Lecture 3+4: Plate tectonics and earthquakes

Question 1

solar nebula

Answer 1

• the sun and planets were born from a rotating disk of cosmic dust
• accretion of planetesimals into larger planets

Question 2

what is the crust of earth made of

Answer 2

• silicon and oxygen
• think crust is continental and less dense than oceanic crust

Question 3

mantle

Answer 3

• made of iron and magnesium

Question 4

outer core

Answer 4

• liquid iron
• metalic

Question 5

inner core

Answer 5

• solid iron

Question 6

order of layers of the earth based on strength

Answer 6

• atmosphere (gas)
• liquid hydrosphere (ocean)
• rigid lithosphere (mantle)
• soft plastic asthenosphere (lower mantle)
• stiff plastic mesosphere (part of the earths atmosphere)
• liquid outer core
• solid inner core

Question 7

plate tectonics

Answer 7

• rigid lithospheric plates slide over the plastic asthenosphere
• convection in the asthenosphere and mesosphere set plates into motion

Question 8

subduction

Answer 8

• a lithospheric plate descends beneath another pulled down by gravity
• less dense plate on the top more dense plate on the bottom

Question 9

internal geomagnetic field

Answer 9

• due to the movement of liquid iron in outer core
• sometimes throughout history the polar magnetization switch

Question 10

age of oceanic crust

Answer 10

• no ocean crust is older than ~200 Ma because it is constantly bring recycled

Question 11

bathymetry

Answer 11

• depth of the ocean measured at different locations
• shows mid ocean ridges and that the ocean isnt the same depth throughout

Question 12

hypocenter

Answer 12

• point or origin of an eathquake in the subsurgace

Question 13

epicenter

Answer 13

• point on earth’s surface directly above the hypocenter

Question 14

foreshocks

Answer 14

• smaller earthquakes that happen in the same place as the larger earthquake

Question 15

mainshocks

Answer 15

• largest main earthquake

Question 16

aftershocks

Answer 16

• smaller earthquakes that occur afterward in the same place as the mainshock
• can continue for weeks months and even years

Question 17

divergent zone

Answer 17

• tension
• two pal;tes are bring pulled away from eachother
• new lithosphere is formed as molten asthenosphere and forced upon the new gap
• think ocean ridges

Question 18

convergent zone

Answer 18

• compression
• two plates collide

Question 19

subduction zone

Answer 19

• oceanic continental convergence
• oceanic (more dense) plate goes under the continental plate
• at depth >30km: crustal earthquakes due to compression
• at depths ~30km: megathrust earthquakes due to shear stress at the contact between plates
• at depths >100 km: cold rock being consumed into the hot asthenosphere causes a reaction

Question 20

continent - continent collision zone

Answer 20

• both plates are too buoyant to subduct
• plates compress and crumple
• mountain ranges

Question 21

transform fault

Answer 21

• shear
• horizontal movement of tectonic plates against each other
• san andreas fault

Question 22

hot spot

Answer 22

• tension and compression
• plume of slowly rising hot rocks that create volcanism on earths surface
• originates in the mesosphere
• hawaii

Question 23

shallow earthquake

Answer 23

• 0-100 km deep

Question 24

intermediate earthquake

Answer 24

• 100-300 km deep

Question 25

deep

Answer 25

300-700 km deep

Question 26

megathrust earthquakes

Answer 26

• lards largest earthquakes
• shallow hypocenters

Question 27

human triggered earthquakes

Answer 27

• pumping fluids underground
• hydraulic fracturing: liquids are pumped down the well under pressure in order to fracture and crack open the rocks to yield high volume hydrocarbon
• dam earthquake: down warping of land beneath the filling lake mead triggered many small earthquakes in 1935
• bomb blasts