California is home to many fault lines that run throughout the state. The San Andreas fault is known as the most famous fault in the world due to its size and reputation. The major hazard that can be caused by the fault is earthquakes. California is no stranger to the effect of earthquakes. To understand what makes a fault line so dangerous, we must first look into what defines a fault line and what causes earthquakes to form.
A fault is a planar crack in a rock where slippage has taken place. Faults range in various sizes around the world. They can be small (sometimes microscopic), or they can span for miles. There are three set classifications for faults that correspond to the direction in which the space between the rocks on either side move. One kind is a normal fault (or dip-slip). This is when the movement of the block above the fault moves downward. Another type of fault is the reverse fault. This is when the block above the fault plane moves upward instead of downward, compared to the normal fault. The final fault type is the strike-slip (Transform) fault line. This occurs when two blocks move in a horizontal direction, rubbing against one another. The SAF is an example of a right lateral transform fault. This means that if you were to stand on one side of the fault and face the other side, everything will move to the right on the opposite side of you. Transform faults can also be classified as either convergent or divergent. Convergent faults raise pressure ridges and mountain ranges. Pressure ridges form where lateral motions force rocks into small spaces and push them upwards. Divergent faults create gaps, such as trenches.
The San Andreas Fault is made up of the North American plate and the Pacific plate. It is estimated to be about 28 million years old. It began when the East Pacific rise was subducted under the North American plate around what is now called Los Angeles. Over time the fault has gradually grown and still is.
The average slip rate of the fault is about 1.5 inches per year. Meaning the two plates are moving 1.5 inches apart from each other every year. In about 25 million years, the state will be unrecognizable due to the slipping as well as the plate grinding and earthquakes. (To the left is an aerial photo of the San Andreas fault)
The fault is around 700 miles in a straight line and around 800 miles when the curves are measured. It reaches roughly 10 miles into the Earth’s crust. The SAF is the largest fault line in the world and creates many real threats for anyone living on or near it. The largest and most potential threat being an earthquake. The plates are constantly moving and some portions tend to get stuck on one another and build up stress. When the rocks suddenly break or slip, this is called elastic rebound, and is a large cause of earthquakes. Seismic waves are then produced and shake the surface of the Earth. Because of the type of earthquake to be caused by the SAF would be a strike-slip compared to a thrust earthquake, which are far more likely to generate tsunamis. The main way a tsunami could be formed around the San Andreas fault would be if there was a landslide into the ocean that ended up displacing enough water.
As of 2017, California is home to 39.54 million people. That comes around to about 239.1 persons per square mile. In a state that in 2010 was measured at 155,779.22 square miles. The state houses a wide variety of urban and rural dwellers. Many of the urbanites live in large cities such as Los Angeles, San Francisco, San Bernardino and San Diego. There are rural and suburban dwellers as well. Most living just outside cities or not far from them. Farms can be found in the state producing anything from cattle to grapes for wine.
The state has a wide variety for race as depicted in the image below.
California also is known to be a very expensive area to live in no matter what city you’re in. The median income per household in 2016 was $63,783 and the median per capita was $31,458. The state also has a combined poverty total of 13.3%. Many of these people living in poverty or below the median threshold for income are living in poor urban areas. Most of which are inhabited by members of the black and hispanic/latino community. These are the people that are not going to be able to recover from a devastating earthquake due to their low income. Their homes are also not going to be as well built as wealthier people living in suburban or wealthy, center-city areas. They will not be able to withstand such an event, such as a major earthquake, to have much of the house remain standing. California is also heavily populated with tourists all year round due to Hollywood and their always sunny beaches. If an earthquake were to happen, thousands of people would have to rely on wherever they are staying to ensure their safety.
The San Andreas fault has long been known to cause many earthquakes in California despite not producing the largest ones ever recorded for the state. The problem lies with how many people live close to or on the actual fault line which puts them even more at risk of experiencing an earthquake event. One major earthquake resulting from the SAF was the 1906 San Francisco earthquake and fire.
The earthquake began at 5:12 am on April 18, 1906 and was a magnitude of 8.3 on the Richter Scale. The scale in which it inflicted damage was 70 miles wide by 350 miles long. Most of the damage happened in the San Francisco bay area. In San Francisco (which was the largest city in California at the time) there were fires caused by downed electrical lines, cracked gas lines and from damaged stoves. The fire was a secondary hazard caused by the earthquake. The water mains underground had became damage as a result of the shaking and fire departments were not able to battle the fires that had been started. The fire ended up burning for another two and a half days after the earthquake. Most of the central business district was destroyed along with other densely populated residential areas.
At the time, there was a reported 700 dead from the incident, but now, it is estimated to have been in the several thousands. The earthquake and fire combined left more than 200,000 people homeless and displaced. Many homes were destroyed because wood and brick were the main resources used to build structures at the time. Most of the people affected also tended to be poor, lower class citizens living in overcrowded apartment buildings. The total for property damage came to $500 million (1906 dollars). In 2001 dollars it would equal out to around $10 billion in damages to property.
After this event there was definite evidence that shows that California might not be the safest place to live in the U.S. in terms of natural hazards. Today, California is a very popular place to live because of the stigma that all the important and wealthy people live there. This makes people’s judgment on the risk of an earthquake happening clouded. Some people are fine with the idea that it could happen due to the fact that now we can predict these kinds of events more efficiently and we have building codes designed for areas prone to quakes so they can have little to no damage. At the same time, these people might believe that because their building is up to par with safety standards, that they would not need to potentially evacuate when an earthquake erupts. This stigma would interfere with other risk reduction strategies. In other parts of the world, people may have no choice but to live somewhere prone to earthquakes due to the countries economic standings. There could be nowhere else for them to go. So for more affluent people, they might take the risk because they are able to mediate the potential hazard while other poorer people might have to live in a place like this due to low income and instability.