EarthquakesWhat they areWhere they occurHow fast they travelHow to locate their centersTheir strength

The Dynamic Crust – Earthquakes

• Definition- a shaking of the Earth’s crust caused by a release of energy• Question: What might happen to Hauppauge if a

major EQ hit? • Effects of an earthquake on your neighborhood:• buildings could collapse• fires and explosions from broken electric and gas

lines• contaminated water supplies from sewer lines• emergency services overwhelmed or damaged• roads and rails for outside help and supply

damaged

Causes of Earthquakes• Can be small in strength• An explosion• Some manmade action – train tracks!

• Or large in strength• Volcano eruption• Movement of plates

• Elastic Rebound Theory• plates move along the plate boundary (a fault line)• friction may stop or deform the plate’s shape• pressure builds up as plates try to move • plate finally snaps back to normal shape and moves

to new location

Depth and Location of Earthquakes• Depth of Earthquakes• dependent on type of plate boundary• most boundaries produce shallow quakes

- 30 km deep• Many subduction zone quakes are deep

– up to 700 km deep• This point below the surface where the plate

actually slips or snaps is called the FOCUS• Epicenter – the point at the surface directly above

the focus

Detecting Earthquakes• Seismometer • a device used to detect earthquake waves• horizontal form and vertical form• seismograph – the recording of the earthquake’s

motions• P-waves or primary waves• compressional waves – like a slinky’s motion• pass through every phase of matter

(solid/liquid/gas)• FAST waves

• S-waves or secondary waves• shear waves – move side to side like a snake• only pass through solids like the inner core• SLOW waves

Size of Earthquakes• Charles Richter (1940’s)• developed the Richter scale• measures the total amount of energy released• each magnitude from 1-7 is 32 times stronger

than previous magnitude• A magnitude 6 earthquake is: • 32x more powerful than a magnitude 5 • 1000x more powerful than a magnitude 4

• strongest recorded EQ • Chile, 1960 – 8.3 on Richter scale

Highway Damage

Highway Damage

South America

Why you should not build on a fault line

Alaskan Earthquake of 1964

Alaskan Earthquake of 1964

San Francisco Earthquake of 1908

Determining Distance to an Epicenter• EARTHQUAKE RELATIONSHIP # 1• P and S waves travel at specific speeds• P – waves = faster• S – waves = slower

• EARTHQUAKE RELATIONSHIP # 2• the closer to the epicenter a seismograph is• the shorter the time lag between P and S waves

• Look at ESRT on page 11

• The distance can be determined for any given EQ• Example #1• An earthquake’s P wave reaches Hauppauge at

8:00:00 am. Its S wave hits Hauppauge at 8:05:40 am. How far away was the earthquake in km? Note 103 km = 1000 km

• Example #2• Use the seismograph below. How far away is the

earthquake represented by the P and S waves?

9:00:00 9:01:00 9:02:00 9:03:00

•An earthquake occurs, and the P and S waves are recorded at three seismometers across the US

•Lets determine where the epicenter is located….

Use the data from the recording stations:

• Station A: San Francisco, California

P-Wave arrival 3:02:20 S-Wave arrival 3:06:30

What is the time difference between P and S wave arrivals?

Use the data from the recording stations:

• Station B: Denver, Colorado

P-Wave arrival 3:01:40 S-Wave arrival 3:05:00

What is the time difference between P and S wave arrivals?

Use the data from the recording stations:

• Station C: Missoula, Montana

P-Wave arrival 3:01:00 S-Wave arrival 3:03:00

What is the time difference between P and S wave arrivals?

TAKE A PIECE OF PAPER, AND MARK OFF THE DIFFERENCE IN ARRIVAL TIME

2800Km

4:10

MOVE THE PAPER UNTIL THE TWO TICK MARKS LINE UP WITH THE P AND S CURVES

WHEN TICK MARKS LINE UP, GO STRAIGHT DOWN AND READ THE EPICENTER DISTANCE

EPICENTER DISTANCE OF 2800 KM

EPICENTER DISTANCES

San Francisco: 4:10

Denver, Colorado: 3:20Missoula, Montana 2:00

2,800km

1100km

2,000km

Recording BoardDifference in arrival times:

San Francisco: 41:02,800km

1,00

0

2,00

0

3,00

0

4,00

0

5,00

0

Open your compass to the EXACT distance on the scale.

. .

.

Determining Location• Triangulation – a process of finding location• Requires three seismic stations• distance from three different stations used to find

the epicenter

Earthquake Epicenter