Earthquakes 11222020 1999 John Culpepper 1 Earthquakes The

Earthquakes • The movement of tectonic plates creates stress on large areas of rock

Earthquakes • Occur when stress is relieved by rocks breaking 11/22/2020 © 1999 John

Earthquakes (cont. ) • Usually occur along faults and plate boundaries • Energy is

Types of Faults • Normal Fault – Hanging wall slides down the fault plane,

Reverse Fault (Thrust Fault) Hanging wall slides up the fault plane Formed by convergent

• Strike-slip Fault – Hanging wall and foot wall slide horizontally to the

Important Terms • Fault- a weakness or break in the Earth’s crust • Focus-

Seismic waves • In an earthquake 3 kind of waves are produced – P-waves

P-waves (primary waves) • Travel through solids and liquids • Fastest moving seismic waves

S-waves (secondary waves) • Travel only through solid material • Move slower than Pwaves

Surface waves • Do the most damage and move the slowest 11/22/2020 © 1999

Seismic waves are measured by seismometers • Seismic recordings are called seismograms or seismographs

Earthquakes (cont. ) • The exact time of an earthquake is known as its

Earthquakes (cont. ) • Moho discontinuity -the boundary between Earth’s crust and mantle –

Earth’s Interior • Within the Earth density, pressure, and temperature all increase with depth

Faults • Normal fault – Found in areas under tension • Where sections of

Faults (cont. ) • Reverse fault – Found in areas under compression • Zones

Faults (cont. ) • Strike-slip faults – More horizontal movement than vertical movement Like

Shadow zone • A zone on the opposite side of the earth from where

Earthquake damage is measured by 2 scales: • Richter Scale 1 -10 each increase

Deep, Intermediate, & Shallow Earthquakes • Deeper usually = stronger 11/22/2020 © 1999 John

• Shallow EQ’s occur nearer the trench and deeper occur farther inland •

Typical Seismogram 11/22/2020 © 1999 John Culpepper 32

How is an Earthquake’s Epicenter Located? 11/22/2020 © 1999 John Culpepper Seismic wave behavior

How is an Earthquake’s Epicenter Located? Time-distance graph showing the average travel times for

How is an Earthquake’s Epicenter Located? • • • Three seismograph stations are needed

Earthquake Practice: • How many seismic stations do you need to locate the epicenter

Slides: 36

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Earthquakes (cont. ) • Usually occur along faults and plate boundaries • Energy is rapidly released in all directions (causing waves) – Like a pebble dropped in a quiet pool of water 11/22/2020 © 1999 John Culpepper 4

Important Terms • Fault- a weakness or break in the Earth’s crust • Focus- the place underground where the break occurs (actual location of the earthquake) • Epicenter- the location on the Earth’s surface just above the focus (map location of an earthquake) 11/22/2020 © 1999 John Culpepper 8

Shadow zone • A zone on the opposite side of the earth from where an earthquake has occurred where seismic waves will not be felt – Due to the way that seismic waves travel through the different materials within the Earth 11/22/2020 © 1999 John Culpepper 23

Earthquake damage is measured by 2 scales: • Richter Scale 1 -10 each increase of 1=10 fold increase in shaking (exponential) • Mercalli Scale 1 -7 based on the damage to buildings and observed effects 11/22/2020 © 1999 John Culpepper 26

How is an Earthquake’s Epicenter Located? 11/22/2020 © 1999 John Culpepper Seismic wave behavior – P waves arrive first, then S waves, then L and R – Average speeds for all these waves is known – After an earthquake, the difference in arrival times at a seismograph station can be used to calculate the distance from the seismograph to the epicenter. 33

How is an Earthquake’s Epicenter Located? Time-distance graph showing the average travel times for P- and Swaves. The farther away a seismograph is from the focus of an earthquake, the longer the interval between the arrivals of the P- and S- waves 11/22/2020 © 1999 John Culpepper 34

How is an Earthquake’s Epicenter Located? • • • Three seismograph stations are needed to locate the epicenter of an earthquake A circle where the radius equals the distance to the epicenter is drawn The intersection of the circles locates the epicenter 11/22/2020 © 1999 John Culpepper 35

Earthquake Practice: • How many seismic stations do you need to locate the epicenter of an earthquake? • An earthquake occurs 8000 km away, how long will it take P-waves to reach you? S-Waves? • P waves arrived at a seismic station at 12: 03, Swaves arrived at 12: 07. How far is the epicenter? 11/22/2020 © 1999 John Culpepper 36