Geology Final: Earthquakes

What causes an earthquake?

Sudden release of stored elastic strain energy in the Earth's crust, resulting in ground shaking.

What is the elastic rebound theory?

It explains earthquakes as the sudden release of strain accumulated as rocks deform elastically along a fault, snapping back to their original shape.

What is the focus (hypocenter) of an earthquake?

The point within the Earth where the earthquake rupture starts.

What is the epicenter of an earthquake?

The point on the Earth's surface directly above the focus.

What are foreshocks?

Smaller earthquakes that occur before the mainshock in the same region.

What are aftershocks?

Smaller earthquakes following the mainshock, occurring as the crust adjusts to the new stress state.

What are P waves (Primary waves)?

Compressional seismic waves that travel fastest through solids, liquids, and gases.

What are S waves (Secondary waves)?

Shear seismic waves that travel slower than P waves and only through solids.

What are surface waves?

Seismic waves that travel along the Earth's surface causing the most damage; include Love and Rayleigh waves.

How does earthquake magnitude relate to distance on a seismograph?

The amplitude of seismic waves decreases with distance, so magnitude estimates require correcting for distance.

What is the P-S wave interval?

The time difference between arrival of P and S waves at a station, which increases with distance from the epicenter.

How is the epicenter located using seismographs?

By triangulating distances from at least three stations based on P-S wave intervals.

What is the Richter scale?

A logarithmic scale based on the amplitude of seismic waves recorded by seismographs, historically used for local earthquakes.

What is the moment magnitude scale?

A scale based on seismic moment (fault area × slip × rock rigidity), providing a more accurate measure of earthquake size, especially large quakes.

What is the Mercalli intensity scale?

A qualitative scale measuring the observed effects and damage of an earthquake, ranging from I (not felt) to XII (total destruction).

What is a Benioff zone?

A zone of earthquake foci that trace the subducting slab downward in a subduction zone.

How do subduction zones relate to earthquakes?

They produce deep, large-magnitude earthquakes due to the descending plate's friction and deformation.

What kind of earthquakes occur at transform margins?

Shallow, often large earthquakes caused by lateral slip along strike-slip faults.

Can earthquakes occur in continental interiors?

Yes, although less frequent, intraplate earthquakes can occur on old fault zones reactivated by regional stress.

What are the main seismic hazards?

Ground shaking, landslides, liquefaction (loss of soil strength due to shaking), and tsunamis.

What causes liquefaction?

Saturated, unconsolidated sediments temporarily lose strength during intense shaking and behave like a liquid.

How are tsunamis generated by earthquakes?

Tsunamis are generated by the displacement of water due to an underwater earthquake.

Tsunami

Large underwater earthquakes at subduction zones can displace the seafloor, generating tsunami waves.

Earthquake Prediction

Can earthquakes be reliably predicted? No; while some precursors (foreshocks, strain changes) are studied, precise prediction of time, location, and magnitude is currently not possible.

Fault Movements

What types of fault movements cause most earthquakes? Strike-slip, normal, and reverse (thrust) faults.

S Waves

Why don't S waves travel through the Earth's outer core? Because S waves are shear waves and cannot propagate through liquid.

Seismic Moment

What is seismic moment and how does it relate to earthquake size? Seismic moment = (rigidity of rock) × (fault area slipped) × (average slip); it measures the total energy released, correlating with moment magnitude.

P Waves

Which seismic waves arrive first at a seismic station? P waves.

Surface Waves

Which seismic waves cause the most structural damage? Surface waves, particularly Love and Rayleigh waves.

Love Waves vs Rayleigh Waves

How do Love waves differ from Rayleigh waves? Love waves move the ground side to side horizontally, while Rayleigh waves cause elliptical rolling motion like ocean waves.

Locating Earthquake Epicenter

Why are three seismograph stations needed to locate an earthquake epicenter? Because the epicenter is found by intersecting three circles, each representing distance from a station based on P-S wave interval.

P-S Wave Interval

What does a large P-S wave interval indicate? The earthquake is farther from the seismic station.

Richter Scale

How does the Richter scale amplitude change with each unit increase? Amplitude increases by a factor of 10 for each whole number increase.

Energy Release and Magnitude

How does energy release change with magnitude increase? Each whole number increase corresponds to roughly 32 times more energy released.

Moment Magnitude Scale

Why is the moment magnitude scale preferred over Richter for large earthquakes? Because Richter saturates and underestimates large earthquakes, while moment magnitude accurately reflects total energy.

Subduction Zone Earthquakes

What kinds of earthquakes are common in subduction zones? Both shallow megathrust quakes and deep-focus earthquakes along the subducting slab.

Transform Faults

Why are transform faults seismically active? They accommodate lateral motion between plates causing frequent strike-slip earthquakes.

Shaking Intensity Factors

What factors influence earthquake shaking intensity? Magnitude, distance from epicenter, local geology, and depth of focus.

Earthquake-Induced Landslides

How can earthquake shaking cause landslides? By destabilizing slopes through ground acceleration and soil saturation.

Tsunami Risk Regions

What regions are at highest risk for tsunami generation? Coastal areas near subduction zones with potential for large megathrust earthquakes.

Seismic Gap

What is a seismic gap and why is it significant? A segment of an active fault that has not experienced recent earthquakes, possibly indicating future seismic risk.

GPS Monitoring

What role does GPS monitoring play in earthquake science? It measures crustal deformation and strain accumulation to assess earthquake potential.

Earthquake Prediction Precursors

What are some common precursors studied for earthquake prediction? Foreshocks, ground uplift/subsidence, radon gas emissions, and changes in groundwater chemistry.