Plate Tectonics Paper

Plate Tectonics Press Release
GLG/220
November 17, 2014
Leticia Kozbial-Brown

Good Afternoon. My name is Leticia Brown and as Director of Earthquake Preparedness for Los Angeles I would like to address public education on earthquake preparedness. Earthquakes happen when the two sides of a fault slip suddenly against each other. The Pacific and North American plates move past each other about one and a half inches a year. The friction between the plates causes stress, which is released when the blocks of crust slip suddenly along a fault plane. This releases waves of energy that travel through the ground and causes the shaking that you feel. Los Angeles is situated along an active transverse plate boundary that is also known as the San Andreas Fault. Other fault lines that cross Los Angeles include the Santa Monica Fault, the San Fernando Fault, and the Northridge/Santa Barbara Fault. A fault is a fracture or break in the crust along which one side has moved relative to the other side. Faults can be small or they can be hundreds of miles long. The earth’s crust is made up of very large plates that are very slowly but constantly moving. Part of California is on the Pacific Plate and part is on the North American Plate. The San Andreas Fault, which is 810 miles long, is the boundary between these plates. It runs from the Salton Sea in Imperial County to Cape Mendocino in Humboldt County. Faults can up and down, or horizontally. The San Andreas Fault is moving horizontally in opposite directions, which means that Los Angeles is moving closer to San Francisco ("A Whole Lotta Shakin' Goin' On", 2014). Some faults are well known and easy to see, while others are underground with nothing on the surface to reveal their presence. These are called blind thrust faults. The 1994 Northridge earthquake was caused by a blind thrust fault. There are hundreds of identified faults in California. More than 70 percent of the state’s population resides within 30 miles of a fault where high ground shaking could occur. Every year California averages two or three earthquakes that are large enough to cause moderate damage to structures. That is, an earthquake with a magnitude of 5.5 or higher. Building codes are often updated as new information because available to allow us to erect safer buildings and structures. While earthquakes do pose a deadly threat, there are significantly less earthquake related deaths in California as compared to places such as Turkey or China that have less stringent codes and enforcement. In 1857, the Fort Tejon Earthquake measured 8.0 on the Richter Scale. This is classified as the greatest earthquake in modern history. At the time of this quake Southern California was sparsely populated. While the effects of the quake were frightening, if the same earthquake happened today the damage would easily cost billions of dollars and the loss of life would be quite high. Other historical earthquakes include the 1933 Newport-Inglewood Fault that had a magnitude of 6.4 and resulted in 12o deaths and over $50 million in damaged property. Many of the damaged buildings were constructed of unreinforced masonry. More recent earthquakes have caused billions of dollars in damage and hundreds of death and thousands of injuries. These include the San Fernando Earthquake of 1971, the Whittier Narrows Earthquake of 1987 (5.9), the Sierra Madre Earthquake of 1991 (5.8), and the Northridge Earthquake of 1994 (6.7) ("Historical Disaster Information", 2014). Seismic-Hazard is the study of expected earthquake ground movements at the surface of the earth and the likely effects on existing natural conditions and on man-made structures for public safety concerns. The results of these studies are published as Seismic-Hazard Maps

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