Would earthquakes of same strength cause similar damage in other locations? ?
An earthquake of the same magnitude as the 1906 San Francisco quake would not cause the same amount of damage in a less populated or less developed (as in fewer structures) area. The New Madrid quake of 1811, for example, was a magnitude 8.0, but the area was far less populated than San Francisco in 1906, so it caused far less damage and death. The Richter Scale is not used to express damage. An earthquake in a densely populated area which results in many deaths and considerable damage may have the same magnitude as a shock in a remote area that does nothing more than frighten the wildlife. Large-magnitude earthquakes that occur beneath the oceans may not even be felt by humans. In the past three centuries, major earthquakes outside of California and Alaska generally occurred in sparsely-settled areas, and damage and fatalities were largely minimal. But some took place in areas that have since been heavily built up. Among them are three earthquakes that occurred in 1811 and 1812 near New Madrid, MO. They are among the Great earthquakes of known history, affecting the topography more than any other earthquake on the North American continent. Judging from their effects, they were of a magnitude of 8.0 or higher on the Richter Scale. They were felt over the entire United States outside of the Pacific coast. Large areas sank into the earth, new lakes were formed, the course of the Mississippi River was changed, and forests were destroyed over an area of 150,000 acres. Many houses at New Madrid were thrown down. "Houses, gardens, and fields were swallowed up" one source notes. But fatalities and damage were low, because the area was sparsely settled then.
What are the factors influence earthquakes intensity and magnitude?
There is a difference between magnitude and intensity. Magntitude is the total energy released from the earthquake. The level of magnitude depends on the rigidity of the Earth at the epicentre, average amount of slip on the fault and the size of the area that slipped Intensity is the effect of an earthquake on the Earth's surface, humans, objects of nature, and man-made structures. The shaking intensity at a given spot depends on many factors, such as soil types, soil sublayers, depth, type of displacement, and distnace from the epicenter. If you are looking at human impacts then building design/quality are also a factor.
What does an 7.5-8.1 earthquake feel like from 110 miles/180 km?
The actual ground motion that you feel will be dependent on factors such as intervening topography and geology between yourself and the hypocenter, specifically the geology of what you're directly standing on. A 7.5 - 8.1 is an enormous earthquake. In 1964, there was a 9.2 earthquake in Alaska (obviously an order of magnitude larger), and two hundred miles away from the epicenter, significant areas of land were actually permanently raised - very quickly - by thirty feet (Kodiak). That's obviously some significant shaking. In Anchorage, about 78 miles away from the epicenter, there was intense damage to the city and its structures and infrastructures. So an 8.1 at 110 miles? You'd definitely feel it. I'm not sure what you mean by rolling motion *or* violent. Rolling can be very violent. I have no doubt that you'd feel a serious horizontal shock, and yes, you'd probably experience significant vertical motion at the same time. Again, dependent on exact conditions, poorly-engineered buildings would very likely be damaged.
Can you, guys, please give me a clear definition of soil amplification?
Clear definition of soil amplification - The ground has the capability to amplify earthquake shaking. - Soft soils amplify ground shaking - Velocity is a contributor to the site amplification - The underlying soil influencing the local amplification of earthquake shaking is called the site effect Ground shaking is the primary cause of earthquake damage to man-made structures. When the ground shakes vigorously, buildings can be damaged or destroyed and their occupants may be injured or killed. Seismologists have observed that some districts tend to repeatedly experience stronger seismic shaking than others. This is because the ground under these districts is relatively soft. Soft soils amplify ground shaking. If you live in an area that suffered stronger shaking than that felt in other areas at a comparable distance from the source in past earthquakes, you are likely to experience relatively strong shaking in future earthquakes as well. An example of this effect was observed in San Francisco, where many of the same neighborhoods were heavily damaged in both the 1906 and 1989 earthquakes. The influence of the underlying soil on the local amplification of earthquake shaking is called the site effect. One contributor to the site amplification is the velocity at which the rock or soil transmits shear waves (S-waves). Shaking is stronger where the shear wave velocity is lower. The National Earthquake Hazards Reduction Program (NEHRP) has defined 5 soil types based on their shear-wave velocity (Vs). The ground has the capability to amplify earthquake shaking. The National Earthquake Hazards Reduction Program recognizes 5 categories of soil types and assigns amplification factors to each. Type E soils in general have the greatest potential for amplification. Type A soils have the least. These soil types are recognized in many local building codes. Records from many earthquakes show that ground conditions immediately beneath a structure affect how hard the structure shakes. For example, sites underlain by soft clayey soils tend to shake more violently than those underlain by rock.Subsurface conditions can vary abruptly and borings are required to estimate amplification at a given location.
Soil fertility vs soil productivity?
Soil fertility is the characteristic of soil that supports abundant plant life. In particular the term is used to describe agricultural and garden soil. Fertile soil has the following properties: It is rich in nutrients necessary for basic plant nutrition, including nitrogen, phosphorus and potassium. It contains sufficient minerals (trace elements) for plant nutrition, including boron, chlorine, cobalt, copper, iron, manganese, magnesium, molybdenum, sulfur, and zinc. It contains soil organic matter that improves soil structure and soil moisture retention. Soil pH is in the range 6.0 to 6.8. Good soil structure, creating well drained soil. A range of microorganisms that support plant growth. It often contains large amounts of topsoil. In lands used for agriculture and other human activities, fertile soil typically arises from the use of soil conservation practices Soil formation, or pedogenesis, is the combined effect of physical, chemical, biological, and anthropogenic processes on soil parent material resulting in the formation of soil horizons. Soil is always changing. The long periods over which change occurs and the multiple influences of change mean that simple soils are rare. While soil can achieve relative stability in properties for extended periods of time, the soil life cycle ultimately ends in soil conditions that leave it vulnerable to erosion. Little of the soil continuum of the earth is older than Tertiary and most no older than Pleistocene.[7] Despite the inevitability of soils retrogression and degradation, most soil cycles are long and productive. How the soil "life" cycle proceeds is influenced by at least five classic soil forming factors: regional climate, biotic potential, topography, parent material, and the passage of time. An example of soil development from bare rock occurs on recent lava flows in warm regions under heavy and very frequent rainfall. In such climates plants become established very quickly on basaltic lava, even though there is very little organic material. The plants are supported by the porous rock becoming filled with nutrient bearing water, for example carrying dissolved bird droppings or guano. The developing plant roots themselves gradually breaks up the porous lava and organic matter soon accumulates but, even before it does, the predominantly porous broken lava in which the plant roots grow can be considered a soil.
Earthquake?
No
Liquefaction?
Liquefaction is a phenomenon in which the strength and stiffness of a soil is reduced by earthquake shaking or other rapid loading. Liquefaction and related phenomena have been responsible for tremendous amounts of damage in historical earthquakes around the world. Liquefaction occurs in saturated soils, that is, soils in which the space between individual particles is completely filled with water. This water exerts a pressure on the soil particles that influences how tightly the particles themselves are pressed together. Prior to an earthquake, the water pressure is relatively low. However, earthquake shaking can cause the water pressure to increase to the point where the soil particles can readily move with respect to each other. Click on the picture to start animation. Schematic behavior of sand grains in a soil deposit during liquefaction. The blue column represents the pore water pressure. Here is an MPEG version (222 Kb)of the animation. Earthquake shaking often triggers this increase in water pressure, but construction related activities such as blasting can also cause an increase in water pressure. When liquefaction occurs, the strength of the soil decreases and, the ability of a soil deposit to support foundations for buildings and bridges is reduced as seen in the photo (SC) of the overturned apartment complex buildings in Niigata in 1964. The type of ground failure shown above can be simulated in the laboratory,as seen in the video. Click on the picture or on the play button to start video. Here is an MPEG version (298 Kb) of the video. Liquefied soil also exerts higher pressure on retaining walls,which can cause them to tilt or slide. This movement can cause settlement of the retained soil and destruction of structures on the ground surface (left, GH) Increased water pressure can also trigger landslides and cause the collapse of dams. Lower San Fernando dam (left, SC) suffered an underwater slide during the San Fernando earthquake, 1971. Fortunately, the dam barely avoided collapse, thereby preventing a potential disaster of flooding of the heavily populated areas below the dam. --------------------------------------... | Home | What | When | Where | Why | How | | Research | Links |