create your own banner at!
Copy this code to your website to display this banner!

Diploma and Research Projects.

The suggest a topic, presenting undergraduate or research students from polytechnic institute’s and Architecture Faculty. The persons concerned Captured can send us the diplomatic work.

Contact [email protected]




Friday, March 11, 2011

Earthquakes. Why is it done, and how we measure them?

by Michael Balaroutsos architect

About earthquakes
The earthquake is a sudden movement or vibration of the earth's crust. Usually comes from the rupture of geological strata and the sudden shift in two parts below the surface of the Earth. The cracks are directly related to the creation of surface earthquakes, so I marked seismic faults.
Depending on the focal depth are divided into surface (h <60 km), at intermediate depth and deep (h> 300 km). The last two named and plutonium.

The movement of tectonic plates
The lithosphere is divided into seven very large plates, but there's a host of other smaller ones. Eg in the Aegean region are several small plates. The plates float on the plastic asthenosphere.
Three types of movements can occur at the boundaries between plates
Creation (extension) plate. In mid-ocean rifts removed by a few cm / year in areas leaving molten rock emerged, creating new ocean floor on both sides of the fault. At the threshold of creating a mid-ocean ridge (mountain) which is the latest pop-rock. As cool new rock magnetic material of oriented depending on the orientation of the magnetic field at the time. As the geomagnetic field changes every 1x106 waiting years to see layers (on the edge of the back) with alternating magnetization.
Destruction plate (the part of precipitation). One plate slides under another and melts and penetrates into the mantle. This area is called the subduction zone and creates a mid-ocean trenches. Where the lighter parts of the submerged plate melts are rising to the surface, creating volcanoes. When continental plates from opposite parts are compressed into a subduction zone, because it is lighter than the submerged substrate, forced to bend to form mountain ranges.
Movement plates. Some limits are neighbors plates slide together without conflict or separated. These limits which have only horizontal movement called fracture zones (or transform faults). Where earthquakes are frequent due to friction between the plate boundaries. In general, therefore, an ideal plate would have a hand in the subduction zone, an area opposite the lift and side to slide horizontally to the neighborhood.

Seismic waves

To assess the effects of earthquakes should be established various elements, which serve as the basis of assessment. The first is the focus of the earthquake, the underground where the earthquake is born. The second element is the epicenter of the earthquake, ie the region of Earth's surface located vertically above the fireplace. Next you need to distinguish the various seismic waves and the effects of earthquakes (disasters, floods, fires, human victims). Results vary depending on the conditions (underground resistance, construction of houses, population density, local time, habits population.

When an earthquake hits, the first pulse of energy that comes from the location of the outbreak, including primates, or pressure waves (P - primary). Longitudinal waves at all the Earth and arrive first at a seismological stations. Moving rocky soils 6, approximately, km / s while the water with one third of that speed. When they reach the Earth's surface can move in the air, like sound waves. Depending on their frequency can be heard by humans or just animals.
The next waves arriving at a site is secondary (S - secondary). It spread through body fluids (eg sea or outer core of Earth). It is slower (running on about 2 km / sec), but more powerful and destructive of the longitudinal and the following in pairs.
P waves travel faster than twice the secondary (S) waves are bringing strong destructive movement of soil, characteristic of large earthquakes. The S waves are traditionally used to evaluate the size of a seismic event, but this information is gleaned only after the earthquake.
These two waves are governed by all the authorities of waves (reflection, refraction, Fermat's principle and Huygens).
wave direction
Finally, when the energy of an earthquake reaches the Earth's surface, creating two other types of surface waves that follow the other two. Their name comes from the person who discovered and created when the source is shallow.
The first wave is Love (the discovered theoretically H. Love 1911), which in spreading the material points of the average swing horizontally, perpendicular to the wave's direction. They create that lateral movement of the surface soil. Indeed, it is linearly polarized.
And the second wave is Rayleigh (discovered in the 1887, Strutt Rayleigh), which in disseminating the material points of the average move in elliptical orbits whose major axis is vertical and parallel to the small wave's direction. Disseminated in the surface layers of the Earth and therefore not shown almost no earthquakes deeper into homes.
The last two waves move more slowly than the first (P and S) but is more devastating, especially the waves of Love. Especially the latter is often responsible for the collapse of buildings.
The earthquakes recorded by a seismography network. Each seismic station in the network measures the movement of soil in that place. The slip of rock over another in an earthquake releases energy that makes the ground vibrate. That vibration pushes the side of the soil and causes it to vibrate. So continue to spread the energy of seismic wave.
How devastating would be an earthquake has more to do with less intensity and size. This depends on various natural and artificial conditions, among which are the following:

The depth of seismic outbreak. The smaller the focal depth of greater intensity.

The seismic acceleration. This is proportional to the intensity of an earthquake as a unit we use the gravitational acceleration g. Roughly speaking, 1g is 10m/sec2. The magnitude of the acceleration depends on the soil in each have different earthquake ground motion acceleration, according to the region. For example, the 1999 earthquake of the mountain had other accelerations in the Athens area and larger Parnitha.
The duration of an earthquake like the 1999 earthquake. Generally, major earthquakes last longer.
The soil foundation. In sandy (loose) soils have more damaged buildings.
The effects of an earthquake in a populated area would be dramatically higher than in a sparsely populated village. For example, the earthquake of Rhodes in 1926, size (calculated later) 8 on the Richter scale, had 12 deaths and relatively little property damage than the earthquake 5.9 on the Richter scale, which was held in 1999 in Parnitha populated basin of Athens. 

Τhe increase in urban populations around the world, is threatened by earthquakes

On page of the University of Colorado, 2 May 2003

A new study by a professor of geology at the University of Colorado at Boulder indicates that an earthquake of sufficient cause as one million casualties each century could happen if no action is taken on buildings and materials to withstand earthquakes.
The findings of Professor Roger Bilham based on a study of the rapid growth of population in cities of the world in the 21st century, and the locations of these cities located near the imaginary line where previously we had earthquakes.
Before 1600 few cities exceeded the 1,000,000 inhabitants. In 1950 there were 43 "super-cities" with populations of 2 million to over 15 million. Today there are nearly 200 such super-cities on Earth, and their number could be doubled up to stabilize the population of Earth.
Approximately 8 million people died from the collapse of buildings due to earthquakes in the past 1000 years if we do not have sufficient data before 1600. But it is clear that between the 17th and 20th century, quadrupling the number of fatalities per year for earthquakes associated with increasing urbanization.
The emergence of super-cities has increased tenfold since 1700 says the professor. Of those over 40 are less than 120 miles from the boundaries of tectonic plates or the location was historically a devastating earthquake. Examples we have in parts of Jakarta in Indonesia, Tehran in Iran, and Mexico City in Mexico. Mexico City now has a population of around 16 million.
"50% of super-cities of the world are located near areas where earthquakes are likely to have 7.5 on the Richter scale in the future," says Bilham.
"A statistical analysis of 1997 foresaw a future rate of loss of the order of 8,000 deaths per year. This study has underestimated the extreme events with losses of more than 30,000 people. The predictions of this analysis are even more unreliable if we take into account our extreme events in the 21st century where the world's population expected to reach 6 billion, "says Bilham.
From 1998 to 2002, earthquakes have caused approximately 10,500 casualties per year. On the basis of the past, the Bilham make the following considerations:
Each year there is an earthquake that killed 100 people.
Every 2 years an event occurs that kills 1,000 people.
Every 5 years an event occurs that kills 10,000 people.
Every 100 years an event occurs that kills 300,000 people.
But the future of the 300,000 people is probably an underestimate, because the size of these huge cities doubled in the last century and is expected to xanadiplasiastei in the current century. In the past we had such terrible attacks simply because it could have. Now we have many cities as targets of the giant earthquakes.
Nearly 100,000 people were killed by an earthquake in India in 2000, and recent research by Bilham and his colleagues suggest the possibility of an earthquake of 8.1 to 8.3 degrees in northern India from the side of the Himalayas. Such an earthquake could happen in 12 other countries if it occurs near a super-city.
The Bilham believes that nonetheless there is still ground for optimism, although it describes this period as an era of construction, when you have 3 billion to build new homes, to a future doubling of world population. "We can at least make these new buildings are safe to be occupied," he says. "We understand that it is not earthquakes that kill people, but buildings and manufacturers of unsafe buildings is to kill them."

The scales of earthquake

There are many different scales and sizes of earthquakes and M. We find that each (Seismological Institute) for the same earthquake announces a different size. Why is notified every time a different size?
There are many different ways to measure different aspects of an earthquake. The size of M is the most common measure of an earthquake. As a measure of the magnitude of the earthquake source is the same number wherever we like and to feel. The Richter scale measures the more-impaired movement on record, but there are other size scales measuring different parts of the earthquake.
An increase in size by one (for example, from 4.6 to 5.6) represents a tenfold increase in amplitude of the wave at a seismograph or approximately an increase of about 25 times the energy of substance. In other words, a magnitude 6.7 earthquake releases over 700 times (25 to 25) the energy of a 4.7 earthquake.

The figures used to measure an earthquake are the following:

ML is local magnitude (Magnitude Local: local magnitude presented by Charle Richter in 1935). The Richter scale is a mathematical formula. The magnitude of an earthquake is determined by the logarithm of the amplitude of waves recorded by seismographs in a certain period. The ML is reliable when measured by seismographs that there are more than 600 kilometers from the epicenter of the earthquake. Applies only to a certain frequency seismic waves for a certain distance from the epicenter. Thus, for different distances from the epicenter of the earthquake that seismologists are based on different seismic waves to their calculations.
Ms is the magnitude of the measurement of surface wave. Please note that Ms is greater than the ML. For example, if a magnitude 5 earthquake as measured on the Richter Scale (ML), can be measured as 5.5 Ms. The Ms are reliable for superficial (<50 km depth) earthquakes and large distances from the epicenter. Used in Greece and was proposed by Papazachos. The energy released is given in erg by the formula: logE = 12,24 + 1,40 Ms. MB is an extension of the Richter scale and thus better exploit the network of seismograph. It is the size obtained by measuring the primary P wave (Compressional Body Wave Magnitude). It is reliable with larger magnitude earthquake focal depths and for large distances from the epicenter. Mw All previous figures come from formulas that contain a specific amplitude of a seismic wave at a time. The Mw, which is used for the measurement of large earthquakes is estimated by a complex formula and is very reliable. Md is the magnitude of durability. Mo The seismic moment magnitude scale, which is considered the most accurate. Nominated in 1979 and does not depend on the period of seismic waves but to measure the seismic moment. Me (Choy and Boatwright 1995), which reflects the potential destructiveness of an earthquake and is used to quantify the seismic energy emitted large events. By type logE = 12,24 + 1,40 Ms shows that 5 Richter earthquake energy is released 24.1019 erg while 6 Richter energy is 64.1020 erg. That is an increase of 1 Richter release of energy approximately 25 times more. Note that the bomb tested at Bikini island was 1019 erg. How much energy is released in an earthquake? Earthquakes release a tremendous amount of energy and that is why we can be so destructive. The table shows the sizes of the approximate amount of the quantity of TNT needed to release the same amount of energy. Size Approximate energy equivalent TNT 4.0 1010 tons 5.0 31800 tons 6.0 1,010,000 tons 7.0 31,800,000 tons 8.0 1,010,000,000 tons 9.0 31,800,000,000 tonnes Sizes are classified as follows: Large: M> = 8
Major: 7 <= M <7.9
Powerful: 6 <= M <6.9
Moderate: 5 <= M <5.9
Weak: 4 <= M <4.9
Potty: 3 <= M <3.9
Mini: M <3
Depending on the geology of the area corrections made in various sizes. Also selected that size is the most accurate seismic event. For example, if a seismic source located at great depth, no surface waves are produced, as is the most shallow earthquakes, and will not be calculated or rather not disclosed the size-Ms, but the ML or MB. If the focus is off (several hundred kilometers), then more reliable size is MB.
But if the earthquake is big enough, its size will give the instantaneous magnitude Mw, because while large earthquakes are longer than the smaller, the MB is determined by the width of the P wave in the first 5 seconds of vibration. So the MB, will not yield exactly the actual size of large earthquakes, which usually last longer and give the actual size after a few seconds.

The Mercalli scale

The intensity of the other is a measure of turmoil and damage caused by the earthquake, and this value naturally varies from place to place. It depends not only on the size of the earthquake but also the distance from the epicenter of the earthquake and the geological form of the site.
The intensity scales, such as the modified Mercalli scale and the scale Rossi-Forel, measure the amount of seismic disturbances at a particular location. Thus the intensity of an earthquake will vary depending on the place we are. Sometimes earthquakes are referred to the maximum intensity produced. The size scales, like the Richter scale measures the magnitude of the earthquake at its source. So it depends where it is measured.
On the seismology-related harm to earthquakes measured by the seismic intensity, which is a measure of aisthitotitas and effects of the earthquake and related to the size of various empirical relations. The measurement of intensity is the dodekavathmi scale Mercalli, whose ratings are based on the assessment of macroseismic effects of an earthquake.
What you should know is that every size is valid for a specific frequency and type of seismic signal. All these seismic scales, when calculated within the limits of their validity is equivalent to the Richter scale.
Previously (thirty years ago) could be a deviation of what was announced by the actual size of an earthquake up to 0.4%. Today, the gap is even smaller and therefore should not worry about whether any given time the right size. Small differences in communications, due to geological peculiarity of each region.
When an earthquake occurs, the raw information is processed and relayed is usually based on a subset of seismic stations of the seismic network, especially if a large earthquake. This is so some information may be taken immediately without waiting for the information of all stations on the network, which is later. Consequently, the first reported size is usually based on a small number of recordings by the seismograph network. Later coming extras is a new process and changing the size and center with more accuracy.
Sometimes the earthquake magnitude reported by different networks based only on recordings. In that case, the different figures reported are the result of small differences in the organs and their location in the epicenter of the earthquake. Indeed, after a few days seismologists generally agree on a figure for the size.
Often referred to a different earthquake, slightly different sizes. This is because the relationship between seismic measurements and size is complex and different procedures will often give slightly different figures for the same earthquake.
Thus, a common mistake made during the announcement of the magnitude of an earthquake in the media that reduces all magnitude earthquake on this scale: "The earthquake was magnitude-magnitude 7 Richter''. And soon followed by another announcement Seismological center with different size of the earthquake. But as I said the right size of the earthquake comes later and the figures reported may be slight variations.

The team van to the fore

From  Newscientist

Unusual electromagnetic signals were detected two months before a big earthquake in Japan. These signals support questionable work of Greek researchers say they may one day be used to forecast earthquakes.
For several years, seismologists have been considerable public discussion whether or not it can be predicted earthquakes by electromagnetic signals emitted from rocks under pressure.
Advocates of the idea - known as VAN method from the initials of the Greek researchers who discovered, Panayiotis Varotsos, Alexopoulos Caesar and Constantine Nomikos, all physicists at the University of Athens - claim that the electric and magnetic activity in the soil can predict location, timing and size of some earthquakes.
Other researchers, however, had difficulties to resume the results of the Greek team. But now his team Seiya Uyeda of the Research Center for Earthquake Prediction in the Tokai University in Japan report measure abnormal changes in the Earth's electric and magnetic fields in the Izu Islands of Japan by the end of March 2000. And two months later, on June 26, began a series of earthquakes.
The researchers used telephone wires as antennas to measure electromagnetic waves of very low frequency every 10 seconds.

Rocks with cracks

These scientists say that the signals of geoelectric field show "clear, unusual changes. The strength of the signal increases with time, reaching the peak just shortly before the first earthquake of magnitude 6.4 on the Richter scale on July 1, 2000. After the fall of seismic activity, the fields returned to normal.
The team also saw changes in the strength of Earth's magnetic field at the same time. Having searched for other possible causes of magnetic noise, like a rain drop or sources due to human activities, the researchers saw a tiny but sudden deformation. These changes were approximately one million times smaller than the Earth's natural magnetic field.
The signals peaked at only two antennas, the researchers put a thought. They think that strong signals can be produced, disseminated, along channels of high conductivity, as abnormalities in the rock that contains a small water tank, making them detectable only in certain areas.
Seismologists are divided over the significance of the results. The Varotsos says the results of the experiment Uyeda is impressive, and confirm the signals has been seen in Greece over the past 20 years.
The Max Wyss of the University of Alaska Fairbanks, in turn, distrusts the measurements of the Japanese. The group claims that these brands provide earthquakes are completely unfounded, "says Wyss.
The Phil Reppert of the University of Clemson in South Carolina, says that while the work of Japanese Uyeda is clearly proven that it can predict earthquakes, shows the need for more research. "I agree with the authors that the origin of the signal can not be noises of human origin.

0 reviews:

Post a Comment