In March, 1964, a man walking down the street in Valdez, Alaska, Felt something strange. The earth was moving underneath him. The ground rolled and shook for about of minutes. The man experienced one of the biggest earthquakes ever recorded on Earth. The earthquake nearly destroyed the town of Valdez, Killed more than 100 people, and caused millions of dollars ofdamage.
What is an Earthquake?
An earthquake is exactly what its name states: a quaking, or shaking, of the Earth. The effects of an earthquake can range anywhere from barely noticeable to incredibly damaging and life-threatening.
Earthquakes occur when large masses of rock move suddenly against each other and break. The point where the earthquake begins is called the focus. The focus can be veryclose to the surface, or hundreds of miles underground. The point on the surface of the Earth directly above the focus is the epicenter. The epicenter in the Valdez earthquake was 45 miles west of the town. The focus was 14 miles below the Earth’s surface.
What causes Earthquakes?
The Earth has layers. The outer layer is made up of about twelve large rocky plates that move very slowly. In someplaces, the plates move away from each other. In other places, they grind past each other, and in still others, they crash into each other. As the plates move, pressure builds in the rock. The rock actually bends a little, but in time, it can break and cause an earthquake. Most earthquakes occur where two plates meet.
What effects does an earthquake have?
When an earthquake takes place, thesnapping or breaking of rock sends seismic (SIZE-mik) waves through the Earth. Seismic waves move in a similar way to sound waves and water waves. They make the entire Earth vibrate. When the waves get to the surface, they make the ground roll up and down and shake back and forth. Seismic waves also cause rumbling sounds in the air.
Earthquakes have many effects on the land and the ocean. They cancause rock falls and landslides. They can also create huge gashes in the ground. Sometimes a piece of land drops down, while another piece rises up.
If an earthquake occurs below the ocean, part of the ocean floor can move suddenly. This can cause a giant wave called a tsunami (soo NAH mee). Tsunamis travel across the ocean at hundreds of miles per hour. When they hit land, they can be huge. Some aremore than 100 feet high.
Earthquakes have many effects on people and building. Earthquakes cause buildings and bridges to shake and crack. If the earthquake is strong, building can collapse. Fires can start when gas pipes break. If water pipes break, it can be hard for people to get clean water. Often, there is not enough food or medicine after a big earthquake.
How do scientists measureearthquakes?
Scientists measure the size or strength of an earthquake by using special instruments called seismometers. A seismometer is attached to the ground, so it shakes as the ground shakes. A pen scribbles a zig-zag line on roll of paper. The Height of the zig-zag helps scientists determine the strength of an earthquake.
Earthquakes occur every day, but often nobody notices them. These are smallearthquakes, which cause little or no damage. Large earthquakes can cause enormous damage and kill many people.
Think about the article “shake, rattle, and roll”. Circle the letter next to the best answer.
1. The ground shakes during an earthquake, because?
A Seismic waves move through the Earth.
B The epicenter is hundreds of miles away from the focus.
C Landslides makemud and rocks slide down hills.
D Water waves move through the ocean and crash onto land.
2. When an earthquake occurs, which of these happens first?
A Rocks break.
B Rocks move away from each other.
C Giant waves crash into the shore.
D Waves shake the ground.
3. In which way are seismic waves different from tsunami waves?
A Seismic waves travel through rock.
B Seismic waves can cause a...