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Update to US seismic hazard map triggers research into human-induced quakes

Investigations into increased seismicity as a result of human activities is underway following an update to the US national seismic hazard map by the United States Geological Society (USGS).

The map reflects the best and most current understanding of where future earthquakes will occur, how often they will occur and the magnitude of the event.

USGS has identified 42 of the 50 US states as having a reasonable chance of experiencing damaging earthquakes in the next 50 years.

Research is now under way into the involvement of human interaction in causing earthquakes, such as the disposal of wastewater in deep wells and fracking for shale gas. The focus for the future is on adding an additional layer to earthquake hazard maps to account for earthquakes potentially triggered by human activity. The USGS reported that injection-induced earthquakes are challenging to incorporate into hazard models because they may not behave like natural earthquakes and their rates change based on man-made activities.

The updated map shows the eastern US has the potential for larger and more damaging earthquakes than previously considered, such as the magnitude 5.8 earthquake that struck Virginia in 2011. New York City tall buildings have been shown to be less at risk than previously thought.

The New Madrid seismic zone in central US also has a potential larger range of earthquake magnitudes and locations.

On the western coast the earthquake hazard area is greater than previously thought and new knowledge of the Tacoma Fault identified changes to the geometry of the Whidbey Island fault in the northern Puget Sound.

These maps contribute to various risk analyses by considering factors like population levels, building exposure, and building construction practices. This is used for establishing building codes and in the analysis of seismic risk for key structures. The USGS updates the national seismic hazard models typically every six years, in sync with the building code updates. 

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