Seismic imaging of the Alpine Fault near Inchbonnie, New Zealand

S. F. A. Carpentier; A. G. Green; R. Langridge; F. Hurter; A. Kaiser; H. Horstmeyer; M. Finnemore

doi:10.1029/2012jb009344

3D seismic imaging of the Alpine Fault and the glacial valley at Whataroa, New Zealand

10.5194/egusphere-egu21-9743 ◽

2021 ◽

Author(s):

Vera Lay ◽

Stefan Buske ◽

Franz Kleine ◽

John Townend ◽

Richard Kellett ◽

...

Keyword(s):

New Zealand ◽

Fault Zone ◽

Seismic Data ◽

Seismic Imaging ◽

P Wave ◽

Seismic Survey ◽

Fault System ◽

3D Seismic ◽

Alpine Fault ◽

Drill Site

The Alpine Fault at the West Coast of the South Island (New Zealand) is a major plate boundary that is expected to rupture in the next 50 years, likely as a magnitude 8 earthquake. The Deep Fault Drilling Project (DFDP) aimed to deliver insight into the geological structure of this fault zone and its evolution by drilling and sampling the Alpine Fault at depth. Here we present results from a seismic survey around the DFDP-2 drill site in the Whataroa Valley where the drillhole almost reached the fault plane. This unique 3D seismic survey includes several 2D lines and a 3D array at the surface as well as borehole recordings. Within the borehole, the unique option to compare two measurement systems is used: conventional three-component borehole geophones and a fibre optic cable (heterodyne Distributed Vibration Sensing system (hDVS)). Both systems show coherent signals but only the hDVS system allowed a recording along the complete length of the borehole.Despite the challenging conditions for seismic imaging within a glacial valley filled with sediments and steeply dipping valley flanks, several structures related to the valley itself as well as the tectonic fault system are imaged. The pre-processing of the seismic data also includes wavefield separation for the zero-offset borehole data. Seismic images are obtained by prestack depth migration approaches.Within the glacial valley, particularly steep valley flanks are imaged directly and correlate well with results from the P-wave velocity model obtained by first arrival travel-time tomography. Additionally, a glacially over-deepened trough with nearly horizontally layered sediments is identified about 0.5 km south of the DFDP-2B borehole.With regard to the expected Alpine fault zone, a set of several reflectors dipping 40-56&#176; to the southeast are identified in a ~600 m wide zone between depths of 0.2 and 1.2 km that is interpreted to be the minimum extent of the damage zone. Different approaches image one distinct reflector dipping at 40&#176;, which is interpreted to be the main Alpine Fault reflector. This reflector is only ~100 m ahead from the lower end of the borehole. At shallower depths (z<0.5 km), additional reflectors are identified as fault segments and generally have steeper dips up to 56&#176;. About 1 km south of the drill site, a major fault is identified at a depth of 0.1-0.5 km that might be caused by the regional tectonics interacting with local valley structures. A good correlation is observed among the separate seismic data sets and with geological results such as the borehole stratigraphy and the expected surface trace of the fault.In conclusion, several structural details of the fault zone and its environment are seismically imaged and show the complexity of the Alpine Fault at the Whataroa Valley. Thus, a detailed seismic characterization clarifies the subsurface structures, which is crucial to understand the transpressive fault&#8217;s tectonic processes.

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Advanced seismic imaging techniques characterize the Alpine Fault at Whataroa (New Zealand)

Journal of Geophysical Research Solid Earth ◽

10.1002/2016jb013534 ◽

2016 ◽

Vol 121 (12) ◽

pp. 8792-8812 ◽

Cited By ~ 14

Author(s):

V. Lay ◽

S. Buske ◽

A. Lukács ◽

A. R. Gorman ◽

S. Bannister ◽

...

Keyword(s):

New Zealand ◽

Seismic Imaging ◽

Imaging Techniques ◽

Alpine Fault

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3D active source seismic imaging of the Alpine Fault zone and the Whataroa glacial valley in New Zealand

Journal of Geophysical Research Solid Earth ◽

10.1029/2021jb023013 ◽

2021 ◽

Author(s):

Vera Lay ◽

Stefan Buske ◽

John Townend ◽

Richard Kellett ◽

Martha Savage ◽

...

Keyword(s):

New Zealand ◽

Fault Zone ◽

Seismic Imaging ◽

Alpine Fault ◽

Active Source

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Determining hydrological and soil mechanical parameters from multichannel surface-wave analysis across the Alpine Fault at Inchbonnie, New Zealand

Near Surface Geophysics ◽

10.3997/1873-0604.2013019 ◽

2013 ◽

Vol 11 (4) ◽

pp. 435-448 ◽

Cited By ~ 18

Author(s):

L.A. Konstantaki ◽

S. Carpentier ◽

F. Garofalo ◽

P. Bergamo ◽

L.V. Socco

Keyword(s):

New Zealand ◽

Surface Wave ◽

Mechanical Parameters ◽

Wave Analysis ◽

Alpine Fault

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The fluid budget of a continental plate boundary fault: Quantification from the Alpine Fault, New Zealand

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2016.03.046 ◽

2016 ◽

Vol 445 ◽

pp. 125-135 ◽

Cited By ~ 22

Author(s):

Catriona D. Menzies ◽

Damon A.H. Teagle ◽

Samuel Niedermann ◽

Simon C. Cox ◽

Dave Craw ◽

...

Keyword(s):

New Zealand ◽

Plate Boundary ◽

Boundary Fault ◽

Continental Plate ◽

Alpine Fault

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Erosion rates of the New Zealand Southern Alps reflect long-term tectonics and transient climate

10.5194/egusphere-egu21-6571 ◽

2021 ◽

Author(s):

Duna Roda-Boluda ◽

Taylor Schildgen ◽

Hella Wittmann-Oelze ◽

Stefanie Tofelde ◽

Aaron Bufe ◽

...

Keyword(s):

New Zealand ◽

Strike Slip ◽

Southern Alps ◽

Fault System ◽

Tectonic Deformation ◽

Seismic Cycle ◽

Erosion Rates ◽

Alpine Fault ◽

Oblique Convergence

The Southern Alps of New Zealand are the expression of the oblique convergence between the Pacific and Australian plates, which move at a relative velocity of nearly 40 mm/yr. This convergence is accommodated by the range-bounding Alpine Fault, with a strike-slip component of ~30-40 mm/yr, and a shortening component normal to the fault of ~8-10 mm/yr. While strike-slip rates seem to be fairly constant along the Alpine Fault, throw rates appear to vary considerably, and whether the locus of maximum exhumation is located near the fault, at the main drainage divide, or part-way between, is still debated. These uncertainties stem from very limited data characterizing vertical deformation rates along and across the Southern Alps. Thermochronology has constrained the Southern Alps exhumation history since the Miocene, but Quaternary exhumation is hard to resolve precisely due to the very high exhumation rates. Likewise, GPS surveys estimate a vertical uplift of ~5 mm/yr, but integrate only over ~10 yr timescales and are restricted to one transect across the range.To obtain insights into the Quaternary distribution and rates of exhumation of the western Southern Alps, we use new 10Be catchment-averaged erosion rates from 20 catchments along the western side of the range. Catchment-averaged erosion rates span an order of magnitude, between ~0.8 and >10 mm/yr, but we find that erosion rates of >10 mm/yr, a value often quoted in the literature as representative for the entire range, are very localized. Moreover, erosion rates decrease sharply north of the intersection with the Marlborough Fault System, suggesting substantial slip partitioning. These 10Be catchment-averaged erosion rates integrate, on average, over the last ~300 yrs. Considering that the last earthquake on the Alpine Fault was in 1717, these rates are representative of inter-seismic erosion. Lake sedimentation rates and coseismic landslide modelling suggest that long-term (~103 yrs) erosion rates over a full seismic cycle could be ~40% greater than our inter-seismic erosion rates. If we assume steady state topography, such a scaling of our 10Be erosion rate estimates can be used to estimate rock uplift rates in the Southern Alps. Finally, we find that erosion, and hence potentially exhumation, does not seem to be localized at a particular distance from the fault, as some tectonic and provenance studies have suggested. Instead, we find that superimposed on the primary tectonic control, there is an elevation/temperature control on erosion rates, which is probably transient and related to frost-cracking and glacial retreat.Our results highlight the potential for 10Be catchment-averaged erosion rates to provide insights into the magnitude and distribution of tectonic deformation rates, and the limitations that arise from transient erosion controls related to the seismic cycle and climate-modulated surface processes.&#160;&#160;

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Alpine Fault of New Zealand and Gondwanaland reconstruction

Nature ◽

10.1038/252756a0 ◽

1974 ◽

Vol 252 (5485) ◽

pp. 756-756

Author(s):

DAVID J. CULLEN

Keyword(s):

New Zealand ◽

Alpine Fault

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Measuring Crustal Seismic Anisotropy through Shear Wave Splitting

10.26686/wgtn.17151191 ◽

2021 ◽

Author(s):

◽

Kenny Graham

Keyword(s):

Numerical Simulation ◽

New Zealand ◽

Shear Wave ◽

Seismic Anisotropy ◽

Shear Wave Splitting ◽

Anisotropic Structure ◽

Crustal Anisotropy ◽

Physical Mechanisms ◽

Alpine Fault ◽

Wave Splitting

This thesis involves the study of crustal seismic anisotropy through shear wave splitting. For the past three decades, shear wave splitting (SWS) measurements from crustal earthquakes have been utilized as a technique to characterize seismic anisotropic structures and to infer in situ crustal properties such as the state of the stress and fracture geometry and density. However, the potential of this technique is yet to be realized in part because measurements on local earthquakes are often controlled and/or affected by physical mechanisms and processes which lead to variations in measurements and make interpretation difficult. Many studies have suggested a variety of physical mechanisms that control and/or affect SWS measurements, but few studies have quantitatively tested these suggestions. This thesis seeks to fill this gap by investigating what controls crustal shear-wave splitting (SWS) measurements using empirical and numerical simulation approaches, with the ultimate aim of improving SWS interpretation. For our empirical approach, we used two case studies to investigate what physical processes control seismic anisotropy in the crust at different scales and tectonic settings. In the numerical simulation test, we simulate the propagation of seismic waves in a variety of scenarios. We begin by measuring crustal anisotropy via SWS analysis around central New Zealand, where clusters of closely-spaced earthquakes have occurred. We used over 40,000 crustal earthquakes across 36 stations spanning close to 5.5 years between 2013 and 2018 to generate the largest catalog of high-quality SWS measurements (~102,000) around the Marlborough and Wellington region. The size of our SWS catalog allowed us to perform a detailed systematic analysis to investigate the processes that control crustal anisotropy and we also investigated the spatial and temporal variation of the anisotropic structure around the region. We observed a significant spatial variation of SWS measurements in Central New Zealand. We found that the crustal anisotropy around Central New Zealand is confined to the upper few kilometers of the crust, and is controlled by either one mechanism or a combination of more than one (such as structural, tectonic stresses, and gravitational stresses). The high correspondence between the orientation of the maximum horizontal compressive stress calculated from gravitational potential energy from topography and average fast polarization orientation around the Kaikōura region suggests that gravitationally induced stresses control the crustal anisotropy in the Kaikōura region. We suggest that examining the effect of gravitational stresses on crustal seismic anisotropy should not be neglected in future studies. We also observed no significant temporal changes in the state of anisotropy over the 5.5 year period despite the occurrence of significant seismicity. For the second empirical study, we characterized the anisotropic structure of a fault approaching failure (the Alpine Fault of New Zealand). We performed detailed SWS analysis on local earthquakes that were recorded on a dense array of 159 three-component seismometers with inter-station spacing about 30 m around the Whataroa Valley, New Zealand. The SWS analysis of data from this dense deployment enabled us to map the spatial characteristics of the anisotropic structure and also to investigate the mechanisms that control anisotropy in the Whataroa valley in the vicinity of the Alpine Fault. We observed that the orientation of the fast direction is parallel to the strike of the Alpine Fault trace and the orientations of the regional and borehole foliation planes. We also observed that there was no significant spatial variation of the anisotropic structure as we move across the Alpine Fault trace from the hanging wall to the footwall. We inferred that the geological structures, such as the Alpine Fault fabric and foliations within the valley, are the main mechanisms that control the anisotropic structure in the Whataroa valley. For our numerical simulation approach, we simulate waveforms propagating through an anisotropic media (using both 1-D and 3-D techniques). We simulate a variety of scenarios, to investigate how some of the suggested physical mechanisms affect SWS measurements. We considered (1) the effect on seismic waves caused by scatterers along the waves' propagation path, (2) the effect of the earthquake source mechanism, (3) the effect of incidence angle of the incoming shear wave. We observed that some of these mechanisms (such as the incidence angle of the incoming shear wave and scatterers) significantly affect SWS measurement while others such as earthquake source mechanisms have less effect on SWS measurements. We also observed that the effect of most of these physical mechanisms depends on the wavelength of the propagating shear wave relative to the size of the features. There is a significant effect on SWS measurements if the size of the physical mechanism (such as scatterers) is comparable to the wavelength of the incoming shear wave. With a larger wavelength, the wave treats the feature as a homogeneous medium.

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Frictional properties of exhumed fault gouges in DFDP-1 cores, Alpine Fault, New Zealand

10.26686/wgtn.13818845.v1 ◽

2021 ◽

Author(s):

Carolyn Boulton ◽

D Moore ◽

D Lockner ◽

V Toy ◽

John Townend ◽

...

Keyword(s):

New Zealand ◽

Friction Coefficient ◽

White Mica ◽

Rate Dependence ◽

Experimental Conditions ◽

Alpine Fault ◽

Negative Rate ◽

Sample Depth ◽

Fault Gouges ◽

Increasing Temperature

Principal slip zone gouges recovered during the Deep Fault Drilling Project (DFDP-1), Alpine Fault, New Zealand, were deformed in triaxial friction experiments at temperatures, T, of up to 350°C, effective normal stresses, σn′, of up to 156 MPa, and velocities between 0.01 and 3 μm/s. Chlorite/white mica-bearing DFDP-1A blue gouge, 90.62 m sample depth, is frictionally strong (friction coefficient, μ, 0.61-0.76) across all experimental conditions tested (T = 70-350°C, σn′ = 31.2-156 MPa); it undergoes a transition from positive to negative rate dependence as T increases past 210°C. The friction coefficient of smectite-bearing DFDP-1B brown gouge, 128.42 m sample depth, increases from 0.49 to 0.74 with increasing temperature and pressure (T = 70-210°C, σn′ = 31.2-93.6 MPa); the positive to negative rate dependence transition occurs as T increases past 140°C. These measurements indicate that, in the absence of elevated pore fluid pressures, DFDP-1 gouges are frictionally strong under conditions representative of the seismogenic crust.

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