1. 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
2. • A series of waves
generated by various
geological processes
Tsunami Hazard
• Japanese term
meaning “harbor
waves”
• ”
3. 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
4. Tsunami
• Danger continues for
hours
• High fatality hazard
• Global impact blind to
political boundaries
5. Recent Tsunami in the Philippines
1976 Moro Gulf Tsunami
1992 Eastern Mindanao Tsunami
1994 Mindoro Tsunami
6. The Science of Tsunami
• Generation
• Propagation
• Inundation
7. Tsunami Generation
• Generally by
EARTHQUAKES
• Less commonly by Sub-
aerial to Submarine
LANDSLIDES
• Infrequently by
VOLCANIC ERUPTIONS
• Very rarely by
METEORITE IMPACTS
12. 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
13. 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)
14. 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
15. 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, Caraga
Bay, Moro Gulf area)
• Minimum earthquake
magnitude is 5.4.
• Largest tsunamis occurred
in the Zamboanga-
Cotabato-Sarangani areas
Reference: Bautista, 2002
16. Tsunami Deposits
• Geologic materials (including grain sizes from
boulders to mud) deposited above mean sea
level during the passage of a tsunami.
17. Tsunami Deposits
• Landward limit of
inundation
• Direction of flow over
an area
• Infer the passage of
prehistoric tsunamis
and the occurrence of
an earthquake.
18. Tsunami Deposits
• Identify ancient
tsunami deposits
– Difference in facies
between 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
19. Tsunami Warning System
• Sensors /
Instrumentation for
seismic and tidal data
– Seismographs
– Wet Sensors
– Tide Gauge
– Pressure Gauge
– Deep-sea bottom
pressure gauge
21. Lubang Island Setup
Concrete Pier
The height of stainless tube
and elevation of
probes and collecting
vessel could be
adjusted to set the
tsunami height
measurement 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
23. 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
24. 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)
25. 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
26. 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)
29. PHIVOLCS Tsunami Alert Levels (distant earthquakes)
• life threatening
tsunami generated
near epicenter
• IMMEDIATE
EVACUATION
of 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/observeReady
Level 3Level 2Level 1
30. 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
32. 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
34. 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
38. 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
39. Damage Scenario
• Trees and posts are
uprooted from their
locations
• Cars and boats are
inundated;
• Tsunami debris can
cause injuries during
inland & back flows
40. 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.
41. 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
42.
43.
44. 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;
52. 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
53. • 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 use
Clustering 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
54. 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
55. 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
56. 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
