Paragraph on how measuring changes in the land.

• Zhang Heng, an astronomer, designed and built a earthquake detector device in Chine nearly 2,000 years ago. People say that it can detect a earthquake several thousand miles away. 
• A seismograph can consist of a heavy weight attached to a frame by a spring or wire. 
• A pen connected to the weight rests its point on a drum that can rotate. As the drum rotates slowly, the pen draws a straight line on the papers wrapped tightly around the drum.
• Seismic waves cause the seismograph's drum to vibrate. But the suspended weight with the pen attached moves very little. Therefore, the pen stays in place and records the drum's vibrations.  
• Along a fault, scientists may detect a slight rise or fall in the elevation and tilt of  the land. 
• To monitor faults, geologists have developed instruments to measure changes in elevations, tilting of the land surface, and ground movements along faults. 
• A tiltmeter measures tilting or raising of the ground. A tiltmeter used by geologists is made up of two bulbs that are filled with a liquid and connected by a hollow stem. 
• A Creep Meters is used a wire stretched across a fault to measure horizontal movement of the ground. On one side of the fault, the wire is anchored to a post. On the other side, the wire is attached to a weight that can slide if the fault moves. 
• A laser- Ranging devices uses a laser beam to detect horizontal fault movement. The device times a laser beam as it travels to a reflector and back.  
• Faults are usually hidden by a thick layer of rock and soil. When seismic waves encounter a fault, the waves are reflected off the fault. 

1. A seismograph is a tool used to detect how far a earthquake is and how big it is. 
2. a seismograph uses lines to record the earthquake. 
3. It would compare the big one and the small one and tell which ones stronger and has more power. 
4. The four tools are tiltmeters, creep meters, laser- ranging devices and GPS satellites. 
5. Same measure the speed, the height and how long until it happens. 

     7. they can use them to see how often there are earthquakes in that area.