Why Tsunami and Earthquake Happens?

Why Do Earthquakes Happen?

Earthquakes are caused when rocks underground suddenly breaks along a crack.

As believed, beyond the earth surface, layers of earth are made up of water and rocks.  And as the earth rotates, these rocks rub to each other tightly.  They don't roll down. They stick together and catch to each other tightly, but because of the pressure that build ups, some rocks break and cracks travel upward the earth surface and earthquake occurs. Afterwards, these plates and blocks of rocks underground the earth surface also move and catch each other until they stuck up again. These series of movements after the earthquake is what we called "aftershock".  Intensity of earthquake depends on how hard is the movement underground and how fast it reaches the earth surface where people and  animals live.  The crack that was created upward the earth surface is called Fault.  The spot where rocks break is called Focus of the earthquake, while the spot on the earth surface right above the focus is called Epicenter.

When the Epicenter  or Fault is situated in the seabed (bottom of the ocean), earthquake and Tsunami may go hand-in-hand. Tsunami is generated when huge dense of water erode and finds it way to fill the gap. As the Fault absorb the water, a rotating motion occurs,  generating a rapid and strong energy that changes the normal flow of water on the sea surface.  It cannot tell how quake has affected the seafloor until hours, days or even months after the event. And a tsunami is almost imperceptible on the open ocean, rising to full ferocity only as it nears the shore.

As a tsunami approaches shore,  it begins to slow and grow in height. Just like other water waves, tsunamis begin to lose energy as they rush onshore - part of the wave energy is reflected offshore, while the shoreward-propagating wave energy is dissipated through bottom friction and turbulence. Despite these losses, tsunamis still reach the coast with tremendous amounts of energy. Tsunamis have great erosional potential, stripping beaches of sand that may have taken years to accumulate and undermining trees and other coastal vegetation. Capable of inundating, or flooding, hundreds of meters inland past the typical high-water level, the fast-moving water associated with the inundating tsunami can crush homes and other coastal structures. Tsunamis may reach a maximum vertical height onshore above sea level, often called a run-up height of 10, 20, and even 30 meters.