POWERPOINT:
EARTHQUAKES
Review: Plate Tectonics • Plate tectonics is a theory of geology developed to explain the phenomenon of con$nental dri- • Currently the theory accepted by the vast majority of scien$sts working in this area • The earth's crust is broken into plates that move around each other • Three types of plate boundaries are formed: divergent, convergent, and transform boundaries
Review: Plate Tectonics • 2 layers: – The lithosphere "floats" on the asthenosphere & is broken-‐up into 7 major plates
Why do plates move? • Remember, convec$on currents in the Earth’s mantle are what drive plate moIons • The plates spread apart at divergent boundaries • Mid-‐AtlanIc Ridge allows mantle to seep to the surface through cracks and pushed plates of the earth apart
Review: Boundaries • All major interacIons among individual plates occur along their boundaries • Three main types of boundaries: convergent, divergent, & transform fault boundaries
transform
convergent
divergent
Volcanoes & Earthquakes Location • Earthquakes & volcanoes are located at plate boundaries
What is seismology? • Seismology is the study of Earthquakes & seismic waves that move through & around the earth • A seismologist is a scienIst who studies earthquakes and seismic waves
How Earthquakes Occur • As plates move, they release energy in vibraIons & waves called seismic waves • The waves begin below ground @ the focus of the earthquake (the locaIon of the originaIon of the waves) • The area above ground directly above the focus is called the epicenter – This locaIon experiences the largest seismic movement
Epicenter • The point on the surface of Earth that is right above the focus of an earthquake
Focus • Also called hypocenter • Located within the Earth where the earthquake occurred
What are Seismic Waves? • Seismic waves are the waves of energy caused by the sudden breaking of rock within the earth or an explosion • They are the energy that travels through the earth and is recorded on seismographs • There are two main types of body waves & surface waves
Body & Surface Waves • Surface waves travel along Earth’s surface • Body waves (P and S) travel inside the Earth • P & S waves radiate outward in all direcIons • Surface waves travel along the surface of the Earth
Body Waves
• Traveling through the interior of the earth, body waves arrive before the surface waves • These waves are of a higher frequency than surface waves P (Primary) Wave
• Fastest • 1st to arrive • Can move through solid rock & fluid • Push & pull moIon
S (Secondary) Wave
• Slower than P • 2nd to arrive • Can only move through solid rock • Up & down moIon
P Waves • P waves are compressional/longitudinal • Like a slinky o When you push it together and pull it apart, a wave is sent through the slinky o Each coil in the slinky vibrates back-‐and-‐ forth, the wave also travels back-‐and-‐forth o Therefore, the mo$on of the vibra$on is parallel to the direc$on the wave moves
S Waves • S waves are transverse; also called shear waves • Like shaking a rope o By shaking the rope, you create waves that move up and down o However, the energy is moving from le- to right o These two moIons are perpendicular to one another
Surface Waves • Travelling only through the crust, surface waves are of a lower frequency than body waves, and are easily disInguished on a seismogram as a result • Though they arrive aZer body waves, it is surface waves that are almost en$rely responsible for the damage and destruc$on associated with earthquakes
Surface Waves: 2 Types • Two types of Surface waves: • Love waves: the fastest surface wave & moves the ground from side-‐to-‐side; produce enIrely horizontal moIon • Rayleigh Waves: rolls along the ground just like a wave rolls across a lake or an ocean; because it rolls, it moves the ground up and down, and side-‐to-‐side in the same direcIon that the wave is moving
Surface Waves
• A surface wave is a wave that travels along a surface separaIng two media
Types of seismic waves P wave
Fast
S wave Surface waves
Intermediate
Slow Love
Rayleigh
Earthquakes • Earthquakes can be very small or large. Over 1 million earthquakes occur each year
HAPPY THURSDAY! Sept.
th 24
2015
Today’s Objective:
• • • •
Discuss Earthquakes & take notes Complete Earthquake worksheet Earthquake: ET Seismograph Activity
GET OUT SUMMARY HOMEWORK
Types of seismic waves P wave
Fast
S wave Surface waves
Intermediate
Slow Love
Rayleigh
Measuring Earthquakes
• Seismic acIvity and waves are measured using a seismograph • An earthquake can be quanIfied in two ways: o Richter Scale: Invented by Charles Richter o Each increase of "1" on the Richter scale indicates and increase of 30x magnificaIon in power of the earthquake o The Moment Magnitude Scale: o Typically used to measure Earthquakes larger than 6.5 o Measures the total energy released by the earthquake
Seismograph
• Records the energy waves of the earth • The goal of a seismograph is to accurately record the moIon of the ground during a quake • hdp://www.iris.edu/hq/programs/ educaIon_and_outreach/animaIons/8
Richter Scale
• The Richter scale is a standard scale used to compare earthquakes • It is a logarithmic scale, meaning that the numbers on the scale measure factors of 10 • Example: An earthquake that measures 4.0 on the Richter scale is 10 Imes larger than one that measures 3.0 • Anything below 2.0 is undetectable to a normal person and is called a microquake • Earthquakes measuring > 6.0 can cause significant damage • The biggest quake in the world since 1900 was a 9.5 (It rocked Chile on May 22, 1960)
How do scientists detect earthquakes? • When an earthquake occurs, the seismic waves travel through the Earth to the seismic staIon where the info. is transmided to distant computers
Effects of Earthquakes
• Magnitude 5 earthquakes usually damage property • Magnitude 2 earthquakes are generally too small to feel • Approximately every 5 years a magnitude 8 earthquake occurs, causing massive property damage and death • Earthquakes usually have an aZer-‐effect result of landslides and tsunamis
Mass Movements • Earth’s land surface consists of slopes, some more steep & other very gradual • While most slopes appear stable, they are always changing • The force of gravity causes material to move downslope • The transfer of rock and soil downslope due to gravity is called mass movement
Mass Movements: Landslides
• Some mass movements are very slow; others are really fast & sudden like landslides • The combined acIons of weathering & mass movement produce most landforms
Landslides
• Landslides occur when the shaking causes regions of the rock & soil to slide downhill • The same material would eventually fall with increased Ime, but earthquakes trigger many slides that do much bit of damage
Triggers of Mass Movements • Gravity is the force behind mass movements
Triggers of Mass Movements:
• Satura$on of surface materials with water • Oversteepening of slopes • Removal of vegeta$on • Earthquakes
Tsunamis
• An underwater earthquake, volcanic erupIon, or landslide that causes an intense wave through ocean water • This wave can travel through water at more than 750 km or 450 miles per hour. • Tsunamis may start at about 1 m high in ocean water but reach 30 m high (a 10 story building) as they approach the shallower waters near a shoreline
Tsunamis Initiation
Effects of Tsunamis
① Coastal degradaIon from the impact & current of the wave ② Displaced animals leZ ashore aZer the wave leaves ③ DestrucIon of coastal infrastructure ④ PolluIon of local coastal area by saltwater ⑤ Oil & gasoline from overturned vehicles causes water polluIon ⑥ Damage of reefs & offshore coastal environments
Famous Earthquakes • San Francisco, California: – April 18, 1906 (Magnitude: 8) – Death toll: 500 people
• Tokyo, Japan:
– September 1, 1923 (Magnitude 8.25) – Death toll: 140,000 people
• Chile: May 22, 1960 (Magnitude: 9)
• Anchorage, Alaska:
– March 27, 1964 (Magnitude: About 8.5)
• Sumatra, Indonesia
– Dec. 26, 2004. (Magnitude: About 9.0) – Caused a powerful tsunami – Death toll: 150,000 +