Seismic activity in intraplate regions -- Midwest US

Embargoed: Contents not for release until 12:01 a.m. the day of session. All times Pacific Standard Time.All sessions will be held at the Marriott Downtown Waterfront Hotel in Portland, Ore.Press may receive complimentary registration at the Ballroom Lobby.

The Seismological Society of America (SSA) is an international scientific society devoted to the advancement of seismology and its applications in understanding and mitigating earthquake hazards and in imaging the structure of the Earth.

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Friday, April 23

State of Stress in Intraplate Regions8:30 a.m. – Noon, Salon GThis session reports on the latest research on the causes of intraplate (within the plate) earthquakes, which occur far from plate boundaries and continue to be poorly understood.

New Madrid Seismic Zone:

  • One of the most exciting discoveries to be made within the New Madrid Seismic Zone (NMSZ) in recent years is the possibility that non-volcanic tremors may be occurring within this intraplate fault system. Usually associated with subduction zones or the San Andreas Fault, the characteristics of non-volcanic tremors within the New Madrid fault system are critical parameters that potentially reflect strain within the fault zone. This speaker reports preliminary data from the array and initial findings. Charles Langston, University of Memphis,
  • With the retreat of the glaciers from the North American continent, the decrease in surface weight on the Earth's crust led to slow, ongoing uplift -- or glacial rebound -- of the land and the return flow of mantle material back under the area. This process can generate enough stress to generate a M6.8 earthquake every 500 years or a M7 earthquake every 1,000 years in the New Madrid Seismic Zone. Although these magnitudes are significantly less than previously published estimates for the sizes of the principal 1811-12 New Madrid earthquakes, they are consistent with values determined in a new study presented in this talk. Sue Hough, U.S. Geological Survey,

Man-induced earthquakes?

  • On June 2, 2009, the USGS reported a M 2.8 earthquake located 1.6 km northwest of Cleburne, Texas, in a region of active gas development and related waste fluid disposal. The town has no historical seismicity and has no previously reported active faults. As part of an undergraduate senior research project, a Southern Methodist University team deployed seismometers to observe and locate the subsequent earthquakes. Ashley Howe, Southern Methodist University,
  • Were recent earthquakes near Greenbriar, Arkansas, induced by waste-water injection or part of the history of seismic activity that has characterized the region? Preliminary analysis of the local network of three seismometers indicates the occurrence of hundreds of small earthquakes located about 2km south of the waste-water injection well with source depths ranging between 6.7 and 7.6 km. While a relationship between the earthquake activity and waste-water injection at depths around 2.4 km is possible, a causal relationship has not been substantiated. Steve Horton, University of Memphis,

Seismicity of North American plate:

  • Greater integrative lithospheric strength correlates with lower rates of continental crustal seismicity and with lower maximum earthquake magnitudes, according to a new study. (Poster) Walter Mooney, U.S. Geological Survey,
  • A new study that maps the density structure of the North American (NA) upper mantle shows a pronounced negative anomaly (-50 to -400 mgal) beneath western NA and the adjacent oceanic region, and positive anomalies (+50 to +350 mgal) east of the NA Cordillera. These structures correlate with the tectonically-active western region and the stable eastern region, respectively. The close correlation of large scale features of the mantle anomaly map with the topographic map confirms that a significant amount of the topographic uplift in western NA is likely due to buoyancy in the hot upper mantle. Walter Mooney, U.S. Geological Survey,

Lessons from January 2010 Earthquakes in Haiti and Offshore Northern California 8 – 8:30 a.m., Salon A, E, F and G

A field reconnaissance was conducted in Haiti Jan. 26 through Feb. 3, 2010, by a five-member team with expertise in seismology and earthquake engineering. This study has revealed a number of factors that led to catastrophic losses of life and property. Soil liquefaction, ground motion amplification, triggered landslides and rockslide, and soil embankment failures were observed to be significant factors contributing to extensive damage in Port-au-Prince and elsewhere. The historic pattern of prior earthquakes in Haiti indicates that a strong earthquake with M7 or larger could strike southern Haiti near Port-au-Prince at any time. Walter Mooney, U.S. Geological Survey

Source: Seismological Society of America