TSUNAMI GENERATION MECHANISMS

Earthquake Parameters

• Moment measures earthquake strength.

• Mechanism specifies the orientation of the earthquake fault and the direction of slip on it.

• Earthquake depth :deep earthquakes would produce less potent tsunamis than similar shallow earthquakes.

Earthquake Zones

Faults: Strike Slip

Faults: Dip Slip

Faults: Dip Slip

Fault Structures - Normal Faults

Fault Structures - Reverse Faults

Faults: Strike Slip

Pull Apart Mechanism

How does the earthquake generate tsunami?

When the bottom of the ocean was deformed

by this megathrust quake, the upward force

acted like that fist, creating massive waves of

tsunamis, which spread out in all directions.

Imagine a fist rising up from under the water.

Water rolls down off the sides of the fist.

NASA

EARTHQUAKE INITIATION

Synthetic record sections of vertical tsunami motions at distances of 200, 500, 1000 and 2000km from point dip slip (top) and strike slip (bottom) earthquakes of magnitude Mw=7.5 and depth 10 km. Time runs for five hours and the peak amplitude of each trace is given in cm at the right. The lower half of the focal sphere and azimuth of observation are shown toward the right (Stewe Ward, Encyclopedia of Physical Science and Technology)

Volcanic Eruptions

• Animation

Submarine Landslide

Scientific terms:

Run-up: Vertical height a wave reaches

above a reference sea level as it washes ashore.

Wave height: Vertical measurement of the wave before it reaches shore.

Inundation distance: Horizontal distance a tsunami reaches landward from shoreline.

USGS-NEIC

Appearance of a tsunami when reaches the shore

A rapidly rising or falling tide

A series of waves

A bore

Run-up height:

Tsunamis of distant origin: > 50 ft (15 m)

Tsunami generated near the earthquake

epicenter: > 100 ft (30 m)

First wave may not be the largest in

the series of waves.

Do tsunamis stop once on

land?

Energy reflection back

Edge waves

Complicated behavior of

tsunami waves near the coast !

The first run-up of a tsunami is

often not the largest.

Do not return to a beach several

hours after a tsunami hits.