Tuesday, April 29, 2008
What is an Earthquake?An earthquake is the shaking and vibration at the surface of the earth caused by underground movement along a fault plane or by volcanic activity.It is the result of sudden release of energy in the Earth's crust which creates seismic waves, which are recorded with a seismometer.The magnitude is recorded and categorised with the Richter scale, while the intensity is measured on the Mercalli scale.What causes an Earthquake? How does it occur?The majority of earthquakes happen due to plate tectonics; the plates moving towards, away from, or past each other, causing frictional stress. When this stress exceeds a certain level, a sudden failure occurs, following which the violent displacement of the crust will release energy, triggering an earthquake.The seismic waves, which is essentially stored-up energy, can be classified into two categories: Body waves and Surface waves.Body waves travel through the interior of the earth, and can be further sorted into two types: P waves, and S waves.P waves are compressional waves, meaning they deform rocks by changing its volume, alternately compressing and expanding matter.S waves are shear waves, and deforms material by change of shape, adopting a side-to-side sliding motion.Surface waves occur when P and S waves reach the earth's surface, therefore travelling along the surface, and causing the ground to ripple. There are also two types of Surface waves: Rayleigh waves (which cause vertical ground movement), and Love waves (which cause horizontal ground movement).
Environmentalists Blogged:7:56 AM
Monday, April 28, 2008
Hi people!Just a quick introduction:This blog is started by Catharina Cheung and Kirti Dodani.We are utilising it for our Geography mini project (how's this for creative eh?).We are students of 08A3, under Mr Desmond Tan, and from Millennia Institute.Our mini project is on earthquakes, and we're supposed to educate the general public on its nature and destructive powers.There. よろしくおねがいします!:D
Environmentalists Blogged:7:19 AM