ESAY+2.2

toc

Vocabulary
Primary Waves**:An earthquake wave in which rock particles vibrate parallel to the direction of wave travel. It can travel through solids and liquids** S waves**:An earthquake wave in which rock particles vibrate at right angles to the direction of wave travel. It can travel through solids but not through liquids.** Surface waves: **Move slowly, but they produce the most severe ground movements.** Magnitude: **A measurement of earthquake strength based upon seismic waves and movement among faults.** Seismograph: **An instrument used by geologists to record the ground movement caused by seismic waves.** Mercalli Scale: **A scale of earthquake intensity based on observed effects and ranging from I (detectable only with instruments) to XII (causing almost total destruction).** Richter scale: **A logarithmic scale used to express the total amount of energy released by an earthquake. Although the scale has no upper limit, values are typically between 1 and 9, and each increase of 1 represents a 32-fold increase in released energy.** Moment Magnitude scale **- A logarithmic scale of 1 to 10 (a successor to the Richter scale) that enables seismologists to compare the energy released by different earthquakes on the basis of the area of the geological fault that ruptured in the quake**
 * Epicenter**:The point on the earth's surface directly above the location in the earth (focus) where an earthquake originatesFocus**:the point beneath Earth's surface where rocks that are under stress break and trigger or make an earthquake the focus** Seismic Waves**:waves that carry the vibrations or energy of an earthquake**

Outline
Introduction**:**
 * Earth is never still
 * Every day any time there are about 8000 earthquakes that happen.
 * most of them are too small to notice but when an earthquake is strong enough to rattle dishes in kitchen cabinets ,people sit up and take notice "how big was the earthquake "and where was it centered" are two questions which each other.
 * To know where earthquake was centered you need to know where it began.
 * earthquake always begin in rock below the surface .most earthquake began in lithosphere within 100 kilometres of earths surface an earthquake starts on a particular point.

Seismic Waves:
 * A drumbeat produces vibrations called sound waves.
 * During an earthquake,seismic waves race out from the focus in all directions. They carry the energy from the focus through the Earth's interior, and across the surface.
 * There are three types of Seismic waves.

Primary waves or P waves**, are the first waves to arrive, which compresses and expands the ground like an accordion,** = = = = Secondary waves **or S waves** **come next, which vibrates side to side as well as up and down. Surface waves** **produce the most severe ground movements.

Detecting Seismic waves:**


 * To record and measure the vibrations of seismic waves geologists use instruments called seismograph.
 * Today, scientists use electronic seismograph that converts ground movements into a signal that can be recorded and printed.
 * There are three types of scales to measure earthquakes.
 * The Mercalli scale, the Richter scale, and the Movement magnitude scale.

Locating the epicenter:**


 * **Geologists use seismic waves to locate an earthquake's epicenter.**
 * **They draw three circles using data from different seismographs.**
 * **The center of each circle is a particular seismograph location. The point where the three circles intersect is the epicenter.**

= =

back to homepage