Dynamic Earth

Topics:

-Earth’s Interior

-Continental Drift

-Seafloor spreading

-Plate Tectonics

-Earthquakes & Epicenters

Earth’s Interior

As depth increases so does:

-pressure

-temperature

-density

Earth’s Interior

• Crust

- outer thin rock layer– Mostly silicon and magnesium

Oceanic: thin; basalt rock (dense)

Continental: thick, granite rock (less dense)

Earth’s Interior

• Mantle– thickest layer of plastic molten rock– Mostly silicon and magnesium

asthenosphere: upper part; where convection currents are found

Earth’s Interior

• Outer core

-iron and nickel

-liquid due to intense heat

-S waves cannot travel through

• Inner core

-iron and nickel

-solid due to intense pressure

Continental Drift

• Continents were once joined together• Evidence:

-jigsaw fit of continental coastlines-matching geologic features (Mts) across continents-fossils of tropical plants found in continents now in polar regions-fossils of the same species found across oceans

Seafloor spreading

• Age of rocks at mid ocean ridge increase as you move away from ridge

• Magnetic mineral alignment in basalt (igneous rock) shows poles reversal

forms mirror image on both sides of MOR

Plate Tectonics• Driven by convection currents in mantle

caused by Density Differences:

heat from Earth’s interior causes hot, less dense magma to rise and cool, more dense magma to sink

• Lithospheric plates slide along with the moving magma

• Plate boundary: where one plate makes contact with another

earthquakes and volcanoes occur at zones of crustal activity (boundaries)

Converging Plate Boundary• Plates collide • Continent to Continent: mountain building

-uplift of rock: oceanic fossils seen on mts

• Continent to oceanic: dense oceanic crust sink below continental crust

-subduction zone

-volcanoes form on continent

Diverging Plate Boundary

• Plates move apart

• Ex: mid ocean ridge

• New crust is formed

Transform Plate Boundary

• Plates slide past each other

• Cause rocks to fault (crack)

-produces Earthquakes

Hot Spots

• Form volcanic islands (Hawaii)

• Stationary plume of rising magma

• As lithospheric plate moves over hot spot, magma pushes through crust

• Islands older the further away from hot spot

Earthquakes & Epicenters

• Stress builds up and causes rock to shift

• Energy released as seismic waves:

-P Wave: travels quickly through solids and liquid layers of Earth

-S Wave: travels slower though solids but NOT liquid layer (outer core)

Locating the Epicenter

• One seismic station gives you its distance from epicenter but no direction

• 3 seismic stations are required to locate

Finding difference in arrival time

• Given the arrival times of each wave, use their difference to determine distance traveled

The distance from Albany, New York, to the epicenter of an earthquake is 5600 km. Approximately how much longer did it take for the S-wave to arrive at Albany than the P-wave?

a. 4 minutes and 20 secondsb.  16 minutes and 10 secondsc. 9 minutes and 0 secondsd.  7 minutes and 10 seconds

     

Finding Travel Time/distance

• Given distance from epicenter, you can find how long it takes a P or S wave to travel to that seismic station

• Or you can find the distance the wave traveled based on how long it took the wave to travel there

Approximately how long does an earthquake P-wave take to travel the first 6500 kilometers after the earthquake occurs?

6.5 min 8.0 min10.0 min 18.5 min

In 8 minutes, an earthquake P-wave travels a total distance of 2,100 km 6,600 km

4,700 km 11,300 km

Calculating Arrival Time

• If you know how long it takes one wave type to travel a given distance, you can find out

-the time the earthquake happened

or

-the arrival of the other wave type

A seismic station recorded an earthquake with an epicenter distance of 4,000 kilometers. If the origin time of the earthquake was 11:00 a.m., what time did the P-wave arrive at the seismic station? 10:53 a.m. 11:05 a.m.11:07 a.m. 11:12 a.m.

An earthquake's P-wave arrived at a seismograph station at 02 hours 40

minutes 00 seconds. The earthquake's S-wave arrived at the

same station 2 minutes later. What is the approximate distance from the

seismograph station to the epicenter of the earthquake? 1,100 km

2,400 km3,100 km 4,000 km

• An earthquake occurs at 12:02 p.m. A seismic station records the first S-wave at 12:19 p.m. Which set of data shows the approximate arrival time of the first P-wave and the distance to the epicenter?

a. 12:11:25 p.m. and 4000 kmb. 12:11:25 p.m. and 6000 kmc. 12:19:40 p.m. and 4000 kmd. 12:19:40 p.m. and 6000 km

Tsunami

• Underwater Earthquake pushes water onto shore

• Wave height grows at it approaches shore