing: the far northern route of the Walker Lane remains something of a mystery. If you’ve read the Wired piece, you’ll know that, for the Walker Lane to become a future continental edge, it must eventually rip back through California and southeastern Oregon to reach the sea. However, the route it might take—basically, from Pyramid Lake to the Pacific—is unclear, to say the least.

One place that came up several times while I was researching my Wired article was the northern California town of Susanville. Susanville is apparently a promising place for study, as geologists might find emergent faults there that could reveal the future path of the Walker Lane.

If you draw a straight line from the Reno/Pyramid Lake region through Susanville and keep going, you’ll soon hit a town called Fall River Mills. Interestingly, following the long aftershock sequence of these Ridgecrest quakes, there was a small quake in Fall River Mills this morning.

While seeing patterns in randomness—let alone drawing magical straight lines across the landscape—is the origin of conspiracy theory and the bane of serious scientific thinking, it is, nevertheless, interesting to note that the apparently linear nature of the Walker Lane could very well continue through Fall River Mills.

[Image: The Ridgecrest quakes and their aftershocks seem to support the idea of a linear connection along the Walker Lane; note that I have added a straight orange line in the bottom image, purely to indicate the very broad location of the Walker Lane].

While we’re on the subject, it is also interesting to see that, if you continue that same line just a little bit further, connecting Pyramid Lake to Susanville to Fall River Mills, you will hit Mt. Shasta, an active volcano in northern California. Again, if you’ve read the Wired piece, you’ll know that volcanoes seem to have played an interesting role in the early formation of the San Andreas Fault millions of years ago.

In any case, in cautious summary, I should emphasize that I am just an armchair enthusiast for the Walker Lane scenario, not a geologist; although I wrote a feature article about the Walker Lane, I am by no means an expert and it would be irresponsible of me to suggest anything here as scientific fact. It does interest me, though, that aftershocks appear to be illuminating a pretty dead-linear path northwest up the Walker Lane, including into regions where its future route are not yet clear.

Insofar as the locations of these aftershocks can be taken as scientifically relevant—not just a seismic coincidence—the next few weeks could perhaps offer some intriguing suggestions for the Walker Lane’s next steps.