Tsunami: Hazard, Mitigation and Warning Ishmael C. Narag Officer-in-Charge Seismological Observation and Earthquake Prediction Division PHIVOLCS-DOST School Teachers’ Seminar-Training on Natural Hazards Awareness and Preparedness 24 April 2007 PHIVOLCS
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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
• 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)