Ralph Waldo Emerson once said, “we learn geology the morning after the earthquake.” Fortunately for those living along the San Andreas Fault line in California, there are people behind the scenes, from geologists to city and emergency planners, who have no intention of waiting that long.
The San Andreas Fault Line, first identified in 1895 by Professor Andrew Lawson of UC Berkeley, is an 800-mile fracture in the Earth’s surface, stretching from the Gulf of California to San Francisco, and is one of the longest faults in the world. It forms the boundary between the Pacific Plate and the North American Plate, with a complex network of smaller faults branching off the main San Andreas line which are responsible for a majority of the areas earthquakes.
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It was named after the San Andreas Lake, a small body of water that had formed in a valley between the two plates. The fault was first exposed to geologists when the cliffs of Mussel Rock collapsed during the 1906 earthquake.
Back then, no one understood how or why the two rocks were next to each other until around 40 years ago when the theory of plate tectonics was introduced. The purpose of the tectonic theory was to explain the process of earthquakes, not just around the San Andreas Fault, but also on the others that ran concurrent to it.
The theory concluded that around 200 million years ago, the heavy Pacific Plate collided with the lighter North American Plate, and started sliding underneath, a process known as subduction. This continued for 100 million years, until some 20 million years ago, when the Pacific Plate was forced to change direction and started sliding north, creating the San Andreas Fault. Most of California’s population sits on the west side of the fault, the Pacific plate, while the rest of North America is sitting on the east side of the fault, the North American
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plate. California’s earthquake history is short.
Since record keeping began, sometime in the 18th century, there have been 13 major earthquakes along the San Andreas Fault. However, radiocarbon dating has proved that earthquakes have been happening along the fault for thousands of years. The earliest recorded earthquake happened on July 28, 1769, and was experienced by Spanish explorer Gaspar de Portola while he camped along a small lake he named “San Andreas Lake”. Other notable early earthquakes occurred in 1836, 1838, 1865, 1868, and 1890. Unfortunately, there is no seismographic data recorded for these early earthquakes since it was not until 1887 that seismographs began being used in the United
States. Even before modern historical records, the Native American inhabitants living along the fault line experienced their own disasters, and with them came their own legends and mythology. On the night of January 29, 1700, an earthquake rocked the northern coast of California, up through Washington, and even into Vancouver. The Yurok tribe of northern California believed the God, Earthquake, was running up and down the coast, causing the earth to “quake and quake again and quake again.” The Quileute and Hoh people thought that Thunderbird and Whale were having a terrible fight, making the mountains shake and uprooting trees, and the Nuu-Chah-nulth people said that while in the mountains, a person accidentally kicked a drum and got “earthquake foot” and every step he took caused an earthquake. The two most famous earthquakes in California since the area was first settled by the Europeans were the 1857 Fort Tejon earthquake in Southern California and the 1906 San Francisco earthquake. Both grabbed the attention of the nation and thrust California into the spotlight as the earthquake capital, and the San Andreas as an earthquake research hotspot. The first of the two biggest earthquakes happened when on the morning of January 9, 1857, central and southern California shook as an estimated 7.9 magnitude earthquake hit the coast, rupturing the earth along the southern section of the San Andreas for approximately 225 miles. The shocks of the earthquake are reported to have last anywhere between one and three minutes. Despite the severity of the earthquake, and the distance it traveled, the greatest of the damage was in Fort Tejon, an area that was nowhere near the epicenter. As such, the event was, and is still today, referred to as the Fort Tejon earthquake. The earthquake was the last big one to occur along that section of the fault. Despite its magnitude, only two casualties were recorded. This was most likely due to the landscape of the area at the time with that part of California being sparsely populated. However, the environmental damage was extensive. Many of the area’s lakes and rivers had their water tossed over the banks, displacing fish, and creating dry beds. In some cases, streams even turned upstream, changing the direction the water ran. Cracks opened in the ground, trees were uprooted, artisan wells either dried up or overflowed, and new springs were formed as a result. Lasting evidence of the earthquake can still be seen today in the Carrizo Plain, an area which crosses the line of the San Andreas Fault. In this plain is a dried up river bed known as Wallace Creek, which travels an unusual path. The river once flowed straight, but as a result of the 1857 earthquake, the creek was dragged away from its original course. Today, aerial photos show the bed making a sharp turn to the right, and a few hundred feet later, a 90 degree turn to the left.
The Long Point Fault is located in Harris County, which covers 83,450 square miles located with in Houston, Teaxas City Limits. Research specifies that there are three sections of the Long Point fault that appear to be active; some sections of the Long Point fault have averaged more than 2 cm per year of vertical offset over the last 20 years. Evidence of the faults concludes it is a natural fault. The reason for activity is not caused by man, even though man’s activities are not helping the issues, but clearly humans are not the initial cause, biological activity can be in fact an adiitional cause for its movement. A brief description of the type of fault and its relationship with the strata and the faults beneath the Houston area, are at depths of 1,000 to 4,000 m. They have been well-defined through the study of well logs and seismic lines. Studies have resuted in assumuptions that some of these subsurface faults penetrate younger sediments at shallower depths, and contain faults that have of set the present land surface to produce recognizable scarps. (Gabrysh)
Most of Arizona’s earthquakes are associated with the San Andreas fault as most of Arizona’s earthquakes are shocks from epicenters located in California. Arizona has had earthquakes with epicenters located in its borders and just like the ones located near the San Andreas fault, they are linked to a transform plate boundary and are dip-slip earthquakes. Much of the focus of these earthquakes can be centered around the Grand Canyon as much of the after-effects of these earthquakes caused phenomenons to occur in the Grand Canyon. Many rockslides took place in the Grand Canyon and plenty of the cracks found in the canyon’s rock layers are attributed to some of the earthquakes that took place in Arizona since the geologic landscape formed its current
Earthquakes are a natural part of the Earth’s evolution. Scientific evidence leads many geologists to believe that all of the land on Earth was at one point in time connected. Because of plate tectonic movements or earthquakes, continental drift occurred separating the one massive piece of land in to the seven major continents today. Further evidence supports this theory, starting with the Mid-Atlantic ridge, a large mass of plate tectonics, which are increasing the size of the Atlantic Ocean while shrinking the Pacific. Some scientists believe that the major plate moveme...
The west coast of North America has been tectonically and volcanically active for billions of years. The Sierra Nevada Mountains in eastern California were born of volcanoes, and magma has been erupting in the Long Valley to the east of the mountains for over three million years (Bailey, et. al., 1989). However, the climactic eruption of the region occurred relatively recently in the region's geologic history. About 760,000 years ago, a huge explosion of magma warped the Eastern Sierra into the landscape that exists today. The eruption depleted a massive magma chamber below the earth's surface so that the ceiling of the chamber imploded, forming what is now known as the Long Valley caldera. The caldera is at the eastern base of the Sierra Nevada Mountains, about 50 km northwest of the town of Bishop, and 30 km south of Mono Lake (Bailey, 1976).
The science of the natural disaster has baffled many, but from studying the San Francisco earthquake, scientists have made a number of important discoveries and they have a better understanding of earthquakes. At 5:12 on a fateful April morning in 1906, the mammoth Pacific and North American plates sheared at an incredible twenty-one feet along the San Andreas fault, surpassing the annual average of two inches (“San Francisco Earthquake of 1906”)(“The Great 1906 Earthquake and Fires”). The shearing caused a loud rumble in the Californian city of San Francisco. A few seconds later, the destructive earthquake occurred. The ground shifted at almost five feet per second, and the shaking could be felt all the way from southern Oregon to southern Los Angeles to central Nevada (“Quick”)(“The Great 1906 San Francisco Earthquake”). Moreover, the earthquake could be recorded on a seismograph in Capetown, South Africa, an astounding 10,236 miles away from San Francisco (“San Francisco ea...
From studying the science behind the San Francisco earthquake, scientists have made a number of important discoveries involving how earthquakes function. At 5:12 on a fateful April morning in 1906, the mammoth Pacific and North American plates sheared each other at an incredible twenty-one feet along the San Andreas fault, surpassing the annual average of two inches (“San Francisco Earthquake of 1906”) (“The Great 1906 Earthquake and Fires”). A few seconds later, the destructive earthquake occurred. The ground shifted at almost five feet per second, and the shaking could be felt all the way from southern Oregon to southern Los Angeles to central Nevada (“Quick”) (“The Great 1906 San Francisco Earthquake”). In fact, the earthquake could be registered in a seismograph on Capetown, South Africa, an astounding 10,236 miles away...
...tectonic movement of the plates, the stress forms along the fault and ultimately releases as an earthquake. On the pacific plate, Transform boundary along with the San Andreas fault. Transform-fault boundaries is when two plates that slide horizontally past another. Transform boundaries are usually found on ocean floor, but a few occur on the land. San Andreas fault zone is a transform fault, which connects East Pacific rise, in the south a divergent boundary, with South Gorda-Juan de Fuca-Explorer Ridge, yet another divergent boundary to the North. Ultimately because it’s a transform boundary, convergent boundary is strike-slipping past each of the plates in order to release pressure. As the San Andreas Fault is prime transform boundary between the North American Plate and the Pacific Plate, the Hayward Fault assumes a share of the total motion between the plates.
Before examining the Northridge event, understanding the naturally occurring hazard that is an earthquake will help to better understand exactly what happened and why it was such an important geological event. With four distinct layers, two layers, the crust and upper portion of the mantle, compose the skin that is the surface layer of the Earth. The crust is not a single, continuous piece. It is actually several different pieces, or plates, that come together to form the puzzle that comprises the surface of the Earth. These plates are in constant motion rubbing against one another. These areas, known as fault lines, where the plates rub up against one another have spots where one plate ”gets stuck while the rest of the plate keeps moving. When the plate has moved far enough, the edges unstick and is how most of the earthquakes around the world occur” (Wald, 2012). The energy stored from the friction of the two plate...
study of the San Andreas fault system." (USGS) When the 1906 earthquake struck scientist set
It is well known that glaciation is the cause for how Yosemite looks today, but it is not as well known what happened before the relatively recent glaciation which happened about 15,000 years ago. The geologic history of Yosemite and the surrounding area starts 500 million years ago in the Paleozoic Era when the area was still under the waters of the Pacific Ocean (Beatty). This area had a passive fault, similar to the east coast of the United States today. The mud and silt from the ocean settled in the Yosemite area and eventually became shale, siltstone, and carbonate rocks (United States of America). By the end of the Ordovician Period, the fault changed from a passive to an active fault. The oceanic plate started to subduct under the continental crust and push the shale upward, forming the first mountains in the western United States. At first, these were volcanic islands off the coast. This formation is called the Shoo Fly Complex. T...
The earth is split into four layers, inner and outer core, the mantle and crust. The top of the mantle and crust make up what is like the skin of our earth (see source 2). The skin is split up like a puzzle and we call these puzzle pieces’ tectonic plates (see source 1). These plates are constantly moving and the plate boundaries (edges of the plates) move and slide past one another. Sometimes as the plates move the plate boundaries become stuck. Pressure builds up in the stuck area over time and eventually breaks. This is why earthquakes occur due to the sudden movement of the plate sliding and breaking creating a fault line to go off. The fault line is the line on which the
Tectonic Plates are what cause many of earths natural disasters. These can come in forms such as volcanoes, earthquakes and tsunamis. The earthquake of San Francisco was one of the most devastating earthquakes in the earths history and had ended in tragedy (Quinton et al, 2012, p189). These tectonic plates also resulted in the change of earths continents. More than 200 million years ago, all of Earth’s continents were combined into one super continent called Pangea. This continent slowly separated into 7 others we know of today (Quinton et al, 2012, p176). There are many known theories to why the Earth’s continents have changed overtime, such as the Continental Drift and Seafloor Spreading theories. These two theories help to explain the worlds creation, one of the most unknown mysteries of today.
In conclusion the world that we live in has many interesting things. From different types of faults to different types of fault zones. Each with their own interesting facts and information about them. What is know about the San Andreas and what it does for the earth either good or bad might not that extensive but what we do know is that nature will find a way to make something happen on the earth so that it will better benefit it in some way. So that by having this giant crease looking thing stretching almost the entire length of the state of California it some how benefits us.
Understanding the plate tectonics theory is very important, especially when investigating natural disasters like earthquakes, and volcanic eruptions. It is also gives scientists the ability to understand how mountains were formed between two tectonic plates. There are three types of interactions between plate boundaries: convergent, divergent and transform. Looking back at the history of these three different interactions, earthquakes, like the one in Haiti, volcanic eruptions, like at Mount St. Helens, and the creation of mountain belts, like the Mid-Atlantic Oceanic ridge, gives information on future consequences of tectonic movement, and what can happen when the plates interact with each other.
Earthquakes belong to the class of most disastrous natural hazards. They result in unexpected and tremendous earth movements. These movements results from dissemination of an enormous amount of intense energy in form of seismic waves which are detected by use of seismograms. The impact of earthquakes leaves behind several landmarks including: destruction of property, extensive disruption of services like sewer and water lines, loss of life, and causes instability in both economic and social components of the affected nation (Webcache 2).