3.2 understanding tsunami
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Tsunami:Hazard, Mitigation and Warning
Ishmael C. NaragOfficer-in-Charge
Seismological Observation and Earthquake Prediction DivisionPHIVOLCS-DOST
School Teachers’ Seminar-Training on Natural Hazards Awareness and Preparedness
24 April 2007PHIVOLCS
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• A series of waves generated by various geological processes
Tsunami Hazard
• Japanese term meaning “harbor waves”
• ”
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Tidal Wave / Storm Surge
• Tsunami waves are not “tidal waves”– Gravitational attraction
between earth and a heavenly body (e.g. moon, sun & other planets)
• Wind-generated waves– Surfs
– Storm surges
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Tsunami
• Danger continues for hours
• High fatality hazard
• Global impact blind to political boundaries
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Recent Tsunami in the Philippines
1976 Moro Gulf Tsunami
1992 Eastern Mindanao Tsunami
1994 Mindoro Tsunami
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The Science of Tsunami
• Generation
• Propagation
• Inundation
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Tsunami Generation
• Generally byEARTHQUAKES
• Less commonly by Sub-aerial to SubmarineLANDSLIDES
• Infrequently byVOLCANIC ERUPTIONS
• Very rarely byMETEORITE IMPACTS
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Tsunami Generation
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Tsunami Propagation
• Speed depends on
Water Depth
– Fast in deep ocean (>1000 kph)
– Slows near shore (30-50 kph)
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Tsunami Propagation
• Height depends on Water Depth
– Small in deep ocean (few cm to 1 m)
– Grows near shore (can be > 30 m)
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Run-up & Inundation
• Last stage of the evolution of a tsunami
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Scientific Development
• Run-up data used to improve models
• New generation of inundation models– Better inundation maps– Tsunami wave-height
forecasting
• Distributed global historical databases
• Paleotsunami studies– More complete and
longer tsunami histories– Improved hazard ID &
risk assessment
• Slump-generated tsunamis
• Real-time deep ocean data– New monitoring
strategies– Direct confirmation of
tsunami
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Tsunami Hazard Assessment
• Compile complete catalogue for earthquakes and tsunamis. Understand local and regional geology and tectonics
• Identify most hazardous tsunami source areas and its tsunami-generating mechanism (earthquake, landslide, volcanic eruption)
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Tsunami Hazard Assessment
• Identify most vulnerable coastal locations from sources (historical or expected)
• For these coastal locations, conduct modelling for inundation and run-up to determine impact
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Tsunami in the PhilippinesTsunami in the Philippines
• About 44 earthquakes from 1589 to present generated tsunamis.
• Enclosed bays are the usual sites where tsunami waves are observed.
• Some areas have more than one tsunami reports (ex. Songsong Bay, Manila Bay, Calauag Bay, CaragaBay, Moro Gulf area)
• Minimum earthquake magnitude is 5.4.
• Largest tsunamis occurred in the Zamboanga-Cotabato-Sarangani areas
Reference: Bautista, 2002
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Tsunami Deposits
• Geologic materials (including grain sizes from boulders to mud) deposited above mean sea level during the passage of a tsunami.
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Tsunami Deposits
• Landward limit of inundation
• Direction of flow over an area
• Infer the passage of prehistoric tsunamis and the occurrence of an earthquake.
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Tsunami Deposits
• Identify ancient tsunami deposits
– Difference in faciesbetween tsunami and storm deposits
• Post-depositional alteration
– Depositional extent
– Thickness
– Internal structure
• Understand tsunami hydraulics
– Where tsunami might transport sediments
– Depth and velocity of flow
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Tsunami Warning System
• Sensors / Instrumentation for seismic and tidal data
– Seismographs
– Wet Sensors
– Tide Gauge
– Pressure Gauge
– Deep-sea bottom pressure gauge
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Deep-ocean Assessment and Reporting of Tsunamis
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Lubang Island Setup
Concrete Pier
The height of stainless tube and elevation of probes and collecting vessel could be adjusted to set the tsunami heightmeasurement level H(I.e. 1 m, 3 m, 6 m or 10 m)
Water collecting
vessel
Stainless Tube
Air Vent
Tsunami Water Intake
H
Electric Cable
Sea Water
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PHIVOLCS Proposed Deployment of Tsunami
Wet Sensors
1 m
5 m10 m
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Tsunami Warning System
• Data Transmission /Retrieval System
– Radio
– Microwave
– Landline
– Satellite
– Internet
• Data Evaluation– Earthquake Location &
Magnitude Estimate
– Coastal amplitude forecast
• Emergency Communications for Info Dissemination
– Sirens
– Emergency Alert Systems
– Radios
– Telephones/Hotlines
– Wire
– Data Systems
– Satellite
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Warning Guidance
• Very Rapid Earthquake Evaluation
• Very Rapid Sea Level Evaluation
– Early Detection
– Wave Forecast
– Warning Disseminated to the last kilometer
• Rapid (as soon as possible)
• Accurate (minimize false warnings)
• Reliable (continuous operation)
• Effective (to save lives)
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Two Tsunami Threats
• LOCAL/REGIONAL TSUNAMI
• Generated nearby
• Strikes shore quickly (within minutes)
• Highest Run-ups
• Damage only to limited areas
• DISTANT / PACIFIC-WIDE TSUNAMI
• Generated far away
• Strikes shore later (5+ hours for official evacuation)
• Widespread Damage
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Two Tsunami Threats
• LOCAL/REGIONAL TSUNAMI
• Philippine National Seismic Network
• DISTANT / PACIFIC-WIDE TSUNAMI
• Pacific Tsunami Warning Center (PTWC)
• Northwest Pacific Tsunami Information Center (NWPTIC)
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Two Tsunami Threats
• Chile
• Alaska
• Aleutian Islands
• Marianas
• Japan
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Distant Tsunami
1960 Chilean Earthquake & Tsunami1960 Chilean Earthquake & Tsunami
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PHIVOLCS Tsunami Alert Levels (distant earthquakes)
• life threatening tsunami generated near epicenter
• IMMEDIATE EVACUATIONof areas projected to be affected
• NDCC flow of info• Community-based
alarms• Media, military
• Major shallow earthquake in Pacific (magnitude > 7.0)
• Waiting for confirmation of tsunami
• Information released to general public
• BE READY, wait for further information
• NO EVACUATION ORDER!
• Confirmed tsunami near epicentral area
• wave heights NON-LIFE threatening
• WATCH in effect,
• NO EVACUATION!
• Observe precautionary measures near coastline- stay away from the coastline
Go!!Watch/observe Ready
Level 3Level 2Level 1
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False Warnings
• False Warnings will occur– Small, non-destructive
tsunami observed
– Expensive: In 1994, false warning in Hawaii cost $50M
– High number of false alarms reduces credibility
– Evacuations place citizens at greater risk
• Balance number of false warnings with missed events
– No warning system, no false warnings
• Prepare & educate public, media and emergency officials
– Statistics
– Reliability
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1993 Okushiri TsunamiAonae Peninsula
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Aonae Peninsula – Rebuilding
• 10 years & > $600 M later– Memorial Park
– Memorial Hall
– Elevate (3 m fill) and/or relocate town
– 10-m high platform at harbor
– Sloping (not stairs) covered evacuation routes
– Four water gates
– Concrete sea-walls
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Aonae Peninsula - Rebuilding
1993
2000
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Lessons Learned
• Education is essential for local tsunamis
– Hard sell
– All hazards approach
• Land use management is least expensive way to mitigate tsunami damage
– Rebuild or Relocate?
• Surveys of tsunami damage immediately after the tsunami provides vital data for numerical model development and education
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Tsunami: Education and Safety
• Inundation Maps
• Tsunami Evacuation Procedures
• Tsunami Educational Materials
• Tsunami Markers
• Tsunami Awareness Month
– Tsunami Safety Drills
– Essay Contests
• Tsunami Museums
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Pacific Tsunami Museum
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Pacific Tsunami Museum
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Tsunami Damage
• Run-Up & Inundation
• Ground Subsidence
• Wave-related damage
– Best case: Quickly rising tide
– Worse case: Wall of turbulent water with rocks and debris
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Damage Scenario
• Trees and posts are uprooted from their locations
• Cars and boats are inundated;
• Tsunami debris can cause injuries during inland & back flows
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Damage Scenario
• Sea water is murky and may cause health complications when ingested.
• Water in wells become salty and not potable
• Agricultural lands are rendered useless for two years.
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Signs of an Impending Tsunami
• Large off-shore earthquake
• Unusual rise or fall of coastal waters
• Exposure of corals and underwater rocks
• Sound of approaching train
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Safety Procedures
• If any news of a nearby earthquake, stay alert and be ready to move to higher ground;
• If you feel an earthquake wherein you cannot stand, immediately move to higher ground;
• If the water receded, immediately move to higher ground;
• Never attempt to watch an approaching tsunami;
• Listen to instructions and do not return until authorities issue an all’s-clear bulletin;
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Structural Countermeasures
• Sea walls at breakwaters
• Tide control gates
• Flood gates
• Elevated Structure
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Non-structural Countermeasures
• Planting of trees and preservation of mangrove
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Non-structural Countermeasures
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Non-structural Countermeasures
• Sufficient road networks & paths to elevated areas
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Non-structural Countermeasures
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Non-structural Countermeasures
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Non-structural Countermeasures
• Regulation of coastal population
• Peace and security of the area
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Issues on Land Use Planning
� Uncoordinated special
purpose plans such as for
transportation or economic
development with hazard
planning
� Location of the hazard
does not seem to have
impacted the land use
allocation decision
making process
� Definitions of hazard
zones vary in accordance
with technique
Safety related criteria < Economically viable project
Private and other government agencies
would perform beyond their mandates
and capabilities;
Evacuation routes are non-
existent or unmaintained and are
located in hazard zones
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• Restrict land use by strategically controlling development
• Support land-use plans through capital improvement planning and budgeting
• Existing land-use restrictions can be modified
Land Planning Measures
• Designate tsunami hazard areas for open-space use (agriculture, parks, recreation);
� Acquire tsunami hazard areas for open-space use
Very low-density residential useClustering of development
Extension of water supply, public facilities etc.
Keep development at a minimum in hazard areas
floodplain restrictions, hillside and landslide control, environmental, scenic, recreational and wildlife-protection requirements
�Simple acquisition
�Development rights
�Leasing
�Land exchange
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Land Use Planning
• Tsunami effects must be addressed if administration decides to build in hazard zones;
• Damage to life and property may be due to:
– Simple flooding
– Force of waves
– Horizontal currents such as drawdown
� Organization and
arrangement of three
primary elements :
�Structures
�Elevated Open Spaces
�Roads & Alleys
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Inventory of Physical Conditions
• Opportunities & Limitations
– Areas of high and low relief
– Dangerous to other calamities
– Characteristics of the coastline (narrow bays, steep cliffs, etc)
– Soil condition
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Review of the Plan
• Requirements for the implementation of the plans
• Conform to the site’s physical characteristics;
• Expected cost and benefits of the plan