1. Warm Up 10/21(22)
When an earthquake occurs, energy radiates in all directions from its source, which is called the ____.
a. fault c. seismic center
b. epicenter d. focus
The hypothesis that explains the release of energy during an earthquake is called the ____.
a. moment magnitude hypothesis c. Richter hypothesis
b. elastic rebound hypothesis d. vibration hypothesis
Most earthquakes are produced by the rapid release of which kind of energy stored in rock subjected to great forces?
a. thermal c. chemical
b. elastic d. Mechanical
1. d, 2. b, 3. b

2. Earth’s Layered Structure
Chapter 8, Section 4

3. Layers Defined by Composition
If Earth were made up of the same materials throughout its interior, seismic waves would travel in straight lines at constant speeds
Seismic waves reaching seismographs located farther from an earthquake travel at faster average speeds, due to increased pressure at depth
Earth’s interior consists of three major zones defined by its chemical composition – the crust, mantle, and core

4. Paths of Seismic Rays

5. The Crust
Crust – thin, rocky, outer layer of Earth; divided into oceanic and continental crust
The oceanic crust is roughly 7 kilometers thick and composed of the igneous rocks basalt and gabbro
The continental crust is 8-75 kilometers thick (avg. 40 km) and consists mostly of the granitic rock granodiorite
The rocks of the oceanic crust are younger then the rocks of the continental crust

6. Mantle and Core
Mantle – a solid, rocky shell that extends to a depth of 2890 km
Over 82% of Earth’s mass is contained in the mantle
The boundary between the crust and mantle represents a chemical composition change
Core – a sphere composed of an iron-nickel alloy

7. Concept Check What is the composition of the core?
An iron-nickel alloy

8. Layers Defined by Physical Properties
Earth’s interior has a gradual increase in temperature, pressure, and density with depth
Depending on the physical environment (temperature and pressure), a material may behave like a brittle solid, a putty, or a liquid
Earth can be divided into layers based on physical properties – the lithosphere, asthenosphere, outer core, and inner core.

9. Lithosphere and Asthenosphere
Lithosphere – relatively cool, rigid shell consisting of the crust and upper most mantle
Averages about 100 kilometers in thickness
Asthenosphere – soft, comparatively weak layer beneath the lithosphere
The rocks within the asthenosphere are close enough to their melting points that they are easily deformed

10. Lower Mantle
From a depth of 660 km down to near the base of the mantle
More rigid layer that is still prone to gradual flow
At the bottom of the mantle, rocks behave more like those in the asthenosphere

11. Inner and Outer Core
The core, which is composed of an iron-nickel alloy, is divided into two regions with different physical properties
Outer Core – liquid layer 2260 km thick, flow produces Earth’s magnetic field
Inner Core – sphere with a radius of 1220 km, compressed into a solid state by immense pressure

12. Earth’s Layered Structure

13. Concept Check Why is the inner core solid?
It is under extreme pressure and is compressed into a solid as a result

14. Discovering Earth’s Layers
Moho – boundary separating the crust from the mantle where the velocity of seismic waves abruptly increases
Seismic waves from even small earthquakes can travel around the world
The outer core causes P waves that travel through it to arrive several minutes after expected and are bent by 100o away from the earthquake (shadow zone)
It was further shown that S waves do not travel through the outer core, making geologists conclude that the outer core is composed of a liquid

15. Concept Check What is the Moho?
The boundary between the crust and the mantle

16. Discovering Earth’s Composition
Early seismic data and drilling technology indicate that the continental crust is mostly made of lighter, granitic rocks
The crust of the ocean floor has a baslatic composition
The composition of the mantle and core is known from more indirect data
Scientists use lava and meteorites to infer the composition of the mantle and core
Earth’s core is thought to be mainly dense iron and nickel, similar to metallic meteorites. The surrounding mantle is believed to be composed of rocks similar to stony meteorites

17. Earth’s Interior Showing P and S Wave Paths

18. Assignment Read Chapter 8, Section 4 (pg. 233-237)
Do 8.4 Assessment #1-6 (pg. 237)