Kita dikejutkan dengan satu lagi bencana alam yang mana Jepun telah dilanda Tsunami yang paling teruk dalam sejarah negara "Samarui" itu. Gegaran dengan Skala Richter 8.9 memberikan amaran serta membangunkan warga dunia. Walau sehebat mana sekalipun teknologi, bencana alam tetap akan mengatasinya. Namun, mungkin masih ada antara kita tidak mengenali "sang malapetaka" ini. Saya percaya anda kerapkali mendengar perkataan "tsunami" apa ke jadahnya itu.?? Kalau anda rasa belum kenal "bendalah" ni, let do read bout it here!!
The most common causes of tsunamis are underwater
earthquakes. To understand underwater earthquakes, you must first understand
plate tectonics. The theory of plate tectonics suggests that the
lithosphere, or top layer of the Earth, is made up of a series of huge plates. These plates make up the continents and seafloor. They rest on an underlying viscous layer called the
asthenosphere.
Think of a pie cut into eight slices. The pie crust would be the lithosphere and the hot, sticky pie filling underneath would be the asthenosphere. On the Earth, these plates are constantly in motion, moving along each other at a speed of 1 to 2 inches (2.5-5 cm) per year. The movement occurs most dramatically along
fault lines (where the pie is cut). These motions are capable of producing earthquakes and
volcanism, which, when they occur at the bottom of the ocean, are two possible sources of tsunamis.
 Japan's most powerful earthquake since records began has struck the north-east coast, triggering a massive tsunamiFormation of a tsunami |
When two plates come into contact at a region known as a plate boundary, a heavier plate can slip under a lighter one. This is called subduction. Underwater subduction often leaves enormous "handprints" in the form of deep ocean trenches along the seafloor.
In some cases of subduction, part of the seafloor connected to the lighter plate may "snap up" suddenly due to pressure from the sinking plate. This results in an earthquake. The focus of the earthquake is the point within the Earth where the rupture first occurs, rocks break and the first seismic waves are generated. The epicenter is the point on the seafloor directly above the focus.
When this piece of the plate snaps up and sends tons of rock shooting upward with tremendous force, the energy of that force is transferred to the water. The energy pushes the water upward above normal sea level. This is the birth of a tsunami. The earthquake that generated the December 26, 2004, tsunami in the Indian Ocean was a 9.0 on the Richter scale -- one of the biggest in recorded history
