Warm Up Which of the following areas would most likely be the safest during a major earthquake? a. area with granite bedrock b. area with steep slopes of unconsolidated sediments c. area with loosely consolidated soil d. area with structures built on a landfill A tsunami can occur when there is vertical movement at a fault under ____. a. the ocean floorc. the San Andreas Fault b. a mountain ranged. a small inland lake Which of the following is used in an attempt to make short-range predictions of when earthquakes will occur? a. height of ocean waves after earthquakes b. study of historical records c. changes in the color of rocks near faults d. strain in rocks near faults Answers: 1) a. 2) a. 3) d.

Earth’s Layered Structure Chapter 8, Section 4

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 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 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 Earth’s interior consists of three major zones defined by its chemical composition – the crust, mantle, and core

Paths of Seismic Rays

The Crust Crust – thin, rocky, outer layer of Earth; divided into oceanic and continental 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 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 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 The rocks of the oceanic crust are younger then the rocks of the continental crust

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

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

Layers Defined by Physical Properties Earth’s interior has a gradual increase in temperature, pressure, and density with depth 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 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. Earth can be divided into layers based on physical properties – the lithosphere, asthenosphere, outer core, and inner core.

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

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

Inner and Outer Core The core, which is composed of an iron-nickel alloy, is divided into two regions with different physical properties 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 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 Inner Core – sphere with a radius of 1220 km, compressed into a solid state by immense pressure

Earth’s Layered Structure

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

Discovering Earth’s Layers Moho – boundary separating the crust from the mantle where the velocity of seismic waves abruptly increases 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 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 100 o away from the earthquake (shadow zone) The outer core causes P waves that travel through it to arrive several minutes after expected and are bent by 100 o 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 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

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

Discovering Earth’s Composition Early seismic data and drilling technology indicate that the continental crust is mostly made of lighter, granitic rocks 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 crust of the ocean floor has a baslatic composition The composition of the mantle and core is known from more indirect data 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 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 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

Earth’s Interior Showing P and S Wave Paths

Assignment Read Chapter 8, Section 4 (pg ) Read Chapter 8, Section 4 (pg ) Do Chapter 8 Assessment #1-29 Do Chapter 8 Assessment #1-29 (pg ) For Section 4: Do #’s 3, 6, 16, & 23 For Section 4: Do #’s 3, 6, 16, & 23 Study for the Chapter 8 Quiz! Study for the Chapter 8 Quiz!