Geophysics on EARTH Magazine

Thirsty mantle: Subduction zones swallow more water than thought

Wed, 30 Jan 2019 15:26:27 -0500

A seismic study of part of the Pacific Plate diving beneath the Mariana Trench has revealed that old and cold subducting plates, like the Pacific, likely carry a lot more water into the mantle than previously realized. Credit: K. Cantner, AGI

For all the water stored in oceans, ice and other reservoirs at Earth’s surface, there’s likely even more in the planet’s interior, where it plays important roles in many geological processes, including the formation of magma and the lubrication of earthquake-producing fault zones. Uncovering just how much water is inside Earth — and the extent to which it moves back and forth between the surface and subsurface — has long been a challenge for scientists interested in understanding the planet’s water cycle. A new study peering beneath the Mariana Trench in the Western Pacific has revealed that some subduction zones might pull significantly more water into Earth’s interior than previously thought.

Sounding Out Earth's Hum

Fri, 11 Jan 2019 16:01:16 -0500

Scientists are working to isolate and identify the various sources and mechanisms of Earth's vibrations. Credit: Lucia Gualtieri, based on seismic data from the Incorporated Research Institutions for Seismology (IRIS); background: Adobe stock photo/Andrej Pol.

Earth has a song, a symphony composed of ubiquitous, continuous subtle seismic signals that thrum beneath the hustle and bustle of modern society. Scientists first observed this ambient seismic noise — everything recorded on seismograms that cannot be attributed to earthquakes — at the end of the 19th century. Since then, they have been trying to determine what causes it, how to measure and track it, and how to use the information from it.

Earth's "hum" heard at ocean bottom

Tue, 03 Apr 2018 16:09:49 -0400

An ocean-bottom seismometer is deployed in the Indian Ocean. Credit: RHUM-RUM experiment/Meteor Cruise

Lapping waves or crashing surf may come to mind for most people when they imagine the sounds of the ocean. But the ocean has other voices as well, including one produced by interactions of waves with the seafloor along the continental slope. Unlike waves on the shoreline, this steady, low sound, or “hum,” is inaudible to the human ear and has even proven difficult to detect in recordings made by ocean bottom seismometers (OBS). But in a new study in Geophysical Research Letters, researchers analyzing OBS data have now clearly identified the hum for the first time, which may allow it to be used to develop a better picture of Earth’s interior structure.

Small-scale factors influence mantle flow under the seafloor

Tue, 15 Nov 2016 11:21:27 -0500

Deployment and recovery of an ocean-bottom seismometer (OBS) from the R/V Langseth in the Pacific Ocean more than 1,900 kilometers southeast of Hawaii. The OBS was lowered into the water via crane, where it then fell to the seafloor under its own weight. It stayed on the seafloor for 13 months; researchers then returned to the location, sent the instrument a message to disconnect from its anchor weight, and it rose to the surface where researchers scooped it up. Credit: both: James Gaherty.

In December 2011, scientists and technicians aboard the research vessel Marcus G. Langseth dropped several ocean-bottom seismometers into the deep Pacific more than 1,900 kilometers southeast of Hawaii to measure seismic activity and electrical conductivity to a depth of about 300 kilometers below the seafloor. Now, these measurements are providing new insights into how the mantle flows and deforms below the rigid tectonic plates that make up Earth’s surface.

Mauna Loa's mysterious Ninole Hills were once a rift

Tue, 26 Jul 2016 09:57:04 -0400

The Nīnole Hills (orange area) on the southeast flank of Mauna Loa are suggested to be a failed rift (blue dashed line) that migrated toward the current Southwest Rift Zone (yellow dashed line). Credit: U.S. Geological Survey.

Hawaii’s Nīnole Hills, jutting out from Mauna Loa’s southeast flank, are one of the most striking features on the Big Island, though their geologic origins have long been a mystery. A new study looking at gravity anomalies under the hills is revealing that the hills are part of an older rift system that predates the currently active Southwest Rift Zone. The seemingly sudden switch from one rift system to another may provide some clues as to how Mauna Loa grew to be the largest volcano on Earth. “A lot of different ideas have been proposed to explain how the Nīnole Hills were created,” says Jeff Zurek, a geophysicist at Simon Fraser University in Burnaby, British Columbia, and lead author of the new study published in Geophysical Research Letters. It’s been suggested that the hills could be the remnants of an older summit of Mauna Loa, or its predecessor, Mohokea, or that faulting and landslides could have created the unusual topography of the hills, or that they could be from an older, inactive rift system.

Radar reveals unmarked graves

Mon, 16 May 2016 11:30:53 -0400

Kevin Williams (left) and Trevor Jennings conduct a ground-penetrating radar survey at a cemetery in western New York. Credit: courtesy of Kevin Williams.

The occasional excursion to Death Valley or mineralogical study of bloodstone notwithstanding, geoscientists don’t often delve into the macabre in the course of their work. But when the administrators of two cemeteries in western New York came calling in 2014, researchers from Buffalo State College ended up using their geophysical field skills to hunt for centuries-old graves.

Subducting seamounts blocked a big quake in Chile

Thu, 07 Jan 2016 11:12:21 -0500

Map of Chile's coastline showing the locations of the April 2014 earthquake and the seamounts that may have prevented the rupture from propagating farther. Credit: K. Cantner, AGI, adapted from Geersen et al., Nature Communications, 2015.

Off the coast of Chile, the Nazca Plate is subducting beneath the South American Plate. Friction between the two plates creates stress along the contact area between them, which is occasionally released in the region’s frequent earthquakes. But the section of the megathrust fault near Iquique has been locked and accumulating stress since the last big event to strike that part of the fault in 1877.

Down to Earth With: Marine Geophysicist Maya Tolstoy

Fri, 08 May 2015 11:38:09 -0400

Marine geophysicist Maya Tolstoy is an associate professor at Columbia University's Lamont-Doherty Earth Observatory. Credit: LDEO.

Growing up in Scotland, Maya Tolstoy was drawn to the theater, and even briefly considered majoring in the subject in college. Instead, she chose to follow another lifelong passion and became a marine geophysicist.

Down to Earth With: Brian Tucker

Thu, 18 Dec 2014 10:40:34 -0500

Brian Tucker, founder and president of GeoHazards International (GHI). Credit: courtesy of the MacArthur Foundation.

Some of the world’s most densely populated cities are at highest risk for earthquake-related disasters. Geophysicist Brian Tucker has spent the last two-plus decades trying to help the developing world avoid such disasters, and in 1991, he founded the nonprofit GeoHazards International (GHI) to bring the developed world’s risk-mitigation techniques to high-risk communities in the developing world.

Are slow-slip earthquakes under Tokyo stressing faults?

Mon, 21 Jul 2014 15:33:45 -0400

Japan sits at the intersection of multiple tectonic plates. Just east of the island is a deep trench called the Sagami Trough. To monitor slow slip in the region, scientists are tracking the surface motion of the Boso Peninsula on the eastern side of Tokyo Bay, where the Philippine Plate plunges beneath the Eurasian Plate, creating the trough. Credit: Kathleen Cantner, AGI, after Ozawa et al., Geophysical Research Letters (2014).

To study plate movements under Tokyo, Shinzaburo Ozawa of the Geospatial Information Authority of Japan in Tsukuba used GPS sensors to track the surface motion of the Bōsō Peninsula on the eastern side of Tokyo Bay, where the Philippine Plate plunges beneath the Eurasian Plate, creating the Sagami Trough. His results were published in Geophysical Research Letters.

Humans causing California's mountains to grow

Wed, 14 May 2014 09:56:28 -0400

A study of more than 500 GPS stations in Southern California and Nevada found an anthropogenic signal in uplift of the Sierra Nevada and the California Coast Ranges related to long-term water withdrawal from aquifers in the San Joaquin Valley. Credit: UNAVCO

Humankind has proven time and again that it can reshape mountains, or even tear them down. Now, it appears, we can make them rise as well. Geologists studying growth rates of the Sierra Nevada and of central California’s Coast Ranges have identified an anthropogenic contribution to the mountains’ uplift that they suggest is tied to the decades-long depletion of groundwater in the state’s Central Valley. What’s more, the researchers report in a study published today in Nature, the long-term water loss may be affecting how stress builds up on faults like the San Andreas.

Observing a plate boundary

Wed, 23 Apr 2014 07:48:13 -0400

Credit: UNAVCO

More than 280 continuous GPS (cGPS) stations in Cascadia are part of the U.S. Plate Boundary Observatory (PBO), a component of EarthScope, which includes more than a thousand cGPS stations arrayed across the western United States and Alaska. Operated by UNAVCO, PBO provides continuous data to researchers studying tectonics and earthquakes. Each PBO station operates autonomously to record and transmit up to one sample per second. In addition to PBO, the U.S., New Zealand, Japan and Canada have implemented similar networks of cGPS stations with the intent of capturing both slow and rapid motion. By combining simultaneous data from multiple receivers, scientists can use cGPS networks to produce positioning and ground motion data with millimeter precision. Data from continuous stations can be blended with campaign studies, many of which share a fleet of GPS receivers managed by UNAVCO, to provide an effective tool for seismic research.

A truly global system

Wed, 23 Apr 2014 07:43:02 -0400

Credit: Kathleen Cantner, AGI

Like the GPS navigation system in your car or smartphone, a high-precision GPS receiver uses signals from satellites to determine the distance from the receiver to the satellite. But that’s where the similarities end. Today’s scientific and commercial-grade GPS receivers use two frequencies and carrier phase measurements (distance expressed in units of cycles of the carrier frequency) to produce precise results. In addition to the U.S. GPS satellites, many receivers use data from Russia’s GLONASS navigation satellites and are capable of using signals from the planned European (Galileo) and Chinese (BeiDou) systems. New U.S. satellites will provide an additional third frequency. The combination of the new and existing satellites is collectively known as the Global Navigation Satellite System, or GNSS. GNSS will provide significant benefits to commercial applications such as surveying, agriculture and construction, as well as earth science research.

A new tool for atmospheric studies

Wed, 23 Apr 2014 07:31:18 -0400

Scientists are putting GPS to work in some unexpected new ways. For example, John Braun, a project scientist at the University Corporation for Atmospheric Research (UCAR) in Boulder, Colo., is using GPS to measure precipitable water vapor.

Precise to a fault: How GPS revolutionized seismic research

Mon, 14 Apr 2014 12:57:55 -0400

The Global Positioning System is a constellation of more than 30 satellites orbiting Earth twice a day at an altitude of more than 20,000 kilometers. Geoscientists use GPS to make precise measurements of position and ground motion. Credit: Kathleen Cantner, AGI

In the late 1980s, Ken Hudnut, a Columbia University graduate student studying plate tectonics in Southern California, began experimenting with a new technology, called the Global Positioning System (GPS), as a way to measure the slow, relentless motion of Earth’s crustal plates.

Faking quakes at full scale: Giant shake tables simulate earthquakes to make buildings safer

Fri, 11 Apr 2014 13:29:41 -0400

The largest shake table experiment ever conducted shook this full-size seven-story condominium built at the Japanese National Research Institute for Earth Science and Disaster Prevention's Earth-Defense facility ("E-Defense") in 2009. Credit: John van de Lindt

On a muggy day in mid-July 2009, a lone seven-story condominium complex northwest of Kobe, Japan, was violently shaken by seismic forces similar to those that struck Northridge, Calif., in 1994 — only stronger. Onlookers watched the 23-unit, wood-frame tower sway and bounce while, inside the building, furniture toppled and plates clattered to the floor.

Slab tear explains perplexing Colombian earthquake activity

Fri, 08 Nov 2013 10:08:56 -0500

Four plates converge at the northwest corner of Colombia, leading to a complicated pattern of earthquake activity. Kathleen Cantner, AGI

Colombia sits atop a restless intersection of tectonic plates: The Caribbean Plate is subducting along the country’s northern coast while the oceanic Nazca Plate subducts along its western edge. In between, the narrow but buoyant Isthmus of Panama continues to crash into South America like a battering ram. The complex pattern of earthquake activity produced by these disparate forces has long confounded scientists hoping to decipher the plate structure beneath Colombia. In a new study, researchers have identified a feature called the Caldas Tear that may explain many long-standing riddles of Colombia’s geology.

Hidden graves give up their secrets to geologists

Mon, 05 Aug 2013 09:55:50 -0400

As of April 2013, more than 61,000 people were registered as missing in Colombia, many of whom are feared to be victims of the country’s narcotics-fueled gang wars and, presumably, buried in clandestine graves. Now a new study comparing the most effective remote sensing tools for finding hidden graves may help bring justice for victims and closure for families.

Iowa impact crater confirmed

Thu, 13 Jun 2013 12:21:53 -0400

An airborne geophysical survey has confirmed the discovery of an impact crater under the town of Decorah in northeastern Iowa. Adam Kiel, U.S. Geological Survey

An airborne geophysical survey mapping mineral resources in the Midwest has confirmed that a 470-million-year-old impact crater nearly five times the size of Barringer (Meteor) Crater in Arizona lies buried several hundred meters beneath the town of Decorah, Iowa.

Danger in the Deep: Chemical weapons lie off our coasts

Thu, 05 Jan 2012 06:41:58 -0500

After the two world wars, many weapons were dumped into the oceans. Roy Wilkins

Flash back to 1944: It’s a misty Hawaiian morning and a military vessel carries a nervous crew and deadly cargo from Pearl Harbor into the Pacific. The crew’s instructions are clear: Travel eight kilometers out to sea and dump tons of unused chemical weapons that are piled on deck. As the ship reaches the open ocean, the captain slows the vessel and sailors start pushing their lethal freight into the water. During the next half-hour, several thousand chemical bombs go overboard and into the abyss.

Geoscientists Without Borders: Geologists Lend a Hand

Thu, 05 Jan 2012 06:41:58 -0500

Seismic profiling in Chiang Mai, Thailand. Boise State University - Geoscientists _Without_ Borders

Boise State University student Eric Rothwell collects sediment cores in northern Thailand. Spencer Wood

Rothwell and Chiang Mai University student Tharaporn Bundarnsin collect magnetic data at an archaeological site in northern Thailand. Spencer Wood

Craig Beasley’s one-year term as president of the Society for Exploration Geophysicists had a challenging start. After about two months in office, a magnitude-9-plus earthquake struck off the coast of Sumatra on Dec. 26, 2004, triggering a powerful tsunami that killed more than 225,000 people and left hundreds of thousands homeless.

Natural gas production linked to earthquakes in Texas

Thu, 05 Jan 2012 06:41:58 -0500

A saltwater disposal well, a part of the natural gas production process, may have been responsible for triggering a series of minor earthquakes in the Dallas-Fort Worth area of Texas in 2008, according to a recent study.