At first glance, the streets of Taft, in central California, are no different from the streets of any other city in North America. Houses and gardens along wide avenues, car parks, street lights every few steps. However, a closer look reveals that the line of the same lanterns is not entirely flat, and the street seems to be twisted, as if it was taken by the ends and pulled in different directions.
The reason for these oddities is that Taft, like many of California's major urban centers, is built along the San Andreas Fault, a crack in the earth's crust that runs 1,050 km across the United States.
The strip, stretching from the coast north of San Francisco to the Gulf of California and extending into the depth of the earth for about 16 km, is a line connecting two of the 12 tectonic plates on which the oceans and continents of the Earth are located.
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The average thickness of these plates is about 100 km, they are in constant motion, drifting on the surface of the liquid inner mantle and colliding with each other with monstrous force when their location changes. If they creep on top of one another, huge mountain ranges, such as the Alps and Himalayas, rise into the sky. However, the circumstances that gave rise to the San Andreas Fault are completely different.
Here, the edges of the North American (on which most of this continent rests) and Pacific (supporting most of the Californian coast) tectonic plates are like poorly fitted cogs that do not overlap, but do not fit neatly into their slots. The plates rub against one another, and the frictional energy generated along their boundaries does not find a way out. Where such energy is accumulated in the fault determines where the next earthquake will occur and how strong it will be.
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In the so-called "floating zones", where the movement of plates is relatively free, the accumulated energy is released in thousands of small shocks that do little harm and are recorded only by the most sensitive seismographs. Other sections of the fault - they are called "castle zones" - seem completely immovable, where the plates are pressed against one another so tightly that displacement does not occur for hundreds of years. The tension gradually builds, until finally both plates move, releasing in a powerful jerk all the accumulated energy. Then earthquakes occur with a magnitude of at least 7 on the Richter scale, similar to the devastating San Francisco earthquake of 1906.
Between the two described above there are intermediate zones, whose activity, although not as destructive as in the castle, is nevertheless significant. The city of Parkfield, located between San Francisco and Los Angeles, is in such an intermediate zone. Earthquakes with magnitudes up to 6 on the Richter scale can be expected here every 20-30 years; the last happened in Parkfield in 1966. The phenomenon of earthquake cyclicality is unique for this region.
Since 200 A. D. e. California was hit by 12 major earthquakes, but it was the catastrophe of 1906 that attracted the attention of the whole world to the San Andreas Fault. This earthquake, with its epicenter in San Francisco, caused devastation in a colossal area stretching from north to south for 640 km. Along the fault line, in a matter of minutes, the soil shifted 6 m - fences and trees were toppled, roads and communications systems were destroyed, the water supply stopped, and the fires that followed the earthquake raged throughout the city.
As geological science advanced, more sophisticated measuring instruments appeared that were able to constantly monitor the movements and pressure of water masses below the earth's surface. For a number of years before a major earthquake, seismic activity slightly increases, so it is quite possible that they can be predicted many hours or even days before the start.
Architects and civil engineers consider the possibility of earthquakes and design buildings and bridges that can withstand a certain amount of vibration in the earth's surface. Thanks to these measures, the San Francisco earthquake of 1989 destroyed mainly buildings of the old structure, without damaging modern skyscrapers.
Then 63 people died - most due to the collapse of a huge section of the Bay Bridge. According to scientists' forecasts, in the next 50 years, California is facing a serious catastrophe. An earthquake with a magnitude 7 on the Richter scale is expected to occur in southern California, in the Los Angeles area. It could cause billions of dollars in damage and claim 17,000-20,000 lives, while smoke and fire could kill 11.5 million more. And since the energy of the friction that occurs along the fault line tends to accumulate, each year that brings us closer to an earthquake increases its probable strength.
Lithospheric plates move very slowly, but not constantly. 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 cross the San Andreas Fault, with shifted road markings and signs of regular pavement repairs visible at the fault.
In the San Gabriel Mountains north of Los Angeles, street pavement sometimes swells as forces build up along the fault line press against the ridge. As a result, on the western side, rocks are compressed and crumbled, annually forming up to 7 tons of fragments, which are getting closer and closer to Los Angeles.
If the stress of the layers is not discharged for a long time, then the movement occurs suddenly, with a sharp jerk. This happened during the 1906 earthquake in San Francisco, when in the epicenter the "left" part of California shifted relative to the "right" by almost 7 meters
The shift began 10 kilometers below the ocean floor in the San Francisco area, after which, within 4 minutes, the shear pulse spread over 430 kilometers of the San Andreas Fault, from the village of Mendocino to the town of San Juan Bautista. The earthquake was magnitude 7.8 on the Richter scale. The whole city was flooded.
By the time the fires broke out, more than 75% of the city had already been destroyed, 400 city blocks lay in ruins, including the center.
Two years after the devastating earthquake in 1908, geological research began, which continues to the present day. Studies have shown that over the past 1500 years, major earthquakes have occurred in the San Andreas Fault, approximately every 150 years.
Plate tectonics is the primary process that largely shapes the face of the earth. The word "tectonics" comes from the Greek word "tecton" - "builder" or "carpenter", while plates in tectonics are called pieces of the lithosphere. According to this theory, the Earth's lithosphere is formed by giant plates that give our planet a mosaic structure. On the surface of the earth, not continents move, but lithospheric plates. Moving slowly, they carry the continents and the ocean floor with them. Plates collide with each other, squeezing out the earth in the form of mountain ranges and mountain systems, or pushed inward, creating super-deep depressions in the ocean. Their mighty activity is interrupted only by brief catastrophic events - earthquakes and volcanic eruptions. Almost all geological activity is concentrated along the plate boundaries.
The San Andreas Fault The bold line down from the center of the figure is a perspective view of the famous California San Andreas Fault. The image, created with data collected by SRTM (Radar Topographic Exposure), will be used by geologists to study the dynamics of faults and the shape of the Earth's surface resulting from active tectonic processes. This segment of the fault is located west of Palmdale, California, approximately 100 km northwest of Los Angeles. The fault represents an active tectonic boundary between the North American Plate on the right and the Pacific Plate on the left. In relation to each other, the Pacific platform from the viewer, and the North American platform towards the viewer. Two large mountain ranges are also visible: on the left - the San Gabriel mountains, on the upper right - Tehachapi. Another fault - Garlock, lies at the foot of the Tehachapi ridge. The San Andreas and Garlock faults meet in the center of the image near the town of Gorman. In the distance, above the Tehachapi Mountains, lies the Central California Valley. Antelope Valley is visible along the base of the hills on the right side of the image.
The San Andreas Fault runs along the line of contact between two tectonic plates - the North American and the Pacific. The slabs are displaced relative to each other by about 5 cm per year. This leads to strong crustal stresses and regularly causes strong earthquakes with an epicenter at the fault line. Well, small tremors occur here all the time. Until now, despite the most careful observations, it has not been possible to identify signs of an impending large earthquake in the data set on weak shocks.
The San Andreas Fault, cutting across the west coast of North America, is a transform fault, that is, one where two plates slide along each other. Near transform faults, earthquake foci are shallow, usually at a depth of less than 30 km below the Earth's surface. Two tectonic plates in the San Andreas system move relative to each other at a speed of 1 cm per year. The stresses caused by the movement of the plates are absorbed and accumulated, gradually reaching a critical point. Then, instantly, the rocks crack, the plates shift and an earthquake occurs.
This is not a frame from the filming of another disaster film, or even computer graphics.