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

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Experiment Provides the Best Look Yet at 'Warm Dense Matter' at Cores of Giant Planets

In an experiment at the Department of Energy's SLAC National Accelerator Laboratory, scientists precisely measured the temperature and structure of aluminum as...

Im Focus: Energy-autonomous and wireless monitoring protects marine gearboxes

The IPH presents a solution at HANNOVER MESSE 2015 to make ship traffic more reliable while decreasing the maintenance costs at the same time. In cooperation with project partners, the research institute from Hannover, Germany, has developed a sensor system which continuously monitors the condition of the marine gearbox, thus preventing breakdowns. Special feature: the monitoring system works wirelessly and energy-autonomously. The required electrical power is generated where it is needed – directly at the sensor.

As well as cars need to be certified regularly (in Germany by the TÜV – Technical Inspection Association), ships need to be inspected – if the powertrain stops...

Im Focus: 3-D satellite, GPS earthquake maps isolate impacts in real time

Method produced by UI researcher could improve reaction time to deadly, expensive quakes

When an earthquake hits, the faster first responders can get to an impacted area, the more likely infrastructure--and lives--can be saved.

Im Focus: Atlantic Ocean overturning found to slow down already today

The Atlantic overturning is one of Earth’s most important heat transport systems, pumping warm water northwards and cold water southwards. Also known as the Gulf Stream system, it is responsible for the mild climate in northwestern Europe. 

Scientists now found evidence for a slowdown of the overturning – multiple lines of observation suggest that in recent decades, the current system has been...

Im Focus: Robot inspects concrete garage floors and bridge roadways for damage

Because they are regularly subjected to heavy vehicle traffic, emissions, moisture and salt, above- and underground parking garages, as well as bridges, frequently experience large areas of corrosion. Most inspection systems to date have only been capable of inspecting smaller surface areas.

From April 13 to April 17 at the Hannover Messe (hall 2, exhibit booth C16), engineers from the Fraunhofer Institute for Nondestructive Testing IZFP will be...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

World Conference On Regenerative Medicine 2015: Registration And Abstract Submission Now Open

25.03.2015 | Event News

University presidents from all over the world meet in Hamburg

19.03.2015 | Event News

10. CeBiTec Symposium zum Big Data-Problem

17.03.2015 | Event News

 
Latest News

Two Most Destructive Termite Species Forming Superswarms in South Florida

27.03.2015 | Agricultural and Forestry Science

ORNL-Led Team Demonstrates Desalination with Nanoporous Graphene Membrane

27.03.2015 | Materials Sciences

Coorong Fish Hedge Their Bets for Survival

27.03.2015 | Ecology, The Environment and Conservation

VideoLinks
B2B-VideoLinks
More VideoLinks >>>