Earthquakes and More

What is Plate Tectonics The Earth’s crust and upper mantle are broken into sections called plates Plates move around on top of the mantle like rafts

Plate Boundaries 1. Divergent 2. Convergent 3. Transformational

Divergent Boundaries Boundary between two plates that are moving apart or rifting   causes SEAFLOOR SPREADING

Convergent Boundaries Boundaries between two plates that are colliding  

Andes Mountains, South America

Aleutian Islands, Alaska

Transformational Plates Boundary between two plates that are sliding past each other They move in Jerks! EARTHQUAKES along faults

Fault? Is a narrow zone in the earth about 10 miles deep.

San Andreas Fault, CA Separates the Pacific Plate and North American Plate The Pacific plate moves about 4 inches per year.

What are Earthquakes? The shaking or trembling caused by the sudden release of energy Usually associated with faulting or breaking of rocks

The Focus and Epicenter of an Earthquake The point within Earth where faulting begins is the focus. The point directly above the focus on the surface is the epicenter

What is the Elastic Rebound Theory? Explains how energy is stored in rocks Rocks bend until the strength of the rock is exceeded Rupture occurs and the rocks quickly Energy is released in waves that radiate outward from the fault

Elastic Rebound

Seismographs record earthquake events & measure seismic waves

Seismograms Electronically recorded ground motion made by seismographs

Where Do Earthquakes Occur and How Often? ~80% of all earthquakes occur in the circum-Pacific belt more than 150,000 quakes strong enough to be felt are recorded each year

The Economics and Societal Impacts of EQs Damage in Oakland, CA, 1989 Building collapse Fire Tsunami Ground failure

Seismic Earthquake Waves? Body waves – in ground P and S waves (Primary and Secondary)

Body Waves (Ground Waves): P and S waves Body waves (in the ground) P or primary waves fastest waves travel through solids, liquids, or gases compressional wave, movement is in the same direction as wave movement S or secondary waves slower than P waves travel through solids only Move perpendicular to wave movement

Earthquakes generate Surface Waves . Surface waves (above the ground – on surface) R and L waves (Rayleigh and Love)

Surface Waves: R and L waves Travel just along the grounds surface Slower than body waves; rolling up and down or side- to-side movement Especially damaging to buildings

To locate an earthquake you need to measure the time between the P and S waves. P waves arrive first, then S waves, then L and R 3 Seismograms are needed to locate the earthquake.

How are the Size and Strength of an Earthquake Measured? Magnitude Richter scale measures total amount of energy released A magnitude 6.0 earthquake is 10 times greater than a 5.0, a 7.0 is 100 times greater, and a magnitude 8.0 is 1,000 times greater.

Layers Defined by Composition Earth’s interior consists of three major zones defined by their chemical composition— Crust Mantle Core (inner & outer) • •

 Crust – thin rocky layer • The Crust is about 25 miles beneath the continents and about 6.5 miles thick beneath the oceans. It is light and brittle. Most earthquakes occur within the crust.

The Mantle  Mantle The region just below the crust extending all the way to the earth’s core is called the mantle. It is relatively flexible so it flows instead of fracturing. (Lava)

The Core (Inner & Outer) • Below mantle is the earth’s core. The core consists of a fluid outer core and a solid inner core. The outer core contains iron, when it flows it generates a magnetic field. This is the source of the Earth’s magnetic field. The inner core is solid

Earth’s Layered Structure