Samenvatting
Summary Natural Hazards Lecture Notes
Lecture notes from Natural hazards. Lecture 7 is missing.
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Door: sharayvoskes • 1 jaar geleden
Voorbeeld van de inhoud
Annelou Hulsker Natural Hazards Periode 3Lecture 1 (03-02): Introduction to natural hazards
Tohoku-Oki earthquake, tsunami and Fukushima, a nuclear disaster: presentatie als voorbeeld hoe je
het eindpaper kan aanpakken.
Outline
- Preconditions (geographical & economical)
- Disaster strikes (natural and economic impact)
- The aftermath/evaluation (long run effects)
NB: good source is the Economist; topic selection for final paper is from February 19th.
Lecture 2 (05-02): Tsunami
Our generation is ‘fortunate’ to have experienced in our lifetime already 2 major tsunamis.
Most recent:
28 september 2018: Palu (Sulawesi) earthquake and tsunami ~2300 casualties
22 december 2018: Anak Krakatoa, generated by vulcano collapse ~437 casualties
- Most generated by earthquakes (82%)
- And most (67%) of these earthquakes have a magnitude of 7.5 or greater
- We therefore focus on the largest earthquake and tsunami of our time
→ 2004 Indian Ocean Earthquake and Tsunami ~ combined casualties: 283 106
Sunday, December 26 at 00:58:53 (UTC), in Islamic world a work day, in Europe, ‘boxing
day’.
Europe and the US are important in this story.
Exceptional earthquake
- Largest earthquake since 1964 (mag = 9.3), second largest we ever observed
- Duration: more than 10 minutes
- Rupture dimensions: 1300 km x 150 km
- Fault slip more than 15 meters
What was causing what damage is not clear, the damage was probably already very extensive.
Even though the water is not deep (10 cm), everyone who is caught has no chance of survival against
the force of the tsunami and the debris flow.
Hollywood ideal: wall of water, is usually not the case.
How do earthquakes generate tsunamis?
1. Relative plate motion bends the plates.
2. Cm/year speeds, so very slow, lasts centuries.
3. Earthquake lets upper plate snap back up.
4. Water column is uplifted and then falls sideways → happens very fast.
5. There are typically after-waves.
Critical element in generating tsunamis: the seafloor has a rapid vertical motion.
Tsunami waves move very slow (relative to seismic waves) → at the same speed of a jet airplane
Facts:
- Travel at speed of more than 800 km/hr
- Maximum height (depends of depth)
- Open ocean: 1-2 meter
- Near shore 10-20 meter
,Annelou Hulsker Natural Hazards Periode 3
- Typical wavelength 250-350 km open ocean
Relation between depth, velocity and
wavelength:
Closer to the shore the waves slows
down, the energy is being pushed into a
smaller compartment, everything is
clogging up.
Shallow ocean floor is good for
protection, large waves break easily.
Inundation is up to 15 km inland (near
rivers and on flat lands), but depends on
the slope and topography.
Maximum run-up: maximum height the water will reach.
- If the slope of the coast is higher, the run-up is also higher.
Inundation: how far inland the water-wave gets. Low relief, more destruction.
Why is the tsunami bigger in some places? offshore bathymetry and shelf slope
After a great tsunami, global oceans remain disturbed for days. The energy of a tsunami is usually
only 10% of the earthquake itself.
Sometimes it is clear to geologist that major earthquakes and tsunami had occurred here in the past;
along the Sumatra coast there have been previously massive tsunamis.
Issues:
- Lacking communication between geologist and society/government
- Poor societal memory/dementia of large earthquakes and tsunamis
Purpose of a warning system
- Reduce casualties by
- Warning people against direct impact
- Training people what to do in case
- Preventing casualties due to secondary impact (fire, collapse, nuclear emergency …)
A warning system is based on seismology observations (these waves travel way faster). For a
warning to be send, the waves need to be registered.
What went wrong in 2004:
- A denser network of seismometers and GPS receivers in Indonesia would have resuted in a
much faster recognition of the exceptional magnitude of the earthquake
- No DART buoys in Indian Ocean to observe the tsunami
- US based earthquake and tsunami institutions with relevant information were poorly
connected to Indonesian and other institutions
- Timing of the event (Boxing day):western world not at work
- Tsunami warning was consequently largely non-existent
- Most people did not recognize the tsunami for what it was
- People had little idea what to do and what to expect
, Annelou Hulsker Natural Hazards Periode 3
Warning and evacuating so many people on such short notice will be close to impossible.
Lecture 3 (10-02): Earthquakes
What is an earthquake?
- An earthquake is a sudden release of energy that occurs by slip along a fault
- The energy for ‘faulting’ is stored in the rocks adjacent to the fault & is derived from tectonic
plate motions. The energy builds slowly (over 10’s to 1000’s of years) but is released quickly
(in seconds or minutes)
- The suddenness of energy release distinguishes earthquakes from other disasters.
For ‘big’ faults, the width of the deformation zone can be 10 km or more, so where the fault exactly is
is hard to distinguish. → difficult to study
Earthquake ‘cylce’
Energy storage along faults → if the faults are moving smoothly, so there is no fricton, there is no
storing of strain energy (relatively safe, e.a. San Andreas fault)
No friction Friction
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