Researchers from NASA’ Jet Propulsion Laboratory (JPL) and the Ohio State University (OSU) used satellite altimeters to observe “merging tsunamis”. The image comes from a data-based computer model that shows Tohoku-oki tsunami waves propagation. Waves peaks are depicted in red-brown, while depressions in sea surface appear in blue-green. Grayscale outlines show the location of mid-ocean ridges, peaks, and islands. Image: NASA.


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).

Related content


In the intermediate webinar Remote Sensing for Disasters, participants learn the usage of NASA products to monitor three kinds of disasters. The webinar takes place in three sessions on each Tuesday from 16 until 30 April 2019, starting 10 to 12 am and 2 to 4 pm. It is taught in English and Spanish and is free of charge.

Learning Objectives

By the end of this training, attendees will be able to:

  • Identify NASA data products to characterize and monitor the disasters, Tropical Storms, Flooding, Landslides and Earthquakes, and support decision-making

  • Understand the different data products available and... read more

Data Source

Screenshot of Global Tsunami Model
Publishing institution: Geoscience Australia
The input tsunami hazard data are based on the global hazard analysis of Davies et al. (2017), developed jointly by Geoscience Australia and NGI, formatted for use in ThinkHazard!. The data serves as data for Global Tsunami Model (GTM, http://globaltsunamimodel.org/). The global tsunami dataset contains maximum inundation heights, calculated at offshore hazard points and projected to shoreline by simple interpolation. Tsunami Maximum Inundation Height (MIH) is defined as the largest elevation the tsunami reaches above still water level, consistent with IOC-UNESCO terminology. The MIH hazard data are at global level for return periods: 10, 50, 100, 200, 500, 1000, and 2500 year. Values above and below extreme values, are referred to as >=20 m and <=0.1 m, respectively.
Publishing institution: European Space Agency (ESA)
ESA's Earth Observation Thematic Exploitation Platform (TEP) is a browser for satellite imagery and specific products on an environmental topic. The TEP platforms are divided into 7 categories: Coastal; Forstry; Geohazards; Hydrology; Polar; Urban; and Food Security. Each platform is a collaborative, virtual work environment providing access to EO data and the tools, processors and Information and Communication Technology resources required to work with them. TEP aims to bridge the gap between the users and the data and tools.
Publishing institution: Airbus Defence & Space
Pleidas, TerraSar-X, SPOT and Elevation data available commercially from airbus, certain sample data sets at various locations available for free.
Publishing institution: Radiant Earth Foundation
The website: https://www.radiant.earth Help and Tutorials: https://help.radiant.earth/ Demos & Use Cases: https://demos.radiant.earth/
Publishing institution: NASA Earth Science Disasters Program
NASA's Earth Observing System Data and Information System (EOSDIS) is a program for archiving and distributing Earth science data from multiple missions to users.
Publishing institution: OceanDataLab
The Ocean Virtual Laboratory is a web platform making satellite and in-situ data for ocean monitoring accessible. It presents one of multiple Syntool Web portals that promote the synergistic use of Ocean Remote Sensing data in a wider context of Oceanic and Atmospheric models or in-situ data. , ESA/SEOM Ocean Virtual Laboratory portal: SAR roughness Sentinel 1: Ocean Color: From Sentinel-2, Sentinel-3 and Meteosat. Chlorophyll: From VIIRS and MODIS Sea Surface Temperature, Sea level, Salinity, Wind, Current, Rain, Mean Square Slope, Sea ice concentration , ESA/DUE GlobCurrent portal: SAR roughness, Ocean Color, Chlorophyll, Sea surface temperature, Sea level, Salinity, Wind, Wave, Current, Rain, ESA SMOS Storm portal: Significant Wave height (SWH) Jason 2 and ALTIKA, SAR roughness Sentinel-1, Wind speed SMOS, SMAP, AMSR2 and ASCAT, wind barbs ASCAT, CNES Aviso'VIZ altimetry portal: Sea Surface Height Anomaly (SSHA) Jason-2 and SARAL, Sea Level Anomaly (SLA) Jason-2 and SARAL, Absolute Dynamic Anomaly (ADT) Jason-2 and SARAL, Mean Sea Level RIse, Sea Level Anomaly, Geostrophic current vectors and streamlines., ESA Sentinel3 Viewer: products from OLCI, SLSTR and SRAL sensors., CNES PEPS Sentinel-1 Ocean Viewer: SAR roughness Sentinel-1, ESA Sea Surface Salinity portal: SMOS salinity, SMAP salinity
Publishing institution: European Organization for the Exploitation of Meteorological Satellites (EUMETSAT)
Map Viewer that allows downloading and time series creation of meteosat products.


In September 2018, an earthquake and tsunami hit the island of Sulawesi in Indonesia, leaving thousands dead and injured. Image: European Union 2018 / CC BY-NC-ND 2.0.

Following a tsunami that hit coastal areas around the Sunda strait between the Indonesian islands of Sumatra and Java on 22 December, the United Nations Office for Outer Space Affairs (UNOOSA) has requested the activation of the International Charter Space and Major Disasters on behalf of the National Institute of Aeronautics and Space (LAPAN) of Indonesia. LAPAN is a UN-SPIDER Regional Support Office (RSO).

According to the Indonesian National... read more

Publishing date: 24/12/2018
Regional Support Offices mentioned:


Hazard group

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