| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | July 31, 2019 |
| Latest Amendment Date: | July 31, 2019 |
| Award Number: | 1944292 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Eva Zanzerkia
EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | August 15, 2019 |
| End Date: | July 31, 2020 (Estimated) |
| Total Intended Award Amount: | $23,814.00 |
| Total Awarded Amount to Date: | $23,814.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
107 S INDIANA AVE BLOOMINGTON IN US 47405-7000 (317)278-3473 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
1001 E. 10th St. Bloomington IN US 47405-1405 |
| 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): | XC-Crosscutting Activities Pro |
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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
The RAPID project responds to the July Ridgecrest earthquakes in Southern California and develops and tests a tool to monitor stress in the Earth and how it changes after large earthquakes. The project takes GPS and satellite radar data and in near real time computes how the Earth's crust and upper mantle are deforming from the mainshocks and aftershock sequences. This project supports two graduate students to work on developing these new tools and testing them in the immediate aftermath of an earthquake. This project could lead to a future real-time aftershock forecasting method.
The first major earthquake in southern California in the last 20 years provides an opportunity to test a postseismic stress evolution monitoring system that would operate in near-real time. Coulomb stress changes from the mainshock of an earthquake are routinely computed to examine the potential for triggering earthquakes on nearby faults. It is known that aftershocks within about one fault-length of the rupture can largely be attributed to coseismic stress changes, but at larger distances, stress changes due to deeper postseismic deformation process such as mantle flow are larger than the coseismic stress change. The Ridgecrest earthquake triggered aftershocks greater than 100 km from the mainshock that are not consistent with Coulomb stress changes from the mainshock.The near real time technique developed through this research has potential to be implemented in future real-time aftershock forecasting. An advantage of this approach is that much of the heavy computation required to compute postseismic deformation is pre-computed and stored. The postseismic deformation calculations are relatively inexpensive and suites of models can be easily computed near real time. The Ridgecrest earthquake sequence provides the first opportunity with modern geodetic data to test a stress evolution monitoring system.
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.
In this study we used Global Position System (GPS) measurements of ground surface motion following the 2019 Ridgecrest, CA earthquake to test a system for routinely computing the spatio-temporal evolution of postseismic stress throughout the crust due to afterslip and mantle flow triggered by the mainshock. Induced stress changes in the crust from the mainshock of an earthquake are routinely computed to examine the potential for triggering earthquakes on nearby faults and these calculations are imporant in time-dependent seismic hazard assessment. However, the contribution to stresses from postsiemsic mantle flow and afterslip are always neglected.
We developed a method to rapidly compute postseismic deformation models and compare with GPS-derived surface displacements. The deformaiton models constrained by GPS data can then predict stress changes in the crust. We used the Ridgecrest earthquake as a case study to develop and test the method.
The biggest challenge in this development was identifying an appropriate rapid calculation of mantle viscosity to use in the calculations. To do this, we generated a suite of postseismically-reduced rheology models based on a 3D steady-state viscosity reference constructed using regional seismic tomography anomalies. We compute postseismic deformation due to coupled afterslip and mantle flow for each trial viscosity model and find that viscoelastic relaxation signatures are already significant in the far field. Our results suggest that compared to our long-term reference, a postseismic viscosity reduction is required to fit the geodetic signal. A stress-dependent, power-law formulation does not fully capture the reduction, and a transient viscosity reduction mechanism is required. Best-fit models require a low effective postseismic viscosity (about an order of magnitude lower than the pre-earthquake viscosity) at 60 - 100 km depth. From this postseismic viscosity we estimate a range of steady-state (pre-earthquake) effective viscosity depth profiles and find that the mantle viscosity in the vicinity of the Ridgecrest earhquake tends towards the lower end of estimates from previous studies of southern California.
We found that these postseismic deformation models predict signifcant stress changes in the crust at distances of 100 km and greater from the earthquake. The posteismic stress change magnitudes after 5 months at 100-200 km from the epicenter range from 30% to 100% of the coseiseismic stress change. We conclude that the posteismic contribtion to the total stress change calculations is important for earthquake hazard calculations at distances greater than 100 km from the earthquake.
Last Modified: 04/01/2021
Modified by: Kaj M Johnson
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