Earth Sci Part 2

Front 1

A sudden, violent dislocation in the subsurface caused by stress buildup on a fault.

Back 1

Earthquakes!

Front 2

Earthquake physics

Back 2

- tectonic forces build up gradually, increasing stresses in crustal blocks

- when tectonic stresses become too large for crustal rocks to sustain, a sudden rupture of the crustal block occurs and the crust rebounds to a new equilibrium position

- Eq is the sudden slip on a fault - energy is released in waves and causes the energy that we feel at the surface

Front 3

Time Sequence of Elastic Rebound Theory

Back 3

1. Before EQ: stress in crustal block slowly accumulates by tectonic forces.

2. During EQ: stress released by motion on a new or pre-existing rupture or fracture zone (called a fault)

3. Immediately after EQ: crust rebounds to an unstressed equilibrium position

4. Following equilibrium, stress begins to reaccumulate slowly!

Front 4

Elastic Rebound Theory: Before, After the Earthquake

Back 4

After EQ: EQ occurs and the fence (lithospheric) distortion is released. Two parts of the fence are again straight, but with an offset

Before EQ: As the pacific plate moves northwest, it gradually distorts the fence. Just before EQ, fence has an 'S" shape

At Start: Fence straddles san Andreas fault

(fence is photograph taken of san francisco earthquake)

Front 5

Henry Fielding Reid

Back 5

Elastic Rebound Theory

Front 6

Faults

Back 6

- fracture (rupture) or zone of fractures between two blocks of rock

- allow the blocks to move relative to each other

- movement may occur rapidly or slowly

- can range in length for a few mm to thousands of km

- produce repeated displacements over geologic time

Front 7

Creep

Back 7

when fault blocks move slowly

Front 8

Strike-Slip Faults

Back 8

occur where one plate slides horizontally past another plate

- all transform faults are strike slip faults, but not all strike slip faults are transform faults!

Front 9

Thrust (reverse) faults

Back 9

- Largest occur at subduction zones, where one plate rides under/above a second plate (e.g. Cascadia, Japan) - potentially the largest events

- occurs where plates are pushing together under compression

- convergent plate boundary

- can also occur at the boundary between converging continental or oceanic lithosphere

Front 10

Normal faults

Back 10

- tends to occur in tensional regimes, as seen in continental rifting

- occurs when plates are pulling apart under tension

- divergent plate boundary

Front 11

Benioff-Wadati Zone

Back 11

Dipping (subduction zone) of EQs are found as deep as 660 km in the mantle

- stresses that occur from pushing the plate deep within the mantle cause earthquakes over subduction zones

- the depth depends on the thermal conductivity of the material - dictated by pressure and temperature

Front 12

Seismic Intensity Map

Back 12

A map that shows the intensity of the seismic waves

Front 13

Glacial Isostatic Readjustment

Back 13

The readjustment of the lithosphere to the original positioning after depression from glaciers-can cause earthquakes

Front 14

Fault

Back 14

A surface (often a plane) across which two blocks can move relative to each other

Front 15

Focus (or hypocenter)

Back 15

The location on a fault where the earthquake rupture initiates

Front 16

Hypocentre

Back 16

The calculated position of an earthquake's focus

Front 17

Epicentre

Back 17

The point on Earth's surface directly above the hypocenter

Front 18

P Waves

Back 18

Primary (compressional) wave

Front 19

S Waves

Back 19

Secondary (shear) waves

Front 20

Rayleigh waves

Back 20

Circular motion surface wave; slow

Front 21

Love waves

Back 21

Slow side by side motion

Front 22

Zhang Heng

Back 22

Invented first seismometer in first century AD - dragon frog thing

Front 23

Pendulum seismographs

Back 23

invented mid 1700s