Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Prior great earthquakes unveiled at the western edge of the 1964 Alaska rupture

28.03.2014

Ever since the great magnitude 9.2 earthquake shook Alaska 50 years ago today, scientists have suspected that the quake’s rupture halted at the southwestern tip of Kodiak Island due to a natural barrier.

However, recent research suggests some large quakes can punch through these obstacles, and have done so in the past, according to a new study accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.


Geologists from the U.S. Geological Survey and Tufts University extract a hand-driven core on Sitkinak Island, Alaska. The cores contain peat with interbedded sand layers that record inundation of the coast by prehistoric tsunamis. A new study suggests that large earthquakes broke through the western edge of the 1964 Alaska earthquake.

Credit: USGS


Geologists drive a core into marsh sediment to document interbedded peat and silt that records sudden vertical land movements associated with megathrust fault slip during large earthquakes.

Credit: USGS

U.S. Geological Survey scientists and researchers from partner institutions working on Sitkinak Island, 15 miles southwest of Kodiak Island, unearthed geologic records from the last 1,000 years of at least three large subduction ruptures – sudden dislocations in which one crustal plate lurches beneath another – that broke through the western edge of the 1964 Alaska earthquake.

Among the new findings is the first geologic evidence of the great 1788 Alaska earthquake and tsunami, a seismic event previously known only from historical writings from Russian settlements in the region at the time.

During the 1964 Alaska earthquake, a sudden slip on the subduction megathrust extended from near Kayak Island in the east to the southwestern tip of Kodiak Island in the west, resulting in widespread ground shaking and a damaging tsunami.

To gather information on great earthquakes prior to 1964, the research team uncovered stratigraphic evidence of land-level change and tsunami inundation along the Alaska-Aleutian megathrust on Sitkinak Island.

Hand-driven cores and tidal outcrops in a lagoon reveal five sharp changes in lithology and microfossils that record sudden upward and downward jerks during large earthquakes. Two of the changes correspond to the 1964 rupture and an earlier analog, while three sharp horizons mark ruptures that passed beneath Sitkinak Island, including the 1788 rupture.

“It’s been proposed that the edge of the 1964 rupture acts as a long-lived and stable barrier limiting the size of great earthquakes,” said Rich Briggs, lead author of the study and a USGS Research Geologist. “However, the geologic record suggests this isn’t the case, and that some, if not most large ruptures break through.

Future studies will aim to determine the sizes of these boundary-busting ruptures. Understanding this problem is important because hazard models depend on an accurate understanding of the locations and sizes of prehistoric earthquakes,” Briggs added.

“The Sitkinak results demonstrate the crucial role that microfossils such as diatoms and foraminifera play in improving our understanding of great earthquake ruptures,” said Simon Engelhart, a University of Rhode Island researcher and study coauthor. “They were the smoking gun that indicated both coseismic uplift and subsidence have occurred and, therefore, that Sitkinak Island is not a persistent rupture boundary.”

Geologic evidence of a sudden uplift and an extensive sand sheet are consistent with Russian accounts of an earthquake and tsunami in 1788, but prior to this study no geologic evidence of this great event had been found.

“The 1788 rupture had important consequences for Kodiak Island because it resulted in evacuation of the Russian outpost at Three Saints Bay (near Old Harbor) and resettlement at the present site of Kodiak (city),” said Briggs.  “Historical documents and our geologic observations suggest the 1788 earthquake ruptured offshore Kodiak and extended toward the Shumagin Islands rather than toward Anchorage.”

Mapping prehistoric earthquakes in subduction zones requires a combination of approaches to indirectly capture evidence of massive undersea ruptures. Land-level changes and tsunami inundation—commonly recorded as raised or downdropped coasts and extensive sand sheets—can be revealed by mapping, coring, microfossil analysis, and a variety of dating techniques.

These findings have implications for hazard maps and tectonics studies, the study authors emphasized.  An upcoming update of the USGS National Seismic Hazard Maps for Alaska will require a reevaluation of fault rupture histories.

“Understanding the ways faults have ruptured in the past is important because the paleoearthquake record gives us at least one set of scenarios to prepare for in the future,” said Briggs.  “Geologic information joins other critical data, such as seismological and geophysical observations, in helping us generate useful hazard models.”

Notes for Journalists
Journalists and public information officers (PIOs) of educational and scientific institutions who have registered with AGU can download a PDF copy of this article by clicking on this link: http://onlinelibrary.wiley.com/doi/10.1002/2014GL059380/abstract

Or, you may order a copy of the final paper by emailing your request to Nanci Bompey at nbompey@agu.org. Please provide your name, the name of your publication, and your phone number.

Neither the paper nor this press release is under embargo.

Title

“Uplift and subsidence reveal a non-persistent megathrust rupture boundary (Sitkinak Island, Alaska)”

Authors:
Richard W. Briggs:  U.S. Geological Survey, Geologic Hazards Science Center, Golden, Colorado, USA;

Simon E. Engelhart: Dept. of Geosciences, University of Rhode Island, Kingston, Rhode Island, USA;

Alan R. Nelson: U.S. Geological Survey, Geologic Hazards Science Center, Golden, Colorado, USA;

Tina Dura: Dept. of Earth and Environmental Science, University of Pennsylvania, Philadelphia, Pennsylvania, USA;

Andrew C. Kemp: Dept. of Earth and Ocean Sciences, Tufts University, Lane Hall, Medford, Massachusetts, USA;

Peter J. Haeussler: U.S. Geological Survey, Alaska Science Center, Anchorage, Alaska, USA;

D. Reide Corbett: Dept. of Geological Sciences, East Carolina University, Greenville, North Carolina, USA;

Stephen J. Angster: U.S. Geological Survey, Geologic Hazards Science Center, Golden, Colorado, USA;

Lee-Ann Bradley: U.S. Geological Survey, Geologic Hazards Science Center, Golden, Colorado, USA.

Contact information for the authors:
Richard Briggs, +1 (303) 273-8465, rbriggs@usgs.gov


AGU Contact:

Nanci Bompey
+1 (202) 777-7524
nbompey@agu.org

USGS Contact:
Heidi Koontz
+1 (303) 202-4763
hkoontz@usgs.gov

Media Contacts

Nanci Bompey | American Geophysical Union

Further reports about: Alaska Geologic Geological Geophysical Island earthquake rupture

More articles from Earth Sciences:

nachricht Giant see-saw of monsoon rains detected
26.09.2016 | Potsdam-Institut für Klimafolgenforschung

nachricht A new 3D viewer for improved digital geoscience mapping
20.09.2016 | Uni Research

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First quantum photonic circuit with electrically driven light source

Optical quantum computers can revolutionize computer technology. A team of researchers led by scientists from Münster University and KIT now succeeded in putting a quantum optical experimental set-up onto a chip. In doing so, they have met one of the requirements for making it possible to use photonic circuits for optical quantum computers.

Optical quantum computers are what people are pinning their hopes on for tomorrow’s computer technology – whether for tap-proof data encryption, ultrafast...

Im Focus: OLED microdisplays in data glasses for improved human-machine interaction

The Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP has been developing various applications for OLED microdisplays based on organic semiconductors. By integrating the capabilities of an image sensor directly into the microdisplay, eye movements can be recorded by the smart glasses and utilized for guidance and control functions, as one example. The new design will be debuted at Augmented World Expo Europe (AWE) in Berlin at Booth B25, October 18th – 19th.

“Augmented-reality” and “wearables” have become terms we encounter almost daily. Both can make daily life a little simpler and provide valuable assistance for...

Im Focus: Artificial Intelligence Helps in the Discovery of New Materials

With the help of artificial intelligence, chemists from the University of Basel in Switzerland have computed the characteristics of about two million crystals made up of four chemical elements. The researchers were able to identify 90 previously unknown thermodynamically stable crystals that can be regarded as new materials. They report on their findings in the scientific journal Physical Review Letters.

Elpasolite is a glassy, transparent, shiny and soft mineral with a cubic crystal structure. First discovered in El Paso County (Colorado, USA), it can also be...

Im Focus: Complex hardmetal tools out of the 3D printer

For the first time, Fraunhofer IKTS shows additively manufactured hardmetal tools at WorldPM 2016 in Hamburg. Mechanical, chemical as well as a high heat resistance and extreme hardness are required from tools that are used in mechanical and automotive engineering or in plastics and building materials industry. Researchers at the Fraunhofer Institute for Ceramic Technologies and Systems IKTS in Dresden managed the production of complex hardmetal tools via 3D printing in a quality that are in no way inferior to conventionally produced high-performance tools.

Fraunhofer IKTS counts decades of proven expertise in the development of hardmetals. To date, reliable cutting, drilling, pressing and stamping tools made of...

Im Focus: Launch of New Industry Working Group for Process Control in Laser Material Processing

At AKL’16, the International Laser Technology Congress held in May this year, interest in the topic of process control was greater than expected. Appropriately, the event was also used to launch the Industry Working Group for Process Control in Laser Material Processing. The group provides a forum for representatives from industry and research to initiate pre-competitive projects and discuss issues such as standards, potential cost savings and feasibility.

In the age of industry 4.0, laser technology is firmly established within manufacturing. A wide variety of laser techniques – from USP ablation and additive...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Laser use for neurosurgery and biofabrication - LaserForum 2016 focuses on medical technology

27.09.2016 | Event News

Experts from industry and academia discuss the future mobile telecommunications standard 5G

23.09.2016 | Event News

ICPE in Graz for the seventh time

20.09.2016 | Event News

 
Latest News

New switch decides between genome repair and death of cells

27.09.2016 | Life Sciences

Nanotechnology for energy materials: Electrodes like leaf veins

27.09.2016 | Physics and Astronomy

‘Missing link’ found in the development of bioelectronic medicines

27.09.2016 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>