Stresses Faults Plate Boundaries Arrows Relationship between stresses, results and locations

The Earth’s Internal Properties Chapter 12 page

Read Section 12.1 How and Where Earthquakes Happen and Section 12.2 Studying Earthquakes Pay special attention to figures and pictures Read pages `

Seismic Waves Earthquake waves have revealed that the Earth is layered

Waves travel through different mediums at different speeds Air is slower than water Water is slower than solids

Waves are measured on a seismograph Seismograph is the instrument Seismogram is the paper readout Modern ones electronic- seismometer Basic variety-heavy mass that resists movement

Two types of seismic wavesseismic waves Body waves— travel through the Earth’s interior—two types P-waves S-waves Surface waves— travel on the Earth’s surface—two types Love waves Rayleigh waves

Body waves two types Primary waves— p-waves Fastest Longitudinal— expand and contract Travel through solid, liquid

Secondary waves—s-waves Slower Transverse— vibrate up and down and side to side Travel through solids

Primary Waves

Secondary waves

Surface Waves Rayleigh waves Love Waves Both are slower than body waves

Rayleigh Waves Move in an up and down fashion

Love Waves Move in a side-to-side, whip-like fashion

Putting it all together

Earthquake terms Epicenter—the point on the surface directly above the focus Focus—the exact location of the break

Focus depths vary and help us see different types of plate boundaries

Earthquakes are measured on the Richter Scale Each magnitude is 10 times more powerful than the preceding

How to Read a Seismogram The p-waves are the first to arrive The secondary are larger and arrive next

Locating Earthquakes Scientists draw lines perpendicular to the time from the first big deviation of the p and s waves

Difference between arrival of p and s waves gives a distance from the earthquake Blue primary waves followed by red secondary waves move outward in concentric circles from the epicenter

Time Travel Curve Next they use a time-travel curve The time difference between arrival times indicates distance Y-axis is time after start of earthquake X-axis-distance from earthquake

Locating an Earthquake The epicenter is where the circles overlap How many stations do you need to locate an earthquake?

Note: when determining arrival times remember, 9:00 AM is the same thing as 8:59:60 AM You will need to use this to subtract Work on Earthquake Information

Do questions Then do Draw lines on seismogram for p and s waves (write on 17) S-P Use time travel curve Fig16.5 Write down distance 18 Locate cities on the map using latitude and longitude Fig 16.7 Draw circles Locate Earthquake

Part II What Seismic Waves Tell Us

Read 23.2 Earth’s Internal Layers Pages ,

You can’t really dig to China So... How do we know what the inside of the Earth is like?

Seismic Waves Earthquake waves have revealed that the Earth is layered Remember the different characteristics of different seismic waves P-waves—solids and liquids S-waves—solids only

Waves travel through different mediums at different speeds Air is slower than water Water is slower than solids

Earth's Internal Layers Andrija Mohorovičić studied seismograms and discovered waves pick up speed at a certain depth Earth is layered Drew a map of the upper boundary of Earth's mantle, Mohorovičić discontinuity Cool geologists call it the Moho

Shadow Zone 104 to 140 degrees does not receive any direct P waves The shadow zone results from S waves being stopped entirely by the liquid core and P waves being bent (refracted) by the liquid core.

Shadow Zones— caused by refraction and s-waves cannot go through liquid

What can you tell by looking at this picture? What kind of wave are the blue lines? What kind of waves are the red lines? Why do the blue lines stop when they reach the core?

Shadow Zone 104 to 140 degrees does not receive any direct P waves. The shadow zone results from S waves being stopped entirely by the liquid core and P waves being bent (refracted) by the liquid core.

Shadow Zones— caused by refraction and s-waves cannot go through liquid

Major Layers Crust Mantle Outer core Inner core

Layers of the Earth Earlier you learned about crust, mantle, and core

Here are some new terms Look over only

Old TermsNew Terms Crust Mantle Core Outer Inner Lithosphere Crust and upper solid mantle Asthenosphere Lower mantle Core Outer Inner

The crust is the uppermost part of the lithosphere

Lithosphere The lithosphere varies from thin on the ocean floor to thick at the mountain ranges

The crust is 10km thick under the oceans Made of basalt Continental crust is between km thick Made of granitic rocks that are less dense than basalt

Crust Thickness

The lithosphere is very narrow and is rigid and brittle. It floats on the asthenosphere.

The Mantle 3000 kilometers thick Hot iron-rich silicate rocks Behaves plastically—a solid that flows Taffy example Lower part asthenosphere Upper lithosphere includes crust Convection currents occur here Hot less dense material rises Cooler more dense material sinks

The Mantle 3000 kilometers thick Hot iron-rich silicate rocks Behaves plastically—a solid that flows Taffy example Lower part asthenosphere Upper lithosphere includes crust Convection currents occur here Hot less dense material rises Cooler more dense material sinks

Asthenosphere The lower part of the mantle is called the asthenosphere Hot, iron-rich silicate rocks The asthenosphere is hot and behaves with plasticity. It is a solid that flows like a liquid

Thermal convection currents occur here

Convection currents: hot material rises, cools, and begins to fall again.

The core is still the core.

The core has two parts: the inner and outer cores Inner core: Solid iron and nickel Outer core: Liquid iron, nickel & sulfur

The Earth's interior is hot Part of the heat and pressure is from depth Part is left over from formation of the Earth (sometimes called residual heat) and part is from the decay of radioactive elements

If its so hot Why doesn’t the inner core melt? Look it up! And tell me next class!

The Earth's inner core spins within the liquid outer core producing a magnetic field

Fxn of magnetic field The magnetic field protects us from the solar wind - a high speed stream of radiation from the sun

Earthquake Lab Read the directions carefully USE PENCIL

Locating Earthquakes Scientists draw lines perpendicular to the time from the first big deviation of the p and s waves

Difference between arrival of p and s waves gives a distance from the earthquake

Next use the Time Travel Curve

Use the distance to draw a circle Use the distance found on the time travel curve Use the latitude and longitude given to find the three cities Use the legend at the bottom of the page to set your compass Draw a circle The earth quake is where all circles overlap

Problems? Did you draw the lines straight down Were you precise in your times Is your subtraction correct Did you use the time travel curve correctly Did you locate the cities in the right place Did you set your compass for the correct distance