Earthquakes – can we predict it?
Earthquake is also called as a quake. A study of Earthquakes is known as seismology . An earthquake is caused due to a sudden release of energy from the earth. This energy is formed due to release of stress between the rocks in the earth crust. however, our planet’s seemingly stable surface is made up of enormous pieces of rock that are slowly but constantly moving. Those pieces continually collide with and rub against one another, and sometimes their edges abruptly crack or slip and suddenly release huge amounts of pent-up energy. These unsettling events are called earthquakes, and small ones happen across the planet every day, without people even noticing. But every so often, a big earthquake occurs, and when that happens, the pulses of energy it releases, called seismic waves, can wreak almost unfathomable destruction and kill and injure many thousands of people
That sort of cataclysm occurred on March 11, 2011, in Japan, when a massive quake, later estimated by Japanese Meteorological Agency to be 9.0 in magnitude on the Richter Scale, struck 81 miles (130 kilometers) east of the city of Sendai on the nation’s northeastern coast. The forces of the quake, the fifth most powerful in the past century, set off a giant wave, called a tsunami , that engulfed villages, destroyed buildings and drowned and crushed people who lived there
. The earthquake and tsunami also badly damaged a six reactor nuclear power plant in Fukushima, 150 miles (241 kilometers) north of Tokyo, destroying the backup generators that powered its cooling systems, and causing a dangerous release of radiation that forced people in the region to flee. In all, the quake claimed the lives of at least 12,500 and possibly up to 27,500 people, according to news reports
If your friend says he is stable and has both his feet on ground well exactly an opposite situation is created when an earthquake occurs. when the energy is released the earth surface trembles. it shakes.
now lets see the theory of an earthquake,
we now know an earthquake is generated due to release of energy which is in turn stress. now when this energy is released it travels through waves. there are mainly three types of waves which are generated due to release of energy. they are as follows ,P wave (primary or pressure wave) , S wave (secondary wave), L wave(surface wave)
Primary and secondary waves are Body waves. while L waves i.e. surface waves are not body waves.
P wave means primary or pressure wave . Primary waves (or P waves) are the fastest moving waves, traveling at 1 to 5 miles per second (1.6 to 8 kilometers per second). They can pass through solids, liquids and gases easily. As they travel through rock, the waves move tiny rock particles back and forth — pushing them apart and then back together — in line with the direction the wave is traveling. These waves typically arrive at the surface as an abrupt thud.
Whenever a major earthquake is in the news, you’ll probably hear about its Richter Scale. rating. You might also hear about its Mercalli Scale rating, though this isn’t discussed as often. These two ratings describe the power of the earthquake from two different perspectives. The most common standard of measurement for an earthquake is the Richter scale, developed in 1935 by Charles F. Richter of the California Institute of Technology. The Richter scale is used to rate themagnitude of an earthquake — the amount of energy it released. This is calculated using information gathered by a seismograph. The Richter scale is logarithmic, meaning that whole-number jumps indicate a tenfold increase. In this case, the increase is in wave amplitude. That is, the wave amplitude in a level 6 earthquake is 10 times greater than in a level 5 earthquake, and the amplitude increases 100 times between a level 7 earthquake and a level 9 earthquake. The amount of energy released increases 31.7 times between whole number values. As we previously noted, most earthquakes are extremely small. A majority of quakes register less than 3 on the Richter scale; these tremors, called microquakes, aren’t even felt by humans. Only a tiny portion — 15 or so of the 1.4 million quakes that register above 2.0 — register at 7 or above, which the threshold for a quake being considered major[source 1=”. The biggest quake in recorded history was the 9.5 quake that struck Chile in 1960. It killed nearly 1,900 people and caused about $4 billion in damage in 2010 dollars
. Generally, you won’t see much damage from earthquakes that register below 4 on the Richter scale.
Richter ratings only give you a rough idea of the actual impact of an earthquake, though. As we’ve seen, an earthquake’s destructive power varies depending on the composition of the ground in an area and the design and placement of man-made structures. The extent of damage is rated on the Mercalli scale. Mercalli ratings, which are given as Roman numerals, are based on largely subjective interpretations. A low intensity earthquake, one in which only some people feel the vibration and there is no significant property damage, is rated as a II. The highest rating, a XII, is applied to earthquakes in which structures are destroyed, the ground is cracked and other natural disasters, such as landslides or tsunamis, are initiated.
Richter scale ratings are determined soon after an earthquake, once scientists can compare the data from different seismograph stations. Mercalli ratings, on the other hand, can’t be determined until investigators have had time to talk to many eyewitnesses to find out what occurred during the earthquake. Once they have a good idea of the range of damage, they use the Mercalli criteria to decide on an appropriate rating.
the websites used here are www.usgs.com, www.howstuffworks.com