# Seismic Waves, Structure of the Earth, Earthquakes, and Plate Tectonics

## 25 terms

### P-waves

fastest seismic wave; longitudinal waves that pass through liquids and solids

### S-waves

second fastest seismic waves; transverse waves that pass only through solids

### Surface waves

third slowest seismic waves; travel along the surface of Earth and not through the interior

### Crust

upper layer of Earth; must be solid because both S-waves and P-waves travel through it

### Upper Mantle

Asthenosphere; plastic-like, but solid, layer; We know it is less dense than the lower mantle due to the refraction of S-waves and P-waves at that barrier

### Lower Mantle

Must be solid because both S-waves and P-waves pass through it

### Outer Core

Must be liquid because only P-waves pass travel through it

### Inner Core

We believe it is solid because P-waves refract at the barrier and move faster through it than the less dense outer core

### Epicenter

Location on the crust where seismic waves originated

### Seismograph

Instrument used to measure the intensity of seismic waves

### Order of waves measured on a seismograph

P-waves hit first, then S-waves, then surface waves

### Richter magnitude

Determined by the maximum S-wave intensity

### Normal fault

the head wall falls down relative to the foot wall

### Reverse fault

The head wall moves up relative to the foot wall

### Strike-slip fault

The two walls move side to side relative to each other

### First theory of the continents

Shrinking Earth Theory

### Shrinking Earth Theory

Continents do not move; Core is cooling down, causing the Earth to slowly shrink; Contraction of the Earth is what causes mountains to form, earthquakes to happen, etc.

### Plate Tectonics

Crust is divided into plates that move

Occurs at ocean ridges; Plates move because magma comes up through the ridge, forming new rock and pushing the old rock outwards

### Plate Boundaries

Convergent boundaries, where to plates more towards eachother

### Oceanic-Oceanic convergence

one of the plates will slide underneath the other, which is called subduction. This creates a trench in the ocean.

### Oceanic-Continental convergence

Oceanic plate subducts under the continental plate

### Continental-Continental convergence

Tends to result in a mountain building episode, and results in a normal fault

### Divergent boundaries

Two plates move away from one another. Oceanic ridges are examples of this; This will give us a reverse fault

### Transform Boundaries

Two plates slide next to each other. This is also a strike-slip fault