What are tsunami? Tsunami are a series of waves caused by a displacement of water.

Transcription

1 What are tsunami? Tsunami are a series of waves caused by a displacement of water. Are long-period waves up to 100 kilometres Travel quickly in the open ocean up to 700 kilometres per hour Slow down and increase in height as they approach land Behave like a rapidly rising/falling tide What causes tsunami? Tsunami are mainly caused by earthquakes, landslides and volcanic activity under the ocean.

2 Types of tsunami There are three main types of tsunami: Local source Travel time between the source, such as an earthquake just offshore, and impact is one hour or less. Regional source Travel time between the source, such as the Southern Tonga Kermadec Trench and impact is between one and three hours. Distant source Travel time between the source such as South America or Japan and impact is greater than three hours, often over twelve hours. Where do most of Tauranga s tsunami come from? Tsunami that impact Tauranga may be from distant sources, such as South America; regional sources, such as the Tonga-Kermadec Trench or from local sources such as earthquakes on the east coast. What are we most concerned about? We are most concerned about tsunami events generated from large earthquakes along the Tonga-Kermadec Trench subduction zone the tectonic plate boundary between the Pacific and

3 Science behind Tsunami in Bay of Plenty Initial modelling by GNS identified the Kermadec trench off the East Cape as source of greatest risk for the Bay of Plenty. Based on fault characteristics and learnings from Japan a Magnitude 9.0 earthquake has been identified as maximum potential event. Tsunami wave terminology AMPLITUDE Inundation line or limit Crest Wave height Run-up Sea level at the time Trough Shoreline Inundation horizontal flooding

4 Flow modelling for Tauranga City Timing of tsunami flow from generation mins to reach coast Then 10 mins to move over first 1km inland Up to 6 hours to reach maximum inland extents

5 How deep? Flow depth Future development scenario at Wairakei

6 A major earthquake is the most reliable way to know that a devastating tsunami might be on the way from a local source (like the Kermadec Trench). This is confirmed by the Ministry of Civil Defence Emergency Management and GNS Science. Formal warning systems will not be able to be activated in time to help you survive such a tsunami. Natural warning signs A big earthquake that knocks you over. Any earthquake that lasts more than a minute. Strange ocean behaviour (loud or strange noises, sudden change in sea level, ocean drawing away from the shore). The first tsunami wave may arrive at Tauranga s coastline 50 minutes after a major earthquake. Don t wait for an official warning. Get inland or to high ground.

7 What do the maps show? Safe zones Safe zones are coloured green and indicate areas outside potential tsunami flow, or safe assembly areas. Tsunami evacuation zones Each map shows three different tsunami evacuation zones. Red zone Every tsunami will affect this part of the coastline. You should always evacuate this area if there is any sort of tsunami warning, whether that warning comes from unofficial sources (like text messages or social media), official warnings, or natural warning signs. Orange zone In a formal Civil Defence evacuation you may be asked to move from the orange zone into the yellow zone. Tsunami from regional or distant sources (further away than 1000km) could take anywhere from 2 to 12 hours to arrive. You won t feel an earthquake for this type of tsunami so this is where things like warning systems, text alerts, s, TV/radio and social media are really important. Yellow zone The most devastating tsunami, similar to the big one that hit Japan in 2011, is predicted to flood the yellow zone. There is a very low chance this will happen in our lifetime but if it does happen there will be no time for official warnings. After a major earthquake it would take about 50 minutes for this tsunami to reach the coast, plus maybe another 30 minutes to flood the yellow zone. The further into the yellow zone you get, the shallower and slower moving the water will be. If you plan ahead and evacuate as soon as you can after that first earthquake you have a very good chance of surviving this devastating tsunami.

8 Evacuation Strategy Safe Evacuation Prioritise evacuation 1. Evacuate from higher to lower hazard (within 40 minutes) Get people out alive 2. Evacuate from hazard to safety (within 60 minutes) Get people to safety Assume evacuation by foot Keep roads free for emergency and evacuation of less mobile People take 10 minutes to feel earthquake and decide to self-evacuate and 10 minutes to depart Aim to have high hazard zones evacuated within 40 minutes All zones evacuated within 60 minutes

9 Evacuation modelling Time to evacuate to safety Most within 40 minutes All within 60 minutes

10 Emergency Alerts There are different ways you can be alerted during an emergency by subscribing to emergency updates. You will be notified any time there is a change to the emergency status or advice on a specific event. What about alert systems and sirens? Alert systems are the topic of earnest, ongoing conversation but a big earthquake is the best warning for the tsunami we are most concerned about. The most important thing is to be aware of the natural warning signs so that you can make your own decision to evacuate if there is an earthquake. Warning systems are useful for tsunami that come would from regional or distance sources (greater than 2 hours away). Civil Defence has a suite of warning systems. Subscribe to emergency alerts at

11 How to evacuate: Use your feet. Help your neighbours. It s natural to think you ll be able to leap into the car and get away before everyone else. But what if everyone else is thinking the same thing? Consider this: if everyone tries to drive out of Papamoa at the same time, traffic modelling undertaken by NZTA show that it will take at least 6 hours to get everyone clear. That s on a good day with no emergency. The best plan is to walk Learnings from the Japan tsunami of 2011 confirm this fact. The evacuation maps we have provided show safe locations and zones that can be reached by foot from every part of the coast within 60 minutes. The distances are modelled on a very conservative walking pace. Plan with your neighbours With less than an hour after a major earthquake before a tsunami arrives, emergency services will not be able to get you out in time. The reality is that you re on your own. The community s best chance to survive a tsunami is to work together as a community. Make an evacuation plan with your neighbours, especially if you know they will need assistance getting to a safe area. Take your emergency pack A tsunami is a large volume of water that surges across the ocean, usually caused by an underwater earthquake. It is like ripples in a pond but on a much larger scale. Tsunami can arrive in several waves over a long period of time. The first wave is not always the biggest. That is why you need your emergency pack. You must be prepared to wait for many hours before the water subsides.

12 This is a local community plan for the escape of tsunami in Tauranga, Mount Maunganui and Papamoa. It is specifically targeted toward local source tsunami and the actions required from first awareness to an official response. Be Prepared Create and practice your household emergency plan Have your getaway kit prepared for fast evacuations Identify safe places in your community and know how to get there Make sure each member of your family knows where the safe zones are Earthquake, think Tsunami Shaking strong enough to knock you off your feet Prolonged shaking (greater than one minute) Sea level suddenly rising or falling The sea makes loud and unusual noises or roars like a jet engine Don't wait for sirens Get inland and move to higher ground Walk or cycle. Don't rely on cars, expect traffic chaos Natural high points (hills or inland) Use strong muli-story Buildings if you can't get to natural high points Signs or blue lines on the road indicate safe evacuation zones After the Tsunami Check yourself for injuries and get first aid if needed Turn on your radio for civil defence advice Stay where you are until you re given the official all clear, a tsunami consists of multiple waves over many hours, Use text messages for contacting family members, save voice calls for emergencies only Register at a welfare centre for assistance and to help locate your family and friends

13 3 things you need to know to survive a tsunami What do the maps show? WHEN TO EVACUATE The best tsunami warning is an earthquake The first tsunami could arrive 50 minutes after a major earthquake. Don t wait for an official warning to evacuate. WHERE TO EVACUATE Inland or high ground We have taken the best possible scientific information to show where tsunami flooding is predicted to go and where you will be safe. Use the map on the other side of this flyer to plan your escape route. HOW TO EVACUATE Use your feet In a big tsunami emergency there will be crippling traffic jams. Most people should be able to walk to a safe area or safe location shown on the map within 60 minutes. Sign up for text and alerts at