On Earthquakes
An earthquake is a shaking or trembling of the crust of the earth
caused by underground volcanic action or by the breaking and shifting
of rock beneath the surface. The volcanic action and shifting rocks
create strain which continues to build to a sudden release of pressure
resulting in a shock wave. The vibrations produced in the crust can
vary from barely noticeable to enormously destructive. Shock waves can
be classified into two broad categories. Waves that send particles
oscillating back and forth in the same direction as the waves are
traveling are called primary. Primary waves, sometimes called
compressional waves, travel through the earth beneath the crust.
Secondary waves cause vibrations which move perpendicular to the wave.
These waves travel on the surface of the earth and move much slower
than primary waves. Thus, when an earthquake occurs, seismic centers
throughout the world record primary waves before the secondary waves
arrive.
Historical Overview
Earthquakes have captured the imagination of people living in
earthquake prone regions since ancient times. Ancient Greek
philosophers thought quakes were caused by subterranean winds, while
others blamed them on fires in the bowels of the earth. About AD 130,
a Chinese scholar named Chang Heng reasoned that waves must ripple
through the earth from the source of an earthquake.
By 1859, an Irish engineer by the name of Robert Mallet proposed that
earthquakes occurred by either a sudden movement of flexible materials
which formed the earth's crust, or by their giving way and fracturing.
In the 1870s, an English geologist called John Milne invented...
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...nia prepares for the
"big one." Despite the tremendous impact of the Northridge earthquake,
no one believes that it is the last nor even the largest which will
strike the greater Los Angeles area. A new 36,000 square foot
Emergency Operations Center has been constructed in East Los Angeles.
A series of laws and procedures entitled the "Standardized Emergency
Management System" has continued to make the Mutual Aid System even
more effective. The Los Angeles Sheriff's Department has taken a
leading role in establishing courses in crisis action planning, crisis
decision making, command and control, operations, logistics and
intelligence. Liaisons and working groups with other agencies and
disciplines has provided additional insight and contributed to a high
state of readiness as they prepare for the next major earthquake.
Earthquakes are best described as a shaking or vibration of the ground caused by breaking of rock. Sometimes they are very strong and other times you would hardly notice them. This shaking occurs when stress that builds up in the crust is suddenly released as the crust breaks free and/or slides against the other pieces of crust. Earthquakes may also be thought of as the breaking of a popsicle stick by applying pressure to both ends at the same time. Should you try this experiment , you will feel the pressure build up as you apply more force until the stick snaps. When the stick snaps you will feel an instant of pain at your fingers as the stress reduces and energy waves move throughout the stick. When the earth's crust is placed under similar types of stress, binding as the stress builds, it will also snap and release the energy into the surrounding rocks, 'ooch'. Thinking about earthquakes will become more clear if you try another experiment.
Earthquakes play a major role into understanding the composition and materials that exist within the Earth (Merali and Skinner, 2009, p.252). Earthquakes are the main source of insight into the inner workings of the earth, due to the nature of the seismic waves they produce. P and S waves are reflected and refracted at different boundaries within the earth, and this enables seismologists to make inferences about the internal composition and structural of planet Earth. (Merali and Skinner, 2009, p.252).
Earthquakes, by Webster’s dictionary definition, are, “a shaking or trembling of the earth that is volcanic or tectonic in origin.” World Book Encyclopedia reports scientists believe that more than 8,000 earthquakes occur each day without causing damage. A little more than 1,000 each year are strong enough to be felt. Earthquakes occur in the general sense, anywhere on land. Other earthquakes go by different names, such as volcanic eruptions and tsunamis, large tidal wave storms that occur underwater, primarily in the Pacific Ocean.
The Whittier earthquake was not the "big one" that Angelenos perpetually wait for. This may be hard to comprehend given the extensive damage caused by the earthquake. Although classified as "moderate," the quake left more than 100 injured and six dead, including an electrical repairman buried in an underground tunnel, a college student struck by falling concrete in a campus garage, and three people who died of heart attacks brought on by the shock.
"The Great Quake: 1906-2006 / Rising from the Ashes." SFGate. N.p., n.d. Web. 10 May 2014.
In the early twentieth century, San Francisco, a bustling city full of people from diverse cultures, stood in the midst of the Second Industrial Revolution. At this time, the brilliant inventions of airplanes, automobiles, and radios were changing the everyday lives of many. San Francisco had just recovered from the four-year burden of the bubonic plague (“Bubonic”). However, right when things were going back to normal, a destructive earthquake hit the city on April 18, 1906. Although the shaking lasted for less than a minute, the devastated city had crumbled buildings and a substantial loss of lives. The San Francisco earthquake of 1906 consisted not only of earthquakes, but also of even more destructive fires; it had a scarring effect on the city and its people, yet it gave much of the knowledge that seismologists have today and allowed San Francisco to stand as a place of intriguing buildings and structures.
Hazards pose risk to everyone. Our acceptance of the risks associated with hazards dictates where and how we live. As humans, we accept a certain amount of risk when choosing to live our daily lives. From time to time, a hazard becomes an emergent situation. Tornadoes in the Midwest, hurricanes along the Gulf Coast or earthquakes in California are all hazards that residents in those regions accept and live with. This paper will examine one hazard that caused a disaster requiring a response from emergency management personnel. Specifically, the hazard more closely examined here is an earthquake. With the recent twenty year anniversary covered by many media outlets, the January 17, 1994, Northridge, California earthquake to date is the most expensive earthquake in American history.
study of the San Andreas fault system." (USGS) When the 1906 earthquake struck scientist set
Exploring Why LEDC's Suffer Greater Damage From Earthquakes Than MEDC's A MEDC is a more economically developed country; therefore it can afford to spend money on improving the countries stability and helping to decrease the damage from an earthquake. An example of a MEDC is Kobe, in Tokyo, where in January 1995; an earthquake that measured 7.5 on the Richter scale hit the city. A LEDC is a less economically developed country and therefore cannot afford to spend money to protect the country from earthquakes. An example of an LEDC is Armenia, in Columbia, where on the 25th January 1999; an earthquake measuring 6.3 on the Richter scale was the worst earthquake the country had experienced since 1983.
Additionally, this earthquake occurred on a thrust fault. This fault was a subduction zone slip which occurred primarily beneath the ocean were the Pacific plate plunges underneath the North American plate. This sudden upward movement of the sea floor along the rupturing fault generated a massive tsunami. This vertical deformation
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
As the tectonic plates slide over each other, they cause earthquakes. Earthquakes produce various damaging effects, this includes damage to structures of buildings, bridges and other standing formations which then result in injuries and people getting killed, wildlife getting disrupted as well as humans. An earthquake can affect the earth as it’s easier to let the lava come out of the earth. Tsunamis- Can cause financial problems such as home loss, job loss which will then result in being homeless, loss of crops and food supplies which causes a lot of harm to us ‘humans’. A tsunami is a series of waves that send surges of water that can travel thousands of miles.
There are four different types of seismic waves: Primary (P), Secondary (S), Love (L) and Raleigh (R). P waves are the first waves to reach recording stations, which is why they are called primary waves. They travel at approximately 20,000km/h and are a push-pull wave, which means they stretch and squeeze rocks as they pass through. S waves are slower than P waves, travelling at 10,000km/h, therefore arriving after P waves at the recording station. They have larger amplitudes th...
Earthquakes are vibrations felt at the surface of the earth which are caused by disturbances of the energy in the earth's interior. These vibrations are known as seismic waves. (Skinner Robinson McVerry 1) There are different type sof seisimc waves such as Primary (P) waves, whcih travel the fastest, Secondary (S) waves which cause the earth to vibrate vertically, Surface (L) waves. P and S waves are "affected by changes in the density and the rigidity of the materials through which they pass." (Columbia Encyclopedia) Earthquakes vary in their intensity and duration. Often times they are strong enough to cause massive destriction. Tall buildings often suffer as a result of these natural disasters. In recent years this has become a larger and larger threat with both the number of large buildings, and their number of occupants increasing. In an effort to try to minimize the damage caused by earthquakes many some engineers focus primarily on designing and constructing earthquake resistant buildings. Earthquake engineers have gathered much of their information from analyzing past earthquakes, and learning which buildings can and can't withstand the tremors. The goals of these engineers is to design buildings that can withstand moderate earthquakes and obtain minimal damage, and that the buildings will not collapse lowering the probability of human deaths.
The interior structure of the earth is made up of crust, the mantle and core (inner core and outer core). Earthquakes occur on the crust. Crust forms the external layer of the earth surface. On the crust, the plate tectonics forces are in charge of causing the abrupt earth movements. Due to the existence of an immense temperature and concurrent pressure difference in the outer layer and inner layer of the earth, convection currents occur at the mantle. This energy results from overwhelming decomposition of radioactive substances contained by the rocks found at the interior of the earth. The developed convection currents lead to movement of lava; cold lava finds its way to the interior of the earth crust, while the molten lava which is generally hot, leaves the interior of the earth to the outside of the earth crust. These kinds of circulations occur at different locations of the earth surface and consequently results in segmentation of the earth due to movement in different directions.