Wednesday, 25 May 2016
what is a eartquake
What is a earthquake!!!!!!!!!
A earthquake is a shaking of the ground caused by the sudden breaking and movement of large sections tectonic plates of the earth's rocky outermost crust.The edges of the tectonic plates are marked by faults lines when the plates slide past each other or collide against each other.
In christchurch there have been over 11,000 since 2010 Here are some photos of what an earthquake has done to houes in christchurch.
WHY DO EARTHQUAKES HAPPEN
Earthquakes are usually caused when rock underground suddenly breaks along a fault. This sudden release of energy causes the seismic waves that make the ground shake. When two blocks of rock or two plates are rubbing against each other, they stick a little. They don't just slide smoothly; the rocks catch on each other. The rocks are still pushing against each other, but not moving. After a while, the rocks break because of all the pressure that's built up. When the rocks break, the earthquake occurs. During the earthquake and afterward, the plates or blocks of rock start moving, and they continue to move until they get stuck again. The spot underground where the rock breaks is called the focus of the earthquake. The place right above the focus (on top of the ground) is called the epicenter of the earthquake.
WHY DOES THE EARTH SHAKE WHEN THERE IS AN EARTHQUAKE?
While the edges of faults are stuck together, and the rest of the block is moving, the energy that would normally cause the blocks to slide past one another is being stored up. When the force of the moving blocks finally overcomes the friction of the jagged edges of the fault and it unsticks, all that stored up energy is released. The energy radiates outward from the fault in all directions in the form of seismic waves like ripples on a pond. The seismic waves shake the earth as they move through it, and when the waves reach the earth’s surface, they shake the ground and anything on it, like our houses and us!see P&S Wave inset.