St. Andreas Fault

Will San Francisco disappear into the earth's crust?

In April 1906, an earthquake hit San Francisco, killing more than 3,000 people and leaving 300,000 homeless. After 83 years, another thing happened, although not so terrible in terms of consequences. Catastrophists predict: sooner or later there will be a big earthquake that will raze San Francisco to the ground, and the city will disappear into huge breaches in the earth's crust. And the reason for this is a crack in the ground, called the St. Andreas Fault. Can a terrible earthquake be caused artificially? Where are the continents rushing to and what forces pushed Africa away from South America - The New Times was looking for answers to these questions

During the Cold War, there was a story that there was a Soviet nuclear missile aimed at a certain point (“water tower”) in California, hitting which would cause the earth’s crust of the state to split into two pieces. After that, the eastern piece would be flooded by the Pacific Ocean, which would cause the death of most of the 30 million Californians, including residents of Los Angeles and San Francisco. Of course, this tale was not born in the USSR Ministry of Defense, but was a distorted presentation of the 1978 Hollywood movie Superman.

1300 km of fear

But is there a grain of reality in this bike? A 1,300-kilometer-long San Andreas fault indeed runs along the coast of California, separating the Pacific and North American tectonic plates. San Andreas (together with the adjacent Hayward, Calaveras and other faults) is a source of large earthquakes.

In some places, San Andreas is visible as a ravine, in other places it is almost invisible. The eastern and western sides of the fault move parallel to each other: the western side moves north, and the eastern side moves south. The movement of the plates occurs approximately at the rate of growth of human nails - 3-4 centimeters per year. This movement can be seen on the roads that traverse the San Andreas, showing shifted road markings and signs of regular pavement repair at the fault. The most visible manifestation of the “work” of the fault is the ancient volcano Ninakh, which formed 23 million years ago, after which it was neatly, like a cake, “cut” into two halves by the San Andreas fault, and the left half “left” along the fault for millions of years. 314 kilometers to the north and became the Pinnacles National Monument.

Where are the continents going?

What forces move thousand-kilometer pieces of the earth's surface? Until the 20th century, the answer to this question was unknown. More precisely, there was not even a question: geological science believed that the continents were motionless, and sections of the earth's crust only moved up and down, according to the theory of geosynclines adopted in the middle of the 19th century.

But since the 16th century, cartographers have noticed that the coasts of Africa and South America can be superimposed on each other, like two pieces of a broken plate, after which some researchers periodically put forward the idea that the continents are moving. Most of the arguments were given by the German scientist Alfred Wegener. In 1915, Wegener showed that the coasts of different continents not only coincided in contour, but also contained the same types of stones, as well as fossils of similar animal species. Wegener suggested that 200 million years ago there was a single supercontinent Pangea, which subsequently split into parts that became modern Eurasia, America, Australia and Antarctica. For 50 years, Wegener's theory was thought to be a set of coincidences, as geophysicists thought it improbable that a continent (a mass of rock) could move across another mass of rock (the hard bottom of the oceans) without being eroded by friction. The situation changed only after World War II, when the US military, using sonar, mapped the oceans and found in the middle of them long chains of seamounts, clearly of volcanic origin. Researcher Harry Hess showed that the bottom of the Atlantic Ocean is moving apart in two directions from the mountain range passing in the middle of the Atlantic. The expanding ocean floor carries the continents like an escalator in a subway carries passengers.

And who drives them...

As a result of the research of Hess and others in the 1960s, a revolution occurred in geology comparable to the Copernican revolution in astronomy. It turned out that the earth's crust consists of several large plates (African, North American, Pacific, Eurasian and others), as well as a large number of small plates that move at a speed of several centimeters per year, colliding with each other. Each slab is about 100 kilometers thick. Beneath the plates that form the "lithosphere" is a hot, viscous layer about 200–400 kilometers thick called the asthenosphere. Tectonic plates “float” on it, carrying the continents.

When plates collide, depending on the nature of the collision, mountains are formed (for example, the Himalayas), chains of islands (for example, the Japanese islands), depressions and volcanoes. When the oceanic and continental plates collide, the oceanic plate goes down. This is due to the fact that the oceanic crust has a different chemical composition and greater density. Gerry Hess called the ongoing process a “conveyor belt”: a new crust is born from hardened lava in the middle of the ocean, slowly moves for millions of years, after which it sinks back into the bowels and melts.

Why are the plates on the San Andreas fault moving sideways and not towards each other? The fact is that for 40 million years in the region there was a complex "dance" of three tectonic plates (Pacific, Farallon (Farallon) and North American), the boundaries between which were at an angle to each other. The Farallon Plate was "pushed" under the North American, after which the Pacific began to slide sideways along the former border of the Farallon and North American plates.

Tectonic plates are like foams driven by convection currents of boiling soup. In the 19th century, scientists did not understand how this "soup" could continue to "boil" at all. According to the calculations of the famous physicist William Thomson (Lord Kelvin), according to the laws of thermodynamics, the Earth should have cooled down in just 20 million years. This contradicted geologists' estimates of the age of the Earth. Thomson did not take into account the heating of the Earth by the decay of radioactive elements, which were discovered only at the beginning of the 20th century. Because of this heating, the Earth continues to be hot after four and a half billion years of its existence. We live on a huge nuclear reactor - the planet Earth!

earth shaking

Okay, the continents are moving, but how does this affect our lives, in addition to the need to periodically repair a few small roads that cross the San Andreas fault? The problem is that the movement is not continuous. Each shift begins with a build-up of stress, which is “discharged” with a jerk during a large or small earthquake. In the central part, the fault “creeps” due to thousands of micro-earthquakes that are not felt by humans. But sometimes the voltage is not discharged for a long time, after which the movement occurs in a jump.

This happened during the 1906 earthquake in San Francisco, when the “left” part of California moved relative to the “right” by almost 7 meters near the epicenter. The shift began 10 kilometers under the ocean floor in the San Francisco area, after which, within 4 minutes, the shift impulse spread to 430 kilometers of the San Andreas Fault - from the village of Mendocino to the town of San Juan Batista.

The villain's plan

Thus, it is impossible to flood coastal California with a point nuclear explosion on the San Andreas Fault. The plates in the fault area do not move towards each other, but to the sides (along the north-south line), so pushing the Pacific plate under the North American one is less realistic than flooding an aircraft carrier with a kick. But is it possible to cause serious damage with an artificial earthquake? Oddly enough, this idea was tested not only in Hollywood films. In 1966, geologists from the United States Geological Survey (USGS) noticed an unexpected sequence of earthquakes near the Rocky Flats military arsenal in Colorado. The timing of the earthquakes exactly coincided with the moments when the military disposed of liquid waste by pumping it under pressure deep underground. Geologists set up an experiment by pumping water into an abandoned oil field near the town of Rangely in Colorado. For the first time in history, humans artificially caused an earthquake.

After that, the USGS discussed for some time the idea of ​​preventing large earthquakes along the San Andreas by relieving fault stress with a large number of micro-quakes. However, the USGS decided not to experiment, since it is clear that they would not have enough money to pay in case of a mistake for the complete destruction of Los Angeles or San Francisco.

It gets worse

Earthquakes notwithstanding, California is one of the nicest places to live on Earth. Most residents of the state live in one-two-story houses and know the precautions. Therefore, the significant San Francisco earthquake in 1989 did not cause much destruction. After all, there are problems elsewhere on the planet - hurricanes, tsunamis or an unfavorable political situation. And the San Andreas fault is not the most dangerous geological object in the United States. For example, there is the Yellowstone supervolcano, which about two million years ago covered the entire western half of the modern United States with ash. A huge number of animals died even thousands of kilometers from the eruption - due to dust that got into the lungs and polluted drinking water. Such eruptions change the climate of the entire planet for years, causing a "volcanic winter". But the topic of volcanoes and supervolcanoes deserves a separate article.