| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | August 10, 2018 |
| Latest Amendment Date: | June 30, 2020 |
| Award Number: | 1833532 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Elizabeth Hearn
EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | August 15, 2018 |
| End Date: | July 31, 2022 (Estimated) |
| Total Intended Award Amount: | $378,757.00 |
| Total Awarded Amount to Date: | $378,757.00 |
| Funds Obligated to Date: |
FY 2019 = $126,738.00 FY 2020 = $130,249.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
10889 WILSHIRE BLVD STE 700 LOS ANGELES CA US 90024-4200 (310)794-0102 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
595 Charles Young Dr. East 3806 Geology Building Los Angeles CA US 90095-1567 |
| 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): |
PREEVENTS - Prediction of and, Geophysics |
| Primary Program Source: |
01001920DB NSF RESEARCH & RELATED ACTIVIT 01002021DB NSF RESEARCH & RELATED ACTIVIT |
| 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
Tsunamis are oceanic gravity waves generated by the displacement of a large volume of water in the ocean, typically resulting from complex geophysical processes including shallow earthquakes that break the oceanic crust and seafloor landslides. Tsunamis can cause large number of casualties and economic loss in coastal regions, which are home to over a third of the world population. Tsunami warning is thus a crucial system to reduce and mitigate tsunami hazards. In order to perform a more rapid and accurate tsunami early warning as well as better understanding the complexity of tsunami source, the investigators propose to apply the adjoint-state method to solve for the initial seafloor deformation of the tsunami source. The method improves the imaging resolution of the earthquake source process and produces little artifacts with a relatively small computational cost. This project takes full advantage of increasing tsunami instrumentations including ocean-bottom pressure sensors and coastal tide gauges and supports the Ph. D work of a female student. The research results are being shared via conferences and journals, as well as outreach to public schools and in undergraduate classes.
Traditional source inversion using tsunamis waves is based on either the finite-fault slip modeling or the time-reversal imaging. Such inversion methods suffer from the uncertainty of fault parameters or crustal rigidity. Moreover, the heavy computational burden of calculating Green's functions result in limited spatial resolution and hinders the real-time applicability of the traditional methods to tsunami early warning. In this work, we transplant the state-of-art adjoint-state full-waveform inversion method from exploration seismology to tsunami source imaging. The adjoint-state method solves the initial-water-elevation pattern with less computational cost, which potentially can improve the speed of tsunami early warning and reduces the blind zone. Our new method does not rely on pre-defined fault parameters and is suitable for tsunami-generating earthquakes with unknown fault geometry. This method also efficiently handles dense mesh grid and is capable of resolving small-scale secondary tsunami sources, such as the seafloor landslide or secondary ruptures on splay faults. Our results will advance tsunami science and earthquake source dynamics and set the stage to improve real-time applications such as tsunami early warning.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
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.
Tsunamis are oceanic gravity waves excited by large seafloor displacement, typically resulting from shallow earthquakes and submarine landslides. Tsunamis cause large casualties and economic loss in the coastal regions, and the early warning is a crucial system to reduce such hazard. In this project, we develop an adjoint-state inversion procedure to recover the initial seafloor motion responsible for tsunamis. Traditional finite-fault tsunami source inversion methods suffer from the uncertainty of fault parameters or crustal rigidity. Moreover, the heavy computational burden of calculating Green's functions limits the real-time applicability of the traditional methods to tsunami early warning. The benefits of the adjoint inversion are twofold: (1) independence of fault parameters, and (2) high computational efficiency, especially for dense tsunami arrays and high-resolution grids. We validate this approach with synthetic tsunami sources and apply it to the several large tsunami events in recent years. In its application to the 2014 Mw 8.1 Iquique earthquake, we find the adjoint inversion resolves a southwest-ward extension of the initial elevation which confirms the predictions of published finite fault models. In a rare tsunami event generated by the mega-normal Mw 8.2 Tehuantepec earthquake, we find the adjoint inversion presents an unique capability of distinguishing the true fault plane from the axillary plane of an intraplate event. Recently, large-scale regional array of ocean-bottom pressure sensors such as the Japanese S-net arrive at the scene. Based on a simulated scenario of the Mw 9.0 Tohoku earthquake, we demonstrate the benefit using the S-net for tsunami adjoint inversion, which delivers high-resolution source imaging and early warning approximately 5-min after the earthquake. We also show that adjoint inversion is capable of resolving the time-dependent seafloor deformation. Such temporal resolution is particular important to resolve tsunamis generated by slow-propagating earthquake ruptures, which often produce disproportionally large tsunami run-up. In summary, the adjoint tsunami inversions enable more rapid and accurate tsunami early warning as well as better understanding the complexity of tsunami source.
Last Modified: 11/21/2022
Modified by: Lingsen Meng
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