| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | July 11, 2013 |
| Latest Amendment Date: | July 11, 2013 |
| Award Number: | 1314910 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Luciana Astiz
lastiz@nsf.gov (703)292-4705 EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | July 15, 2013 |
| End Date: | June 30, 2017 (Estimated) |
| Total Intended Award Amount: | $136,500.00 |
| Total Awarded Amount to Date: | $136,500.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
1200 E CALIFORNIA BLVD PASADENA CA US 91125-0001 (626)395-6219 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
1200 E. California Blvd Pasadena CA US 91125-0001 |
| 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): | Geophysics |
| Primary Program Source: |
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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
A detailed seismic investigation of lithospheric structure will test two hypotheses for the tectonic origin of the Isabella high seismic velocity anomaly in the upper mantle of California's southern Great Valley. Both hypotheses are viable based on existing seismic imaging that uses data from stations spaced about 70 km apart, but they have dramatically different implications for the processes that accompany subduction termination and the evolution of continental arc lithosphere. One hypothesis attributes the Isabella Anomaly to the sinking mafic root of the southern Sierra Nevada batholith. The other attributes the Isabella Anomaly to a fossil slab that is a continuation of the Monterey microplate coherently translating beneath the Great Valley because it is mechanically coupled to the Pacific plate. Importantly, the latter hypothesis places the fossil slab beneath the along-strike extent of the section of the San Andreas fault that dominantly deforms by aseismic creep and hosts deep crustal tectonic tremor, which might be caused by fluids from the slab. Passive source seismic imaging using a dense broadband array with ~7 km station spacing extending from the coast to the Sierra Nevada foothills will robustly test the two hypotheses with detailed mapping of lithospheric interfaces and identification of whether or not they are continuous across a plate bounding fault with >300 km of cumulative right lateral displacement. Scattered wave migration and tomographic imaging methods will be used in concert to constrain lithospheric structure beneath the dense array.
The seismic study will advance understanding of the structural legacy and mechanics of subduction termination, post-subduction evolution of the Sierra Nevada arc lithosphere, and present day basal boundary conditions on the creeping section of the San Andreas fault. A clear opportunity for scientific advance is identified not only by the potential implications for fundamental tectonic processes, but also by the existence of two well-defined hypotheses for lithospheric-scale structure that can be robustly tested with modern passive source seismic imaging methods. Additional impacts of the project include aiding in the development of a new geophysics group at the University of New Mexico (UNM) by supporting a beginning-career PI, a graduate student, and an undergraduate researcher. Expansion of geophysics research and teaching at the state of New Mexico?s largest institution has outstanding potential to attract under-represented minorities to opportunities in the geosciences. A graduate student and undergraduate researcher will be supported at Caltech. The project will develop a new collaboration between UNM and Caltech.
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.
This study is concerned with the tectonic role of the Isabella Anomaly (IA), which a “drip-like” zone of high seismic velocity in the upper mantle beneath the Central Valley, CA. For the past two decades, the interpretation has been that it is the result of the delamination of the lithosphere beneath the Sierra Nevada mountains, or in other words it is denser material descending into the interior of the earth. A competing hypothesis is that is a remnant of the Farallon subduction system that ceased functioning 29 Ma. To distinguish the two hypotheses, a seismic line was deployed from the coast to the Sierras in central California to image the subsurface. The results show an image of the Farallon slab from the coast to a point just east of the San Andreas Fault, at which point it descends into the mantle to the area of the IA. This shows that the IA is clearly part of the Farallon subduction system and not due to delamination. The result is important because it means the slab is still present below the San Andreas Fault, which means it could be a source a water (lubrication) for the fault. It also means that we need to find another process to explain the rapid rise the Sierra Nevada mountains.
Last Modified: 07/30/2017
Modified by: Robert W Clayton
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