Hazards Planning and Risk Management Lecture No. 23 Tsunami Fall 2016 US – Pakistan Center for Advanced Studies in Water

Learning Objective Tsunamis What are they? Where do they occur? Why do they occur? Consequences of their occurrence? 2 2

Reading Material Tsunami Hazard Mapping in Developing Countries – ICHARM Publication. http://www.icharm.pwri.go.jp/publication/pdf/2010/4 184_tsunami_hazard_mapping.pdf International Centre for Water Hazard and Risk Management

Tsunami The Killer Sea Wave

Tsunami Tsunamis are waves generated by earthquakes, volcanic eruptions, or underwater landslides When large areas of the sea floor elevate or subside, a tsunami can be created Can be 15 m or high and can enter inland several hundreds of meters Velocities of normal ocean waves are about 90 km/hr while tsunamis have velocities up to 950 km/hr (about as fast as jet airplanes) Tsu = harbor, nami = waves Consist of series of waves. Source: Together towards a safer India, CBSE Subduction earthquakes are particularly effective in generating tsunamis

Tsunami Unlike ordinary tides, tsunami are barely noticeable in their deep sea formation stage When caused by nearby earthquakes reach the coast in minutes Tsunami danger period can continue for many hours after a major earthquake

Causes Earthquakes Volcanic Eruptions Landslides Meteorite Impacts Tsunami may be generated by Earthquakes Volcanic Eruptions Landslides Meteorite Impacts

Tsunami When caused by far away earthquakes in ocean, waves travel at hundreds of kilometers per hour reaching coast after several hours of earthquake Can occur anytime of the day or night When waves enter shallow waters they may rise in height striking the coast with devastating force Source: Together towards a safer India, CBSE

http://earthsci. org/education/teacher/basicgeol/tsumami/tsunami http://earthsci.org/education/teacher/basicgeol/tsumami/tsunami.html#4StagesinTsunami d = depth of wave to ocean bed

4 Stages of Tsunami Tsunami wave activity is unfelt in the open ocean Source: Together towards a safer India, CBSE 4 Stages of Tsunami

Local and Regional Tsunami Local or Near Field Tsunami Source of the tsunami within 1,000 km of the area of interest. Waves have a very short travel time (30 minutes or less) Regional Tsunami or Mid Field Source of the tsunami greater than 1,000 km of the area of interest Waves have travel times on the order of 30 minutes to 2 hours Also called teletsunami, distant-source or far field tsunami Source: http://nthmp-history.pmel.noaa.gov/terms.html Note: " Local" tsunami is sometimes used to refer to a tsunami of landslide origin. teletsunami: Source of the tsunami more than 1,000 km away from area of interest.

Measurements In terms of Inundation Inundation Inundation Area The depth, relative to a stated reference level, to which a particular location is covered by water Inundation Area An area that is flooded with water Inundation line (limit) Inland limit of wetting measured horizontally from the edge of the coast Source: http://nthmp-history.pmel.noaa.gov/terms.html

Signs of Possible Inundation Level Based on numerical estimation or past inundation record Source: http://www.icharm.pwri.go.jp/publication/pdf/2010/4184_tsunami_hazard_mapping.pdf

Measurements In terms of Wave Amplitude Runup Maximum height of the water onshore observed above a reference sea level Marigram Tide gauge recording showing wave height as a function of time Marigraph Instrument that records the wave height Amplitude: Rise above or drop below the ambient water level as read on a tide gage period: The length of time between two successive peaks or troughs. May vary due to complex interference of waves. Tsunami periods generally range from 5 to 60 minutes. travel time: Time (usually measured in hours and tenths of hours) that it took the tsunami to travel from the source to a particular location.

Source: http://www. icharm. pwri. go

Prediction and Early Warning Areas far from sources of tsunamis may have enough warning time Seismographic stations Tidal stations http://earthsci.org/education/teacher/basicgeol/tsumami/tsunami.html#4StagesinTsunami National Oceanic and Atmospheric Administration (NOAA) has set up a Pacific warning system for areas in the Pacific Ocean, called the Pacific Tsunami Warning Center

Nature’s Tsunami Warning Sometimes Tsunami causes the water near the shore to recede exposing the ocean floor If the trough of the tsunami wave reaches the coast first, this causes a phenomenon called drawdown, where it appears that sea level has dropped considerably Leading-depression wave: Initial tsunami wave is a trough, causing a draw down of water level Source: Together towards a safer India, CBSE

Detecting Tsunami Utilizing satellite technology nearly immediate warning of potentially tsuna-migenic earthquakes Warning time depends on distance of epicenter from coast Warning includes predicted times at selected coastal communities Tsunami detectors ‘Tsunameters’ …… Tide Gauges Satellite altimeters Deep-ocean Assessment and Reporting of Tsunamis (DART) system in Pacific Ocean (NOAA) Source: Together towards a safer India, CBSE Tide gauges measure the height of the sea-surface and are primarily used for measuring tide levels. Satellite altimeters measure the height of the ocean surface directly by the use of electro-magnetic pulses.

Sea surface (in blue) measured by the Jason satellite 2 hours after the initial earthquake hit the region southeast of Sumatra (shown in red) http://www.bom.gov.au/tsunami/info/index.shtml

Reducing Vulnerability of Houses Elevate coastal homes Source: Together towards a safer India, CBSE

Risks Damages caused by Tsunami waves Secondary effects include the debris acting as projectiles Erosions Fires http://earthsci.org/education/teacher/basicgeol/tsumami/tsunami.html#4StagesinTsunami

Mitigation Measure Proper awareness and preparedness is must The giant loss of 2004 IOT was mainly due to the lack of proper awareness and preparedness Tsunami Hazard Map (THM) − one of the most effective ways of raising awareness and reducing tsunami disaster risk Any warning system will be useless if people are not aware about the disaster itself and perform incorrect responses Tsunami events are very rare therefore it is not easy to sustain public awareness towards tsunami disaster mitigation Both structural and non structural measures are to be sought

Structural Measures Source: http://www.icharm.pwri.go.jp/publication/pdf/2010/4184_tsunami_hazard_mapping.pdf To reduce tsunami flow, 50 to 200m thickness of coastal vegetation belt is suggested in combination with 1-2m height of embankment along the coastline. BW: Breakwater All post tsunami disaster investigation results have also shown that coastal vegetation belt posed none mitigation effects for tsunami inundation greater than 5m. For area with tsunami hazard potential of inundation depth greater than 5m, coastal vegetation belt would provide no protection at all. In such cases coastal vegetation belt may be used as a supplement to the main protection structure such as seawall etc. Even for tsunami inundation less than 5m coastal vegetation belt never provide a hundred percent protection.

Mitigation Measures

Public Awareness

Indian Ocean Tsunami disaster 2004 Source: http://www.icharm.pwri.go.jp/publication/pdf/2010/4184_tsunami_hazard_mapping.pdf More than half of Asian people live in the coastal zone [Yu, 2007].

Tsunami Hazard Maps See Figs 4.4 and 4.6 of reading material 1

Discussion/Comment/Question