Chapter 8 Earthquakes
Section 1: What are Earthquakes?
Earthquakes Mainly occur along faults near the edges of tectonic plates. Elastic rebound is the direct cause of earthquakes- return to original shape
EQs differ depending on what type of plate motion causes them. Seismic waves are classified as body waves or surface waves.
Body waves travel through the Earth’s interior, while surface waves travel along the surface. 2 types of body waves: P waves S waves
Seismic Waves 2 types of body waves: P waves: fastest waves that travel thru solid, liquid, and gases Called Primary Waves
S waves: second fastest waves, cannot travel thru parts of the Earth that are completely liquid Secondary waves
Seismic Waves Surface Waves: travel on surface of Earth Do most damage to buildings and structures
Deformation: change in shape of rock due to stress 2 types: Plastic deformation: bends like a piece of molded clay; does not lead to earthquakes Elastic deformation: breaks like a stick; does lead to earthquakes
All Earthquakes are NOT the Same Plate Motion Major Fault Type EQ Characteristics Transform Strike-slip fault Moderate, shallow Convergent Reverse Fault Strong, deep Divergent Normal Fault Weak, shallow
Section 2: Earthquake Measurement
Earthquake Measurement Seismographs can tell when and where an earthquake took place. Epicenter is the point on Earth’s surface directly above where an EQ started. Focus is inside the Earth where the EQ began.
The S-P time method is the simplest to use to find an earthquakes epicenter. Seismologists use the Richter scale to measure an earthquake’s strength.
Seismologists use the Modified Mercalli Intensity Scale to measure an earthquakes intensity.
Section 3: Earthquakes and Society
Earthquake Hazards Earthquake hazard measures how prone/likely an area is to experiencing EQ in the future. Some EQ predictions are based on the relationship b/w EQ strength and EQ frequency. As frequency decreases, strength increases.
EQ usually collapse a structure by displacing the structure's center of gravity.