INTRO TO MARINE SCIENCE - Chapter 2

Earth's Structure and Plate Tectonics

Seismic Waves

energy is released that travels through Earth in the form of vibrations when Earthquakes occer

Surface Waves (definition)

move over earth’s surface like ocean waves

Surface Waves

• generally do the most property damage

• don’t reveal much about what Earth is like deep beneath the surface

Body Waves (definition)

travel beneath the surface and through the “body” of the planet before returning to the surface some distance away

Body Waves

• typically cause less damage

• useful in studying Earth’s interior

P-waves (definition)

primary waves that travel faster than any other kind of waves and arrive first at a location

P-waves

• AKA compressional waves because they cause the material they pass through to alternatively compress and stretch, parallel to the direction the waves travel

• Can travel through all three states of matter (solid, liquid, gas)

S-waves (definition)

primary waves that travel faster than any other kind of waves and arrive first at a location

S-waves

• AKA shear waves because they cause the material they pass through to shake from side-to-side, perpendicular to the direction they travel

• can only travel through solids, CANNOT travel through liquid or gases

Shadow Zones

areas on the surface where body waves do not travel directly

P-wave Shadow Zone

angular distances of roughly 104-140 degrees from location of Earthquake

S-wave Shadow Zone

angular distance greater than roughly 104 degrees from location of the Earthquake

Why are S-wave shadow zones greater than p-wave shadow zones

s-waves are stopped entirely by the liquid outer core

Crust

thin, rocky layer, comprises about .4% of Earth’s mass and less than 1% of its volume

Continental Crust

(0-50 km) — granite, silicates rich in sodium, potassium, and aluminum

Oceanic Crust

(0-10 km) — basalt; silicates rich in calcium, magnesium, and iron

Mantle

rock Is denser than crustal rocks, and comprises about 84% of Earth’s volume and 68% of it's mass

Core

metallic rather than rock; 15% of earth’s volume but 30% of earth’s mass because of iron alloy

Lithosphere

(0-150 km) — solid, rigid behavior

Asthenosphere

(base of lithosphere - 350 km) — solid, ductile behavior

Mesosphere

(350- 2890 km) — solid, mobile

Outer Core

(2890 - 5150 km) — liquid

Inner Core

(5150-6371 km) — solid

Isostasy

a balance kept between the internal pressures under the latch blocks and those under the ocean basins

Why is isostasy possible?

the greater thickness of low-density granitic crust in the continental region is compensated for by the elevated higher-density mantle material under the thinner crust of the oceans (compared to the floating of an iceberg)

Seafloor Spreading

result of the lateral movement of oceanic lithosphere

Spreading Centers

areas in which new seafloor and oceanic lithosphere are formed above rising magma

Subduction Zones

areas of descending older oceanic lithosphere

What mechanism provides the forces causing movement of the lithosphere?

seafloor spreading

Epicenters

the points on Earth’s surface directly above the actual Earthquake

Where are earthquakes shallower than 100 km prevalent?

in ocean basins along ridges and rises and at trenches where the lithosphere bends and fractures as it is subjected into the mantle

What are earthquakes deeper than 100 km associated with?

the subduction of oceanic lithosphere

Heat flow is ______ in young crust closer to the ridge crest and _______ in old crust farther from the ridge crest

higher, younger

Paleomagnetism

the investigation of fossil magnetism in rocks

Seafloor age ________ away from the oceanic spreading centers

increases

Plate Tectonics

drifting continents and the motion of the seafloor both result from the fragmentation and movement of the outer rigid shell of Earth called the lithosphere

What is the largest major plate?

Pacifc

What is the 2nd largest major plate?

African

What is the 3rd largest major plate?

Eurasian

What is the 4th largest major plate?

North American

What is the 5th largest major plate?

Antarctic

What is the 6th largest major plate?

South American

What is the 7th largest major plate?

Australian

What is thought to be responsible for the creation of divergent boundaries in continental lithosphere?

Upwelling of hot mantle rock

Escarpments

significant and rapid changes in elevation of the seafloor