Earthquakes

What are earthquakes? Vibration in the ground that result from movement along faults. Fault = a break in Earth’s lithosphere where one block of rock moves toward, away from, or past another.

Why do earthquakes occur? Result from the buildup and release of stress along active plate boundaries.

Where do earthquakes occur? The deepest earthquakes occur at convergent plate boundaries where the denser oceanic plate subducts into the mantle (ocean-continent or ocean-ocean boundaries) Shallow earthquakes are common along divergent and transform plate boundaries.

Most earthquakes occur in oceans and along edges of continents. Why?

Types of Faults – where earthquakes occur

Seismic Waves Energy that travels as vibration on and in Earth as rocks move along a fault.

Epicenter = the location on the Earth’s surface directly above the earthquake’s focus. Focus = the location deep inside the Earth where the waves originate – where the rocks first move along the fault.

How do scientists classify seismic waves? Use: Wave motion Wave speed Type of material the waves travel through

3 Types of Seismic Waves

Who studies these waves? Seismologists = scientists that study earthquake waves Use these waves to map Earth’s interior Also try to predict future earthquakes

How do earthquake waves map Earth’s interior? P-waves and S-waves at different depths within Earth’s interior travel at different speeds.

How are these waves measured? Seismometer (seismograph)= measures and records ground waves and the distance and direction the seismic waves travel. Seismogram = graphical illustration of the waves.

Triangulation The method used to locate an earthquake’s epicenter. P. 299 of textbook

Scientists can use three different scales to measure and describe earthquakes. The Richter magnitude scale uses the amount of ground motion at a given distance from an earthquake to determine magnitude. The moment magnitude scale measures the total amount of energy released by the earthquake. Measuring an Earthquake’s Magnitude

The Modified Mercalli scale measures earthquake intensity based on descriptions of the earthquake’s effects on people and structures.

Areas that experienced earthquakes in the past will likely experience earthquakes again. Seismologists assess earthquake risk by studying past earthquake activity and local geology.