Earthquakes & Hazards

Vocabulary flashcards covering fundamental earthquake concepts, seismic wave behavior, measurement scales, epicenter location methods, geological hazards, and prediction methods from Lecture 12. For chapter nine.

A vibration of Earth produced by the rapid release of elastic energy caused by deformation.

Earthquake

Changes in the form and/or size of a rock body, categorized into displacement, rotation, and distortion.

Deformation

A type of rock deformation characterized by a change in location, commonly occurring along a fault.

Displacement

A type of rock deformation characterized by a change in orientation, such as a tilted rock block.

Rotation

A type of rock deformation characterized by a change in shape.

Distortion

The source or point of origin of an earthquake located beneath Earth's surface from which seismic waves radiate.

Hypocenter

The geographic point on Earth's surface located directly above the earthquake focus (hypocenter).

Epicenter

Seismic waves that travel along the outer part of Earth, possessing the slowest velocity, exhibiting the greatest amplitude, and causing the greatest destruction.

Surface Waves

A type of surface wave characterized by a back-and-forth ground motion.

Love Wave

A type of surface wave characterized by a rolling ground motion.

Rayleigh Wave

Seismic waves that travel through Earth's interior, divided into Primary ($\text{P}$) waves and Secondary ($\text{S}$) waves.

Body Waves

Compressional body waves with push-pull (compression-dilation) motion that travel through solids, liquids, and gases at higher velocities than $\text{S}$ waves.

Primary Waves

Shear body waves that shake at right angles to the direction of travel, move only through solids, and have a slower velocity and greater amplitude than $\text{P}$ waves.

Secondary Waves

An instrument that records the arrival of seismic waves by measuring ground motion in relation to a stationary suspended mass that remains fixed due to inertia.

Seismograph

The physical record or chart of seismic wave arrivals obtained from a seismograph.

Seismogram

An earthquake scale that describes size based on human perception of shaking intensity and observed physical destruction.

Mercalli Intensity Scale

A logarithmic scale based on the amount of elastic energy released, calculated from the amplitude of the largest recorded seismic wave and the arrival-time difference between $\text{P}$ and $\text{S}$ waves.

Richter Magnitude Scale

The quantitative relationship where each whole unit increase in Richter magnitude represents a $10\text{-fold}$ increase in wave amplitude and an approximate $32\text{-fold}$ increase in elastic energy released.

Richter Logarithmic Scaling Ratio

A master modeling graph depicting the travel times of $\text{P}$ and $\text{S}$ waves over distance, used to convert an $\text{S}-\text{P}$ delay time interval into station-to-epicenter distance.

Standard Travel-Time Curve

The procedure of locating an earthquake epicenter by drawing circles corresponding to calculated distances around at least three separate seismic stations to find their point of intersection.

Triangulation (Epicenter Determination)

The major tectonic zone where approximately $80\%$ of global earthquakes occur and where deep-focus earthquakes are concentrated.

Circum-Pacific Belt

The depth ranges of earthquake foci: shallow ($< 70\,\text{km}$), intermediate ($70\text{ to }300\,\text{km}$), and deep ($> 300\,\text{km}$).

Earthquake Focal Depths

The phenomenon where ground motion and shaking intensity increase dramatically in poorly consolidated sediments and water-saturated bay mud compared to solid igneous bedrock.

Material Amplification

The transformation of loosely packed, water-saturated unlithified sediment into a liquid-like fluid due to earthquake shaking compaction and pore pressure.

Liquefaction

A massive ocean wave (Japanese for 'harbor wave') produced by sudden vertical displacement of ocean water resulting from seafloor faulting, submarine landslides, or volcanic eruptions.

Tsunami

Small earthquakes occurring days to several years before a major earthquake, caused by the development of minor cracks in the vicinity of the future rupture zone.

Foreshocks

Smaller seismic events occurring after a major earthquake as the crust adjusts along the rupture zone.

Aftershocks

The study of ancient, prehistoric earthquakes using geological evidence such as fault scarps and displaced strata before the advent of modern seismographs.

Paleoseismology

A quiet segment along an active fault zone that has not slipped recently, identifying a region under accumulated strain with high future earthquake potential.

Seismic Gap

The average time between repeating earthquake events on a fault segment, used to calculate single-year occurrence probability via $P = \frac{1}{\text{RI}}$.

Recurrence Interval