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Research Spending & Results

Award Detail

Awardee:UNIVERSITY OF ALASKA FAIRBANKS
Doing Business As Name:University of Alaska Fairbanks Campus
PD/PI:
  • Carl H Tape
  • (907) 474-5456
  • ctape@alaska.edu
Award Date:06/28/2012
Estimated Total Award Amount: $ 285,937
Funds Obligated to Date: $ 285,937
  • FY 2012=$193,344
  • FY 2014=$92,593
Start Date:09/01/2012
End Date:08/31/2016
Transaction Type:Grant
Agency:NSF
Awarding Agency Code:4900
Funding Agency Code:4900
CFDA Number:47.050
Primary Program Source:040100 NSF RESEARCH & RELATED ACTIVIT
Award Title or Description:Seismic Imaging of Alaska Using Spectral-Element and Adjoint Methods
Federal Award ID Number:1215959
DUNS ID:615245164
Parent DUNS ID:048679567
Program:Geophysics
Program Officer:
  • Luciana Astiz
  • (703) 292-4705
  • lastiz@nsf.gov

Awardee Location

Street:West Ridge Research Bldg 008
City:Fairbanks
State:AK
ZIP:99775-7880
County:Fairbanks
Country:US
Awardee Cong. District:00

Primary Place of Performance

Organization Name:University of Alaska Fairbanks Campus
Street:903 Koyukuk Drive
City:Fairbanks
State:AK
ZIP:99775-7320
County:Fairbanks
Country:US
Cong. District:00

Abstract at Time of Award

This project will apply spectral-element and adjoint methods to develop a three-dimensional seismic reference model for the crust and uppermost mantle of Alaska. Finite-frequency surface waves and body waves will be extracted from full seismic waveforms in order to provide the greatest resolution for seismic imaging. Major sedimentary basins will be incorporated within the initial three-dimensional models by using existing information such as gravity data and industry seismic data. A new catalog of seismic moment tensors will be constructed by inverting measurements of body waves and surface waves for earthquake depth and radiation pattern. Active tectonic settings exhibit deformation in the form of earthquakes, geodetic strain rate, erosion, and sedimentation. On longer time scales, these processes create a highly heterogeneous crustal composition. For example, faults may offset two distinct rock types, or a basin may open and accumulate kilometer-thick layers of sediment. On shorter time scales, these settings experience abundant earthquakes in response to stresses within the crust. By using these abundant earthquakes, seismic imaging with accurate numerical methods can reveal the extreme complexity within active tectonic settings. Spectral-element methods have been used to model wave propagation in complex geological settings, such as those with strong topographic variations and sedimentary basins. The accuracy of these wave propagation methods can be embedded in an adjoint inverse problem to improve subsurface images of Earth's crust. The primary product will be a three-dimensional reference model for Alaska. This model will describe the spatial variations in compressional wave speed, shear wave speed, and density in Alaska. The quality of the model will be highest in the crust, and it will provide opportunities for larger-scale tomographic studies of the entire subduction and collisional setting. The reference model will be useful as a framework for the upcoming GeoPRISMS focus in Alaska as well as the anticipated EarthScope Transportable Array.

Publications Produced as a Result of this Research

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C. Alvizuri and C. Tape "Full moment tensors for small events (Mw < 3) at Uturuncu volcano, Bolivia" Geophysical Journal International, v.206, 2016, p.1761. doi:10.1093/gji/ggw247 

V. Silwal and C. Tape "Seismic moment tensors and estimated uncertainties in southern Alaska" Journal of Geophysical Research: Solid Earth, v.121, 2016, p.2772. doi:10.1002/2015JB012588 

W. Tape and C. Tape "The classical model for moment tensors" Geophysical Journal International, v.195, 2013, p.1701. doi:10.1093/gji/ggt302 

C. Tape and M. West and V. Silwal and N. Ruppert "Earthquake nucleation and triggering on an optimally oriented fault" Earth and Planetary Science Letters, v.363, 2013, p.231-241. doi:http://dx.doi.org/10.1016/j.epsl.2012.11.060 

Yun Wang and Carl Tape "Seismic velocity structure and anisotropy of the Alaska subduction zone derived from surface wave tomography" Journal of Geophysical Research Solid Earth, v.119, 2014, p.8845. doi:10.1002/2014JB011438 

W. Shen and C. Alvizuri and F.-C. Lin and C. Tape "A one-dimensional velocity model for Uturuncu volcano, Bolivia, and its impact on full moment tensor inversions" Geosphere, v.13, 2017, p.1. doi:10.1130/GES01353.1 


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.

The subsurface structure of Alaska is largely unknown and remains a frontier for seismological research. Geological complexity at the surface reveals a complicated tectonic history of large pieces (terranes) being accreted over the past hundreds of millions of years to form Alaska. Today Alaska exhibits two extensive volcanic arcs (Wrangell and Aleutian-Alaskan), widespread crustal deformation, and one of the world's most seismically active regions. The objective of this project was to examine how the seismic wavefield from modern earthquakes interacts with the three-dimensional subsurface structure of Alaska.

The central contribution of this project was to establish a high-quality catalog of source parameters for earthquakes to be used to image the subsurface structure of Alaska. The source parameters we are most interested in are the six that define the seismic moment tensor, which characterizes the orientation of the fault and the possibility of opening or closing on a fault. We used seismic data recorded in Alaska to estimate moment tensors, including uncertainties, for hundreds of earthquakes in Alaska.

High-performance computer simulations were performed to examine the details of seismic wave propagation for earthquakes in Alaska. Sedimentary basins, such as in Cook Inlet and northwest of Nenana, strongly influenced the seismic wavefield. These simulations provided modeled (or `synthetic') seismograms that were compared with recorded seismograms in order to evaluate the quality of the subsurface structure models for Alaska. The computer simulations also provided a education opportunity, as the animations provided an accurate perspective on how earthquake waves interact with Earth's structures. These animations were made available on YouTube, including for the 1964 magnitude 9.2 Alaska earthquake and the 2016 magnitude 7.1 earthquake west of Cook Inlet and within the downgoing Pacific plate (https://youtu.be/KdiETNfyaUo and https://youtu.be/uNkGdYhJgE4).

During the project we analyzed an earthquake in central Alaska that had been triggered by seismic waves that had originated from a magnitude 8.6 earthquake in the Indian Ocean. The Alaska earthquake also exhibited a 20-second-long nucleation signal that was recorded by dozens of seismic stations. We also produced a three-dimensional model of the subsurface structure of the Alaska subduction zone by using differences in wave arrival times of surface waves from distant earthquakes. The resulting tomographic image of the subduction zone revealed the large-scale structure of the subducting Pacific plate, as well as an intriguing pattern of anisotropy, suggesting that mantle flow is influenced by the position of the downgoing plate.


Last Modified: 02/09/2017
Modified by: Carl H Tape

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