As a heavy user of geographic information systems in the Geography and Map Division, I am always interested to see new scientific research that fuses geography and technology in order to advance understanding of our world. Today, Worlds Revealed wanted to highlight the fascinating work of researchers at the United States Geological Survey (USGS) in using geography to study earthquake hazards in the U.S.
The USGS has a long history of studying earthquakes, assessing their impacts, and investigating how to potentially forecast this hazard. Much of this work has taken place through their Earthquakes Hazard Program (which has been the subject of Library of Congress web archiving). A recent study published by the USGS produced a 1-year 2016 forecast of “seismic hazard” (or, the occurrence of earthquakes and related ground shaking) covering central and eastern portions of the United States. This forecast prominently features a series of maps to illustrate the geography of earthquake risk according to the model the researchers designed. The study also marks an important milestone: it is the first time that the analysis has considered both natural and human-induced earthquakes.
The researchers looked at spatial and temporal patterns of earthquake reports in their efforts differentiate natural from induced seismic activity. The report also references literature suggesting links between wastewater disposal practices at mining and industrial sites (particularly the injection of wastewater into subterranean disposal wells) with increases in nearby seismic activity. That said, the report is more concerned with quantifying earthquake hazards rather than exploring in-depth the causes of increased seismicity.
Altogether, the model used to create the forecast considers a wide range of variables: geology, oil and gas plays, sedimentary basins, well sites, ground-shaking data, historical earthquake rates, and other information. Through a careful consideration of these factors, the researchers arrived at a model for earthquake risk prediction and applied that model across geographic space.
One of the final outputs from the study is a map of the Modified Mercalli Intensity (MMI) forecast with “a 1-percent probability of exceedance in 1 year” (meaning, the likelihood of the intensity of shaking exceeding what is forecasted is one percent over the course of one year). The MMI scale describes the intensity of shaking felt in an earthquake, ranging from not-felt and weak intensities (I, II, and III) up to violent and extreme shaking (IX and X). Among numerous areas of elevated intensity risk, particularly striking areas of increased risk are central Oklahoma and the New Madrid Seismic Zone. The report issues concern over “higher hazard levels in active injection areas” across numerous states in the central U.S.
The geography of elevated shaking intensity risk shown in the MMI map is similar to that of the second major output map of the study: the chance of damage from an earthquake in 2016.
The study represents an important step towards more comprehensive earthquake forecasting techniques and a better understanding of earthquakes themselves. There is still much to learn in the scientific community about how human activities could be contributing to seismic events and how areas affected by increased risk of earthquakes can mitigate their effects. At the broader scale of geographic science, this study shows the power of geospatial models for not only being scientifically rigorous but also producing clear outputs that can be communicated to a wide audience.