SCIENCE CHAPTER 8

• Earthquake is a weak to violent shaking of the ground caused by the sudden movement of the rocks below the surface of Earth
• Crust - a solid material that composes the Earth's surface.
• Theres about 20 plates along the surface of the Earth.
• mantle - the layer underneath the crust
• lithosphere - the crust together with the upper mantle
• oceanic plates - the plates under the ocean and the rest are called continental plates
• earthquakes usually originate from a tectonic plate boundary
• faults are the lines or cracks in earth's surface
• tectonic earthquakes are the most common type of earthquake, this is caused by the sudden movements along the tectonic faults and plate boundaries
• volcanic earthquakes are caused by volcanic activities such as rising magma or lava beneath active volcanoes
• collapse earthquakes are small quakes that occur in caverns or mines, often caused by underground blasts during mining operation
• explosion earthquakes result from the explosion of a nuclear or chemical material or device
• seismology is the study of seismic waves, or energy waves that cause earthquakes
• the scientists who specialize on this discipline are called seismologists
• seismologists use an instrument called a seismograph to detect and record earthquakes
• once the motion is recorded, a seismogram is created
• primary waves are the fastest seismic waves and can move through any phase of matter
• secondary waves only moves through solids
• surface waves, although they are the last to reach the seismograph, occur longest
• there are 2 ways to measure the strength of an earthquake : magnitude and intensity
• the magnitude refers to the size of the seismic waves that are recorded on the seismograph
• to measure the magnitude, scientists use the moment magnitude scale (mms, also called the richter scale) which is represented by hindu-arabic numerals
• the intensity is the strenght of the earhtquake based on the observed effects on humans and animals
• an earthquake is usually followed by aftershocks or smaller earthquakes
• philippine institute of volcanology and seismology (PHIVOLCS)