The geological structure of our planet's Earth's crust has numerous geographical features. One of them is faults. The most well-known fault worldwide is the San Andreas Fault. It is one of the best known with one of the strongest displacements that it has had in the whole world and it is the one that frequently causes high-level earthquakes.
In this article we are going to tell you everything you need to know about the San Andrés fault, what is a fault and what are the types of faults that exist.
What is a failure
Geological faults are cracks or crevice zones between two rocks in the earth's crust. It is a discontinuity formed by the rupture of two large rocks due to the tectonic force exceeding their resistance. This causes slippage between each other. Failures can occur quickly or slowly, and can also be a few millimeters or thousands of kilometers.For example, the San Andreas fault is considered the most dangerous fault in the world.
Before any construction takes place on undeveloped land, geologists must analyze the soil to determine its suitability for construction. Some faults are clearly visible, but over time, other faults can become very unclear. Although not all are classified as hazardous, the movement of this "scar" earth is unpredictable. To learn more about the effects of faults, you can check out our article on cleats and its relationship with earthquakes.
Cause of earthquakes
The natural forces derived from the earth's crust cause the movement of rock blocks or large areas of tectonic plates. The edges and composition of these plates are full of bumps, roughness and unevenness, which slow down the speed of movement and accumulate energy.
This energy accumulated at a certain point must be released, so it will suddenly break and slide due to weight and gravity. Finally, the arrangement of the plates is represented by seismic waves that produce vibrations. To better understand this phenomenon, we invite you to read about the earthquakes and how they are measured.
All these activities are not always perceived by the outside world in the form of violent earthquakes, unless the movement is too fast and the block slides a few meters.
Types of failures
There are three types of failures in the world. Let's see what they are:
- Inverse: They are also vertical slip faults, the difference is that the roof block moves up with respect to the other block. The forces generated by these types of faults are large, which means that the two blocks are pushed towards each other, forming an oblique slit.
- Normal: It is a slide by immersion where one block is lower with respect to the other. That is, it is a vertical movement. It originates from tectonic plate distension or separation. These types of faults are usually small, with a displacement of approximately one meter, but there are exceptions that extend for tens of kilometers.
- Horizontal or scrolling: As the name suggests, the movement is horizontal, parallel to the direction of the fault. It can move to the right, called a right rotation, or it can move to the left, called a synesthetic.
The most studied and well-known horizontal or strike-slip fault is the San Andreas Fault, which has produced earthquakes due to rightward or dextral movement. The magnitude of these events can be tracked through studies that analyze the California seismic activity.
San Andrés fault
On April 18, 1906, the world gave full attention to the San Andreas fault. A displacement of the fault caused a strong earthquake in San Francisco, United States, killing more than 3.000 people.
The San Andreas Fault is a huge deformed fissure in the Earth's crust, about 1.300 kilometers long, that extends from the northern edge of the Gulf of California and passes through western California in the United States. The tectonic movement recorded by this 15-20 million-year-old fault has attracted public attention due to the intensity of the earthquake. After that day in 1906, in 1989 and 1994, the failure clearly indicated that it would continue to operate.
The San Andreas is not just any fault. It represents two major plates of the Earth's crust: the Pacific Plate and the North American Plate. Unlike the United States, the Pacific Plate slides laterally. Therefore, it is classified as a strike-slip fault. The complexity of this behavior is also related to studies on the force of earthquakes.
Changes of the San Andrés fault
The fault has undergone several changes during its existence, moving only a few centimeters a year, and it partially slid at 6.4 m in the 1906 earthquake. Some scientists engaged in their research have even discovered vertical movement.
In other current studies, the San Andreas Fault near Parkfield, California, has been found to have an earthquake of approximately magnitude 6 every 22 years. Seismologists predicted it would happen once in 1993, but it didn't happen until 2004. Scientifically speaking, this is a relatively close number, so this area of California has served as the subject of important research on earthquakes and their behavior. For those interested in visualizations, a shocking video showing all earthquakes since 2001.
Danger of the San Andreas fault
The San Andrés Fault is part of the Pacific Ring of Fire, which covers more than 40.000 kilometers of areas with frequent earthquakes and volcanic activity. The fire zone or ring of fire extends from New Zealand to South America, bordering Japan to the north, the Oletian Trench, and North and Central America.
Very close to the San Andreas fault zone is California, as well as smaller communities with an average population of 38 million. Experts warn that earthquakes triggered by the tectonic movement of fault plates will be devastating. However, people should prepare for possible mild and frequent tremors. Likewise, the most modern buildings, bridges and roads are being built to resist earthquakes and absorb seismic waves. It is impossible to actually predict the earthquake, but the fact is that San Andrés is still alive.
The threat that geologists are most concerned about comes from the south side. Soil investigation shows that the north was destroyed in 1906 and the central part was destroyed 160 years ago, but the south kept everyone on guard.
There is an earthquake in the far south about every 150 years, but almost 300 years have passed without any record of movement. Therefore, once released to the outside, the accumulation of energy underneath can be devastating. In the event of a major earthquake with a Richter scale greater than 7 degrees, the population of Los Angeles will be more severely affected, with at least 2,000 people in danger of death.
I hope that with this information you can learn more about the San Andrés fault and its characteristics.