Earthquakes and Earth's Layers

• Earth and Space, Fourth Quarter

Learning Objectives

• Defining and explaining how earthquakes occur
• Understanding the difference between magnitude and intensity
• Identifying preparedness measures for before, during, and after an earthquake

Layers of the Earth: Crust

• Outermost and thinnest layer
• Life exists in the crust
• Continental and oceanic are the 2 types of crust
• The Mohorovicic Discontinuity is the boundary between the crust and the mantle; discovered in 1909 by Andrija Mohorovicic
• The lithosphere comprises the solid, outermost part of the planet
• Lithosphere comprised of the crust and the uppermost part of the (rigid) mantle
• The lithosphere is broken into plates

Mantle

• 2,900 km thick, making it the thickest layer
• The mantle makes up 84% of the earth's layers
• The asthenosphere is a semi-fluid layer below the lithosphere
• Asthenosphere is key to understanding plate tectonics and earthquakes
• The upper mantle is also known as the asthenosphere
• The lower mantle is denser and more rigid
• The Guttenberg discontinuity marks the boundary between the lower mantle and outer core

Core

• The core is like a ball of very hot metals
• The outer core is fluid (magma-like)
• The inner core is the deepest part of the Earth, made of iron-nickel alloy
• The inner core is solid due to extreme pressure

Knowledge Check

• The mantle is the Earth's largest layer
• The asthenosphere cannot be found in the core
• The inner core is solid while the outer core is fluid
• The Guttenberg discontinuity is the boundary between the mantle and the outer core
• Asthenosphere is responsible for the movement of plates

Earthquakes

• Earthquakes are the shaking of the Earth's surface
• They result from a sudden release of energy in the Earth's lithosphere
• Seismology: study of earthquakes and seismic waves
• Seismologists investigate earthquake's strengths and its damage
• A seismometer records the shaking of the Earth's surface caused by seismic waves
• Filippo Cecchi invented the first true seismometer
• The seismograph is a combined seismometer and recording device
• The seismogram is a record made by the seismograph at a specific location
• In a seismogram the horizontal axis = time
• In a seismogram the vertical axis = ground displacement/shaking

Magnitude vs. Intensity

• Magnitude describes the total amount of energy released by an earthquake
• Magnitude is determined by seismographs
• The Richter Scale was developed by Charles Richter
• Intensity describes how much a certain area was shaken
• Intensity refers to the effects of the earthquake at a specific location
• Intensity is determined by the earthquakes effect on people, human structures, and natural environment
• Intensity factors:
• Distance from the epicenter
• Defective building designs
• The kind of ground where the structures are built
• Duration of earthquake

Marshmallow Quake Tower (Activity)

• The class is divided into six groups
• Each group brainstorms what kind of structure to build using marshmallows and toothpicks
• The structure should be stable and flexible or able to move without collapsing in the earthquake simulator
• Each group will have 20 minutes to finish
• The structures will be situated in an earthquake simulator with gentle, moderate, and strong shaking
• Pointing system:
• 3 points for intact and stable structure after gentle shaking
• Another 3 points for intact and stable structure after moderate shaking
• Another 4 points for intact and stable structure after strong shaking
• Guide questions:
• What happened to the structures?
• Did they fall apart , lean or remain standing in three different shakings?
• Which parts were most vulnerable to shaking?
• What changes can make to improve the stability of the structure?

Seismic Waves

• Two main types of seismic waves:
• Body waves (P-waves and S-waves)
• Surface waves (L-waves and R-waves)

Body Waves: P-Waves

• Longitudinal waves, also known as compressional waves
• Fastest moving waves
• First to be recorded in seismographs
• P-waves can travel through solids, liquids, and gases

Body Waves: S-Waves

• Transverse wave
• Slower than P-waves
• S-waves only travel through solids

Surface Waves: L-Waves

• Love waves or q-waves
• Fastest surface waves, produced horizontal motion because of side-to-side movement of ground

Surface Waves: R-Waves

• Rayleigh waves
• They move ground, up and down, side to side
• Slowest of surface waves

Activity: Roleplay

• The class will be divided into 3 groups to present an Earthquake Preparedness roleplay
• Group 1: BEFORE an Earthquake
• Group 2: DURING an Earthquake
• Group 3: AFTER an Earthquake
• Groups will have 30 minutes to prepare
• After 30 minutes, each group will show their presentation
• Groups that are not performing, will need to identify the precautionary measures presented by the group
• Rubrics:
• Performance - 10 points
• Content accuracy - 10 points
• Collaboration - 5 points
• Engagement - 5 points