For more than a century, the San Andreas Fault has been considered the undisputed heavyweight champion of large-scale deformation in the West. It is here that the North American and Pacific Plates meet, jostling for position with often violent results. Eventually, the theory goes, the thin sliver of land between the fault and the ocean—from the southern tip of the Baja Peninsula to the Santa Cruz Mountains—will break off from the mainland and slide north, until LA drifts past San Francisco.
Northwest of LA, near the town of Frazier Park, the fault is kinked out of alignment so dramatically that many geologists suspect the pent-up tectonic strain will have to seek release somewhere else. He believes that, over the next 8 million to 10 million years, the North American continent will unzip along this stretch of land, east of the San Andreas. The Gulf of California, which separates the Baja Peninsula from Mexico, will surge north into Nevada, turning thousands of square miles of dry land into ocean floor.
Mapmakers, if they still exist, may label the new body of water the Reno Sea. It represents a radical shift in how geologists use up-to-the-minute tools—satellite data, aerial surveys, computer simulations—to fathom age-old processes. And for residents of the West, it is an invitation to think in an altogether new way about the familiar-seeming ground beneath them.
Now is the time: Already the Walker Lane region, with its booming population and burgeoning tech economy, is beginning to feel the rumblings of a new seismic regime. It may be difficult to persuade them otherwise: Unlike the San Andreas, which is visible from space, the Walker Lane has yet to form a single, continuous line across the landscape.
Still, Faulds has a pretty good idea of where it begins. Using a combination of old-fashioned fieldwork and modern technologies, he is now busily trying to find the rest. Last fall, I drove the nearly miles up Route from LA to Reno to meet him and learn how his tectonic premonition might come to pass. Faulds picked me up outside my hotel early one morning in a Chevy Tahoe.
Strips of neon light cast garish shades of pink and purple over the empty sidewalks. We were about to spend a few days hiking through light rain, cold and exposed, and Faulds had come prepared.
Fracture or discontinuity in rock across which there has been displacement. These example sentences are selected automatically from various online news sources to reflect current usage of the word 'fault line. What Is a Fault Line? At the fault, rocks have broken. This type of curriculum would be offered by public schools and its implementation authorized, monitored and evaluated by the Ministry of Education. Shaded relief image of the Santa Rosa area showing active faults black lines and the detailed rupture pattern of the Rodgers Creek Fault where it crosses central Santa Rosa in red. Radiocarbon dating of organic material buried next to or over a fault shear is often critical in distinguishing active from inactive faults.
Our destination that day was a trio of faults near Pyramid Lake, roughly a mile drive northeast of Reno. The three features appear to be related, Faulds said, and seeing them would give me a good sense of how the larger Walker Lane is taking shape. As we headed out of town, he began miming different kinds of fault configurations, rubbing his knuckles together or abruptly knocking one palm against the other.
Wrapped up in talk of subduction zones and transform boundaries, he took his hands off the steering wheel for a bit too long and the SUV began to drift. We hit a rumble strip. A mile or two later, it happened again. Although Faulds is now the leading advocate of the Walker Lane hypothesis, he is not the first person to suggest that something big is coming to the region.
In the late s, Stanford geologist Amos Nur coauthored a paper speculating that the San Andreas Fault might be looking for a new outlet in the Mojave Desert. Several years later, a strong 7. This was the Walker Lane.
Geodesists make precise measurements of where landforms are at any given moment—mountain peaks, ocean basins, remote islands, entire continents. When GPS satellite data was made available to the general public in the s, geodesists saw an opportunity. They began installing fixed GPS monitoring stations, called benchmarks, out in the landscape, then waiting patiently to see how each one moved over time.
For geologists, seeing the Walker Lane for the first time was like discovering that a quarter of the Mississippi River is somewhere out in Colorado. In the s, Nevada received funding from the US Department of Energy to install an unusually dense network of benchmarks in the southwest part of the state.
This was not because the feds were worried about the overnight rupture of a new continental margin, but because they were hoping to bury the nation's nuclear waste beneath Yucca Mountain. Radioactive materials were meant to be entombed there for hundreds of thousands of years, and the DOE wanted to ensure the site was safe. The project was shelved because of political squabbling, though it's resuscitated from time to time.
An unexpected benefit of the new sensor network was that it opened a window on the Walker Lane. The results were astonishing. GPS stations indicated that only about 75 percent of the tectonic movement between the Pacific and North American Plates was actually occurring along the San Andreas Fault. For geologists, it was like discovering that a quarter of the Mississippi River is somewhere out in Colorado. Almost overnight, plate tectonics was no longer something geodesists had to speculate about with fieldwork or maps; it had become something they could watch unfold in real time. GPS technology is now capable of recording millimeter-scale changes in the landscape, accurate enough to measure the growth rate of a human fingernail.
The past 30 years' worth of data has been breathtaking enough, but in another few decades GPS geodesy is likely to reshape our entire understanding of Earth's crust. Every geodesist I spoke with described the field with a barely contained sense of awe and excitement. Yet the discovery did not, as one might expect, trigger a surge of interest in the Walker Lane.
In this sense, Faulds' idea makes him an outlier. But, Bennett added, just look at a map. The zone stretching away from the Salton Sea, where the San Andreas begins, up into the southern part of the Walker Lane has been quite seismically active of late. Something must be going on there. As Faulds and I neared Pyramid Lake, he brought up the work of Tanya Atwater, widely considered a visionary in the field of plate tectonics. In the s, Atwater began creating a series of animations depicting the birth and evolution of the San Andreas Fault.
They suggest a precedent, Faulds said, for what is happening along the Walker Lane. Early on in the animations, it appears that the modern-day Baja Peninsula is destined to remain a part of the North American Plate; then, at about 7 million years ago, it abruptly cleaves away, creating the Gulf of California.
This shift, Faulds said, was largely due to the presence of a chain of old volcanoes on the inland side of the San Andreas. They warmed and softened the continental crust, creating a line of weak spots like the perforations between two rows of postage stamps. That's where the land ripped apart. An uncannily similar situation may be playing out today, Faulds told me. As you head north from the Gulf of California into the Mojave Desert, an area known as the Eastern California Shear Zone, you pass scores of beautiful old volcanic craters and lava tubes. These features, many of which have become popular hiking destinations, form a line of perforation all the way up the Eastern Sierra, right along the highway that brought me to Reno.
As the North American and Pacific Plates jostle for position, where will the growing tectonic pressure find an outlet? Pyramid lake is a remote, unearthly place ringed with tufa towers. It is located on a reservation belonging to the Paiute people, who consider it sacred. A mere 13, years ago, well within the time frame of human habitation in the West, it was part of an immense inland sea called Lake Lahontan.
Since at least then, a series of linear features has been emerging south and west of the current water's edge. They show up clearly in satellite imagery, however, as strange lines cutting many miles through the bare, rolling landscape. Faulds believes they may be on track to connect eventually. First Known Use of fault line , in the meaning defined above. Learn More about fault line. Resources for fault line Time Traveler! Explore the year a word first appeared. Dictionary Entries near fault line faultful fault gouge faultless fault line fault-line scarp fault-line valley fault plane. Time Traveler for fault line The first known use of fault line was in See more words from the same year.
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