GEOLOGY MACC Bill Palmer

GEOLOGYMACC

Bill PalmerLecture 12

Earthquakes

GEOLOGY-Earthquakes Probably the most terrifying geologic event Occur suddenly, often without warning May last less than 5 minutes and cause tremendous

destruction Remember that Earthquakes create Tsunamis

TSUNAMI-Dec. 26, 2004

300,000 killed

GEOLOGY-Earthquakes Don’t damage the land very much but destroy the

built environment We cannot control or predict with accuracy Most powerful earthquake in lower 48 state

recorded history took place in Missouri

GEOLOGY-Earthquakes Measuring Earthquakes (Two different scales)

Richter ScaleA Measure of MAGNITUDE of an EarthquakeMeasured by instrumentsEach number is ten times larger than preceding numberA 5 is 10X greater than a 4A 7 is 1000X greater than a 4Largest measured are 9Damage to structures begins at 5.5


Mercalli Scale (handout provided) INTENSITYMeasures damages to the built environment I. Not felt II. Felt by most people III. Felt indoors; pictures swing IV. Heavier objects swing, fells like passing truckV. Felt outdoors, sleepers awake, doors swing open


Mercalli ScaleVI. Felt by all; Walk unsteady; plaster cracks; small

bells ringVII. Difficult to stand; chimneys breakVIII. Smokestacks fail; driving difficult; some walls

fail IX. Panic; Frames crack; underground pipes broken;

cracks in ground; bridges fail


Mercalli ScaleX. Many buildings fail; dams damaged; landslidesXI. Rails bent; underground pipelines failXII. Damage nearly total, large rock masses dispalced

objects thrown into air

(see handout for more details)

GEOLOGY-Earthquakes Focus and Epicenter

FOCUS-The exact place in the ground where the earthquake takes place

EPICENTER-The point on the earth’s surface directly above the focus.

GEOLOGY-Earthquakes

Focus and Epicenter

GEOLOGY-Earthquakes Finding the Epicenter Earthquakes produce three types of waves

P-Travel at the fastest speedS-Travel at medium speedL-Travel the slowest

These waves can be measured on a Seismograph and the distance from the seismograph determined

Using THREE seismographs the exact epicenter can be determined

GEOLOGY-Earthquakes

SeismographThe seismograph is basically a pendulum with moving paper beneath. Waves cause the pendulum to swing and the result is shown on paper

GEOLOGY-Earthquakes

GEOLOGY-Earthquakes What Mercalli

rating would you

give each of the

earthquakes?

GEOLOGY-Earthquakes Some infamous

earthquakes-San Francisco 1906

3,000 dead 225,000 homeless 28,000 buildings

destroyed



Richter = 7.8-8.0 Mercalli=8.0-9.0



The damage from this earthquake was worsened by the fire that was caused when natural gas pipelines burst and caught fire.


earthquakes-Alaska 1964 Richter=9.2 Largest in North America Lasted 4 minutes 10,000 aftershocks Created 70 ft Tsunami

GEOLOGY-Earthquakes

Alaska-1964

GEOLOGY-Earthquakes Missouri 1811-1812 New Madrid Earthquake Felt over 50,000 square

miles Richter=8.0 Seismologist estimate

there is a 90% chance of a 7.0 or greater EQ in next 50 yrs

GEOLOGY-Earthquakes

Created Lakes-ReelfootBells Rang in PhiladelphiaBuildings in Savannah GA

crackedMississippi River course was

alteredNot many people in area so

loss of life and damages minimal

GEOLOGY-Earthquakes Comparison of the impact

of the New Madrid EQ to the 1906 San Francisco EQ.

GEOLOGY-Earthquakes Mercalli Impact-Columbia

is in V.

GEOLOGY-Earthquakes

12,000,000 people live in EQ zone-St. Louis, Memphis, Evansville, Louisville, Cape Girardeau

Same quake today could kill 100,000 and trillions of dollars of damage

PROBLEM-Minor quakes relieve pressure and prevent larger quakes. We need minor quakes!

GEOLOGY-Earthquakes

http://www.weather.com/images/maps/special/usa_earth_720x486.jpg

LINKS TO DAILY EARTHQUAKE REPORTS

http://neic.usgs.gov/neis/qed/

GEOLOGY-Earthquakes-Wrap ups

1. Define an Earthquake 2. What are the Focus and Epicenter? 3. How is the epicenter determined? 4. What is the Richter scale and what does it

measure? 5. What is the Mercalli scale and what does it

measure?

GEOLOGY-Earthquakes-Wrap ups 6. What are the characteristics of the 1906 San

Francisco EQ? 7. What are the characteristics of the 1964 Alaska

EQ? 8. What are the characteristics of the 1811-1812

New Madrid EQ? 9. What are the chances for a major EQ in MO? 10. Why should be be concerned everyday there is

not a major EQ in New Madrid?

GEOLOGY MACC Bill Palmer

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