Embed Size (px)
Citation preview
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
• A series of waves generated by various geological processes
Tsunami Hazard
• Japanese term meaning “harbor waves”
• ”
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
Tsunami
• Danger continues for hours
• High fatality hazard
• Global impact blind to political boundaries
Recent Tsunami in the Philippines
1976 Moro Gulf Tsunami
1992 Eastern Mindanao Tsunami
1994 Mindoro Tsunami
The Science of Tsunami
• Generation
• Propagation
• Inundation
Tsunami Generation
• Generally byEARTHQUAKES
• Less commonly by Sub-aerial to SubmarineLANDSLIDES
• Infrequently byVOLCANIC ERUPTIONS
• Very rarely byMETEORITE IMPACTS
Tsunami Generation
Tsunami Propagation
• Speed depends on
Water Depth
– Fast in deep ocean (>1000 kph)
– Slows near shore (30-50 kph)
Tsunami Propagation
• Height depends on Water Depth
– Small in deep ocean (few cm to 1 m)
– Grows near shore (can be > 30 m)
Run-up & Inundation
• Last stage of the evolution of a tsunami
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
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)
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
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
Tsunami Deposits
• Geologic materials (including grain sizes from boulders to mud) deposited above mean sea level during the passage of a tsunami.
Tsunami Deposits
• Landward limit of inundation
• Direction of flow over an area
• Infer the passage of prehistoric tsunamis and the occurrence of an earthquake.
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
Tsunami Warning System
• Sensors / Instrumentation for seismic and tidal data
– Seismographs
– Wet Sensors
– Tide Gauge
– Pressure Gauge
– Deep-sea bottom pressure gauge
Deep-ocean Assessment and Reporting of Tsunamis
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
PHIVOLCS Proposed Deployment of Tsunami
Wet Sensors
1 m
5 m10 m
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
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)
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
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)
Two Tsunami Threats
• Chile
• Alaska
• Aleutian Islands
• Marianas
• Japan
Distant Tsunami
1960 Chilean Earthquake & Tsunami1960 Chilean Earthquake & Tsunami
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
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
1993 Okushiri TsunamiAonae Peninsula
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
Aonae Peninsula - Rebuilding
1993
2000
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
Tsunami: Education and Safety
• Inundation Maps
• Tsunami Evacuation Procedures
• Tsunami Educational Materials
• Tsunami Markers
• Tsunami Awareness Month
– Tsunami Safety Drills
– Essay Contests
• Tsunami Museums
Pacific Tsunami Museum
Pacific Tsunami Museum
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
Damage Scenario
• Trees and posts are uprooted from their locations
• Cars and boats are inundated;
• Tsunami debris can cause injuries during inland & back flows
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.
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
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;
Structural Countermeasures
• Sea walls at breakwaters
• Tide control gates
• Flood gates
• Elevated Structure
Non-structural Countermeasures
• Planting of trees and preservation of mangrove
Non-structural Countermeasures
Non-structural Countermeasures
• Sufficient road networks & paths to elevated areas
Non-structural Countermeasures
Non-structural Countermeasures
Non-structural Countermeasures
• Regulation of coastal population
• Peace and security of the area
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
• 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
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
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
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
