Tsunami

Definition

A tsunami is a series of travelling waves of extremely long length and period, generated when a large volume of ocean water is rapidly displaced by a sudden displacement of the seabed. These series of waves are generated by a displacement of massive amounts of water through underwater earthquakes, volcanic eruptions or landslides. Tsunami waves travel at very high speed across the ocean but as they begin to reach shallow water they slow down and the wave grows steeper (IRDR Glossary).

The majority of tsunami are generated by shallow large earthquakes in subduction zones. Tsunami is also known as seismic sea waves because it is most often generated by earthquakes (UNESCO).

Facts and figures

The word tsunami is derived from the Japanese word “tsu” and “nami”, meaning “Harbor” and “Wave” respectively.

The speed of tsunami waves depends on ocean depth rather than the distance from the source of the wave. Scientists can predict when a tsunami will arrive at various places by knowing the source characteristics of the earthquake that generated the tsunami and the characteristics of the seafloor along the paths to those places. When the ocean is over 19,685 feet (6,000 m) deep, unnoticed tsunami waves can travel over 500 mph (804.67 kmh). One coastal community may see no damaging tsunami wave activity while in another nearby community destructive waves can be large and violent. Reefs, bays, entrances to rivers, undersea features and the slope of the beach help to modify the tsunami as it approaches the coastline (NOAA).

Dependent on the distance of the tsunami from its source, it may be classified as a:

  • Local/near field tsunami A tsunami from a nearby source for which its destructive effects are confined to coasts less than 1 hour tsunami travel time or typically within about 100 km from its source.
  • Regional tsunami A tsunami that is capable of destruction in a particular geographic region.
  • Destructive tsunami Happens when tsunami waves become extremely large in height, they savagely attack coastlines, causing devastating property damage and loss of life. A small wave only 30 cm high in the deep ocean may grow into a much larger wave 30 m high as it sweeps over the shore.
  • Non-Destructive Tsunami Mostly happens as a result of minor earthquakes and/or other events. It can be due to the source being far away from land or the earthquake being too small to have any effect when approaching the shore. When a small tsunami comes to the shoreline it is often seen as a strong and fast-moving tide (Caribbean Tsunami Information Center).

UN-SPIDER Regional Support Offices with hazard-specific expertise

Related content on the Knowledge Portal

  •  

    The Center for Satellite Based Crises Information (ZKI), a service of the German Remote Sensing Data Center (DFD) of the German Aerospace Center (DLR), provides rapid processing and analysis of satellite imagery during natural and environmental disasters, for humanitarian relief activities and civil security issues worldwide. Contributions of ZKI are mainly made during the emergency response phase, but activities for preparedness, early warning and recovery are equally important tasks.

    This post describescontribution made by ZKI during the Padang Earthquake of 2009 and the Mentawai Tsunami of 2010. Using Quickbird, IKONOS, ALOS and WorldView-1 nad -2 images situation and disaster extend maps were provided for initial response activities.

  •  

    The Center for Satellite Based Crises Information (ZKI), a service of the German Remote Sensing Data Center (DFD) of the German Aerospace Center (DLR), provides rapid processing and analysis of satellite imagery during natural and environmental disasters, for humanitarian relief activities and civil security issues worldwide. Contributions of ZKI are mainly made during the emergency response phase, but activities for preparedness, early warning and recovery are equally important tasks.

    This post describescontribution made by ZKI during the Padang Earthquake of 2009 and the Mentawai Tsunami of 2010. Using Quickbird, IKONOS, ALOS and WorldView-1 nad -2 images situation and disaster extend maps were provided for initial response activities.

  • A magnitude 7.9 earthquake occurred at 2:46 pm on March 11, 2011 near the east coast of Honshu, Japan. Tsunami warnings are issued along the Pacific coast line. (source: http://glidenumber.net/glide/public/search/details.jsp?glide=19439&record=1&last=4953)

    Japan has suffered a massive earthquake and tsunami in its northeast coast. Meanwhile, nations in the western pacific from Indonesia to the Philippines are bracing for the possibility of tsunamies of their own. (source: http://www.dw-world.de/dw/article/0,,14904492,00.html)

     

    UNOOSA/UN-SPIDER

    Email: un-spider [at] unoosa.org

    read more
  • A powerful earthquake (Richter magnitude 9.2) occurred near to the northwest shore of Sumatra, on 26 December, 2004. It triggered a giant tsunami that devastated Banda Aceh, Indonesia. Many donors provided recovery aid, without coordination or proper auditing. This may have led to waste, fraud and corruption. This study investigated an application of remote sensing to enhance financial accountability and transparency in managing reconstruction projects following natural disasters, by automatically identifying buildings constructed as a result of the disaster response, using Banda Aceh as a test area. The increasing availability of high-resolution satellite images, such as the KOMPSAT-2 used in this study, together with aerial orthophotos, makes such a procedure potentially a practical part of a disaster recovery audit.The segmentation algorithm of eCognition was used to generate image segments. These segments were then classified as "building" and "background"…

    read more
  •  

    This paper introduces the Recovery Project,which aims to identify indicators of post-disaster recoveryusing satellite imagery, internet-based statistics andadvanced field survey techniques. This paper reviews therecovery literature as a means of introducing the recoveryprocess and the considerations that must be made whenevaluating recovery. This is followed by an introduction tothe Recovery project and its two case study sites: 1. BanNam Khem, Thailand and 2. Muzaffarabad, Pakistan. Areview of the recovery process at Ban Nam Khem ispresented along with a diagram of potential indicatorsobtained from the literature research. The paperconcludes with a short discussion on how remote sensingmay be used to monitor some of these indicators.

  •  

    In order to evaluate emergency response and rehabilitation planning after a disaster, it is important to grasp the distribution of the damaged buildings as soon as possible. Images remotely sensed from satellites are quite useful to widely capture the condition of the surface ground. Visual detection method of the building damage has been applied to the high-resolution satellite images observed before and after recent large earthquakes [Chiroiu et al. (2002) and Kouchi et al. (2004)]. However, characteristics of the image in the building damage area due to other disasters such as tsunami have not been examined in detail.

    The Sumatra earthquake on 26th December 2004 (Mw9.3) brought great tsunami damage to the countries in the Indian Ocean. Sri Lanka is one of the countries that are severely damaged due to the tsunami. In order to evaluate the damage distribution in the eastern part of Sri Lanka, the visual detection method of the damage is applied to the high-…

    read more
  •  

    An attempt was made to conduct spatial assessment of the pattern and extent of damage to coastal aquaculture ponds along the east coast of Aceh province in Sumatra, Indonesia, resulting from the tsunami event of 26 December 2004. High-resolution satellite imagery, i.e., SPOT-5 multispectral scenes covering the 700 km stretch of the coast, acquired before and after the tsunami, were digitally enhanced and visually interpreted to delineate pockets of aquaculture ponds that were discerned to be damaged and relatively intact. Field checks were conducted at 87 sites in the four eastern coastal districts. The results indicate that SPOT-5 multispectral imagery was minimally sufficient to detect areas of damaged and relatively intact aquaculture ponds, but the 10-m spatial resolution poses limitations to evaluating the extent of pond damage. Nevertheless, the 60 km swath of the imagery makes it reasonably affordable for large-area assessment to identify pockets of severe…

    read more
  •  

    This paper highlights the use of remote sensing technologies in disaster management, notably post-earthquake/tsunami damage detection due to the 2003 Bam Earthquake and the 2004 Indian Ocean Tsunami, and seismic risk assessment based on land use classification in Metro Manila, the Philippines. QuickBird (QB) images taken before and after the 26 December 2003 Bam Earthquake were used in visual damage interpretation based on the European Macroseismic Scale (EMS-98) building by building. An automated damage detection method was also applied to the post-event Ikonos and QB images. The results of these damage inspections were compared with field survey data and the accuracy and limitation of visual and automated damage detections were presented. QB images and GPS-synchronized photo/video were employed in the damage survey after the 2004 Indian Ocean Tsunami in the south Thailand. Terra-ASTER images were also used to identify tsunami inundation areas comparing the pre-event…

    read more
  •  

    There is an increasing interest in assessing the strengths and weaknesses of remote sensing imagery and geographic information system products as they relate to estimating populations at risk before, during, and after natural hazards. This research examines the spatial and temporal effectiveness of satellites and extent of damage products that were created for Banda Aceh, Indonesia after the 26 December 2004 tsunami. SPOT, FORMOSAT, MODIS and Landsat ETM+imagery provides high temporal resolution data within three days of the tsunami. However, highresolution commercial satellites (Quickbird, IKONOS) provide the most accurate data that can be used to assess infrastructure damage in cities like Banda Aceh before and after natural disasters. Of the six extent of damage products (USAID, USGS, Dartmouth Flood Observatory, DLR, SERTIT, DPRC) created after the tsunami, DLR provided the most accurate data on the extentof damage in Banda Aceh (94% agreement with Quickbird…

    read more
  •  

    The earthquake triggered near Banda Ache of Indonesia on December 26, 2004 was the fifth most strong for the last 100 years and the worst in 40 years, registering a magnitude of 9.0. The epicenter was located about 300 km west of Medan, west coast of the Indonesian island of Sumatra. The earthquake was followed by tsunami, surge of waves that killed nearly a quarter of a million people, mostly in Indonesia, Sri Lanka, and India. The coastal regions of India, Sri Lanka, Thailand, Indonesia, Maldives, Malaysia, and Myanmar were all severely affected.
    This paper summarizes the effort of international agencies taken to utilize satellite remote sensing and other mapping tools to provide critical information that may have used for various relief activities and subsequent recovery activities. Services, products provided by various national and international agencies are discussed and summarized. Further, a summary of field survey conducted in Sri Lanka to identify…

    read more

Term Parents

UN-SPIDER Regional Support Offices with hazard-specific expertise