PHYSICS OF TSUNAMI

EARTHQUAKE AT SEA1st possibility:

EARTHQUAKE AT SEA

2nd possibility:

TSUNAMI

Tsunami (tsoo – nah – mee)Tsu (harbor) & nami (wave)

“A natural phenomenon consisting of a series of waves generated when water in a lake or the sea is rapidly displaced on a massive scale” (www.wikipedia.org)

THEORY OF WAVES

Traveling Wave Wave moves energy,

not matter! Energy E ~ f ~ v/

T = 1/fT = 1/f

OCEAN WAVES- Wind blows grab water molecules- Water’s surface stretches ripples

(capillary waves)

- Ripples moves more molecules collected- Size and momentum increase reach the

beach

TSUNAMI WAVES

BASIC TSUNAMI MECHANISM

An earthquake causes a vertical movement of the seafloor, which displaces the sea water.

Large waves then radiate from the epicenter in all directions.

TSUNAMI EXPLAINED A tsunami is series of traveling ocean waves of extremely long length generated primarily by earthquakes occurring below or near the ocean floor.

Tsunami waves propagate across the deep ocean with a speed exceeding 800 km/h ( 500 mph) and a wave height of only a few tens of centimeters or less.

As they reach the shallow waters of the coast, the waves slow down and their height increases up to tens of meters (30 ft) or more.

Source: NOAA

WATER RECESSION: A PRECURSOR

From: Nature Publishing GroupFrom: Nature Publishing Group

Wave Generation Draw Down Effect

From: Digital Globe

Kalutara Beach, Sri Lanka

TSUNAMI WAVE APPEARANCE

A tsunami wave crest has three general appearances from shore: Fast-rising tide Cresting wave A step-like change in the

water level that advances rapidly (called a bore)

Series of wavesSeries of waves Most tsunamis come in a series of waves that may last for several Most tsunamis come in a series of waves that may last for several

hourshours The outflow of water back to the sea between waves can cause The outflow of water back to the sea between waves can cause

more damage than the original incoming wave frontsmore damage than the original incoming wave fronts The first wave is rarely the largestThe first wave is rarely the largest

A bore on the Qian Tang Jiang River, China

Source: www.waveofdestruction.org

TSUNAMI AT SEA

Unlike a normal wave, energy of a tsunami moves through the water, not on top of it.

Velocity:

d = water depth

Moves fast in deep waters 400 km/hour! No more than 1 meter high can not be

seen.

dgv

ENERGY LOSS

Waves loses energy as it moves away from its source

Energy loss rate ~ 1 / wavelength The longer the wavelength, the less energy it loses

Tsunami wavelength = 200 km! Energy is almost constant far from epicenter

NORMAL WAVE VS TSUNAMI WAVE

Ocean Wave Speed = 8-100 kph Wave Period = 5-20

seconds apart Wave Length = 100-

200 meters apart

Tsunami Wave Speed = 800-1000

kph Wave Period = 10

min-2 hours apart Wave Length = 100-

500 km apart

AS TSUNAMI MOVES…

AT THE BEACH

Shallow water compresses the energy Tsunami moving away the beach: fast, short

height v & increase, A decrease

Tsunami moving toward the beach: slow, tall height

v & decrease, A increase

SOME PICTURES FROM SATELLITE

TSUNAMI 12/26

Magnitude of earthquake = 9.0 SR Slipped plate length = 1,200 km Slip over = 15 m Height of wave reach up to 30 m with

speed ~ 800 km/hr

DETECTED EARTHQUAKE

TSUNAMI ANIMATION

TSUNAMI IN ACEH

Magnitude: 9.0 on the Richter scaleThe Energy possessed (roughly):~ 5 MTons of TNT = 2*1018 Joules~ 2 x explosive energy during all WW II~ 30% energy consumed in USA a year~ 70 days Hurricane Isabel

IMPACT ON EARTH Some smaller island southwest Sumatera

moved ~ 20 m to southwest Northern tip of Sumatera moved ~ 36m to

southwest Some small islands near Aceh province are

gone forever New lakes/rivers created in ex-land in Aceh,

disconnecting transportation to ex-villages

EARTHQUAKE ENERGY

Source: Earthquakes by Bruce A. Bolt

Sumatra-Andaman (2004)

MANGROVES

CASUARINA PLANTATIONS

WIDE BEACH

BEACH WITH CLIFFS

SAND DUNES

School of Earth and Atmospheric SciencesDepartment of Applied Geology, University of Madras

TSUNAMI RISK REDUCTION

3. Locate and configure new development in the run-up areas to minimize future tsunami losses

Avoid inundation areas

i.e. build on high ground

Slowing water currents

i.e. Conserve or replant coastal belts

of forest and mangrove swamps Steering water forces

i.e. angled, by-pass walls

Blocking water forces

i.e. Build sea walls

SLOWING

STEERING

BLOCKINGSource: National Tsunami Hazard Mitigation Program (NTHMP)

TSUNAMI RISK REDUCTION

Elevated restaurant in Hilo, Hawaii. Lower level is designed to allow waves to pass through.

Source: National Tsunami Hazard Mitigation Program

4.4. Design and construct new buildings to minimize Design and construct new buildings to minimize tsunami damagetsunami damage

Heavy and rigid structure

Raise building on stilts*

Many openings on the ground floor *

Orient perpendicular to theshoreline:

*Use caution with this design in areas with high earthquake-shaking risk.

TSUNAMI RISK REDUCTION

WAVE

Overturning

Sliding

Scouring

Buoyancy

Water pressure & debris impact

WAVE

Overturning

Sliding

Scouring

Buoyancy

Water pressure & debris impact

4. Tsunami-resistant buildings (cont.)

Tsunami forces on structures

Lowest horizontal structure above wave-crest

Horizontal member perpendicular to the wave

Lateral bracing

Deep protected piles

Rigid connection

Lowest horizontal structure above wave-crest

Horizontal member perpendicular to the wave

Lateral bracing

Deep protected piles

Rigid connection

Structure designed to resist tsunami forces

Source: National Tsunami Hazard Mitigation Program (NTHMP)

BASE ISOLATION