Earthquake generated Tsunami Wave Propagation

Modeling

Gopinath GopalakrishnanIRS

Anna University

Chennai

Lecture Objectives

• To provide the best possible information about the science of Earthquake and Tsunami

• To develop the tsunami wave propagation model

• To learn how the science can help us to prepare for primary and secondary prevention consequences of Tsunamis

PrimaryGround shaking and surface ruptureLandslidesTsunami

SecondaryFiresFloods

EARTHQUAKE HAZARDS

How an earthquake happens?

• In geologic terms, Plate is one of the very large pieces of rock that form the earth’s surface and move slowly. Subduction zone is the place where two lithosphere plates come together, one riding over the other. Most volcanoes on land occur parallel to and inland from the boundary between the two plates.

• One of the many tectonic plates that make up Earth’s outer shell descends, or “subducts,” under an adjacent plate. This kind of boundary between plates is called a “subduction zone.”

• When the plates move suddenly in an area where they are usually stuck, an earthquake happens.

INTERSEISMIC:

Relative plate rate about 50 mm/yr

Fault interface is locked

EARTHQUAKE (coseismic):

Fault interface slips, overriding plate rebounds, releasing accumulated motion

HOW OFTEN:

Fault slipped ~ 10 m = 10000 mm / 50 mm/yr

10000 mm / 50 mm/yr = 200 yrLonger if some slip is aseismic

Richter Magnitude is a measure of the strength of an earthquake, as determined by seismographic observations.

Intensity is a measure of the effects of an earthquake at a particular place on humans, structures and (or) the land itself.

The intensity at a point depends not only upon the strength of the earthquake (magnitude) but also upon the distance from the earthquake to the point and the local geology.

Earthquake Magnitude and Intensity

EarthquakesEarthquakes Types of seismic wavesTypes of seismic waves

1. Body waves -- travel through interior

2. Surface waves -- travel on surface of earth

 

Specific Body WavesSpecific Body Waves

Primary or "P" Waves:

Primary waves Highest velocity Causes compression and expansion in direction of wave travel.

Secondary or "S" Waves:

Secondary or shear waves Slower than P waves but faster than surface waves.

 Surface WavesSurface Waves

Cause vertical & horizontal shaking

Travel exclusively along surface of earth

Primary Primary or “P” or “P” WaveWave

SecondarSecondary or “S” y or “S” WaveWave

Seismogram PrintoutSeismogram Printout

Determining the location of an earthquakeDetermining the location of an earthquake

First, distance to earthquake is determined.

From seismograph record called the seismogram, measure time delay between P & S wave arrival

Use travel time curve to determine distance to earthquake as function o f P-S time delay  Now we know distance waves traveled, but we don't know the direction from which they came.

We must repeat the activity for each of at least three (3) stations to triangulate a point (epicenter of quake). Plot a circle around seismograph location; radius of circle is the distance to the quake.

Quake occurred somewhere along that circle. Do the same thing for at least 3 seismograph stations; circles intersect at epicenter. Thus, point is triangulated and epicenter is located. 

Time-Travel CurveTime-Travel Curve

Triangulation of 3 stations to locate earthquake Triangulation of 3 stations to locate earthquake epicenterepicenter

Determining the magnitude of an earthquakeDetermining the magnitude of an earthquake

Waves are the undulatory motion of a water surface.

Wave Motions

There are three types of waves defined by water depth:

• Deep-water wave

• Intermediate-water wave

• Shallow-water wave

Wave Motions

What is a Tsunami?

• Tsunamis are caused by events that drastically and suddenly shift a large volume of water.

Japanese word:

“Tsu“ means “harbor”

“Nami“ means “wave”

English translation: “Harbor wave”

TSUNAMI GENERATED ALONG FAULT, WHERE SEA FLOOR DISPLACED, AND SPREADS OUTWARD

Long wavelength and period, high speed

wavelength and speed reduced – height increased

Wave steepens as shore is approached

Geist, Titov and Synolakis, Tsunami: Wave of Change, Scientific American, January, 2006.

Tsunami-generating EQs and sources

India subducts beneath Burma microplateat about 50 mm/yr

Earthquakes occur at plate interface along the Sumatra arc (Sunda trench)

These are the destructive results of many years of accumulated plate motion

Tsunami Movement:Tsunami Movement:

Determinant factors of the size of the tsunami at initial phase and along the coast

Initial size of a tsunami: Amount of vertical sea floor deformation is the main factor, which determines the initial size of a tsunami. This is controlled by the earthquake's magnitude, depth, fault characteristics and coincident slumping of sediments or secondary faulting.

Size of a tsunami along the coast: Other features which influence the size of a tsunami along the coast are the shoreline and bathymetric configuration, the velocity of the sea floor deformation, the water depth near the earthquake source, and the efficiency which energy is transferred from the earth's crust to the water column.

Do tsunami stop once on land

Energy reflection back

Edge waves

Why are tsunami so destructive?

“As the tsunami enters the shoaling water near the coast, its velocity decreases and its height increases. It is in these shallow waters that tsunamis become a threat to life and property, for they can crest to heights of more than 30-50 meters and strike with devastating force.

Tsunamis are among the most terrifying natural hazards known to man. They have been responsible for tremendous loss of life and property throughout history.”

An Example• Tsunami Wave Example: Sumatra 2004 • How long does it take to get to Sri Lanka?

Distance ~2000 kmWater Depth ~4000 m

T= 2000/713=2.2 hr

v gD 9.8* 4000 198m

s713

km

hr

An Example• Tsunami Wave Example: Sumatra 2004 • How long to get to Thailand?

Distance ~500 kmWater Depth ~1500 m

T= 500/430=1.1 hr

v gD 9.8*1500 120m

s430

km

hr

An Example• Tsunami Wave Example: Sumatra 2004 • How high is the wave?

HD12

HD22

vD 2

vD1

gD2

gD1

1

1

2

HD12

HD22

0.62

HD 22

gD2

gD1

9.8 *10

9.8 * 4000 HD2 7.6m

NOAA

Earthquake generated Tsunami wave propagation modeling using

Mike 21

MIKE Zero is the common name of DHI's fully Windows integrated graphical user interface for setting up simulations, pre- and post-processing analysis, presentation and visualisation within a project oriented environment.

– 1 Dimensional MIKE 11

– 2 Dimensional MIKE 21

– 3 Dimensional MIKE SHE MIKE 3

MIKE 11MIKE 3

MIKE SHEMIKE 21

HYDROLOGICAL AND HYDRODYNAMIC MODELS

MIKE 21-IntroductionMIKE 21 is a professional engineering software package for 2D free surface flows, developed by Danish Hydraulic Institute (DHI).

Its comes in modular form with four main application areas such as:

1. Coastal hydraulics and Oceanography.

2. Waves.

3. Sediment processes

4. Environmental hydraulics.

MIKE 21 solves the shallow water equation for given boundary condition to variety of Environmental forcing and processes such as

1. Bottom Shear Stress.

2. Wind Shear Stress.

3. Barometric Pressure gradient.

4. Coriolis forces.

5. Momentum Dispersion.

6. Source and Sink.

7. Evaporation flooding and Drying.

8. Wave Radiation Stresses.

MIKE 21-HD (Mike 21 Hydrodynamic Module)

The hydrodynamic (HD) module is the basic module in the MIKE 21 Flow Model.

The MIKE 21 HD Module simulates the water level variations and flows in response to a variety of forcing functions in lakes, estuaries, bays coastal areas and seas.

MIKE 21 HD solves the vertically integrated, fully dynamic equations of continuity and conservation of momentum in two horizontal directions, using implicit finite difference methods.

It includes a wide range of hydraulics phenomena in the simulations. Can be used for any 2D free-surface flow in which stratification can be neglected.

Input Data

Bathymetry

Initial Condition Water Surface level.

Boundary Condition Water level / Flow Magnitude. Flow direction.

Other Driving Forces Wind Speed & Direction. Source / Sink discharge. Magnitude & Speed.

Eddy Viscosity

Bed Resistance Coefficient

Wave Propagation Mw 9.3 Tsunami 2004

Profile line of 1, 2, and 3

1. Visakhapatnam2. Chennai3. Sri Lanka

Profile line

1

2

3

Visakhapatnam

Chennai

Sri Lanka

Mw 9.3

Mw 8.5 Fault 2

Mw 8.5 Fault 3

Nested Grid Bathymetry & Initial Surface Elevations

Wave Propagation Mw 9.3 Tsunami 2004 Nagapattinam Coast & Surrounding areas

Mike 21 HD Model 100m Nested Grid Nagapattinam

Tsunami Inundation Map

Geist, Titov and Synolakis, Tsunami: Wave of Change, Scientific American, January, 2006.

Train and tracks destroyed, SW coast of Sri Lanka

Conclusion

Tsunamis….. • Are uncontrollable phenomenon• Causes extensive loss of life• Damage property• Public warning systems provide some

measures of protection.

Thank You