The idea that human activities can cause earthquakes, or so-called induced seismicity, has been around for some time, but demonstrating its role and pinpointing exactly how it happens can be difficult. The July issue of Scientific American features a story by Anna Kuchment on how wastewater injection from oil and gas operations has been triggering earthquakes in the central United States over the past several years. 

Kuchment tells the stories of people affected by this phenomenon and argues for regulation to combat the issue. However, when the narrative becomes more technical—as in, how does this geological phenomenon work?—an information graphic does much of the heavy lifting. In the illustration below by Bryan Christie, saltwater released during hydraulic fracturing (better known as fracking) is injected into the earth, disrupting the natural forces acting on a geologic fault and causing the two sections of rock to slide past each other. 

Credit: Illustration by Bryan Christie

Inherent in scientific illustration is the challenge of how to work within a static format to describe kinetic events occurring over time. This above graphic uses typical and effective methods to insert these elements into the visual narrative: arrows to show directional movement, ordering of components from left to right and top to bottom, and providing numbered steps to make clear how one event leads to the next. However, a digital format offers more possibilities. Below, part of the visualization is enhanced with time and motion to create an animation.

Data also plays an important role in this story. The correlation between the large amount of wastewater injected into the ground in certain areas and the subsequent increase in the number of earthquakes in the same locations is quite telling. Once again, although a verbal explanation might be adequate to convey this message, a graphic can do so more effectively.

I was able to procure several recent years’ worth of data on both injection volumes and earthquakes for Oklahoma, one of the states hit the hardest by this phenomenon, and used d3.js to visualize the data as a “small multiples” series. While the print version of the graphic displays essentially the same content, the web adaptation below exploits the digital medium, allowing users to reveal detailed information about each data point by hovering or tapping on its interactive elements.

Sources: Class II Saltwater Disposal for 2009–2014 at the Annual-, State-, and County- Scales by Geologic Zones of Completion, Oklahoma, by Kyle e. Murray. Oklahoma Geological Survey, December 31, 2015 (wastewater injection data); USGS Earthquake Maps (earthquake data)
Maps by Amanda Montañez

Static visuals are invaluable in the print medium, and are often the best, most accessible format for information graphics, even in digital form. However, the experience of watching a video or using an interactive is potentially even more convincing and memorable than viewing a static image. This feature presents a great example of how digital graphics can build on what is possible in print to tell stories through a multimodal approach.