Nearly 75 percent of the US – an area that’s home to hundreds of millions of Americans – is at risk of experiencing earthquake damage over the next 100 years. That’s according to new maps and data released by the United States Geological Survey (USGS).
The areas at the highest risk are California, Alaska, and the Big Island of Hawai‘i. The chance of damaging earthquake shaking in the next century is over 95 percent across a significant part of these seismically active states.
The new model has upped the risk for Hawai‘i as having greater potential for shaking in light of recent volcanic eruptions and seismic unrest on the islands.
Recent data has also brought some “noteworthy changes” to the possibility of more damaging earthquakes along the central and northeastern Atlantic Coastal corridor, which could impact the cities of Washington DC, Philadelphia, New York, and Boston.
Earthquakes are notoriously tricky to predict, but this huge, multi-year research project has aimed to understand where the risk lies using seismic studies, historical geological data, and cutting-edge data collection technologies. As part of this effort, USGS identified 500 additional fault lines that have the potential to produce damaging earthquakes.
"Earthquakes are difficult to forecast but we’ve made great strides with this new model. The update includes more faults, better-characterized land surfaces, and computational advancements in modeling that provide the most detailed view ever of the earthquake risks we face," Mark Petersen, USGS geophysicist and lead author of the study, said in a statement.
Earthquakes are caused by the movement of the tectonic plates that form the outer layer of the planet. As these plates interact – crashing into each other and grinding past one another – the built-up stress can exceed the strength of the rocks, leading to a sudden rupture and the release of energy in the form of seismic waves that shake the ground.
The US is relatively seismically active for a country. Much of this activity is concentrated on the West Coast and within the Pacific due to the influence of the Ring of Fire, a horseshoe-shaped zone that encircles the Pacific Ocean and is known for high seismic activity.
However, earthquake activity has been documented further afield. During the last 200 years, 37 US states have experienced earthquakes with a magnitude of 5 or higher.
The deadliest on record is thought to be the 1906 San Francisco earthquake, which killed some 3,000 people and destroyed the vast majority of the city, leaving half the population homeless. It was caused by a rupture in the San Andreas Fault – an incident that could happen again in the future.
Geologists believe that the San Andreas Fault causes significant earthquakes every 200 years or so. It’s not a matter of “if” another earthquake will strike the area, but “when.”
This hypothetical earthquake has been dubbed the “Big One". If it were to occur today, a magnitude 7.8 earthquake stemming from the southern San Andreas Fault could lead to more than 1,800 deaths, displace millions, and cost $200 billion in damage.