Earthquakes

Richter magnitude scale

Measures power of earthquake in terms of its magnitude (Mw) 1-9. Objective

Mercalli scale

Measure of damage caused by earthquake I-XII. Subjective

When do earthquakes happen?

Tectonic faults when friction prevents plates form moving past each other. Pressure builds up behind. Release of this pressure in a jolt is an earthquake

Fault

Boundary between 2 plates where earthquakes occur

4 different plate boundaries

constructive / divergent
destructive
collision
transform/conservative

Constructive / divergent plate boundaries

Powered by uplifting mantle (source of magma)
Shield volcanoes
Small earthquakes

Oceanic plates push away from each other

Destructive plate boundary

Denser oceanic plate subducts under continental plate, because of pressure strato volcanoes erupt.

Large Earthquakes

Collision plate boundary

Continental plates push against each other.

Earthquakes
no volcanoes because there is no source of magma

Conservative / transform plate boundary

2 plates slide across each other

Earthquakes
No volcanoes because there is no source of magma
San andreas fault line

Timeline of an earthquake

1. Tectonic plates try to slide past eachother

2. Friction causes plates to stick to eachother

3. Huge amounts of pressure build up

4. Plates suddenly jolt past eachother

5. Shockwaves radiate from epicentre

6. After shocks occur hours and days later

Myanmar earthquake

• EQ - 7.7Mw

• Aftershocks 4.5 - 6.5Mw

Where is the epicentre

a point on the Earth's surface directly above where an earthquake or an underground explosion originates

focus

e point underground where the earthquake originates, the place where the seismic waves begin

shockwaves

energy released by earthquake causing vibrations

seismograph

instrument used to record shockwaves from an earthquake

seismogram

graph produced by a seismograph to show shockwaves

primary wave (p wave)

push and pull motion
longitudinal

Very fast
Travel through solid, gas and liquid
Minimal damages, less than S waves

secondary wave (s wave)

Wavy, up and down
Transverse

Fairly slow
Travel through gas, solid
Heavily damaging, more than P waves

Love wave (L wave)

Side to side snaking
Transverse on a different plane

Slower than P + S waves but faster than R waves
Travel through solids
Very destructive

Rayleigh wave (r wave)

Rolling wave
Moves like an ocean circular particle motion

Irrelevent, slower than all
Travel through solids
Most destructive