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Seismology tip sheet for Dec. 2011: BSSA

December 01, 2011

Dec. 2011 BSSA: Monitoring the earthquake source process in North America; fractured bedrock may amplify shaking; and historic 1909 quake near Montana/Canada re-assessed

Please cite the Bulletin of the Seismological Society of America (BSSA) as the source of this information.

Monitoring the Earthquake Source Process in North America

Earthquake monitoring has yielded a rich database quantifying the last 30 years of activity, particularly moderate and larger quakes in active seismic zones. Now scientists have implemented procedures to routinely determine earthquake source information for the smaller magnitude earthquakes typically observed in central and eastern North America.

The benefits of the approach are reduced uncertainty in earthquake magnitude, improved source depth estimates and information about the tectonic stresses that cause the earthquakes. These parameters, in turn, contribute to assessing seismic hazards by constraining ground motion and source scaling relations impact assessment products such as PAGER -- Prompt Assessment of Global Earthquakes for Response.

This study applied two techniques for source inversion to earthquakes with reported magnitude greater than 3.5 in continental North America to create a catalog that includes 400 new well-calibrated moment magnitudes and source parameters for earthquakes. The catalog provides new detailed information on systematic variations in faulting styles and geometry for central and eastern regions of North America.

"Monitoring the Earthquake Source Process in North America," by Robert B. Herrmann at Saint Louis University, Harley Benz at U.S. Geological Survey and Charles J. Ammon at Penn State. Corresponding author: Robert B. Herrmann, Saint Louis University,, 314-977-3120.

Fractured bedrock may amplify shaking, complicating seismic hazard assessments

Strong earthquakes may induce fracturing of bedrock that amplifies shaking during subsequent seismic events, increasing the likelihood of future rockslides and other earthquake-triggered slope failures, suggests a study of a large, unstable rock slope in Randa, Switzerland.

Unconsolidated soil and sedimentary basins are known to amplify shaking, but bedrock is generally thought to be stable. But at Randa, located within the most seismically active area in Switzerland, scientists evaluated ground motion recordings during small earthquakes and found that fracturing of the rock mass can amplify ground motion by up to a factor of ten.

"Site Effects in Unstable Rock Slopes: Dynamic Behavior of the Randa Instability (Switzerland)," by Jeffrey Moore, Valentin Gischig, Jan Burjanek, Simon Loew and Donat Faeh of ETH Zurich.

Corresponding author: Jeffrey Moore,

Historic 1909 earthquake near Montana/Canada re-assessed

A new study locates the May 16, 1909 earthquake near the Montana-Saskatchewan border along an extension of the mapped 186-mile long Hinsdale fault in Montana, suggesting local seismic hazards may be greater than previously recognized.

The largest historical earthquake in the northern Great Plains of North America, the estimated magnitude 5.3-5.4 earthquake was felt in the states of Minnesota, Montana, North Dakota, South Dakota and Wyoming in the United States and in the provinces of Alberta, Manitoba, Ontario and Saskatchewan in Canada.

The refined location of the quake may have seismic-hazard implications for the region, particularly for the earth-filled Fort Peck Dam constructed in the 1930's on the Missouri River in northeast Montana.

"The 16 May 1909 Northern Great Plains Earthquake," by W. H. Bakun of the U.S. Geological Survey, M. C. Stickney of Montana Bureau of Mines and Geology and G. C. Rogers of Geological Survey of Canada.

Corresponding author: W. H. Bakun,, 650-329-4793

Seismological Society of America

Related Earthquake Articles:

From where will the next big earthquake hit the city of Istanbul?
Scientists reckon with an earthquake with a magnitude of 7 or greater in this region in the coming years.
Dissection of the 2015 Bonin deep earthquake
Researchers at Tohoku University's Department of Geophysics, have been studying the deep earthquake which occurred on May 30, 2015, to the west of Japan's Bonin Islands.
The search for the earthquake nucleus
Where a tectonic plate dives under another, in the so-called subduction zones at ocean margins, many strong earthquakes occur.
Better understanding post-earthquake fault movement
Preparation and good timing enabled Gareth Funning and a team of researchers to collect a unique data set following the 2014 South Napa earthquake that showed different parts of the fault, sometimes only a few kilometers apart, moved at different speeds and at different times.
The maximum earthquake magnitude for North Turkey
The Istanbul metropolitan region faces a high probability for a large earthquake in the near future.
Double dose of bad earthquake news
A team of researchers, including one from the University of California, Riverside, has discovered that earthquake ruptures can jump much further than previously thought, a finding that could have severe implications on the Los Angeles area and other regions in the world.
Discovery of hidden earthquake presents challenge to earthquake early-warning systems
Seismologists at the University of Liverpool studying the 2011 Chile earthquake have discovered a previously undetected earthquake which took place seconds after the initial rupture.
Babe Ruth and earthquake hazard maps
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Experts expected for some time that one of the next mega earthquakes occurs off northern Chile.
Catastrophic landslides post-earthquake
In the last few months, it has once more become clear that large earthquakes can solicit catastrophic landsliding.

Related Earthquake Reading:

The Great Quake: How the Biggest Earthquake in North America Changed Our Understanding of the Planet
by Henry Fountain (Author)

Quakeland: On the Road to America's Next Devastating Earthquake
by Kathryn Miles (Author)

Earthquakes (True Books: Earth Science (Paperback))
by Ker Than (Author)

Earthquakes (Smithsonian-science)
by Seymour Simon (Author)

Soil Liquefaction During Earthquakes (Engineering monographs on earthquake criteria, structural design, and strong motion records)
by I. M. Idriss (Author), R. W. Boulanger (Author)

National Geographic Kids Everything Volcanoes and Earthquakes: Earthshaking photos, facts, and fun!
by Kathy Furgang (Author)

I Survived the San Francisco Earthquake, 1906 (I Survived #5)
by Lauren Tarshis (Author), Scott Dawson (Illustrator)

The 1959 Yellowstone Earthquake (Disaster)
by The History Press

What Was the San Francisco Earthquake?
by Dorothy Hoobler (Author), Thomas Hoobler (Author), Who HQ (Author), Ted Hammond (Illustrator)

Earthquakes (Let's-Read-and-Find-Out Science 2)
by Dr. Franklyn M. Branley (Author), Megan Lloyd (Illustrator)

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