August Research Roundup: Select Papers

Every month, researchers at Lamont-Doherty Earth Observatory and other parts of the Columbia Climate School publish work that deepens our understanding of the planet.

This month, we wrote about a unique long-term analysis that suggests methane emissions from landfills may be far higher than previously estimated. We also shared some new research on unexpected trends in extreme rainfall in the U.S.

Here are additional studies by our researchers that are worth noting.

Hidden Fault Responsible for 2024 New Jersey Earthquake

A new study by Lamont researchers identifies the fault that likely produced the magnitude 4.8 earthquake that shook New Jersey, New York City and much of the Northeast on April 5, 2024. Rather than rupturing the well-known Ramapo Fault, the earthquake appears to have originated on a previously unmapped fault zone in the New Jersey Highlands, which the researchers have named the Mountainville Fault.

The team combined aftershock locations, high-resolution LiDAR imagery, field mapping, laboratory friction experiments and stress analyses to investigate the nature of the fault and why it slipped. The team concluded that Mountainville is an “immature” fault, meaning it lacks the internal structure and prominent surface expression of larger faults even though it remains capable of generating earthquakes.

The findings suggest that moderate earthquakes in the eastern U.S. may occur on previously unrecognized faults that are immature and seismically unstable, and less commonly on the region’s large, well-mapped fault systems. Because seismic waves travel efficiently through the old, hard rocks beneath the eastern United States, even moderate earthquakes can be felt across a broad area, thus heightening the risk from immature but earthquake-prone fault zones.

“This study shows that some of the region’s greatest earthquake hazards may come from faults that are difficult to recognize at the surface,” said lead author Folarin Kolawole, a structural geologist at Lamont. “Identifying and understanding these subtle fault systems is important for improving seismic hazard assessments in densely populated regions.”

Why it matters: The April 2024 earthquake was the strongest to strike New Jersey in more than a century. By identifying the fault responsible, the study provides new insight into earthquake hazards in the highly populated northeastern U.S.

Other Columbia-affiliated authors: Eric Beaucé, Zachary Foster-Baril, Meritxell Colet, Leonardo Seeber, Jacob Tielke, Abhishek Prakash, Won-Young Kim, Rasheed Ajala, Christine McCarthy and Felix Waldhauser.

Tropical Pacific Warming Trend Unlikely to Be Natural Variability Alone

A long-running question in climate science is how the tropical Pacific Ocean will respond to human-caused warming. A new study by Lamont researchers finds that the west-to-east temperature difference across the tropical Pacific has been widening, and that this trend is unlikely to be explained by natural variability alone.

The tropical Pacific plays a central role in Earth’s climate system, influencing rainfall, drought, hurricanes, and El Niño and La Niña events around the world. The researchers analyzed sea-surface temperature records dating back to 1870, examining every period of 20 years or longer and testing the observed trends against multiple statistical and physical models. They found that while both strengthening and weakening trends occurred over shorter periods, the longer-term strengthening of the west-to-east temperature difference observed in recent decades is statistically significant across multiple observational datasets.

“Our results suggest that the changes observed in the tropical Pacific are not just random swings in the climate system,” said lead author Ibuki Sugiura, graduate student in Columbia’s Department of Earth and Environmental Sciences. “They are consistent with the influence of historical radiative forcing.”

Why it matters: How the tropical Pacific responds to climate change influences weather patterns around the globe and remains one of the biggest uncertainties in climate projections. Better understanding whether recent changes reflect natural variability or a forced climate response could improve future climate predictions.

Other Columbia-affiliated authors: Jason E. Smerdon and Richard Seager.

Dating the Forest Where an Ancient Ape Lived

Researchers have narrowed down the age of a fossil-rich site in northern Kenya that was once home to Nyanzapithecus alesi, an extinct ape known from an exceptionally well-preserved infant skull. The new dates place the site, known as Napudet, between about 14 and 13 million years ago, providing a firmer timeline for a period when early apes were diversifying across Africa.

The researchers combined two independent dating techniques to constrain the age of the fossil-bearing sediments: argon dating of volcanic rocks and uranium-lead dating of petrified wood. The agreement between the two methods also demonstrates that fossilized wood can provide reliable ages for terrestrial deposits, offering a new tool for dating ancient landscapes where volcanic rocks may be absent.

“Providing a complete timescale for sedimentary layers that contain important hominid fossils and developing methods to directly date ancient fossil forests help us understand a long-forgotten environment that was key to the early evolution of human ancestors,” said lead author Stephen Cox, a Lamont assistant research professor.

Why it matters: More precise ages help scientists better understand when key evolutionary changes occurred and how ancient apes responded to changing environments.

Other Columbia-affiliated authors: Sidney R. Hemming.

Making Better Use of Research Voyages to Map the Seafloor

Much of the ocean floor has yet to be mapped in detail. Yet research vessels cross unmapped areas on their way to research sites and ports, often carrying sophisticated sonar capable of mapping the seafloor along the way.

A new guidance document from the General Bathymetric Chart of the Oceans (GEBCO)—an international program that compiles ocean-depth data for freely available maps of the global seafloor—aims to put these transits to scientific use. It provides guidance for collecting useful depth measurements along planned routes, without requiring dedicated mapping voyages.

“Every passage of a sonar-equipped vessel is an opportunity to improve our maps of the ocean floor,” said Vicki Ferrini, a senior research scientist at Lamont and coauthor of the guidance document. “By making data collection and sharing a routine part of vessel operations, we can turn time already spent at sea into lasting scientific value.”

Ferrini coauthored the guidance document with Jennifer Jencks of NOAA’s National Centers for Environmental Information.

Why it matters: Better seafloor maps contribute to safer navigation, scientific research and our understanding of natural hazards. Transit mapping could expand global seafloor coverage at relatively little additional cost by making better use of voyages already taking place.