Earthquakes

Objectives 1.Describe how faults can cause earthquakes 2.Identify an earthquake focus and epicenter and describe how to find one 3.Identify earthquake zones and why the regions are prone to earthquakes 4.Compare the different types of seismic waves 5.Describe how tsunami ’ s are caused by earthquakes 6.Describe how earthquakes are predicted and why this is difficult

Recap Question: Where is the ring of fire and why is it called this? Tectonic Plates

What is an Earthquake? A shaking of Earth’s crust caused by a release of energy Caused by: –Volcanic eruption –Collapse of cavern –Meteor impact –Stress building up between lithosphereic plates

Faults are typically active repeatedly because: 1.Plate tectonic processes continue in some locations 2.Fault is a zone of weakness in crust and easier for movement to take place

Yellow to red colors indicate regions experiencing damaging shaking. Isolated regions of intense shaking, like the one near Santa Rosa 20 miles from the fault, result from a combination of the amount of slip nearby on the fault, the geologic materials that the seismic waves travel through, and the local geologic conditions.

How can rocks be stressed? 1.Compression 2.Tension 3.Shear

Compression: Rocks will fold or fracture. Commonly found at convergent plate boundaries…why?

Tension: Rocks will lengthen or break apart. Often found at divergent plate boundaries…why?

Shear: Rock has opposing forces acting on it. Most common at transform plate boundaries.

Elastic Rebound Theory A. Almost all earthquakes occur at plate boundaries B. When stresses build up in the rocks, the rocks will bend elastically building up potential energy in rock C. The rock layer will eventually snap releasing the built up energy. D. This released energy is an earthquake Why do earthquakes happen more often around faults near boundaries?

Earthquakes and Boundaries Divergent Boundary: Typically shallow Ex: Mid-Atlanic Ridge

Earthquakes and Boundaries Transform Boundary: Typically shallow (why?) and highly destructive Ex: San Andreas Fault

Earthquakes and Boundaries Convergent Boundary: Shallow, intermediate or deep. Ex: Juan de Fuca plate

Earthquakes and Tsunami

Types of Waves Body Waves: Primary Waves Fastest traveling Longitudinal motion (back and forth) Can move through solids, liquids and gases

Types of Waves Body Waves: Secondary Waves Slower than P waves Transverse motion (up and down) Can move through solids

Types of Waves Surface Waves: Love Waves: Side to Side motion Rayleigh Waves: Move in rolls (like ocean)

S waves..find pictures to associate with each type of wave??

Types of Waves Review om/watch?v=1939c 9Ydp7s

Locating Earthquakes Seismograph –Instrument that records earthquake waves Seismogram –Record sheet showing waves

How to Read a Seismograph

3 Stations are needed to locate