California Earthquakes

Although living in California is thought to be the epitome of the American dream, the Golden State is home to many hazards and puts a threat to the large population. One of the most threatening and unpredictable hazards to the state are earthquakes. According to the theory of Plate Tectonics, California sits on top of two moving plates, which float on top of flowing magma. These two plates, the continental North American Plate and the oceanic Pacific Plate, form a transforms fault boundary most known as the San Andreas Fault. The millions of years of the fault’s lateral strike slip motion are a direct result of California’s many geological features such as the Transverse Mountain Ranges. When these two plates slide against each other, they create friction and put stress on the earth’s crust causing it to move and shake. This is the cause of an earthquake. Because California sits on top of a plate boundary, there are many transform faults all along the state. With the help of Geographic Information Systems and Technologies, or GIS, we can map the fault boundaries to view which parts of the state are at threat to earthquakes. Also, along with analyzing the fault data, we can spatially analyze population, households, schools, hospitals, buildings, and major freeways that are close to or intersect the faults at a local level to assess the possible damage that could occur from an earthquake. Furthermore, a map of major historic earthquakes could be a helpful visual to help assess and predict when the next possible earthquake could be.

By creating a map of California using ArcMap, we can see where the major and minor faults in California are located. Although knowing where the faults in California may help in predicting earthquakes, many times the epicenter (point on the surface directly above the focus) of earthquakes do not happen directly above a fault. They usually happen around or near a fault boundary as you would notice in the map that locates the major historic earthquakes of California. However, by knowing where the fault boundaries are located in California, we can study the areas around those boundaries and assess the risk and vulnerability of a city. 

Furthermore, mapping the historic earthquakes in the State of California can be very educational. By geotagging the locations of past earthquakes and categorizing them by magnitude, deaths and dollars in loss, we can learn from those past events and try to better prepare for the future. We can use the data information and assess how and why there was so much property damage or loss of life due to an earthquake. For example, the 1906 San Francisco Earthquake was a magnitude 7.8 and caused many deaths, injuries, and property damage. There was so much, now we know how much damage can occur from an earthquake that strong. Also, there are laws like the Public Fields Act, stating that all buildings in California must be retrofitted and earthquake safe to minimize damage. By knowing the magnitude of past earthquakes and learning about how they affected a city or area, we can learn from the damages and be better prepared for the future. 

By locating the fault boundaries in California on a map, we can analyze the possible threats an area is at risk of. In the case of Los Angeles, there are multiple faults that run through the county, as you can see in the map. Therefore many structures are at risk of shaking of the earth. Despite the Public Fields Act stating that all building are to be retrofitted or earthquake safe, these buildings could still be at risk if they are close enough to a fault boundary or epicenter of an earthquake that is rated higher than 6 on the Richter scale. Therefore, it is important to map structures that are within a significant distance of fault boundaries because these structures are at most risk. 

Locating schools and major buildings within 0.25 miles of fault boundaries are at major risk to earthquake damage. From the data provided on the UCLA GIS data site, we can locate these features using the select by location feature and display it in the map. Also, mapping the hospitals a mile away from the faults we can try to determine the possible damage to those important hospitals. The area for hospitals is extended a mile away from the faults because the loss of an important hospital could be a serious problem in a natural disaster because this will reduce the amount of emergency aid and resources. Furthermore, freeways that intersect a fault are at risk of major damage. The resulting map shows that there are 237 schools, 62 buildings, 46 hospitals and 41 freeways at risk of damage in the event of a serious earthquake in Los Angeles area.

Because Los Angeles is one of the most populated areas in the United States, many people and homes are at risk of injury and loss of property. By creating a map with the breakdown of population by city, we can see the areas that are most populated and the areas with the most house units and can analyze what areas could possibly face the most in property damage. 

Of course depending on the magnitude and location of a future earthquake, people and their properties will be affected differently, but by creating this map, we can have a better understanding of the potential damage could be in different scenarios. The most populated area in Los Angeles County is Los Angeles City and it has the most housing units. Other populous cities with many housing units are: Santa Monica, Long Beach, Thousand Oaks, Simi Valley and could potentially face major life risk and property loss. 

In conclusion,  by using GIS, we can evaluate the potential risks that people have by living in Los Angeles. By viewing the past earthquakes and seeing the damage they have done, we have an idea of how to prepare for the next big earthquake. We can not only see what schools, buildings, hospitals and freeways are at risk of damage but also the potential population and house units in danger of being injured or killed or destroyed. By using GIS and technologies we can better understand the occurrence and threat of earthquakes in California and Los Angeles.


Final Map Layout