| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | June 27, 2014 |
| Latest Amendment Date: | June 27, 2014 |
| Award Number: | 1358510 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Gregory Anderson
greander@nsf.gov (703)292-4693 EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | July 1, 2014 |
| End Date: | June 30, 2016 (Estimated) |
| Total Intended Award Amount: | $179,944.00 |
| Total Awarded Amount to Date: | $179,944.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
8622 DISCOVERY WAY # 116 LA JOLLA CA US 92093-1500 (858)534-1293 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
8602 La Jolla Shores Dr La Jolla CA US 92093-0210 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | EARTHSCOPE-SCIENCE UTILIZATION |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
During the last ten years, NSF's USArray Project has deployed thousands of seismometers across the United States to record both local and distant earthquakes. Analyses of these data have provided greatly improved images of the structure of Earth's crust and mantle beneath the United States. This project studies earthquakes and quarry blasts recorded by USArray at distances up to 1600 km away (1000 miles), which are particularly useful for probing crustal thickness and the structure of the uppermost mantle, i.e., immediately below the crust at depths of about 35 to 50 kilometers (about 20 to 30 miles). Maps showing variations in the measured velocities of seismic waves in this region provide clues regarding the history and evolution of mountains, faults, and other geological features, including the Colorado Plateau and Yellowstone volcanism. This project builds on previously NSF funded work in the western United States to focus on more recent USArray data from the eastern United States.
In particular, the project uses regional seismic phases such as Pn, Sn, Pg and Lg, to produce new maps of crustal thickness and both isotropic and anisotropic variations in uppermost mantle P and S velocity that can be related to many surface tectonic features. These results generally agree with previous studies in their large-scale patterns but show more detail in many regions. Owing to its relatively sparse station coverage and lack of earthquakes, the eastern United States has been much less studied than the west, so the most recent USArray station deployments provide a valuable opportunity to probe its crust and uppermost mantle structure. This project will provide new crustal thickness maps, estimates of crustal Vp/Vs ratios, maps of uppermost mantle variations in seismic velocity and azimuthal anisotropy. In addition, analyses of Sn propagation efficiency and Pg and Lg times and amplitudes are planned to resolve lower crustal velocities and attenuation. These results will complement shear-wave splitting and surface- and body-wave tomography studies by providing superior resolution for structures at lower crustal and uppermost mantle depths.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
During the last decade, NSF's USArray Project has deployed thousands of seismometers across the United States to record both local and distant earthquakes. Analyses of these data have provided greatly improved images of the structure of Earth's crust and mantle beneath the United States. This project studied earthquakes and quarry blasts recorded by USArray at distances up to 1600 km away (1000 miles), which are particularly useful for probing crustal thickness and the structure of the uppermost mantle, i.e., immediately below the crust at depths of about 35 to 50 kilometers (about 20 to 30 miles). The main result of this research was improved maps of variations in the velocities of seismic waves in the western United States, which provide clues regarding the history and evolution of mountains, faults, and other geological features, including the Colorado Plateau, Yellowstone volcanism, and the Appalachian Mountains. One important finding was identification of a region of slower seismic velocities centered on the New Madrid Seismic Zone, where large earthquakes occurred in the Midwest in 1811–12. The project provided support for a graduate student, who received her PhD for this research. Two papers were published in peer-reviewed scientific journals describing these results, and two more papers are submitted.
Last Modified: 08/01/2016
Modified by: Peter M Shearer
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