Lecture 9: Earthquakes and Earth's Interior

Earthquake

Sudden energy release from fault slippage.

Stress

Force applied to deform rocks.

Focus

Point within Earth where earthquake originates.

Epicentre

Point on surface directly above the focus.

Elastic Rebound Theory

Energy storage and release mechanism in rocks.

Strain

Deformation resulting from applied stress.

Primary (P) Waves

Compress and expand, travel through all materials.

Secondary (S) Waves

Shear motion, travel only through solids.

Surface Waves

Travel along Earth's surface, causing most damage.

Rayleigh (LR) Waves

Ground roll with up-and-down movement.

Love (LQ) Waves

Side-to-side shaking motion.

Seismogram

Record of seismic waves from an earthquake.

P-S Time-Travel Graph

Graph to determine epicentral distance.

Epicentral Distance

Distance from recording station to epicentre.

Triangulation Method

Using circles to locate earthquake epicentre.

Magnitude

Quantitative measure of earthquake energy.

Intensity

Semi-quantitative measure of earthquake effects.

Richter Scale

Logarithmic scale for measuring earthquake magnitude.

Amplitude

Height of seismic waves recorded.

Logarithmic Scale

Each unit increase represents tenfold amplitude increase.

Seismic Waves

Energy waves generated by earthquakes.

Tectonic Plates

Large sections of Earth's crust that move.

Plate Boundaries

Regions where tectonic plates interact.

M7.1 Earthquake

Magnitude 7.1 earthquake event example.

Fukushima Prefecture

Location of the February 13, 2021 earthquake.

Modified Mercalli Index

Scale for assessing earthquake intensity effects.

Intensity Scale

Ranks earthquake effects from I to XII.

P-waves

Primary waves that travel through solids and liquids.

S-waves

Secondary waves that only travel through solids.

Earthquake Intensity

Observed effects on environment and structures.

Local Geologic Factors

Geological materials affecting earthquake intensity.

Human Factors

Impact of building integrity on earthquake damage.

Tsunami

Destructive ocean waves caused by underwater disturbances.

Tsunami Wave Height

Less than 1 meter in open ocean, over 30 meters near shore.

Surface Rupture

Ground displacement resulting from an earthquake.

Liquefaction

Soil behavior change during shaking, causing instability.

Kola Superdeep Borehole

Deepest human-made hole, reaching 12.3 km.

Crust-Mantle Boundary

Boundary between Earth's crust and mantle (Moho).

P-wave Shadow Zone

Area where P-waves do not arrive due to outer core.

Solid Inner Core

Earth's innermost layer, discovered by Inge Lehmann.

Earthquake Intensity Maps

Visual representation of earthquake effects based on reports.

Death Toll

Number of fatalities resulting from an earthquake.

Seismic Recording Stations

Locations that measure seismic wave activity.

Ultramafic Mantle Rock

Dense rock underlying Earth's crust.

Displacement

Movement of Earth's surface during seismic events.

Evacuation Planning

Strategies for safely relocating people during disasters.

Felt Observations

Reports of earthquake sensations by people.

Damage Observations

Reports of structural damage after an earthquake.