Geomechanical Investigation of Frictional Stability in DFDP Drilling Samples from the Alpine Fault, New Zealand
Final Report Abstract
The slip behavior of plate boundary faults is of great interest due to their ability to generate large earthquakes, and the Alpine Fault in particular because it is considered to be late in its seismic cycle so that a large earthquake (Mw ~8) should be expected soon. The Deep Fault Drilling Project (DFDP) was therefore initiated to learn more about the state of the fault zone. Laboratory friction experiments were conducted to further our understanding of how the fault is expected to behave based on the geologic materials and conditions specific to the Alpine Fault. A key result of this project is that based on laboratory frictnio experiments on natural samples recovered by DFDP drilling, the Alpine Fault is expected to be frictionally unstable (i.e. seismogenic) all the way up to the Earth’s surface. This implies that rupture to the surface should be expected during the next large earthquake, confirming previous speculation based on geodetic and seismologic observations. Some specific indications are relatively large frictional strength, evidence of unstable frictional sliding behavior by velocity weakening friction and laboratory SSEs, and very large time-dependent strengthening (healing) rates in Alpine Fault samples. An intriguing part of this project is that a compilation of multiple fault zone samples, including the Alpine Fault, shows that under realistically slow driving conditions simulating plate tectonic rates, all faults show some evidence of slip instability, which is favorable for earthquake slip and not detected in previous experiments. The Alpine Fault is no exception, and in fact is one of the more unstable fault zones among those tested. Further experiments inspired by the advanced lithification state of the Alpine Fault rocks have revealed the importance of the role of cohesive strength by cementation in driving seismogenic fault slip.
Publications
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(2016), A microphysical interpretation of rate- and state-dependent friction for fault gouge, Geochemistry Geophysics Geosystems 17, 1660-1677
Ikari, M.J., B.M. Carpenter and C. Marone
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(2016), Laboratory observations of time-dependent frictional strengthening and stress relaxation in natural and synthetic fault gouges, Journal of Geophysical Research Solid Earth 121
Carpenter, B.M., M.J. Ikari and C. Marone
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(2017), Seismic potential of weak, near-surface faults revealed at plate tectonic slip rates, Science Advances 3, e1701269
Ikari, M.J., A.J. Kopf
