Tsunami: The Sea Wave Generated by Underwater Earthquakes

Tsunami (Japanese: "harbor wave")—a series of long-period ocean waves caused by sudden seafloor displacement.

Primary Causes

• Subduction zone earthquakes (megathrust, M>7.5) – vertical slip displaces water column.
• Submarine landslides (often quake-triggered).
• Volcanic eruptions (caldera collapse, pyroclastic flow entry).
• Meteorite impact (rare).

Characteristics

• Wavelength: 100–500 km (vs. wind waves 100–200 m).
• Speed: 500–800 km/hr in deep ocean (jetliner speed).
• Amplitude at sea: <1 m—often unnoticed by ships.
• Shoaling: Slows, compresses, grows to 10–30+ m at coast.
• Runup: Inundates land horizontally—destructive force = mass × velocity.

Warning & Response

• DART buoys, seismic networks, tide gauges → Tsunami Warning Centers (PTWC, NTWC).
• Natural warning: strong/long shaking, sea withdrawal ("drawdown"), roaring sound.
• Action: Move inland/up immediately—do not wait for official alert.