Seismology and Earthquake Dynamics

Comprehensive practice flashcards covering earthquake causes, seismic waves, faulting types, measurement scales, vibration dynamics, and attenuation factors.

What is an earthquake?

The shaking of the surface of earth resulting from a sudden release of energy in the lithosphere that creates seismic wave.

How do the Focus (Hypocenter) and Epicenter differ?

The Focus is the actual location where the fault movement begins, while the Epicenter is the point on land directly above the focus.

What is a Fault or Fault Plane?

The surface where a fault slides during an earthquake.

Define Seismology and Seismologist.

Seismology is the study of earthquake and seismic waves that move through the earth, and a Seismologist is a scientist who studies them.

What is the difference between a Seismograph and a Seismogram?

A seismograph is an instrument that measures and records details of earthquakes (force and duration), whereas a seismogram is the record produced by it.

What are the characteristics of P-waves and S-waves?

P-waves are primary waves with longitudinal motion; S-waves are secondary waves with transverse or up and down motion and travel slower than P-waves.

Differentiate between Rayleigh waves and Love waves.

Rayleigh waves cause the ground to shake in an elliptical pattern, whereas Love waves move the surface side to side in a horizontal motion perpendicular to the wave direction.

What are the four causes of earthquakes mentioned in the notes?

1. Tectonic Earthquake (plate movement), 2. Volcanic eruption, 3. Collapse Earthquake (human activities like mining), and 4. Explosion (nuclear or chemical devices).

What is the theory of Plate Tectonics?

The theory that Earth’s outer crust is divided into several plates that glide over the plastic-like and less ridged asthenosphere.

What qualifies a fault as an ACTIVE FAULT?

It is likely to become the source of an earthquake in the future, typically defined by movement or seismic evidence during the last $10,000$ years.

Define a Trench in geological terms.

A deep, narrow depression in the ocean floor formed at convergent plate boundaries where one tectonic plate is subducted beneath another.

How is Intensity measured and defined?

Intensity measures the size of an earthquake based on observed effects at the earth's surface using the Mercalli scale.

How is Magnitude measured and defined?

Magnitude quantifies the energy released during an earthquake as reflected in seismic waves, typically measured using the logarithmic Richter scale.

What is an Accelerograph and an Accelerogram?

An accelerograph (or accelerometer) is an instrument that records ground acceleration, and an accelerogram is the resulting recording.

Define Vibration.

The oscillation of the parts of a fluid or an elastic solid whose equilibrium has been disturbed, or of an electromagnetic wave.

What are the three types of Free Vibration?

1. Longitudinal (moves back and forth parallel to the axis), 2. Transverse (moves perpendicular to the axis), and 3. Torsional (rotates in a circular motion).

Define Force Vibration and Damped Vibration.

Force Vibration occurs from an external periodic force; Damped Vibration is when energy is gradually dissipated by friction and other resistances.

What is Attenuation in the context of seismic waves?

It describes the energy loss experienced by seismic waves as they propagate, controlled by the temperature, composition, melt, and volatile content of rocks.

What three factors affect Attenuation?

1. Geometrical Spreading (energy spreads over a larger area), 2. Absorption (Anelastic Attenuation where energy turns into heat), and 3. Scattering (Elastic Attenuation from hitting rough parts).

What is Time History Analysis in structural engineering?

A method that uses recorded ground motion as input for computer simulations of a building or structure.

What is Scaling in the context of time histories?

An approach where recorded motion is scaled up or down uniformly to match a target spectrum without changing the frequency content.