3.2 understanding tsunami

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

THANK YOU

FOR

LISTENING

PHIVOLCS: http://www.phivolcs.dost.gov.phishma@phivolcs.dost.gov.ph