Tsunami Theory - ISNET Theory.pdf · Most tsunamis do not result in giant breaking waves. Rather, they come in much like very high and fast tides. Much of the damage inflicted by

ISNET/ISA Workshop Tehran12.09.2013 Andreas Hoechner

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Tsunami Theory


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Tsunami Casualties


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Tsunamigenic Sources

(after Gusiakov)


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About 500 m run-up

Landslide: Lituya Bay, Alaska 1958


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Dengler & Preuss (2003)

Google Earth

A tsunami following an earthquake devastated several villages.Run-up up to 15 meters. More than 2100 casualties.

Papua New Guinea Tsunami 17.7.1998


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Okal & Synolakis (2004)

Run-up distribution of Papua New Guinea 1998 and Nicaragua earthquake Tsunami 1992 (MW=7.7)

Earthquake

Landslide

Run-up distribution


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Gisler et al. (2003) Two and Three Dimensional Simulations of Asteroid Ocean Impacts

1200 processors for several weeks. Up to 200,000,000 computational cells were used, and the total computational time was 1,300,000 cpu-hours

Asteroid impact tsunami


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Gisler et al. (2003)

Asteroid impact


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Initial tsunami height > 1 km ! Gisler et al. (2003)

Asteroid impact


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Earthquake distribution


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Plate motions imaged by GPS


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Plate tectonics


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Continental drift


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Mantle convection


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Driving forces


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USGS

Elements of plate tectonics


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McCaffrey (2009)

Subduction Factory


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Subduction earthquake tsunami source


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Tectonic setting SumatraTsunami Generation

Coupling at the subduction interfaceTectonic loading

Sudden releaseTransfer of potential energy


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V=√g⋅d λ=λ0√ hh0

Tsunami velocity and wave length


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Gjevik (2004)

Tsunami properties


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Gjevik (2004)

Tsunami properties table


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Most tsunamis do not result in giant breaking waves. Rather, they come in much like very high and fast tides. Much of the damage inflicted by tsunamis is caused by strong currents and floating debris.

NOAA

Artistic image of the tsunami

Inundation characteristic


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TsunamiModelling


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Modelling steps

● Tsunami generation: Initial condition● Tsunami propagation (nonlinear shallow water)● Tsunami run-up and coastal inundation (high resolution, Boussinesq equations)


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Tsunami is a long wave

Long-waveVx ≠ f(z)

Short-waveVx = f(z)


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● Finite differences on structred grids● Pro: easy to implement, robust, simple grids,

straightforward parallelization of computation● Contra: constant resolution, need for nested grids

in coastal regions● Examples: TUNAMI-family, MOST, FUNWAVE

● Finite elements on unstructured grids● Pro: single computational domain for deep-ocean

propagation and inundation● Contra: time consuming, stability problems, hard

to program, complex grids● Examples: TsunAwi, ANUGA, Uni Bologne

Numerical schemes


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Finite differences on structured grid

Imamura (1996)


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Harig et al. (2008)

Nested grids


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Harig et al. (2008)

GITEWS Indonesian grid:> 4 Mio elements with

resolution down to 50 m

Unstructured grid


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General rule also applies here:Last 10% of model accuracy costs 90% of efforts.

While increasing numerical grid resolution do not forget about physical resolution of bathymetry used.

Source uncertainty is always there...

Limits of modelling


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Sumatra 2004


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Tsunami Animation

tsunami_large_2d

sumatra_3d


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SourceModelling


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Initial condition

● Tsunami generation: Initial condition

● Tsunami propagation (nonlinear shallow water)

● Tsunami run-up and coastal inundation (high resolution, Boussinesq equations)

● How do we get an appropriate initial condition?


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Seismology: Source parameters

GEOFON: Epicenter, Magnitude

Teleseismics:Rupture Timing (D. Roessler)Teleseismics:

Source Extent

Magnitude saturation? Slip Distribution?


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Magnitude Saturation, Kanamori 1983


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Fault Extension

Magnitude is a logarithmic function of moment


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Source is not a point source

● mb=7.2

● MS=8.2

● MW=9.3

Hoechner et al. 2008

Uplift [m]Slip [m]


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Source determination

● Present status: ● Use Epicenter and Magnitude to extract scenarios from

database● Check with buoys, tide gauges, GPS, if available

● Problems and Requirements:● Time-critical: Tsunami can reach coast within 20 minutes● Magnitude might be underestimated for large events (was

8.0 for Sumatra instead 9.3)● Seismological methods measure acustic luminosity, rather

than total energy release ● Epicenter is just nucleation point, Centroid not so easy to

determine● Slip distribution necessary for large events or complex

bathymetry


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Warning center: Data flow

Seismik BojePegel Bodendrucksensor EB DatenGPS

-Lokale Behörden-Gefährdete Bevölkerung

Sensor-Systeme

Messungen

Lagebeurteilung und Entscheidungsunterstützung

-Weitere nationale und internationale Empfänger

Simulation


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Warning center: Decision Support System

Documents

Tsunami Theory - ISNET Theory.pdf · Most tsunamis do not result in giant breaking waves. Rather, they come in much like very high and fast tides. Much of the damage inflicted by