EARTHQUAKES

earthquake: the shaking or vibrating of Earth caused by a release of energy

elastic rebound: as two plates move past each other they get stuck and then slip; the plates suddenly move, release energy and then snap back into place

epicenter: point on the earth’s surface directly above the focus focus: point at which rupture occurs along the fault

If you hear about an earthquake on the news, you will always be told the location of the epicenter. If you are told the depth of the earthquake, that is the focus.

fault: a break in the earth’s surface where movement has occurred

TYPES OF FAULTS normal fault: blocks of rock move apart - found at divergent boundaries

reverse fault: blocks move toward one another - found at convergent boundaries - also called thrust fault

strike slip: rocks move horizontally past one another - found at transform boundaries

seismology: the study of earthquakes seismograph: device that measures earthquakes seismogram: earthquake graph made by a seismograph

Seismic Waves As energy is released from an earthquake, it is distributed in waves Body Waves: travel through the interior of the Earth Surface Waves: travel along Earth’s surface

P-wave (primary wave): Types of Body Waves P-wave (primary wave): - longitudinal wave - can travel through any material - 1st to arrive (6-7 km/s) - shortest period, smallest amplitude

S-wave (secondary wave) - transverse wave - cannot travel through liquids (outer core) - 2nd to arrive (3.5 km/s)

S waves cannot travel through the Earth. P waves refract as they pass through the liquid part of the core.

Surface Waves - most damaging to structures - largest amplitude; slowest - last to arrive (2.5 km/s)

Types of Surface Waves R- Waves Rayleigh Waves Make the ground ripple up and down

L-Waves Love Waves Make the ground ripple side to side

Determining the Location of the Epicenter

Shallow earthquakes tend to occur along transform boundaries Shallow earthquakes tend to occur along transform boundaries. Deep earthquakes tend to occur along subduction zones. * the deeper an earthquake, the less damage it causes at the surface

How do we measure earthquake magnitude?

Richter Scale - measures amplitude of largest seismic wave 100 km from the epicenter - wave height is ten times greater for each step that increases

The energy released is 33 times greater for each step that is increased How many magnitude 6 earthquakes would you need to release the same amount of energy in one magnitude 8 earthquake?

Richter Scale values > 8 = total destruction (about 1/year) 7-7.9 = bad (18/year) 6-6.9 = moderate-serious (120/year) 5-5.9 = felt by everyone (minor damage) (800/year) 4-4.9 = not felt by everyone (6,000/year) < 3.9 very small (about 1 million per year)

Moment Magnitude Scale measures energy released used by scientists factors in amount of movement and rigidity of rocks

Comparison: 1964 Alaskan EQ Richter- 8.4, Moment – 9.2 1906 San Francisco Richter – 8.3, Moment – 7.9

Mercalli Intensity Scale measures damage done by the earthquake - scale of I – XII

I – felt by few people V – felt by everyone (dishes broken) VIII – slight damage to structure X – wooden structures destroyed XII – total destruction; see waves at surface

Earthquakes caused by Humans Hoover Dam – 600 tremors over the 1st 10 years; some as high as magnitude 5 Rocky Mountains – In the 1960’s the US Army drilled a well and injected liquid waste into the mountains This lubricated the fault and earthquakes began When the Army stopped injecting the waste, the earthquakes stopped too

Earthquake Prediction long term  years, not days or hours short term  Good Luck!

In order to study earthquake predictions, you need to predict an earthquake. (in order to set up equipment, etc.)

- how often an earthquake of a specific magnitude occurs Recurrence Interval - how often an earthquake of a specific magnitude occurs

looking at gaps along faults where there is no seismic activity Seismic Gap Method looking at gaps along faults where there is no seismic activity

Earthquake Damage 1. Ground Displacement examples: 1906 San Fran – 7 m of displacement 1964 Alaska – 12 m of displacement (vertical) 1989 Loma Prieta 2.2 m 1994 Northridge 1 foot

Alaska, 1964

2. Landslides 1970 Peru – killed 70,000 people

3. Liquefaction sediments act as fluids Kobe, Japan

Tsunami - seismic sea wave ex. Sumatra 2004 Fire ex. Tokyo, San Francisco

1906 – San Francisco

6. Valley Fever disease sewage lines break - dust associated with fires causes bronchial problems

Most Devasting EQs 1500’s  China 850,000 dead 1923  Tokyo 143,000 dead 1976  China 250,000 dead 1985  Mexico 10,000 dead 1995  Kobe, Japan 5,000 dead $100 billion in damages

Northridge 1994

Northridge, CA 1994

Northridge 1994

Northridge 1994

Alaska, 1964

San Francisco Bay Bridge, 1989                                        

Kobe Japan, 1995