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 Impacts of mass coral die-off on Indian Ocean reefs revealed
21.02.2017 | University of Exeter

nachricht How much biomass grows in the savannah?
16.02.2017 | Friedrich-Schiller-Universität Jena

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Impacts of mass coral die-off on Indian Ocean reefs revealed

21.02.2017 | Earth Sciences

Novel breast tomosynthesis technique reduces screening recall rate

21.02.2017 | Medical Engineering

Use your Voice – and Smart Homes will “LISTEN”

21.02.2017 | Trade Fair News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>