On Aug. 23, 2011, the east coast of the United States was hit with a rare earthquake. The epicenter was in Virginia, but the tremors could be felt as far away as New England.
The colored lines show connections in AT&T's network infrastructure that exceeded certain capacity thresholds -- not necessarily outages, but a sign of much of higher-than-average traffic.
Up and down the East Coast, AT&T's network was flooded with voice and data traffic. Most wireless networks went down for a short period of time in New York and Washington immediately after the earthquake.
In another version of the map, AT&T could actually see the earthquake moving up the East Coast in near-real time as call volume and data traffic exploded.