Earthquakes
...few of the smaller plates are the Anatolian, Arabian, Caribbean, Cocos, Phillipine, and Somali plates.” (2) California’s diverse landscape and complex geology can be attributed to faulting. Many of the State’s valleys, mountain ranges, and desert areas show the effects of faulting. Faults create underground traps in which valuable reservoirs or petroleum form, and spaces in which underground waters deposit valuable metals in the form of ore. As previously mentioned, a fault is a weak point in the Earth’s crust and upper mantle. Also, a fault is a fracture along which there is movement. “Faults are distinguished by abrupt changes in rock structure or composition. Sometimes a fault can be recognized by the displacement of a particular feature such as a bed or a vein.” (Pridmore 80) To better understand faults, it is important to understand how they are classified. Faults and fault zones are classified by how the rocks on each side of the fault or fault zone move past each other. There are two main types of movement along faults, a sideways movement called strike-slip, and an up or down movement called dip-slip. “The movement along a strike-slip fault is approximately parallel to the strike of the fault, meaning the rocks move past each other horizontally... The San Andreas is a strike-slip fault that has displaced rocks hundreds of miles. As a result of horizontal movement along the fault, rocks of vastly different age and composition have been placed side by side. The San Andreas fault is a fault zone rather than a single fault, and movement may occur along any of the many fault surfaces in the zone. The survace efectsof the San Andreas fault zone can be observed for over 600 miles (1,000 km)” (81) “Dip-slip faults are faults on which the movement is parallel to the dip of the fault surface. Normal faults are Dip-Slip faults on which the rocks above the fault surface, called the hanging wall, move down relative to the rocks below the fault surface which is the foot wall. Normal faults are the result of forces that pull rocks apart,usually called extension.” (82) Another type of Dip-slip fault is a reverse fault. The reverse faults are very different from normal faults mainly because they are the result of compression, that is, forces that push rocks together. “Where the dip of a normal fault's surface is steep, it is called a high-angle normal fault, or simply a normal fault. The Owens Valley and the Sierra Nevada fault zones are examples of high-angle normal faults. Together they produce a down-dropped block which forms the Owens Valley. This type of fault-bounded valley is called a graben. A fault-bounded ridge is called a horst.” (83) “Opposite a high angle normal fault is what is referred to as a detachment fault or low angle normal fault. This occurs where the dip ofa normal fault is very gentle of almost flat.” (83) Detachment faults are common in the Desert areas of California. “Reverse faults are dip-slip faults in which the hanging wall moves up relative to the footwall. Reverse faults are the result of compression (forces that push rocks together). The Sierra Madre fault zone of southern California is an example of reverse-fault movement. There the rocks of the San Gabriel Mountains are being pushed up and over the rocks of the San Fernando and San Gabriel valleys. Movement on the Sierra Madre fault zone is part of the process that created the San Gabriel Mountains.” (84) California has several major fault systems. Probably the most notable is the San Andreas fault zone. This is a right-lateral strike-slip type of fault which is 1200 kilometers in length. Communities closest to the fault are Parkfield, Frazier Park, Palmdale, Wrightwood, SanBernard, Banning, and Indio. This major fault was responsible for the great earthquake of 1906 that measured 7.9. Other major faults in California are the Hayward fault which caused the 1868 earthquake, the Calaveras fault and the Northcoast fault where both the Hayward fault subsystem and the Calaveras fault system exist. A complete discussion of earthquakes must include all hazards associated with them. The most destructive of all earthquake hazards is caused by seismic waves reaching the ground surface at places where human-built structures,such as buildings and bridges, are located. When seismic waves reach the surface of the earth at such places, they give rise to what is known as strong ground motion. “ Strong ground motion causes buildings and other structures to move and shake in a variety of complex ways. Many buildings cannot withstand this movement andsuffer damages of various kinds and degrees. Most deaths, injuries, damages and economic losses caused by earthquakes result fromstrong ground motion acting uponbuildings not capable of withstanding such motionl It is for this reason that it is often said that ‘Earthquakes don’t kill people, buildings do.’ ” (Hazardmaps fact sheet, 1) A second major hazard is ground failure which is a result of strong ground motion. There are basically three hazards related to ground failure. One of the most important types of groundfailure is known as liquifaction. “Liquefaction takes placewhen loosely packed, water-logged sediments at or near the ground surface lose their strength in response to strong ground shaking. Liquefaction occuring beneath buildings and other structurescan cause major damage during earthquakes. (2) During the 1989 Coma Prieta, California earthquake, liquefaction of the soils and debris used to fill in a lagoon caused major subsidence, fracturing, and horizontal sliding of the ground surface in the Marina district of San Francisco. A second type of ground failure that is often highly destructive is the landslide which is an abrupt movement of soil and bedrock downhill in response to gravity. Landslides can be triggered by an earthquake or other natural cause. The third and last type of ground failure is actually a landslide under water which creates a tsunami. Earthquakes which have occured beneath the Ocean floor create immense sea waves. Tsunami is actually a Japanese wordmeaning “huge wave.” “These waves travel across the ocean at speeds as great as 597 miles per hour and may be 15 meters (48 feet) high, or higher by the time they reach the shore.” (NEIC: Common Terms in Seismology) Earthquakes can not be prevented but those who live in earthquake-prone areas can certainly be prepared. One form of preparation is called Earthquake Engineering. “Earthquake Engineering can be defined as the branch of engineering devoted to mitigating earthquake hazards. In this broad sense, earthquake engineering covers the investigation and solution of the problems created by damaging earthquakes, and consequently the work involvedin the practical application of these solutions, i.e. in planning, designing, constructing, and managing earthquake-resistant structures and facilities.” (Earthquake Engineering, 1) Another form of preparation is training that can be provided to citizens who live and work in earthquake-prone areas. The city of Berkely in California has an excellent training program that covers disaster first aid, search and rescue, fire suppression, and disaster mental health. Additionally lists ...