GEO 005 Exam 1

Earth's Four Layers

1) Crust (silicate rock), 2) Mantle (solid silicate rock), 3) Outer Core (liquid iron-nickel), and 4) Inner Core (solid iron-nickel).

How Earth Acquired Internal Heat

1) Kinetic energy from gravitational accretion and early planetary impacts, and 2) Radioactive decay of isotopes (Uranium, Thorium, Potassium-40).

Why Earth's Interior is Layered

Planetary differentiation during early molten state: dense iron and nickel sank to form the core, while lighter silicates floated up to form mantle and crust.

Why Outer Core is Liquid and Inner Core is Solid

Outer core heat melts iron-nickel at its pressure; inner core's extreme confining pressure prevents melting despite higher temperatures.

Lithosphere

Cold, rigid, strong outer shell comprising the entire crust and uppermost mantle, broken into tectonic plates.

Asthenosphere

Hot, weak, ductile layer in the upper mantle directly beneath the lithosphere that can flow slowly over geological time.

Wegener's Evidence for Continental Drift

Fit of continental shelves, identical fossil distributions across oceans, matching rock units/mountain chains, and aligned glacial striations.

How We Know Magnetic Field Reversed

Cooling basalt records Earth's magnetic orientation; symmetrical magnetic anomaly "stripes" on ocean floors proved continuous seafloor spreading and field reversals.

Mid-Ocean Ridge

A divergent plate boundary where oceanic plates move apart and new oceanic lithosphere is created by upwelling mantle.

Subduction Zone

A convergent plate boundary where a denser oceanic plate sinks beneath an overriding plate into the mantle.

Transform Plate Boundary

A plate boundary where plates slide horizontally past one another without creating or destroying crust (e.g., San Andreas Fault).

Passive Plate Margin

A continental coastline that is not a plate boundary (e.g., US East Coast) and lacks major earthquake or volcanic activity.

Supercontinent

A single landmass comprising all or most of Earth's continental blocks (e.g., Pangaea, which broke apart ~180 million years ago).

Cause of Himalayan & Tibetan High Topography

Continent-continent collision between the Indian and Eurasian plates; buoyant continental crust thickens and uplifts instead of subducting.

Wilson Cycle

The cyclical opening (rifting) and closing (subduction/collision) of ocean basins over hundreds of millions of years.

Convection in Crystalline Solids

Yes, mantle rock is a crystalline solid that can slowly convect via solid-state creep over long geological timescales.

What Drives Plate Tectonics

Slab pull (cold, dense subducting plates sinking due to gravity) and ridge push (gravity sliding plates away from elevated mid-ocean ridges).

Components Required for Earth's Magnetic Field

1) Electrically conductive fluid (liquid iron outer core), 2) Thermal/chemical convection currents, and 3) Planetary rotation (Coriolis effect).

Consequences of Losing Magnetic Field

Solar wind strips away the atmosphere, oceans evaporate, and life is exposed to lethal solar/cosmic radiation.

Largest Earthquakes in Past 100 Years

1960 Valdivia Chile (M9.5), 1964 Alaska (M9.2), 2004 Sumatra (M9.1), and 2011 Japan (M9.0-9.1).

Stick-Slip Behavior

Stress accumulates along a locked fault ("stick") until it overcomes friction, causing sudden rupture and movement ("slip").

Elastic Rebound

Rocks deform elastically as stress accumulates, then snap back to their original unstrained shape during rupture, releasing seismic waves.

Asperity

A rough, high-friction patch on a fault plane where strain accumulates until it breaks and initiates an earthquake.

Plate Deformation Before Subduction Earthquake

The overriding plate is dragged down by the subducting plate and compressed/flexed upward elastically.

Plate Deformation During Subduction Earthquake

The locked megathrust snaps forward and downward, releasing stored strain and generating a tsunami.

Thrust Fault Setting

Occurs in compressional settings (plates pushing together); common at convergent boundaries and subduction zones.

Normal Fault Setting

Occurs in extensional/tensional settings (plates pulling apart); common at divergent boundaries and continental rifts.

Strike-Slip Fault Setting

Occurs in shear settings (plates sliding past each other horizontally); common at transform plate boundaries.

How Movies Incorrectly Depict Earthquakes

Depicting giant gaping ground chasms swallowing cities, M9.5+ earthquakes on strike-slip faults, and megatsunamis from strike-slip faults.

P-waves (Primary Waves)

Fastest seismic waves; compressional/push-pull motion; travel through solids, liquids, and gases.

S-waves (Secondary Waves)

Shear waves; side-to-side motion perpendicular to wave travel direction; travel ONLY through solids.

Surface Waves (Love & Rayleigh)

Slowest seismic waves; travel along Earth's surface and cause the vast majority of ground shaking and structural damage.

Seismograms Required to Locate an Earthquake

Minimum of 3 seismogram stations (triangulation) using P-S wave arrival time differences.

Evidence Outer Core is Liquid

S-waves cannot pass through liquids, creating an S-wave shadow zone on the far side of Earth.

Evidence Inner Core is Solid

P-wave refraction and reflection patterns passing through Earth's center confirm a solid inner core.

Magnitude vs. Shaking Amplitude

Each whole unit increase on the Moment Magnitude scale represents a 10-fold increase in measured wave shaking amplitude (~32x energy release).

Theoretical Maximum Earthquake Magnitude

Around M 9.5 to 10.0, limited by the continuous surface area of unbroken fault plane available on Earth.

Influence of Loose Sediments on Shaking

Unconsolidated soft or wet sediments amplify seismic shaking and prolong shaking duration compared to solid bedrock.

Modified Mercalli Intensity Scale

Measures the local severity of shaking felt by people and structural damage; ranges from I to XII.

Factors Influencing Earthquake Intensity

Magnitude, distance from epicenter, focal depth, local geology/soil conditions, and building structural quality.

Eastern vs. Western US Earthquake Shaking

Eastern US quakes are felt much farther away because older, colder, less-fractured bedrock transmits seismic energy with less attenuation/damping.

Biggest vs. Deadliest Earthquakes

Magnitude doesn't equal fatalities; deaths depend heavily on population density, building construction quality, and secondary hazards.

Why Earthquakes Are Hard to Predict

Fault systems are complex and non-linear with non-uniform stress distribution and no reliable, consistent short-term precursors.

Basis of Earthquake Probability Forecasting

Calculated using historical earthquake frequency, paleoseismology (fault trenching), and slip rate calculations along seismic gaps.

Problem with Earthquake Precursors

Precursors (foreshocks, groundwater changes, radon emissions) are unreliable and inconsistent—they don't reliably occur before major quakes.

Using GPS in Earthquake Studies

GPS tracks continuous crustal movement and strain accumulation across faults to estimate future earthquake slip deficits.

USGS Seismic Hazard in Midwest

High seismic hazard centered on the New Madrid Seismic Zone (ancient intraplate rift zone) which generated massive earthquakes in 1811-1812.

Things to Do to Minimize Earthquake Deaths

Secure heavy furniture/appliances to walls, retrofit buildings, maintain emergency supplies, and practice "Drop, Cover, and Hold On."

Why Diagonal Beams Help Buildings

Cross-bracing converts lateral shear forces into compression and tension along the diagonal members, increasing structural rigidity.

Building Code Collapse Goal

Seismic building codes aim for a 90-95%+ probability of preventing structural collapse during a maximum considered earthquake to safeguard life.

Importance of Proper Foundations

Foundations must anchor into solid bedrock or engineered soil to prevent settling, tilting, or structural failure during intense ground shaking.

Liquefaction

Loss of soil strength occurring when water-saturated, unconsolidated sediment behaves like a liquid during intense earthquake shaking.

Preventing Excessive Building Sway

Base isolation (uncoupling building from ground motion) and tuned mass dampers (heavy suspended counterweights) counteract sway.

Earthquake Early Warning Systems

Sensors detect fast, non-damaging P-waves near the epicenter and transmit electronic alerts before slower, destructive S/surface waves arrive.

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Covers Earth structure, internal heat, differentiation, continental drift, seafloor spreading, plate boundaries, and magnetic field mechanics.

Unit 2 Topic Coverage

Covers historical quakes, fault mechanics, seismic wave types, triangulation, Mercalli intensity vs. magnitude, and regional wave attenuation.

Unit 3 Topic Coverage

Covers earthquake forecasting, GPS strain tracking, New Madrid zone hazard, building engineering, retrofitting, and early warning systems.

The Core Science Comparison

Analyzed core stoppage, magnetic field breakdown, unobtainium, deep geodes, and nuclear restarting vs. actual geophysical reality.

San Andreas Science Comparison

Analyzed megathrust vs. strike-slip scale, ground chasms, precursor magnetic pulses, building collapse, and tsunami generation mechanics.

Aftershock Science Comparison

Analyzed historical 1976 Tangshan and 2008 Wenchuan quakes, animal behavior precursors, structural failure of unreinforced masonry, and rescue logistics.