Tsunami Lecture Notes

This set of vocabulary flashcards covers the mechanics of wind-caused waves, the characteristics and causes of tsunamis, and the technologies used for tsunami monitoring and mitigation.

Wind-Caused Waves

Waves created by frictional drag from wind that transfer energy away from a disturbance, causing water particles to rotate in an orbital motion.

Orbital Motion

The circular movement of water particles that occurs at the surface when a wave moves through; this motion ceases at a depth of $\frac{1}{2}$ the wavelength.

Fetch

The length of the water surface over which the wind blows, which helps determine how tall a wind-caused wave will become.

Wave Breaking Ratio

The wave height to wavelength $( ext{H:L})$ ratio of $1:7$ at which a wave topples forward as a breaker.

Velocity of Wind-Caused Wave

The speed of a wave determined by the formula $1.25 imes ext{length (L)}$, or specifically $1.25 imes ext{wavelength}^{1/2}$, expressed as $1.25 imes ext{L}^{1/2}$ or $1.25 imes ext{\sqrt{L}}$.

Rogue Waves

Unusually tall waves, measured up to $112\,ft$, created when several wave systems briefly and locally combine their energies through constructive interference.

Tsunami

A Japanese word ($Tsu$ = harbor, $nami$ = waves) describing giant, long-period sea waves caused by oceanic disturbances like fault movements, volcanic eruptions, or landslides.

Velocity of a Tsunami

The speed of a tsunami calculated by the formula $\sqrt{gD}$, where $g$ is acceleration due to gravity ($9.8\,m/s^2$) and $D$ is the depth of the ocean.

Drawdown

The retreat of water near the shore pulled out toward the sea, occurring when the trough of a tsunami wave arrives at the shoreline first.

Earthquake-Caused Tsunami

A tsunami created by the vertical uplifting or downdropping of the seafloor, typically requiring an earthquake magnitude of at least $7.5$.

Lituya Bay, Alaska (1958)

The location where a rockmass shaken loose by an earthquake created a $30\,m$ ($100\,ft$) wave that stripped a mature forest from the surrounding area.

DART II

Deep-ocean Assessment and Reporting of Tsunami station, a system using pressure sensors anchored to the seafloor to provide early watches and warnings.

P-waves

Seismic signals that reach warning centers first, allowing scientists to quickly determine the epicenter, depth, and magnitude of an earthquake to issue tsunami watches.

Bottom Pressure Recorder

A sensor anchored to the seafloor that uses bi-directional acoustic telemetry to communicate with a surface buoy as part of a tsunami detection system.