| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | August 7, 2012 |
| Latest Amendment Date: | July 9, 2014 |
| Award Number: | 1215711 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Eva Zanzerkia
EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | September 1, 2012 |
| End Date: | August 31, 2017 (Estimated) |
| Total Intended Award Amount: | $234,000.00 |
| Total Awarded Amount to Date: | $234,000.00 |
| Funds Obligated to Date: |
FY 2013 = $92,635.00 FY 2014 = $37,354.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
21 N PARK ST STE 6301 MADISON WI US 53715-1218 (608)262-3822 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
WI US 53715-1218 |
| 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): |
Tectonics, Geophysics |
| Primary Program Source: |
01001314DB NSF RESEARCH & RELATED ACTIVIT 01001415DB 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
Scientists have long known that most large, destructive earthquakes are caused by the slow buildup of stress on fault zones at the boundaries between tectonic plates. Friction between the two sides of the fault holds it together and prevents slip while stress accumulates until the point of failure, precipitating the earthquake itself. However, the nature of how and why that failure occurs and grows into a large earthquake remains poorly understood. It is thought to be governed in large part by the materials that make up the fault zone ? the rock that is fractured and broken down by past earthquakes and the water that fills pore spaces in that rock, as well as the tectonic stresses at the depth of earthquakes.
To further our understanding of how faults work, an international team of scientists is conducting a 3-stage project to drill into New Zealand?s Alpine Fault, a major fault zone similar to the San Andreas of California, with a history of magnitude 7-8 earthquakes, and future potential for more. Drilling into the Alpine Fault will provide fresh samples from the fault zone unaltered by the negative effects of earth-surface weathering and erosion. The first stage, already drilled to 150 meters depth, obtained core samples across the fault zone and made measurements of the rock properties made by instruments placed down the holes. In the next stage, one or more holes will be drilled to more than 1500 meters depth, and is intended to sample across the fault at earthquake depths. As part of that effort, the University of Wisconsin-Madison and Penn State University partnership will measure a range of properties of these samples, including their strength (friction-based resistance to slip and the capacity to store up strain without breaking), permeability to pore water movement, and the speeds with which they transmit two types of seismic waves (a widely used way to measure rock properties remotely) under realistic conditions.
Furthermore, instruments lowered down the drill holes will be used to measure similar and additional properties at a broader scale. Using the results of sample and the drillhole data, the investigators will evaluate competing hypotheses for the strength of fault zones and the conditions therein, helping discover what happens inside faults between earthquakes, and how they may change leading up to future seismic activity. They will also evaluate the nature of groundwater flow (or lack thereof) in and around the fault zone at depth, important for understanding the pressure and temperature conditions during fault activity. This research, when combined with the complementary work by New Zealand-based collaborators and others, will yield a new understanding of how fault zones work and why earthquakes happen in the ways that they do. It will likely also yield new clues to understanding the future earthquake hazard on the Alpine Fault in particular and on major faults in general.
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 Alpine Fault of New Zealand defines the boundary where the Pacific and Australian tectonic plates meet, much like the San Andreas fault of California. It is known to have magnitude 7 - 8 earthquakes and presents a major hazard in that country. In addition, the Alpine Fault lies in a rugged area of western New Zealand where vigorous erosion has exposed the inner structure of the fault zone better than virtually any other active fault in the world. In order to shed light on the stress conditions, strength of the rocks, and internal temperature and porewater content of the fault zone, an international team assembled to drill several deep boreholes into that fault to study it directly in the subsurface.
Our project focused on measuring the speed of seismic (sound) waves through the rocks of the fault zone in the laboratory and down the drilled borehole. These wave speeds vary with the types and arrangements of minerals in the rock, with the structural damage the rock experiences during past earthquakes, and with the content and pressure of water in the pore spaces. We sampled rocks from a variety of outcrops along approximately 100 kilometers of the Alpine fault at the surface, and also from two boreholes drilled into the fault at about 100 meters depth. We measured the speed of ultrasonic seismic waves under high pressure and stress conditions in our laboratory. We found that the fault zone rocks exhibit much slower wave speeds (up to 40% slower or more) than the undamaged rocks that surrounds it. The fault zone varies in amount of damage and we quantitatively relate that to the reduction of wave speed and how sensitive it is to water pressure and stress.
We analyzed our data by comparing it to measurements made on seismometers that surround the fault, finding that very similar wave speed reductions exist at both the small sample scale (centimeters), borehole scale (tens of centimeters), and the field scale (tens to hundreds of meters). This shows that the thickness and geologic characteristics of the fault zone can be interpreted directly from seismological observations made at the surface. Essentially, we “calibrated” the geophysical structure of the fault by making these laboratory and drill hole observations. This is the most comprehensive data set that exists on these physical properties of fault rocks for any fault anywhere to date.
Through this research, we have learned a great deal about the internal structure of an earthquake-generating fault zone and how the rock properties are modified by the cumulative effects of previous earthquakes and other geologic processes. Integrating our study with many others of different facets of the Alpine Fault zone, we are developing a more comprehensive understanding of an active and dangerous fault zone than exists anywhere else in the world. Information from this research not only helps us understand the Alpine Fault, but also the fundamental processes of faulting in general.
This project has also provided important advanced training in geophysical methods to students. It formed a major part of the doctoral research of a graduate student, and she was awarded the PhD in 2017 on the strength of this research. An undergraduate student also gained firsthand, hands-on research experience through this project; he is now pursuing graduate study in the geosciences researching faults.
Last Modified: 07/30/2018
Modified by: Harold J Tobin
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