Earthquake Dangers to the California State East Bay Campus - Research Paper Example

Earthquake Dangers to the California East Bay Campus Introduction San Francisco Bay area is considered most sensitive to the earthquake as about 100 kilometers long faultline passes through it in the Earths crust. In 1868, the earthquake with magnitude of nearly 7.0 struck around Hayward faultline and considered to be the most destructive one in the California history. As per USGS scientist, the Hayward fault can crack anytime from now and cause a powerful earthquake of the same or higher magnitude. The impending earthquake can cause a huge loss of life in the region. (Alden, 2010) San Andreas Fault–A Main Source of Earthquake San Andreas Fault is a main source of earthquake and it is roughly 625 miles long and passes through California, U.S. The fault is a strike-slip fault and located between the North American Plate and Pacific Plate. Land on the west side of the fault is moving gradually to the northwest while the land on the east side of the fault is moving toward southwest side. This movement is found to be 0.2 inch per year. (Alden, 2010) The study of San Andreas Fault is important from the view point of earthquake science. Californias rich mineral wealth and unusual landscape is due to this fault. The earthquakes along this fault line have affected people enormously and have taught people how to prepare for natural disasters. (Alden, 2010) Relationship between San Andreas Fault and Hayward Fault The San Andreas Fault is not a single break fault. It has several major and minor branches in southern California. The fault is a longest of its kind in the world. Starting from Point Arena, north of San Francisco it ends at Salton Sea covering distance of almost 625 miles. In the San Francisco Bay area, the San Andreas splits into two major branches. The east side of the Bay runs Hayward fault carrying high probability of would-be earthquake. The San Andreas fault extends deep into the earths crust between four to ten miles. Thus, being a shallow fault it is more destructive at the surface compared to the one that originates from deep-seated faults. (The San Andreas Fault System 2011) Map Showing Hayward Fault Source: http://earthquake.usgs.gov/regional/nca/haywardfault/tiled/ Why Hayward Fault is so Important From Fremont to San Pablo Bay running almost 40 miles, the Hayward Fault passes beneath the surface of the most densely populated regions of the California State. It is estimated that two million people stay and work along the faultline. Schools, gas lines, trauma centers and many other establishments are located near the fault. A powerful earthquake of the magnitude 7 or above along the Hayward fault may occur any time in next 30 years making a colossal loss in North California. Geologists have found deformed curbs and cracked lines in areas near the fault giving evidence of creep. Major earthquake along the line had occurred almost 140 years back and that is the usual frequency of a major earthquake along this faultline. That is how Hayward fault in this region has gained special importance among the geologists (Bay Area Faults and Earthquake …2008). The Study of Fault Fault activity is studied using seismographs that help to know about the fault behavior patterns. The study of sediments is done by digging tranches across the fault line. The study done at hundreds of places provides a detailed earthquake history. It has been found that major event on the fault occur almost every 150 years though large uncertainty prevails. The California Geological Survey has been actively studying and mapping states major faults including the Hayward fault. It maps two major hazards: liquefaction, and landlslides. Liquefaction indicates loss of strength of land due to shaking and that may cause buildings to fall. Landslides may take place where steep slopes are there either along riverbank or in the hills. (Alden 2010) Fault Types Fault has caused complex geology and diverse landscape in California. Many underground traps are created by faulting and that has helped construct huge reservoirs of crude oil, water, or precious metal ores. A following map shows various branches of fault across San Andreas Fault. Source: http://www.consrv.ca.gov/cgs/information/publications/teacher_features/Pages/faults.aspx Fault can be classified depending upon the movements of rocks on both sides. Dip-Slip Movement If the movement of rocks on both side of the fault is an up or down type then it is known as dip-slip movement. Source: http://www.consrv.ca.gov/cgs/information/publications/teacher_features/Pages/faults.aspx The Sierra Nevada fault zone is the example of such fault. (California Geological Survey 2007) Strike-Slip Movement If the rocks on each side of the fault make a sideways movement then it is known as strike-slip movement. In strike-slip fault rocks move in parallel passing each other. The San Andreas is an example of strike-slip fault displacing rocks up to tens and hundreds of miles. The horizontal movement causes rocks of different composition to place side by side. Furtehr, the San Andreas Fault is composed of several minor and major faults, this kind of movement may occur anywhere along the faultline. (California Geological Survey 2007) Source: http://www.consrv.ca.gov/cgs/information/publications/teacher_features/Pages/faults.aspx Previous Earthquakes along the Hayward Fault Dating the soils across a fault is a technique used to find the past history of the Hayward fault. This determines how often the earthquakes have occurred in the past and its magnitude. Geologists do various observations such as fault trenches, geomorphic expression and fault creep (Urbanization of the Hayward Fault 2010). New Findings along the Hayward Fault The two terms recurrence interval and seismic gap are meaningful from the standpoint of happening of earthquakes which can be defined as per the following. Recurrence Interval The recurrence interval is defined as the average time period between two large earthquakes at a specific site. (Recurrence Interval 2009) Seismic gap A locked fault area that is free from any seismic activity for a long time. No earthquakes have been observed in certain seismic gaps. They have potential to cause big earthquakes as stress accumulates in seismic gaps. (Seismic gap 2009) The US Geological Survey has warned the occurrence of big earthquake anytime along the Hayward Fault as it has completed 140 years since the last major earthquake happened in 1868. New results of age-dating studies, imagery of deformation and creep, 3-D geometric as well as mechanical models indicate about a repeat event of the equal magnitude. Data obtained from the studies suggest that the average interval time of 10 earthquakes before 1868 was 170 years; however, last five of these had occurred at a time gap of 140 years. During these years the population in the region has increased several fold and so the risk to the people in the area. A 3-D geological model has been used to understand the Hayward-Calaveras fault junction. Deep seismicity has suggested linkages between Calaveras and Hayward faults and together they can generate an earthquake of magnitude higher than 7. Recent 3-D geologic mapping and relocations of earthquakes have indicated that the fault geology and geometry at depths is different than found at the surface. The inference of these studies now treats the Calaveras and Hayward faults as a single unit. This certainly places San-Francisco Bay region at high risk. (Californias Hayward Fault Revealed 2007) Hayward Mitigation Plan When earthquake of large magnitude is imminent in Hayward, it requires having a good preparedness to reduce the loss of life, economic disruption, personal injuries and property loss. In last three decades following series of actions have been taken to mitigate the effects of earthquake in Hayward city and region through the funding from Federal Emergency Management Agency (FEMA). In 1986, California State enacted a law that required all communities to register potentially hazardous Unreinforced Masonry buildings before January 1990. In 1987, Hayward created a Mitigation Task Force to find seismically hazardous buildings and in all 282 such buildings were found. In 1990, Mitigation Task Force was asked to submit recommendations to city authorities. Based on the recommendation of task force, Hayward City Council retrofits all tilt-up buildings and other hazardous buildings at the total estimated cost of $15 million. State enacted Public Building Rehabilitation Bond Act of 1990 under which Hayward received 7 grants of greater than $2 million. (Porter 2000) With the help of FEMA grants wastewater treatment plant and seismically hazardous fire stations were constructed or retrofitted. It has been observed that Hayward has gone beyond the States URM requirement– establishing a voluntary program providing financial incentives so that people can do the retrofitting job privately. There was no opposition to the programs from the residents of Hayward and FEMA mitigation grants helped Hayward to develop its own mitigation program successfully. (Porter 2000) Conclusion Earthquakes are natural calamities that cannot be avoided; however, recent advances in science and technology have helped us to understand and predict its occurrence so that loss of life and damages to the property in the area could be largely averted. Earthquake mitigation plans undertaken in Hayward and other places will ensure that this time people are saved off from devastating effects of earthquake. References 1. Alden, A (2010); About the Hayward Fault of California, online from December 2, 2011, http://geology.about.com/od/geology_ca/tp/abouthaywardfault.htm 2. The San Andreas Fault System (2011), San Diego State University, online from December 2, 2011, http://www.sci.sdsu.edu/salton/San%20AndreasFaultSyst.html#top 3. Active Traces of the Hayward Fault (2009), U.S. Geological Survey, online from December 2, 2011, http://earthquake.usgs.gov/regional/nca/haywardfault/tiled/ 4. Bay Area Faults and Earthquake Educator Guide (2008), online from December 2, 2011, http://science.kqed.org/quest/files/imp/Radio3_2BAFaultsandEarthquakes.pdf 5. San Andreas Fault (2009), online from December 2, 2011, http://www.sciencedaily.com/articles/s/san_andreas_fault.htm 6. Urbanization of the Hayward (2010), online from December 2, 2011, Faulthttp://earthquake.usgs.gov/regional/nca/1868virtualtour/fault.php 7. California Geological Survey (2007), online from December 2,2011, http://www.consrv.ca.gov/cgs/information/publications/teacher_features/Pages/faults.aspx 8. Californias Hayward Fault Revealed (2007), Sciencedaily, online from December 2, 2011, http://www.sciencedaily.com/releases/2007/12/071214001612.htm 9. Recurrence Interval (2009), Earthquake Glossary, online from December 2, 2011, http://earthquake.usgs.gov/learn/glossary/?term=recurrence%20interval 10. Seismic gap (2009), Earthquake Glossary, online from December 2, 2011, http://earthquake.usgs.gov/learn/glossary/?term=seismic gap 11. Porter, K (2000), Mitigation saves: FEMA Spent $3.5B and Saved $14B, online from December 2, 2011, http://www.earthquakeconference.org/Presentations/Porter%20Mitigation%20Saves_NEC%2008.pdf Read More