Seismology 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.

Seismometers eavesdrop on glacial outburst flood

Thu, 17 Jan 2019 13:36:13 -0500

The Bhotekoshi Valley in Nepal before and after the 2016 flood of the Sunkoshi River. Credit: both: Kristen Cook/GFZ.

On July 5, 2016, a previously dammed glacial moraine in Nepal burst, releasing 100,000 tons of water that barreled down the Sunkoshi River, destroying bridges, hydropower plants and roads in its path. The flood was so massive that ground shaking was felt throughout the river corridor and recorded by seismometers deployed in the wake of the April 2015 Ghorka earthquake.

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.

New measurement shakes up earthquake estimates

Fri, 03 Aug 2018 13:15:26 -0400

Understanding how megathrust earthquakes like the 2011 magnitude-9.1 Tohoku event might rupture, including how long shaking might last, could help scientists prepare for future hazards. Credit: U.S. Navy photo by Mass Communication Specialist 1st Class Matthew M. Bradley.

As tectonic plates collide and sink in subduction zones, huge megathrust earthquakes can produce devastation above. Yet, there are many unknown factors that control how much energy is released in each earthquake. Now, a team of scientists has come up with a new model to help crack the complexity and nature of megathrust earthquakes using global historical records.

Seismic waves are blind to water

Tue, 03 Jul 2018 11:42:26 -0400

Volcanic eruptions, like those at Alaska's Redoubt Volcano, can generate seismic waves that researchers use to interpret Earth's interior. Credit: U.S. Geological Survey.

Geoscientists use the seismic waves produced by earthquakes to image the internal structure of the planet. Some seismic waves travel through liquids, while others do not, which is how we know, for instance, that Earth has a solid inner core and a liquid outer core. Scientists had thought they could use these properties of seismic waves to image the distribution of water within the planet, mainly water within the crystal structures of rocks. But in a new study, researchers reveal that may not be the case.

Yellowstone's Mexican mantle plume

Tue, 05 Jun 2018 16:30:18 -0400

Yellowstone's many thermal features are fueled by a deep mantle plume rooted at the core-mantle boundary under Mexico. Credit: Nelson et al., Nature Geoscience, 2018.

The volcanic activity at Yellowstone National Park is impressive, with thousands of active thermal features dotting a nearly 4,000-square-kilometer caldera. Scientists have long suspected that a massive mantle plume underlies the supervolcano. Now, new imaging has provided the clearest picture yet of the heat source that drives Yellowstone’s volcanism.

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.

Measuring earthquakes using fiber-optic cables

Mon, 19 Mar 2018 14:09:33 -0400

Nathaniel Lindsey of the University of California, Berkeley, buries fiber-optic cable in a trench near Fairbanks, Alaska, to record earthquake seismicity. Credit: left: Anna Wagner; right: Nathaniel Lindsey.

Fiber-optic cables crisscross the world, ferrying digital data and enabling internet access and telecommunication. In a new study, published in Geophysical Research Letters, researchers tested whether fiber-optic cables can also be used to detect and measure earthquakes.

New Zealand quake triggers two large slow-slip events

Thu, 14 Dec 2017 07:00:37 -0500

The 2016 Kaikoura earthquake set off slow-slip events off the east coast of New Zealand's North Island as well as beneath the country's capital, Wellington. Credit: K. Cantner, AGI.

On Nov. 14, 2016, a magnitude-7.8 earthquake struck near Kaikoura on New Zealand’s South Island, setting off a cascade of fault ruptures in the region. Within hours, seismic waves from the quake triggered a two-week-long slow-slip event on a section of the Hikurangi Subduction Zone between 250 and 600 kilometers north of the initial epicenter, as well as ongoing slow slip on the Hikurangi beneath New Zealand’s capital, Wellington, according to a new study in Nature Geoscience. Thanks to New Zealand’s advanced seismic and tectonic monitoring networks, the event is one of the best-documented examples of an earthquake triggering slow slip on distant faults.

Seismic patterns help forecast eruptions from quiet stratovolcanoes

Wed, 15 Nov 2017 14:14:51 -0500

Sinabung Volcano in Sumatra, Indonesia, began erupting in 2010 after a 400-year hiatus, with major eruptions again in 2014 and 2016. Credit: Nekomong, CC BY-SA 4.0.

Earth is home to more than 1,500 potentially eruptive volcanoes on land, each with a unique character and history. Predicting when and how a particular volcano may erupt is notoriously difficult, in large part because each eruption is unique. Recent work tracking pre-eruptive seismic behavior beneath two dozen reawakened volcanoes has revealed a distinctive pattern that seismologists may be able to use to assess when — and how violently — a rumbling volcano could blow its top.

Imaging Iceland's volcanic roots

Thu, 09 Nov 2017 15:28:10 -0500

Ultralow-velocity zones (ULVZ) are patches of molten rock at the core-mantle boundary in which passing seismic waves slow significantly. Such patches may fuel plumes of hot rock that rise through the mantle to feed some volcanic hot spots, such as those beneath Hawaii and Iceland. Credit: Kaiqing Yuan and Barbara Romanowicz; modified by K. Cantner, AGI.

Home to more than 30 active volcanoes, Iceland is one of the most vigorous volcanic settings on Earth. A new look at the core-mantle boundary thousands of kilometers below the island is offering one of the most complete pictures yet of how Iceland’s volcanoes are fueled.

Desktop seismology: How a maker-inspired device is changing seismic monitoring

Wed, 08 Nov 2017 12:37:49 -0500

Created in 2016, the Raspberry Shake is a personal seismograph that can detect local to regional earthquakes. The Shake was developed by OSOP, a geophysical instrument company headquartered in Panama. Marketed toward makers and the earthquake-curious, it also has the potential to help professionals increase the station density of seismic monitoring networks. Credit: OSOP.

Earth groans and shimmies constantly, producing everything from occasional building-collapsing earthquakes to subtle shaking humans don’t even feel. There are many ways to track this shaking, ranging from sensitive, expensive seismograph stations to various citizen-science approaches, including the U.S. Geological Survey’s “Did You Feel It?” program, through which people can report what they felt during an earthquake using an online survey.

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.

Firefighting gets a leg up from earthquake sensor networks

Tue, 16 Aug 2016 13:28:36 -0400

An aircraft makes a fire retardant drop on the American Fire in Tahoe National Forest near Foresthill, Calif. The fire began on Aug. 10, 2013. Credit: U.S. Forest Service.

Seismic networks monitor ground motion in earthquake-prone regions like California and Nevada. Now, they may also help combat other natural hazards like wildfires, which are especially common in drought-stricken western states where parched landscapes create ideal conditions for fires to spread.

Benchmarks: May 15, 1909: The Northern Great Plains earthquake

Mon, 01 Aug 2016 10:55:03 -0400

Scientists recently pinpointed the location and size of the 1909 Northern Great Plains earthquake, about 100 kilometers west of where scientists had previously placed the quake's location.Credit: left: AGI/NASA, right:courtesy of Bill Bakun, USGS.

In Culbertson, Mont., at a quarter past nine on a Saturday evening, Ralph Bush and H.G. Walsh were resting in the third-floor apartment of the Reed Cash Grocery when the floor began to rock, vibrating a small penknife right off their table, and sending a candle lamp clattering to the floor. At the nearby Evans Hotel, confusion reigned as the quake shook the two-story brick building, causing frightened guests to flee into the streets. On the second story of the Farmers & Merchants bank, a piano player was entertaining a social gathering at the home of Professor Dale when the shaking sent a vase crashing to the floor. The 15 seconds of quivering was so pronounced at Skelley’s barbershop that, “It rang up a 50-cent cash sale on the cash register, and it has been keeping me guessing how I can balance the darned thing,” Skelley told a reporter from the Culbertson Republican.

Going with the flow: Mapping the mantle under the Cascadia Subduction Zone

Tue, 22 Mar 2016 19:44:36 -0400

A new study using seafloor seismic instruments has revealed more information about the complex and dangerous Cascadia Subduction Zone. Credit: K. Cantner, AGI.

The Cascadia Subduction Zone (CSZ), off the Pacific Northwest coast of the United States and Canada, is one of the world’s most mysterious — and potentially dangerous — earthquake zones. Eerily quiet since a massive magnitude-9 event in 1700, scientists have long warned that the 1,000-kilometer-long fault zone could produce another devastating earthquake and tsunami. Now, a new effort to map the fault zone’s tectonic environment, including the underlying mantle, is shedding light on some of the dynamic forces that may influence earthquakes in the region.

How deep do the Alps go?

Thu, 07 Jan 2016 11:18:43 -0500

The mountains of the Dora Maira Massif, part of the Western Alps, surround the Maira Valley in northwestern Italy. Seismic data collected in the region suggests that, far below the massif, the buoyant continental crust of the Eurasian Plate is diving under the Adriatic Plate. Credit: Archenzo, CC BY-SA 3.0.

Continental crust was long thought to be too buoyant to subduct into the mantle, unlike denser oceanic crust, which descends into the mantle in many locations around the world. But the discovery of coesite — a type of silica formed at the extreme pressures present in subduction zones — in the Alps in 1984 challenged that long-held idea. Seismic evidence backing up claims that continental crust has indeed been subducted beneath the Alps has been scant, however, until now.

Vital seconds: The journey toward earthquake early warning for all

Thu, 03 Sep 2015 13:38:52 -0400

A mock-up of an earthquake early warning (EEW) alert on a cellphone. An EEW system is under development but not yet available to the public. Credit: K. Cantner, AGI, after Jennifer Strauss.

A ShakeAlert message like this would alert users to how many seconds they have before shaking waves arrive at their location and to the expected intensity of shaking. A shaking intensity of VI, as shown here, would mean the shaking would be strongly felt, people would find it difficult to stand, and structures could suffer damage. The warning message also displays a map with the location of the epicenter, the magnitude of the quake, and the current position of the P and S waves. Credit: USGS.

It is a cool foggy morning in San Mateo, Calif. A small ray of light has just peeked through my window. I listen to the birds chirping as I relish the final moments before my alarm calls for the start of a new day. It’s 6:15 a.m. Fifteen more minutes of a sleeping child.

Seismometers listen for falling rocks

Fri, 21 Aug 2015 11:48:06 -0400

Fresh debris lines part of Yosemite Valley after a rockfall. Credit: National Park Service.

Scores of natural rockfalls occur in California’s Yosemite Valley every year, often with little or no advance warning, posing hazards to people and infrastructure. In 1980, for example, a fall near Yosemite Falls killed three people and injured 19. Efforts to record and document rockfalls are rudimentary, relying only on eyewitness accounts and after-the-fact observations of fresh talus piles, which means many events are likely going unreported. In a new study, however, researchers interested in whether there’s a better way to monitor these events propose that seismic and infrasound sensors can help keep tabs on the granite slabs dropping from Yosemite’s cliffs.

Stalled slabs sometimes stopped by mineral strengthening

Thu, 16 Jul 2015 13:23:14 -0400

In some subduction zones, the downgoing slabs get stuck at depths of about 1,000 kilometers, held up by some unseen barrier that might be related to high-pressure-induced strengthening of minerals in the rocks surrounding the subducting slabs. Credit: K. Cantner, AGI.

Subduction of tectonic plates into the mantle functions as an eons-long recycling system for Earth’s crust and lithosphere. But in some subduction zones, the downgoing slabs seem to get stuck at depths of about 1,000 kilometers, held up by some unseen barrier on their journey deeper into the lower mantle. Now, scientists propose that this barrier might be related to high-pressure-induced strengthening of minerals in the rocks surrounding subducting slabs at these depths.

Introducing Earth's inner inner core

Tue, 16 Jun 2015 11:50:11 -0400

A humongous hunk of iron — that’s how scientists have long thought of Earth’s solid inner core. But new research suggests there’s more to it than that: namely, that the inner part of the inner core may have different physical properties than the outer part. In addition to revealing a new feature in Earth’s layer-cake internal structure, the discovery may shed light on the planet’s formation, say the authors of the study, published in Nature Geoscience.

March 29, 1936: Notes on Earth's Inner Core

Fri, 30 Jan 2015 13:35:48 -0500

Inge Lehmann worked for the Royal Danish Geodetic Institute from 1925 to 1952, heading the seismology department from 1928 until her retirement. Credit: The Royal Library, National Library of Denmark and University of Copenhagen University Library.

On March 29, 1936, Danish seismologist Inge Lehmann wrote a letter to a colleague in which she argued that seismic waves — specifically P-waves — recorded from distant earthquakes showed some anomalous characteristics. “If you had seen so many records from these distances as I have,” she wrote, “I am sure you would not doubt that the amplitudes are abnormally small.” Within the year, Lehmann published a study based on those unusual amplitudes, work that first proposed that Earth has a solid inner core inside its liquid outer core.

Hazard lingers after South Napa earthquake

Wed, 17 Dec 2014 13:36:10 -0500

A damaged building in Napa, Calif., following the magnitude-6 earthquake on Aug. 24, 2014, which struck south of the city. Credit: ©James Gunn, CC BY 2.0.

San Francisco — The magnitude-6 earthquake that shook buildings and rattled wineries in California’s Napa Valley on Aug. 24, 2014, continues to affect homes in at least one neighborhood in the city of Napa more than three months later. The quake’s epicenter was about 6 kilometers south of the city, but post-quake movement, or afterslip, along the principal fault line to the north of the epicenter is ongoing, according to a fast-track report prepared by the U.S. Geological Survey (USGS) for the Federal Emergency Management Agency. Scientists involved in producing the 51-page report — released to the public on Tuesday — discussed it at a press conference at the annual meeting of the American Geophysical Union in San Francisco.

Santiaguito Volcano's clockwork behavior provides an exceptional laboratory

Fri, 29 Aug 2014 10:53:27 -0400

A large eruption as captured from the so-called "Paradise" campsite between the parent volcano, Santa María, and the Caliente dome. Credit: Benjamin R. Phillips.

Self-portrait of the author on the edge of the nearly 2-kilometer-high scarp of Santa María. Credit: Benjamin R. Phillips.

If Earth breathes, Santiaguito Volcano in the Western Highlands of Guatemala could be its mouth. Roughly every half hour, like volcanic clockwork, Santiaguito’s active Caliente lava dome expands, filling with gas from depressurizing magma below. Then it exhales, often explosively, and deflates. Over the course of a day, you could almost keep time by it.

Infrasound reveals lava lake levels

Thu, 21 Aug 2014 18:58:48 -0400

Only rarely can scientists get a view of the lava lake atop Villarrica volcano. Credit: Greg Waite.

The rises and falls of volcanic lava lakes are not easily tracked, especially when the lakes aren’t visible from crater rims. But recently, researchers found a way to monitor the lava lake at Chile’s Villarrica volcano using complementary methods to keep an eye on a feature they can’t always see.

Human-induced earthquakes shake less

Thu, 21 Aug 2014 12:16:09 -0400

Occurrences of earthquakes in the Central and Eastern United States have increased since 2009 — a phenomenon that many scientists attribute to the growing use of hydraulic fracturing for fossil fuel extraction. Most agree that it’s not the fracturing itself, but the reinjection of wastewater into wells for containment beneath the surface that tends to induce seismic activity. Now, new research looking at the effects of induced seismic activity suggests that human-made earthquakes and naturally occurring tectonic earthquakes are felt differently at the surface.

In Turkey, the older the fault, the bigger the quake: Good news for Istanbul?

Tue, 19 Aug 2014 11:18:34 -0400

The North Anatolian Fault Zone is one of the most active, and potentially deadly, fault zones in the world. Credit: Kathleen Cantner, AGI.

For decades, Istanbul has been bracing for a major earthquake from the dangerously active North Anatolian Fault, which passes just 20 kilometers south of Turkey’s largest city. A new study looking at the age of the fault zone may set a cap on the maximum quake size that could hit Istanbul, suggesting that the older, more mature sections of the zone in the east are capable of bigger earthquakes than the younger sections in the west, which are near the city.

Books: The once and future San Andreas Fault

Mon, 28 Jul 2014 13:04:35 -0400

"Earthquake Storms: The Fascinating History and Volatile Future of the San Andreas Fault," by John Dvorak, Pegasus, 2014, ISBN: 978-1605984957.

One of the most famous pictures of the San Andreas Fault — taken by G.K. Gilbert, the pioneering geologist whose late-19th century insights into faults and the earthquake cycle were close to prescient — shows a woman standing next to the ruptured fault immediately after the 1906 earthquake.

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.

Unlocking the Cascadia Subduction Zone's secrets: Peering into recent research and findings

Mon, 30 Jun 2014 22:54:41 -0400

Most people living along the coast in California, Oregon and Washington are aware of the earthquake and tsunami risk posed by the Cascadia Subduction Zone just offshore. Credit: ©iStockphoto.com/4FR.

Once overlooked because of its relative inactivity compared to other subduction zones around the world, the Cascadia Subduction Zone (CSZ) — and the potentially devastating megathrust earthquakes and tsunamis it could unleash — are today well known to both geoscientists and the public.

Longmenshan fault zone in the spotlight after two major quakes in five years

Thu, 15 May 2014 09:46:06 -0400

Credit: David Wald, USGS

In May 2008, a magnitude-7.9 earthquake struck near Wenchuan, China, killing more than 80,000 people in the country’s biggest quake since 1950. Then, in April 2013, the magnitude-6.6 Lushan earthquake hit just 90 kilometers to the south — also within China’s Longmenshan Fault Zone, which separates the Tibetan Plateau to the west from the Sichuan Basin to the east — and caused another 200 deaths. Now, scientists have found that a roughly 60-kilometer segment of the fault zone between the epicenters of the two big temblors could be the next to rupture, although no one knows when or how big it might be.

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.

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.

Giant quake sloshed fjords half a world away

Wed, 20 Nov 2013 11:43:45 -0500

On the morning of March 11, 2011, Leif Hus and his wife Gry Melas Hus were having breakfast in their kitchen overlooking Sognefjord in Leikanger, Norway. It was low tide on a calm and windless day with near-freezing temperatures. As they stood, coffee cups in hand, looking out the window at the fjord, they saw an unusual wave roll in. The wave continued to rise, surging over the seawall into their backyard before receding back into the fjord. Then another wave surged in, and another. As the water rose, engulfing the ladder on their dock, Leif grabbed his cell phone and started filming.

Old photos help scientists relocate 1906 San Francisco quake rupture point

Wed, 20 Nov 2013 11:28:18 -0500

The buttons being in their proper place on the right-hand side of the man's waistcoat indicate that this 1906 photo has not been reversed during the printing process, providing an important clue as to the orientation of the fault trace, seen at the couple's feet. Bancroft Library, University of California, Berkeley

Portola Valley, just south of San Francisco, is famous for its progressive approach to geology. The town was the subject of the first geologic map of California and the first municipality in the state to hire its very own resident geologist. There’s a good reason: The section of the San Andreas Fault that produced the deadly San Francisco quake of 1906 runs right through the town. But where exactly the fault trace lies has long been a mystery. Now, in a new study, researchers have used a combination of new technology and old photographs to relocate the fault line.

World's largest deep earthquake recorded

Tue, 29 Oct 2013 17:06:02 -0400

The seismology world may have a new leader in superlatives: On May 24, 2013, the largest, deep earthquake ever recorded struck beneath the Sea of Okhotsk, between the Kamchatka Peninsula and Russian mainland. Scientists are still puzzling over how such a large event could occur so deep.

Big quakes topple traditional views of fault behavior

Fri, 15 Mar 2013 11:26:46 -0400

Heavy damage was sustained on the Japanese coast, as seen here in Sukuiso, following the magnitude-9 Tohoku earthquake in March 2011. During the quake, a rupture might have been triggered on a slow-moving part of the nearby megathrust fault by heating and pressurization of fluids within the fault. U.S. Navy photo by Mass Communication Specialist 3rd Class Dylan McCord

The oceanic Indo-Australian Plate moves diagonally (purple arrow) with respect to the Sunda Megathrust, subducting beneath the overriding Sunda Plate at an oblique angle. Some of the motion associated with the subduction is oriented perpendicular (red arrows) to the trench, meaning that stress accumulates on the plate interface and occasionally results in megathrust earthquakes. But there is also motion of the Indo-Australian Plate in the direction parallel to the trench (thin blue arrow), resulting in an accumulation of stress on strike-slip faults (oppositely oriented blue arrows) either on the overriding plate — as in the Great Sumatran Fault — or on the oceanic plate. AGI, after Ishii et al., Geology, 2013

If rules are made to be broken, then perhaps conventional wisdom is made to be overturned. The spate of large earthquakes in recent years — the magnitude and location of which have defied scientific expectations in several cases — has provided ample support for these maxims, at least within earth science. For all the confusion, though, data emerging from these events are reshaping and improving our understanding of how faults operate.

Well-healed faults produce high-frequency earthquake waves

Tue, 12 Feb 2013 08:16:29 -0500

This tabletop model consisting of adjacent Plexiglas slabs is used to simulate earthquakes and study fault healing. Gregory McLaskey

Much like our voices create sound waves with a variety of low and high pitches, or frequencies, earthquakes also produce seismic waves over a spectrum of frequencies. The seismic waves’ frequencies determine, in part, how far they travel and how damaging they are to human-made structures. But teasing out the details of how quake-generating faults influence seismic frequencies is no easy task, mainly because faults tend to be buried deep underground. Now, with the help of a tabletop earthquake model, researchers have identified how a process known as fault healing can shape seismic waves.

Voices: Judged unfairly in L'Aquila - roles and responsibilities should have been considered

Fri, 26 Oct 2012 13:39:27 -0400

A goverment building in L'Aquila, Italy, damaged by the April 2009 earthquake. TheWiz83, Creative Commons Attribution-ShareAlike 3.0 Unported

Earlier this week, an Italian judge summarily convicted seven participants in a meeting of the Italian Serious Risks Commission who evaluated the hazard posed by the L’Aquila earthquake swarm before the magnitude-6.3 earthquake on April 6, 2009, for the same offense and to the same penalty: six years in prison. Much has been written about this court decision, but the very different roles played by the seven defendants and their different expertise have not been discussed. Is there no difference among the roles of the “L’Aquila Seven” in the communication disaster?

Hazardous Living: Italian seismologists tragically convicted of manslaughter

Mon, 22 Oct 2012 14:34:09 -0400

Today, six seismologists and one government official were convicted of manslaughter and sentenced to six years in prison. The seismologists and official had been on trial for not adequately warning the public about the danger of a potential earthquake prior to the L'Aquila earthquake in April 2009 that killed 309 people. This ruling makes the earthquake and the aftermath a double tragedy. It was tragic enough that people lost their lives as a result of the natural disaster. Now the court has compounded the tragedy. What it will mean for seismology and hazards mitigation everywhere remains to be seen — but the implications are troubling.

Better warnings for the consequences of earthquakes: Bringing seismic hazard and risk assessments to policy

Fri, 25 May 2012 16:03:11 -0400

Adobe masonry, used throughout the developing world, often collapses in large earthquakes, including the 2010 quake in Haiti. Walter Mooney, U.S. Geological Survey

Schools tend to be especially vulnerable in earthquakes. A school in Coalinga, Calif., was damaged in a 1983 quake. Earthquake Engineering Research Institute, courtesy of NOAA National Geophysical Data Center

Much of Lima, Peru, was devastated in a 1974 earthquake. Some of the city has been rebuilt with earthquakes in mind, but even today if a large temblor were to strike the city, many buildings would likely collapse. U.S. Geological Survey

During the last decade, earthquakes have taken a heavy toll on lives, shocking the world. Two exceptionally large earthquakes off the coasts of Sumatra, Indonesia (December 2004), and Honshu, Japan (March 2011), generated tsunamis that swept more than 250,000 people to their deaths in total. In October 2005, a magnitude-7.6 earthquake devastated Pakistani Kashmir, collapsing buildings and triggering landslides that buried about 87,000 people. About the same number of people were killed in Wenchuan, China, in 2008, when the region was hit by a magnitude-8.0 earthquake. The number of fatalities is poorly known in Haiti from the 2010 magnitude-7.0 event near the capital Port au Prince, but it is suspected of killing 100,000 people and destroying nearly 300,000 buildings, including the national palace.

Managing the seismic risk posed by wastewater disposal

Tue, 17 Apr 2012 13:34:06 -0400

Shale gas and tight oil are produced in the Bakken Formation in North Dakota. Statoil

From an earthquake perspective, 2011 was a remarkable year. While the devastation accompanying the magnitude-9.0 Tohoku earthquake that occurred off the coast of Japan on March 11 still captures attention worldwide, the relatively stable interior of the U.S. was struck by a somewhat surprising number of small-to-moderate earthquakes that were widely felt. Most of these were natural events, the types of earthquakes that occur from time to time in all intraplate regions. For example, the magnitude 5.8 that occurred in central Virginia on Aug. 23 was felt throughout the northeast, damaged the Washington Monument, and caused the temporary shutdown of a nuclear power plant. This earthquake occurred in the Central Virginia Seismic Zone, an area known to produce relatively frequent small earthquakes.

Voices: Italian seismologists: What should they have said?

Fri, 20 Jan 2012 03:51:09 -0500

Many of L'Aquila's buildings were reduced to rubble during the April 6 earthquake. INGV

In Italy, seismologists who failed to predict the L’Aquila earthquake in 2009 could face manslaughter charges. On March 31, 2009, the Major Risks Committee — composed of six seismologists — told the rest of the Civil Protection Department (pdf) and other officials that there was “no reason to suppose a sequence of small earthquakes could be the prelude to a strong event” and that “a major earthquake in the area is unlikely but can’t be ruled out.” In other words, they did not recognize as precursory the sequence of earthquakes in the months that preceded the fatal event of April 6.

Blogging on EARTH: FEMA's plans for New Madrid