scholarly journals The Alpine Fault hanging-wall viewed from within: Structural analysis of the ultrasonic image logs in the DFDP-2B borehole, New Zealand

2021 ◽  
Author(s):  
C Massiot ◽  
B Célérier ◽  
ML Doan ◽  
TA Little ◽  
John Townend ◽  
...  
Keyword(s):  
New Zealand ◽  
Fault Plane ◽  
Hanging Wall ◽  
Anisotropic Permeability ◽  
Ultrasonic Image ◽  
Feature Sets ◽  
Alpine Fault ◽  
American Geophysical ◽  
American Geophysical Union ◽  
Topographic Relief

©2018. American Geophysical Union. All Rights Reserved. Ultrasonic image logs acquired in the DFDP-2B borehole yield the first continuous, subsurface description of the transition from schist to mylonite in the hangingwall of the Alpine Fault, New Zealand, to a depth of 818 m below surface. Three feature sets are delineated. One set, comprising foliation and foliation-parallel veins and fractures, has a constant orientation. The average dip direction of 145° is subparallel to the dip direction of the Alpine Fault, and the average dip magnitude of 60° is similar to nearby outcrop observations of foliation in the Alpine mylonites that occur immediately above the Alpine Fault. We suggest that this foliation orientation is similar to the Alpine Fault plane at ∼1 km depth in the Whataroa valley. The other two auxiliary feature sets are interpreted as joints based on their morphology and orientation. Subvertical joints with NW-SE (137°) strike occurring dominantly above ∼500 m are interpreted as being formed during the exhumation and unloading of the Alpine Fault's hangingwall. Gently dipping joints, predominantly observed below ∼500 m, are interpreted as inherited hydrofractures exhumed from their depth of formation. These three fracture sets, combined with subsidiary brecciated fault zones, define the fluid pathways and anisotropic permeability directions. In addition, high topographic relief, which perturbs the stress tensor, likely enhances the slip potential and thus permeability of subvertical fractures below the ridges, and of gently dipping fractures below the valleys. Thus, DFDP-2B borehole observations support the inference of a large zone of enhanced permeability in the hangingwall of the Alpine Fault.

scholarly journals The Alpine Fault hanging-wall viewed from within: Structural analysis of the ultrasonic image logs in the DFDP-2B borehole, New Zealand

2021 ◽  
Author(s):  
C Massiot ◽  
B Célérier ◽  
ML Doan ◽  
TA Little ◽  
John Townend ◽  
...  
Keyword(s):  
New Zealand ◽  
Fault Plane ◽  
Hanging Wall ◽  
Anisotropic Permeability ◽  
Ultrasonic Image ◽  
Feature Sets ◽  
Alpine Fault ◽  
American Geophysical ◽  
American Geophysical Union ◽  
Topographic Relief

©2018. American Geophysical Union. All Rights Reserved. Ultrasonic image logs acquired in the DFDP-2B borehole yield the first continuous, subsurface description of the transition from schist to mylonite in the hangingwall of the Alpine Fault, New Zealand, to a depth of 818 m below surface. Three feature sets are delineated. One set, comprising foliation and foliation-parallel veins and fractures, has a constant orientation. The average dip direction of 145° is subparallel to the dip direction of the Alpine Fault, and the average dip magnitude of 60° is similar to nearby outcrop observations of foliation in the Alpine mylonites that occur immediately above the Alpine Fault. We suggest that this foliation orientation is similar to the Alpine Fault plane at ∼1 km depth in the Whataroa valley. The other two auxiliary feature sets are interpreted as joints based on their morphology and orientation. Subvertical joints with NW-SE (137°) strike occurring dominantly above ∼500 m are interpreted as being formed during the exhumation and unloading of the Alpine Fault's hangingwall. Gently dipping joints, predominantly observed below ∼500 m, are interpreted as inherited hydrofractures exhumed from their depth of formation. These three fracture sets, combined with subsidiary brecciated fault zones, define the fluid pathways and anisotropic permeability directions. In addition, high topographic relief, which perturbs the stress tensor, likely enhances the slip potential and thus permeability of subvertical fractures below the ridges, and of gently dipping fractures below the valleys. Thus, DFDP-2B borehole observations support the inference of a large zone of enhanced permeability in the hangingwall of the Alpine Fault.

scholarly journals Fluid Flux in Fractured Rock of the Alpine Fault Hanging-Wall Determined from Temperature Logs in the DFDP-2B Borehole, New Zealand

2021 ◽  
Author(s):  
L Janku-Capova ◽  
Rupert Sutherland ◽  
John Townend ◽  
ML Doan ◽  
C Massiot ◽  
...  
Keyword(s):  
Fractured Rock ◽  
Hanging Wall ◽  
Surrounding Rock ◽  
Fluid Flux ◽  
Long Wavelength ◽  
Alpine Fault ◽  
Temperature Signal ◽  
American Geophysical ◽  
Diffusive Processes ◽  
American Geophysical Union

©2018. American Geophysical Union. All Rights Reserved. Sixteen temperature logs were acquired during breaks in drilling of the 893m-deep DFDP-2B borehole, which is in the Alpine Fault hanging-wall. The logs record various states of temperature recovery after thermal disturbances induced by mud circulation. The long-wavelength temperature signal in each log was estimated using a sixth-order polynomial, and residual (reduced) temperature logs were analyzed by fitting discrete template wavelets defined by depth, amplitude, and width parameters. Almost two hundred wavelets are correlated between multiple logs. Anomalies generally have amplitudes <1°C, and downhole widths <20m. The largest amplitudes are found in the first day after mud circulation stops, but many anomalies persist with similar amplitude for up to 15 days. Our models show that thermal and hydraulic diffusive processes are dominant during the first few days of re-equilibration after mud circulation stops, and fluid advection of heat in the surrounding rock produces temperature anomalies that may persist for several weeks. Models indicate that the fluid flux normal to the borehole within fractured zones is of order 10−7 to 10−6 m s−1, which is 2–3 orders of magnitude higher than the regional flux. Our approach could be applied more widely to boreholes, as it uses the thermal re-equilibration phase to derive useful information about the surrounding rock mass and its fluid flow regime.

scholarly journals Fluid Flux in Fractured Rock of the Alpine Fault Hanging-Wall Determined from Temperature Logs in the DFDP-2B Borehole, New Zealand

2021 ◽  
Author(s):  
L Janku-Capova ◽  
Rupert Sutherland ◽  
John Townend ◽  
ML Doan ◽  
C Massiot ◽  
...  
Keyword(s):  
Fractured Rock ◽  
Hanging Wall ◽  
Surrounding Rock ◽  
Fluid Flux ◽  
Long Wavelength ◽  
Alpine Fault ◽  
Temperature Signal ◽  
American Geophysical ◽  
Diffusive Processes ◽  
American Geophysical Union

©2018. American Geophysical Union. All Rights Reserved. Sixteen temperature logs were acquired during breaks in drilling of the 893m-deep DFDP-2B borehole, which is in the Alpine Fault hanging-wall. The logs record various states of temperature recovery after thermal disturbances induced by mud circulation. The long-wavelength temperature signal in each log was estimated using a sixth-order polynomial, and residual (reduced) temperature logs were analyzed by fitting discrete template wavelets defined by depth, amplitude, and width parameters. Almost two hundred wavelets are correlated between multiple logs. Anomalies generally have amplitudes <1°C, and downhole widths <20m. The largest amplitudes are found in the first day after mud circulation stops, but many anomalies persist with similar amplitude for up to 15 days. Our models show that thermal and hydraulic diffusive processes are dominant during the first few days of re-equilibration after mud circulation stops, and fluid advection of heat in the surrounding rock produces temperature anomalies that may persist for several weeks. Models indicate that the fluid flux normal to the borehole within fractured zones is of order 10−7 to 10−6 m s−1, which is 2–3 orders of magnitude higher than the regional flux. Our approach could be applied more widely to boreholes, as it uses the thermal re-equilibration phase to derive useful information about the surrounding rock mass and its fluid flow regime.

scholarly journals Variations in Seismogenic Thickness Along the Central Alpine Fault, New Zealand, Revealed by a Decade's Relocated Microseismicity

2021 ◽  
Author(s):  
K Michailos ◽  
EGC Smith ◽  
Calum Chamberlain ◽  
Martha Savage ◽  
John Townend
Keyword(s):  
Seismic Data ◽  
Hanging Wall ◽  
High Heat ◽  
Earthquake Activity ◽  
Alpine Fault ◽  
Waveform Cross Correlation ◽  
Uplift Rates ◽  
American Geophysical ◽  
Seismic Networks ◽  
American Geophysical Union

©2018. American Geophysical Union. All Rights Reserved. The Alpine Fault is an oblique strike-slip fault that is known to fail in large magnitude (M7–8) earthquakes, yet it is currently seismically quiescent. We examine the low-magnitude earthquake activity occurring along the central portion of the Alpine Fault using seismic data from five temporary seismic networks deployed for various lengths of time between late 2008 and early 2017. Starting from continuous seismic data, we detect earthquake arrivals and construct the longest and most extensive microearthquake catalog for the central Alpine Fault region to date, containing 9,111 earthquakes. This enables us to study the distribution and characteristics of the seismicity in unprecedented detail. Earthquake locations are constrained by high-quality automatic and manual picks, and we perform relocations using waveform cross-correlation to better constrain hypocenters. We have derived a new local magnitude scale calibrated by M w values. Magnitudes range between M L −1.2 and 4.6, and our catalog is complete above M L 1.1. Earthquakes mainly occur southeast of the Alpine Fault (in the hanging wall) and exhibit low magnitudes. We observe a lack of seismicity beneath Aoraki/Mount Cook, which we associate with high uplift rates and high heat flow. Seismogenic cutoff depths vary along the strike of the Alpine Fault from 8 km, beneath the highest topography, to 20 km in the adjacent areas.

scholarly journals Variations in Seismogenic Thickness Along the Central Alpine Fault, New Zealand, Revealed by a Decade's Relocated Microseismicity

2021 ◽  
Author(s):  
K Michailos ◽  
EGC Smith ◽  
Calum Chamberlain ◽  
Martha Savage ◽  
John Townend
Keyword(s):  
Seismic Data ◽  
Hanging Wall ◽  
High Heat ◽  
Earthquake Activity ◽  
Alpine Fault ◽  
Waveform Cross Correlation ◽  
Uplift Rates ◽  
American Geophysical ◽  
Seismic Networks ◽  
American Geophysical Union

©2018. American Geophysical Union. All Rights Reserved. The Alpine Fault is an oblique strike-slip fault that is known to fail in large magnitude (M7–8) earthquakes, yet it is currently seismically quiescent. We examine the low-magnitude earthquake activity occurring along the central portion of the Alpine Fault using seismic data from five temporary seismic networks deployed for various lengths of time between late 2008 and early 2017. Starting from continuous seismic data, we detect earthquake arrivals and construct the longest and most extensive microearthquake catalog for the central Alpine Fault region to date, containing 9,111 earthquakes. This enables us to study the distribution and characteristics of the seismicity in unprecedented detail. Earthquake locations are constrained by high-quality automatic and manual picks, and we perform relocations using waveform cross-correlation to better constrain hypocenters. We have derived a new local magnitude scale calibrated by M w values. Magnitudes range between M L −1.2 and 4.6, and our catalog is complete above M L 1.1. Earthquakes mainly occur southeast of the Alpine Fault (in the hanging wall) and exhibit low magnitudes. We observe a lack of seismicity beneath Aoraki/Mount Cook, which we associate with high uplift rates and high heat flow. Seismogenic cutoff depths vary along the strike of the Alpine Fault from 8 km, beneath the highest topography, to 20 km in the adjacent areas.

Thermal properties of the hanging wall of the central Alpine Fault, New Zealand

2020 ◽  
pp. 1-12
Author(s):  
Lucie Janku-Capova ◽  
Rupert Sutherland ◽  
John Townend ◽  
Weiren Lin
Keyword(s):  
Thermal Properties ◽  
New Zealand ◽  
Hanging Wall ◽  
Alpine Fault

scholarly journals Fluid Flux in Fractured Rock of the Alpine Fault Hanging-Wall Determined from Temperature Logs in the DFDP-2B Borehole, New Zealand

2018 ◽  
Vol 19 (8) ◽  
pp. 2631-2646 ◽  
Author(s):  
Lucie Janku-Capova ◽  
Rupert Sutherland ◽  
John Townend ◽  
Mai-Linh Doan ◽  
Cécile Massiot ◽  
...  
Keyword(s):  
New Zealand ◽  
Fractured Rock ◽  
Hanging Wall ◽  
Fluid Flux ◽  
Alpine Fault

scholarly journals Crustal Thermal Structure and Exhumation Rates in the Southern Alps Near the Central Alpine Fault, New Zealand

2021 ◽  
Author(s):  
K Michailos ◽  
Rupert Sutherland ◽  
John Townend ◽  
Martha Savage
Keyword(s):  
New Zealand ◽  
Thermal Structure ◽  
Hanging Wall ◽  
Southern Alps ◽  
Seismogenic Zone ◽  
Fixed Temperature ◽  
Alpine Fault ◽  
Brittle Ductile Transition ◽  
Orogenic Uplift ◽  
Exhumation Rates

© 2020. American Geophysical Union. All Rights Reserved. We investigate orogenic uplift rates and the thermal structure of the crust in the hanging wall of the Alpine Fault, New Zealand, using the hypocenters of 7,719 earthquakes that occurred in the central Southern Alps between late 2008 and early 2017, and previously published thermochronological data. We assume that the base of the seismogenic zone corresponds to a brittle-ductile transition at some fixed temperature, which we estimate by fitting the combined thermochronological data and distribution of seismicity using a multi-1-D approach. We find that exhumation rates vary from 1 to 8 mm/yr, with maximum values observed in the area of highest topography near Aoraki/Mount Cook, a finding consistent with previous geologic and geodetic analyses. We estimate the temperature of the brittle-ductile transition beneath the Southern Alps to be 410–430°C, which is higher than expected for Alpine Fault rocks whose bulk lithology is likely dominated by quartz. The high estimated temperatures at the base of the seismogenic zone likely reflect the unmodeled effects of high fluid pressures or strain rates.

scholarly journals Slow slip on the northern Hikurangi subduction interface, New Zealand

2021 ◽  
Author(s):  
A Douglas ◽  
J Beavan ◽  
L Wallace ◽  
John Townend
Keyword(s):  
New Zealand ◽  
Surface Displacement ◽  
Seismogenic Zone ◽  
Gps Data ◽  
Slow Slip ◽  
Slow Slip Event ◽  
Slip Event ◽  
American Geophysical ◽  
Continuous Gps ◽  
American Geophysical Union

In October 2002, a surface displacement episode of 20-30 mm magnitude was observed over a ∼10 day period on two continuous Global Positioning System (GPS) instruments near Gisborne, North Island, New Zealand. We interpret this to result from slow slip on the northern Hikurangi subduction interface. Using ten years of regional campaign GPS (1995-2004) and recent continuous GPS data, we estimate the recurrence interval for similar events to be 2-3 yrs. In November 2004, a similar slow slip event occurred within this recurrence period. The 2002 event can be modeled by ∼18 cm of slow slip near the down-dip end of the seismogenic zone on the subduction interface offshore of Gisborne. The campaign GPS data show that the 2002 slow slip event had little effect on regional strain patterns. Copyright 2005 by the American Geophysical Union.

scholarly journals Tidal Behavior and Water-Level Changes in Gravel Aquifers in Response to Multiple Earthquakes: A Case Study From New Zealand

2021 ◽  
Author(s):  
KC Weaver ◽  
ML Doan ◽  
SC Cox ◽  
John Townend ◽  
C Holden
Keyword(s):  
New Zealand ◽  
Water Level ◽  
Dynamic Stress ◽  
Near Field ◽  
Water Levels ◽  
Water Level Fluctuations ◽  
Water Level Changes ◽  
Canterbury Earthquake Sequence ◽  
American Geophysical ◽  
American Geophysical Union

©2019. American Geophysical Union. All Rights Reserved. Earthquakes have been inferred to induce hydrological changes in aquifers on the basis of either changes to well water-levels or tidal behavior, but the relationship between these changes remains unclear. Here, changes in tidal behavior and water-levels are quantified using a hydrological network monitoring gravel aquifers in Canterbury, New Zealand, in response to nine earthquakes (of magnitudes M w 5.4 to 7.8) that occurred between 2008 and 2015. Of the 161 wells analyzed, only 35 contain water-level fluctuations associated with “Earth + Ocean” (7) or “Ocean” (28) tides. Permeability reduction manifest as changes in tidal behavior and increased water-levels in the near field of the Canterbury earthquake sequence of 2010–2011 support the hypothesis of shear-induced consolidation. However, tidal behavior and water-level changes rarely occurred simultaneously (~2%). Water-level changes that occurred with no change in tidal behavior reequilibrated at a new postseismic level more quickly (on timescales of ~50 min) than when a change in tidal behavior occurred (~240 min to 10 days). Water-level changes were more than likely to occur above a peak dynamic stress of ~50 kPa and were more than likely to not occur below ~10 kPa. The minimum peak dynamic stress required for a tidal behavior change to occur was ~0.2 to 100 kPa.

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