Regional Impact of Earthquake and Tsunami in Japan

Effects of the disaster on BitTorrent population correlates with earthquake and tsunami intensity.

As a follow-up to our previous article on the Tohoku earthquake and tsunami, we investigated the regional impact of the disaster on the BitTorrent population. We analyzed BitTorrent usage, along with reported earthquake and tsunami data for each prefecture to see if there was a correlation between the data sets.

We began by checking which regions saw the largest drops in users and as well as the regions that were most affected by the disaster. The graphs below show for each prefecture, the change in the BitTorrent population after the disaster (left), the intensity of the earthquake (center), and the height of the tsunami (right). To understand the impact on the BitTorrent population, we compare the number of users seen 24 hours before and after the disaster. In the BitTorrent population graph, a prefecture colored red means that the prefecture saw a drop in BitTorrent users and green means there was an increase. The brighter the color, the greater decrease or increase in BitTorrent users. In the earthquake and tsunami intensity graphs, the brighter the red means a stronger earthquake and a higher tsunami, respectively. The maps show that the BitTorrent population in prefectures closest to the epicenter (marked by the "X" on the maps) saw a greater decrease in BitTorrent users.

We quantified the relationship between BitTorrent and the disaster by performing correlation analysis. Here we found a a significant negative correlation between the drop in population and the height of the tsunami (r = -0.62), meaning the higher the tsunami, the larger the drop in the number of peers in that prefecture. We found an even stronger negative correlation between the logarithm earthquake intensity and BitTorrent impact (r = -0.81). This means that regions with higher earthquake intensity, tended to see greater drops in BitTorrent usage.

Change in BitTorrent population

Earthquake intensity

Tsunami intensity