 |
| Titel |
Evolution of the structural, geochemical and mechanical properties of the Alpine Fault zone from the Deep Fault Drilling Project (DFDP): current achievements and future goals |
| VerfasserIn |
E. Mariani, D. R. Faulkner, D. A. H. Teagle, C. D. Menzies, R. Sutherland, J. Townend, V. G. Toy, D. J. Prior |
| Konferenz |
EGU General Assembly 2012
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250068808
|
|
|
|
|
|
| Zusammenfassung |
| Major plate boundaries, such as the Alpine Fault zone (AFZ), have fundamental influences on
the crust’s mechanical and transport properties. These faults can generate large earthquakes
and represent major geohazards. In-situ observations and sampling of active fault zones at
depth are possible only through drilling, and are imperative to develop predictive models of
fault zone behaviour.
The Deep Fault Drilling Project (DFDP), led by New Zealand scientists with international
collaborators, aims to drill and recover core, wireline log, and instrument boreholes of
progressively greater depths into the AFZ. The main scientific goal is to understand
the mechanics and structural evolution of major faults and the conditions under
which large earthquakes occur. The DFDP exploits the rapid regional slip rates of
the AFZ, its elevated geothermal gradient, extensively described surface geology,
seismic observations, and the fact that the AFZ is in the late stages of its seismic
cycle.
Phase 1 of the DFDP successfully drilled two shallow boreholes, DFDP-1A
to 101 m and DFDP-1B to 151 m, at Gaunt Creek. Hanging-wall and foot-wall
cataclasites were sampled with high recovery, and the Principal Slip Zone (PSZ)
of the AFZ was intercepted at 90 m and 128 m. Following geophysical wireline
logs that measured density, spontaneous potential, resistivity and neutron porosity,
borehole DFDP-1B was instrumented with seismometers, piezometers, and temperature
probes.
Hanging-wall cataclasites are altered, cemented rocks with low permeability values of
10-16 – 10-18 m2. Resistivity decreases with depth from 275 Ωm to 125 Ωm, while
spontaneous potential and neutron porosity increase from 200 mV to 230 mV and
from 1% to 15% respectively. Porosity values are interpreted to represent water
bound to clays and not water in pore spaces. Individual geophysical logs show
little difference between the foot-wall and hanging-wall cataclasites. However a
diagram of resistivity versus spontaneous potential identifies unequivocally each of the
foot-wall cataclasites, the PSZ, the hanging-wall cataclasites and the mylonites. The
PSZ has the lowest resistivity ( |
|
|
|
|
|
|