Earthquake risk zones: A people’s perspective

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A M7.8 earthquake has occurred in Nepal “as the result of thrust faulting on or near the main frontal thrust between the subducting India plate and the overriding Eurasia plate to the north.” As the USGS summarises, “although a major plate boundary with a history of large-to-great sized earthquakes, large earthquakes on the Himalayan thrust are rare in the documented historical era. Just four events of M6 or larger have occurred within 250 km of the April 25, 2015 earthquake over the past century”.
In a paper for the Journal of Maps published in 2014 I have analysed and visualised data documenting earthquakes that have occurred since 2150 BC. The following map was part of the material supplementing the publication showing the results of the analysis shown on an equal population projection. The gridded cartogram gives every person on the planet an equal amount of space while highlighting the most densely populated spaces in relation to the earthquake risk (calculated via the intensity of earthquakes recorded since 2150 BC). Also shown are the world’s megacities (over 5 million population). The map shows the large populations that make even Nepal (with its almost 28 million people) much more visible than it would be on a conventional map, highlighting why this event turns out to be quite disastrous. The map also shows what the USGS statement above mentions that Nepal is amongst the areas in the region which are far less subject to major earthquakes (as indicated by the yellow to blue shading in the map there – Nepal is the rather large spot squeezed on top between the areas that represent the large populations of India and China):

Map of earthquake risk zones on an equal-population projection
(click for larger version)
Download as poster (PDF, 62MB)

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Tsunami 2004: Ten years on

On December 26, 2004, at 7:58 am local time an undersea earthquake with a magnitude of 9.1 approximately 160 km west of the shores of Sumatra (Indonesia) and 30 km below the sea surface triggered tsunamis in the Indian Ocean. They hit the coasts of countries East and West of the epicenter, among them Indonesia, Sri Lanka, India, Thailand, the Maldives, the Seychelles, Myanmar, Malaysia, Bangladesh and reaching as far as Somalia and Tanzania on the African coastline over 6000 km away.
The coastal populations of the affected countries were hit the hardest, suffering deaths, injuries, displacement and the destruction of their livelihoods. Indonesia was affected most, with an estimated number of 170,000 casualties and approximately 500,000 displaced people. The following cartogram shows the distribution of the estimated 230,273 deaths allocated to the country where the deaths occurred, making each country as large as its total share of the people who dies at the 2004 Boxing Day Tsunami:

Map of the distribution of people who died in the 2004 Tsunami
(click for larger version)

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Megacities and Earthquake Risk

Read more about this map:
Paper in the Journal of Maps: Gridded cartograms as a method for visualising earthquake risk at the global scale

The following map is a modified version of the earthquake vulnerability map published on this website last month (see that page for more details on the underlying earthquake map). The map itself does not show much new information, but includes an aditional layer containing the largest cities of the world, the so-called megacities (depending on the definition, these are cities with a population of more than 5, 8 or 10 million). The circles reflect the category in which each city belongs (based on 2015 estimations by the UN), and they are placed on the location of the city related to the total population distribution. As the map is resized according to the population (equal-population projection), the map also help to understand the setting of each city within the global population density, explaining why the artificial boundaries of a city do not always tell the full story of the urban population structure within a region. In some areas, such as Hong Kong and Guangzhou in the Pearl River Delta, cities are just one of several centres in a highly urbanised region – an urban sprawl – while other megacities like Mexico City or Moscow are in a more solitary location (although even here the extent of the populated area goes beyond the urban boundaries, and certainly the population is far from solitude). Without the city labels the map already showed the relation between human settlements and earthquake risk. The following map now allows to better understand the underlying geography if one is not so familiar with that kind of map transformation.
On a more technical note, the following map feature also includes another jQuery feature (I experimented with the image slider applied to maps on the earth at night map): This map uses the Zoomy Plugin to reveal a more detailed version of the map using an interactive magnifier. Click on the map map to enable the magnifier and see more detail (or if you don’t like that, click here for the usual large version of the map).

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People at Risk: Visualising Global Earthquake Intensity

Read more about this map:
Paper in the Journal of Maps: Gridded cartograms as a method for visualising earthquake risk at the global scale
University of Sheffield Press Release
German-language news article: Weltkarte zeigt Menschen in Erdbebengefahr

Besides all the disturbing images in media, the devastating Japan earthquake has already been intensively documented in the world of mapping, ranging from USGS’s geophysical maps, ESRI’s Social Media mashup, and media features such as the excellent New York Times features (see here and here). More online map and imagery resources have been compiled by the editors of Directions Magazine (see here). Similar responses could already be observed during the Christchurch earthquake, which demonstrates, how fast such information is released and processed nowadays.
The following map shows a more general approach of mapping the risk of earthquakes. It is a visualisation of all major earthquakes that have been complied in the Global Significant Earthquake Database. The database created by NOAA’s National Geophysical Data Centercontains information on destructive earthquakes from 2150 B.C. to the present that meet at least one of the following criteria: Moderate damage (approximately $1 million or more), 10 or more deaths, Magnitude 7.5 or greater, Modified Mercalli Intensity X or greater, or the earthquake generated a tsunami“.
Following an approach of spatial-analyst.net, a kernel density has been calculated from these records to visualise the areas most at risk of earthquakes during that time period. In a last step, I have transformed the world earthquake intensity map (see map inset) using a density equalising cartogram algorithm applied to a population grid. Simply said, the resulting map gives each person living on earth the same amount of space while also preserving the geographical reference. This map allows to understand the earthquake intensity in relation to today’s population distribution, and thus gives an idea of where most people are of risk related to seismic activity (there is an updated version of this map showing labels for the world’s largest cities here: Megacities and Earthquake Risk).

Global Earthquake Intensity Map visualised on a gridded population cartogram.
(click for larger map)

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