By Alutsyah Luthfian, senior high school student of Indonesia
To the point: Earthquake has occurred in Japan at Magnitude 8.9.
This earthquake is sourced from collision of Pacific plate with Eurasian plate (colliding region is shown by a tetragon). The shallow depth of this earthquake trigger tsunami across Japan and Pacific Ocean including Hawaii, Guam, and Eastern Indonesia. With absolute magnitude of 9.0, This earthquake has emitted 3,9 x 10E22 J of energy which equivalent to 2 x 10E9 Mt of TNT (30 million times of the Tsar Bomba fusion-fission nuclear explosion at Russia in the year of 1961-it was the most devastating nuclear device ever made by human). I have corrected the calculation, that's final result. By using the energy reservation principle, we can also perceive how big the tsunami is in the beaches near the epicentrum of earthquake: 10 meters. from the map, beaches experienced more acceleration than the mountainous region of central Japan. Not only caused by distance, this deceleration caused by loose sandy beach of Japan. Also, mountainous region tends to have greater gravitation caused by mass bulging, so it decelerates seismic wave.
The seismograph note of the earthquake shows P-wave take longer time to felt by the tool along with its distance from epicentrum, because of deceleration caused by the inner filling of earth. Please note the far left seismograph; That's note made by seismograph in Asahi, just 623 km to the center of earthquake.
Based on wave formula, it is broadly obtained that the energy of 2011 Japan Tsunami is 6.125 x 10E4 Joule per meter squared. The other part of earthquake energy is used to move the plates, to generate heat etc. To gain perception of Japan tsunami Energy, I use this equation:
assume that the specific mass of water is 1000 kg per cubic meter, gravitation acceleration is 9,8 m per second squared, and H, the height of tsunami near the beach is 10 meters. If we want to know how is the power of the tsunami, by assumption that the speed of tsunami near the shore is 80 km/hour or 22 m/s is 1.348 Megawatt per meter. This 2011 Japan tsunami is able to enter the land as far as 24 km as the geographic condition of eastern Japan is mostly lowland; mountains are available north of Sendai as there were many active volcano. This is different when tsunami struck Aceh in 2004. Despite of its earthquake Mw magnitude of 9.1, tsunami just enter the land as far as 9 km because Banda Aceh is akin of small lowland that encircled by fault-made mountains and Seulawah volcano.
PRELIMINARY EARTHQUAKES THAT CREATED AN ILLUSION
Before the main 8.9 earthquake hit, there were also a quite big earthquake with magnitude of 7.2 hit the same region on March 9, 2011 at 11.45 Japan Standard Time. This earthquake triggered another earthquake with smaller magnitude on March 10. This phenomenon could draw an illusion on our mind: earthquakes on that time is just following the main M7.2 shock.
Actually, it is not.
On the early day of March 11, 2011, no earthquakes above M4.5 is perceived in Honshu surroundings. One should think that the aftershock is ceased, and the plates boundary should has moved to a new equilibrium. But at 02.46 PM JST, the real shocking begin--until the time this article written, aftershocks still perceived. It was M8.9, the biggest earthquake known for Japan. Tsunami runs and swept Pacific beaches: North Papua, Chile, Hawaii, Guam, and the entire Eastern Japanese beaches.
This earthquake gets the power from swift moving South Pacific Ridge. With the speed of +/- 6 cm a year, the Pacific Plate pushed the Eurasian Plate while he is storing the energy in the fault. The residual energy of this pushing lifted the Eurasian plate. In the D-day, this residual energy is no more bearable by the plate, thus it wil restore to a new stationary state and tara!! an earthquake is happen (with tsunami if it strong enough to trigger it).
HOW EARTHQUAKE SPEEDS UP OUR DAYS
Earthquake, just like other form of energy, is akin an effort to reach what we call higher entropy state. When earthquake happen, some mass of earth is converted into energy. Note that MASS is another form of ENERGY. Like those atomic bombs, earthquake also converts some of earth's mass into energy. The diminishing mass caused by mass to energy conversion can accelerate the rotational speed of earth. Let the initial angular momentum of earth is L1 = mrv. L2 should be the same amount (momentum reservation law) but the v is higher since some m has been lost into energy and assume that the deduction of r is negligible.
The earth axis, is related to the theorem of mass center. Since there is some deduction in mass, the earth will find a new equilibrium, thus it shifted the earth axis relative to the former axis by some millimeter or even centimeter.
EARTHQUAKE AND ENTROPY
Let we see that earth is a closed system having some amount of available energy (symbolized as B), when this energy released in the form of earthquake, this will increase the entropy (S) of earth. This is evidently shows up how second law of thermodynamics works. Thus, every earthquake happening in this world--will bring this world to a more-messy state. :-)
