Bay Area Fault System

The most dangerous fault in the U.S. is home to the complicates bay area fault system; the Hayward fault. The area surrounding the Hayward fault has a very high population density and a major earthquake along this fault could have deviating results. Since the 1868 Hayward fault earthquake, evidence of creeping has become very apparent along different areas on the fault. This evidence is proof that stress and energy is building in the fault and is ready to be released at any moment.

They San Francisco bay area is no stranger to earthquakes. Studies have shown that earthquakes have been shaking this region since the beginning of time. The North American and the Pacific plates make up the San Andreas fault zone, however, they used to be separated
by a entirely other plate; the Farallon plate. About 25 to 30 million years ago, the Farallon plate subducted completely underneath the North American plate, causing the Pacific plate to remove in (Bay Nature Staff, 2014). Where the two plates meet, they form a transform plate boundary because the Pacific plate moves north and slightly west bound again the North American plate. From this process, a very complicated fault system was formed in the bay area. It is home to many faults that have a high risk of causing major earthquakes. The last time a major earthquake occurred along the Hayward fault was 1868, with a magnitude of 6.8. Today, the fault is overdue for an earthquake of equal or greater size and there is evidence along the fault proving it’s ready to strike at any moment. The only question is when?

The Hayward fault spans across the bay area at about 100 kilometers long.
It branches off of the Calaveras fault in the city of Fremont then runs through the east bay and disappears underneath San Pablo Bay. Back in 1868, this fault cause a very large earthquake. It caused severe damage to towns throughout the bay area, especially Hayward, San Leandro, and Fremont, and killed about 30 people (2010). Today, the bay area is home to three million more people. With such a high population density throughout the bay area, another large earthquake could cause even more damage. The fault runs through major freeways, public transportation services, and many neighborhoods. It is estimated to result in the deaths of hundreds of people and cause more than $120 billion in damage (Alden, 2016). This is why the Hayward fault is suspected to be the most dangerous fault in all of the United
States. Studies have shown that the Hayward fault causes a large earthquake about every 138 years (Alden, 2016). With the last earthquake being 148 years ago, the fault is ready to strike again. In addition, signs of building stress has presented itself along different parts on the fault. These signs come in many different forms. They all show the slow, yet, steady creeping that is occurring along the fault. As the fault continues to creep a couple of inches every year, more and more stress is built up until it finally releases in the form of a major earthquake.

This picture of an offset curb was taken in northern Hayward, on the corner of Rose Street and Prospect Court (37°40’47”N, 122°05’28” W). The offset is very distinct and easy to see between the pavement and brick. The curb has started to move in different directions because of the right lateral slip caused by the Pacific plate moving northbound against the North American plate. In addition, there is also pavement cracking in the intersection along the fault, leading up to the misaligned curb. This is a photo of the outside of the football stadium at UC Berkeley, (37°52’11” N, 122°15’01” W). The Hayward fault runs right through the stadium and presents itself in the structure of the building. There is an expansion joint that is opening in respect to the right lateral offset of the fault overtime. The fault actually lies a few yards east of this opening. The opening represents a weaker area in the stadiums structure that allows the fault to leave its mark. The third photo captures the cracked pavement across a section of Medau Place in Montclair (37°49’37” N, 122°12’38” W).
What the picture doesn’t show is that there are actually several cracks in the pavement in the area around the fault. When following the cracked pavement and fault line, the fault leads straight into a building. On the outside of this building, there are also cracks in the wall right where the fault intersects the building. Like the previous sites, both pieces of evidence show right lateral creeping of the Pacific plate. In this photo, a fence has been parted by the Hayward fault in the outskirts of the city of Hayward (37°38’37” N, 122°03’18” W). The fence was put up with the property line was established in 1858. The gap between the separated fences reaches about 4 feet. This gap is a result of right lateral creeping as well as a slip that probably occurred during the 1868 earthquake. This final image shows a channel along a hillside in Union City that has been offset by the Hayward fault (37°37’34” N, 122°02’11” W). This channel has been shifted about 400 feet by the fault. This is one of the larger slips that can be seen along the fault. Like the fence in the previous example, much of this slip most likely occurred during the 1868 earthquake. When observing the area around the channel, it can be seen how the fault has influenced the formation of this hillside. There are ridges in the hillside along the fault’s
path.

The evidence of creeping along the Hayward fault can be seen at several different locations along the fault. The examples that can be easily spotted include misaligned curbs, fractured or damaged buildings, cracked pavement, separated fences, and misaligned channels. Some areas show more amounts of creep than others but that just shows the varying amounts of stress along the fault. Once the stress in one area is released, it applies the stress to other areas along the fault. As this energy and stress continues to build, it’s creating more potential for a major earthquake such as the one that occurred in 1868. All of this evidence supports the forecast that there is a 2 in 3 chance that the Hayward fault will generate an earthquake of magnitude 6.7 or greater in the next 30 years.