| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | July 20, 2018 |
| Latest Amendment Date: | August 8, 2022 |
| Award Number: | 1800933 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Margaret Benoit
mbenoit@nsf.gov (703)292-7233 EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | September 1, 2018 |
| End Date: | January 31, 2023 (Estimated) |
| Total Intended Award Amount: | $290,478.00 |
| Total Awarded Amount to Date: | $290,478.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
2301 S 3RD ST LOUISVILLE KY US 40208-1838 (502)852-3788 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
Louisville KY US 40292-0001 |
| 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): |
EARTHSCOPE, EPSCoR Co-Funding |
| 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
Based on historic records, surficial geological evidence, and numerous published studies, approximately 150km (90 mile) of the San Andreas Fault in central California, from Hollister to Parkfield, has been recognized as a creeping segment (segment along an active fault that is unlikely to produce damaging tremors). However, cumulative seismological evidence and impressive advances in monitoring technology have lead some scientists to question if the segment will remain creeping for the foreseeable future. Potential hazards from damaging earthquakes in this section of the fault would directly affect 3.5 million people. Since 2006, the San Andreas Fault Observatory at Depth (SAFOD) has provided material evidence including a large suite of rocks drilled from inside the creeping fault zone down to a vertical depth of about 2.7km (1.6 miles). Direct access to rocks that are being actively sheared off has revealed much about how the fault moves by tectonic forces without causing major tremors. But it is uncertain that the same mechanics apply at depths and higher temperatures below the observatory. This project will use drill core samples from the currently inactive rocks in the observatory for conducting basic-science research into the processes that ultimately determine the fault?s tendency to produce damaging earthquakes along the creeping segment. This expectation is realistic because the inactive rocks of the observatory are believed to hold information about the fault movement at greater depths and higher temperatures. The proposal employs traditional tools of information gathering such as x-ray probes and electron microscopes while applying new and innovative techniques of information analysis and processing (the Geographic Information Science) to accomplish the stated objectives of the project. The use of GIS software also makes it possible to provide the results more readily to the public online through web-based mapping applications and visualizations.
The primary objective of the proposed research is to probe the information content of the less studied SAFOD damage zone rocks in order to construct a microstructural-compositional model of the development of aseismic creep in central San Andreas Fault Zone (CSAF). The research will be carried out by combining the traditional methods of data collection including a scanning electron microscope, scanning/transmission electron microscope, electron backscatter diffraction, and x-ray diffraction with non-traditional use of techniques of Geographic Information Science (GIS) to produce results that are easier to visualize and analyze, store, and disseminate. A majority of studies based on the SAFOD samples indicate that shear localization on weak clay mineral phases (coefficient of friction 1-0.01) is responsible for the aseismic creep in the upper sections of CSAF. The current models also point to the presence of serpentinite-derived clay minerals at depths >3km below the SAFOD. However, in view of the presence of deep low velocity zones near SAFOD site, the repeating microearthquakes in CSAF, and evidence from the damage zone gouge bordering the active creep zones, we believe the following questions are worth answering: 1. What cumulative and reactivated deformation processes and patterns define the SAF damage zone and what could we learn about the deformation processes at depths below the SAFOD? 2. What is the spatial extent of possible interactions between damage zone and the actively creeping core of the SAF, and what processes (e.g. deformation mechanisms) drive such interactions? 3. What is the potential for such interactions to affect the aseismic behavior of CSAF? The proposed research provides a material basis for current discussion of whether the creeping section of the San Andreas Fault in central California will remain in a stable aseismic mode as the historical records indicate, or strong seismic events are probable in the future. A directly evidence-based model of aseismic creep in CSAF also contributes to better understanding of similar creeping fault segments in the West Coast plate boundary system. The results of this research are of interest not only to structural geologists, but also serve to provide physical constraints for research in tectonophysics, seismology, and geotechnical engineering. The project contributes to interdisciplinary science by introducing methods of GIS into solid earth and microstructural geology. Graduate and undergraduate students will be trained to use methods and concepts of the two disciplines. Working with analytical equipment and datasets help undergraduate students, in particular, to experience the practice of scientific research and applications of the scientific method.
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.
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.
The central section of the San Andreas Fault (SAF) in California, spanning about 130km from San Juan Bautista to Parkfield, is known as the creeping section of the fault (Fig. 1a). That is a section, which historically has not produced any large earthquakes. In terms of vulnerability and earthquake hazards risks, the human population in central California counties affected by possible earthquakes involving the creeping section of the fault approaches 6.5 million people. The San Andreas Fault Observatory at Depth (SAFOD) initiated in 2004 is a drilling project that among other geophysical and geochemical observations of the fault also sampled the fault material across its living core at about 2.7km below the surface. The core samples have since been studied by the scientific communities worldwide to understand the nature of the SAF 's creep movement. The objective of our project was to critically examine a subset of the drilled fault rocks for chemical and mechanical signs of past activity that may support and/or dispute the historical records of low-magnitude earthquake activity in the creeping segment, at least near the SAFOD site. The project studied 26 samples distributed over a 125-meter distance across the active fault core. We applied the combined methods of analytical electron microscopy and microstructural analyses to do the study. This study, while confirming much of the recent observations, has some significant new findings that we share here. Our results show that earthquakes of undetermined size had occurred episodically as rocks were uplifted to their current depth at the SAFOD site over the past 1-2 million years. It is known that the fault is currently creeping on two narrow, spatially separate, active intervals where rocks are found to have very low frictional resistance to slippage (CDZ and SDZ in Fig. 1b). However, the evidence of episodic earthquakes we find in the damage zone surrounding the active zones are also found, in one form or another, within both low-friction active intervals (Fig. 2 a-g). Our compositional analysis of calcite vein networks in the samples indicate that the CDZ may be acting as a barrier to fluid flow across the fault zone (Fig. 3a). The compositional results also indicate that fluids circulated in the CDZ side of the SAF are more mixed with groundwater than is the case in the SDZ side of the fault (Fig. 3b). The study shows that new minerals, sourced deep in the fault zone, were crystalized along with the calcite veins during the seismic episodes (Fig. 4). We consider these results to be significantly contributory to the ongoing research (e.g., Coffee et al. 2022) for understanding the potential earthquake hazards related to the creeping section of the SAF in central California.
Last Modified: 02/07/2023
Modified by: Jafar Hadizadeh
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