Pascal Audet

Pascal Audet
University of Ottawa · Department of Earth Sciences

PhD

About

96
Publications
12,767
Reads
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2,559
Citations
Additional affiliations
September 2011 - present
University of Ottawa
Position
  • Professor (Assistant)
October 2008 - August 2011
University of California, Berkeley
Position
  • Miller Research Fellow

Publications

Publications (96)
Article
Full-text available
The Mackenzie Mountains (MM) of northwest Canada are an actively uplifting, seismogenic salient of the northern Canadian Cordillera that lie 750 km NE of the main Pacific-North America plate boundary. We present new shear wave splitting measurements from a linear array transecting the region to characterize upper mantle anisotropy and the relative...
Article
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The Hikurangi subduction zone (HSZ) is the collisional boundary between the Pacific and Australian tectonic plates along the eastern coast of the North Island of New Zealand. The region is believed to be capable of hosting large megathrust earthquakes and associated tsunamis. Recent studies observe a range of slip behavior along the plate interface...
Article
Several seismic techniques, both passive and active, exist for estimating the shear-wave velocity (Formula presented.) structure of shallow sedimentary structures. In particular, passive compliance signals recorded by broadband ocean-bottom seismometers (OBSs) can be used to invert for (Formula presented.) structure. While compliance-based imaging...
Article
Measurements of various physical properties of oceanic sediment and crustal structures provide insight into a number of geologic and geophysical processes. In particular, knowledge of the shear-wave velocity (VS) structure of marine sediments and oceanic crust has wide ranging implications from geotechnical engineering projects to seismic mantle to...
Article
Full-text available
We measure fundamental-mode Rayleigh-wave group velocity dispersion from regional earthquakes and employ transdimensional Bayesian tomography to invert for azimuthally anisotropic group velocity maps at 10 – 60 s periods. Seismic azimuthal anisotropy within the crust and uppermost mantle shows fast-axis alignment with principal northern Canadian Co...
Article
Full-text available
Plain Language Summary Geological exploration and sampling in the Arctic Ocean are difficult due to sea ice cover and frigid weather. Gravity and bathymetry data obtained using remote sensing methods can be used to estimate the effective elastic thickness (Te) of the lithosphere, which is a proxy for the strength of the tectonic plates. We draw a n...
Article
Full-text available
The effective elastic thickness (T_e) of the lithosphere is a proxy for mechanical strength and can be used to constrain lithospheric rheology and understand how surface deformation relates to deep Earth processes. Here we map T_e variations over the Pacific Ocean from the inversion of the admittance between free-air gravity anomaly and bathymetry...
Article
Surface wave tomography is a valuable tool for constraining azimuthal anisotropy at regional scales. However, sparse and uneven coverage of dispersion measurements make meaningful uncertainty estimation challenging, especially when applying subjective model regularization. This paper considers azimuthal anisotropy constrained by measurements of sur...
Article
Full-text available
The past several decades have seen an exponential increase in the volume of available seismic data, and with it has come the need to develop fast, automatic earthquake detection, and location algorithms. Some of the most recent and promising tools come from the field of machine learning. In this study, we combine a recent seismic detection and loca...
Article
Full-text available
Moho morphology in orogens provides important constraints on the rheology and density structure of the crust and underlying mantle. Previous studies of Moho geometry in the northern Canadian Cordillera (NCC) using very sparse seismic data have indicated a flat and shallow (∼30–35 km) Moho, despite an average elevation of >1000 m above sea level att...
Article
The northern Canadian Cordillera (NCC) of northwestern Canada is segmented by several margin-parallel, right-lateral, strike-slip faults that accumulated several hundred kilometers of displacement between the Late Cretaceous and the Eocene. The depth extent of these faults, notably the Tintina fault (TF), has important implications for the tectonic...
Article
The effective elastic thickness (Te) of the lithosphere reflects the long-term flexural strength and provides mechanical information about the evolution and deformation of the lithosphere. The Chinese mainland and its surroundings (CMS) comprise sharply contrasting tectonic domains and involve a complex evolution history. In this paper, we apply a...
Article
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The Northern Canadian Cordillera (NCC) is an actively deforming orogenic belt in northwestern Canada. Geochemical and geophysical data show that the NCC is underlain by a thin and hot lithosphere, in contrast with the adjacent cold and thick cratonic lithosphere to the east. This juxtaposition of cold/hot and thick/thin lithosphere across a narrow...
Article
Full-text available
Fault slip behavior during episodic tremor and slow slip (ETS) events, which occur at the deep extension of subduction zone megathrust faults, is believed to be related to cyclic fluid processes that necessitate fluctuations in pore-fluid pressures. In most subduction zones, a layer of anomalously low seismic wave velocities [low-velocity layer (LV...
Article
The maximum depth of magnetization in the Earth’s crust is generally thought to coincide with the Curie temperature of magnetite (580 °C) and is commonly called the Curie depth. A popular approach to estimating the Curie depth is based on comparing the power-spectral density (PSD) of total-field magnetic anomaly data with theoretical expressions th...
Article
Full-text available
The origin of the North American Cordillera and its affinity with the bounding craton are subjects of contentious debate. The mechanisms of orogenesis are rooted in two competing hypotheses known as the accretionary and collisional models. The former model attributes the Cordillera to an archetypal accretionary orogen comprising a collage of exotic...
Article
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In western Canada, geophysical studies infer an abrupt change in crustal temperatures between the Canadian Cordillera and the adjacent North American craton, with important implications for the tectonics and geodynamics of the area. We use a wavelet analysis of magnetic anomaly data in western Canada to map the depth to the bottom of the magnetic s...
Article
Full-text available
Geophysical and geological data indicate that the lithosphere in the northern Canadian Cordillera (NCC) is thin and hot. However, lack of direct constraints on mantle structure is fueling debates on the origin and nature of this lithosphere. Here we image the crust and uppermost mantle beneath the NCC and resolve the Moho at ~35-km depth, the litho...
Article
Cratons are, by definition, the most tectonically stable and oldest parts of the continental lithosphere on Earth. The Archean Slave craton is located in the northwestern part of the Canadian Shield. The propensity of diamondiferous kimberlite pipes in the Central Slave Craton raises many questions regarding their structural environment and source....
Article
Full-text available
EON-ROSE (Earth-System Observing Network-Réseau d’Observation du Système terrestrE) is a new initiative for a pan-Canadian research collaboration to holistically examine Earth systems from the ionosphere into the core. The Canadian Cordillera Array (CC Array) is the pilot phase, and will extend across the Cordillera from the Beaufort Sea to the U.S...
Article
The effective elastic thickness (Te) of the lithosphere provides geophysical information about long-term flexural strength and can be used to constrain thermorheological properties of the lithosphere. Te is typically calculated from the spectral analysis of gravity and topography data; variations in Te are, however, not well resolved in Greenland d...
Article
Full-text available
On 16 July 2014, two moderate earthquakes with similar bodywave magnitude (MB 4.5 and 4.6) and epicentral location occurred within 9 min in the northern Canadian Cordillera (NCC), northwestern Canada. Based on magnitude and waveform similarity, cataloged location, and timing, we refer to them as double earthquakes. In this study, we report their so...
Article
Full-text available
The Beaufort Sea seismic cluster in the western Canadian Arctic is an active seismic zone characterized by approximately one magnitude = 4 intraplate earthquake per year. Determining the tectonic source of seismicity requires accurate hypocenter information, which is severely hampered by the scarcity of the regional and global seismograph networks...
Article
Full-text available
At subduction zones, the deep seismogenic transition from a frictionally locked to steady sliding interface is thought to primarily reflect changes in rheology and fluid pressure and is generally located offshore. The development of fluid pressures within a seismic low-velocity layer (LVL) remains poorly constrained due to the scarcity of dense, co...
Article
The seismic structure and fabric of the lithosphere and underlying mantle beneath the northern Canadian Cordillera provides important constraints on its evolution and current tectonics; however, it is poorly characterized due to historically sparse networks of seismic instruments. We use data from past and recently deployed networks of broadband se...
Article
Studies on the recovery and processing of surface waves from ambient-noise interferometry are now standard practice in seismology. It has recently been shown that body waves propagating within an array of seismic stations can be recovered under appropriate conditions. In this article, we investigate and develop optimal data processing procedures ne...
Article
Full-text available
On 16 July 2014, two moderate earthquakes with similar bodywave magnitude (MB 4.5 and 4.6) and epicentral location occurred within 9 min in the northern Canadian Cordillera (NCC), northwestern Canada. Based on magnitude and waveform similarity, cataloged location, and timing, we refer to them as double earthquakes. In this study, we report their so...
Article
Full-text available
In passive source seismology, seismic interferometry typically refers to the cross correlation of ambient noise to construct an estimate of the Green's function between sensors. The presence of persistent natural and/or anthropogenic sources can bias or prevent the retrieval of these estimated Green's functions. Here we show how these strong persis...
Article
Full-text available
A new method using a machine learning technique is applied to event classification anddetection at seismic networks. This method is applicable to a variety of network sizes andsettings. The algorithm makes use of a small catalogue of known observations across theentire network. Two attributes, the polarization and frequency content, are used as inp...
Article
Full-text available
The northern Canadian Cordillera (NCC) is an active orogenic belt in northwestern Canada characterized by deformed autochtonous and allochtonous structures that were emplaced in successive episodes of convergence since the Late Cretaceous. Seismicity and crustal deformation are concentrated along corridors located far (>200 to ~800 km) from the con...
Article
In active underground mining environments, monitoring of the rockmass has important implications for both safety and productivity. Monitoring can be accomplished by exploiting the many passive seismic sources (microearthquakes, drilling, ore-crushers etc.) around the mine on the condition they can be accurately detected and located. We implement a...
Presentation
This presentation was intended to present the concept of the Canadian Cordillera Array to the Canadian Tectonics community.
Article
Full-text available
Models of the seismic velocity structure of the crust in the seismically active northern Canadian Cordillera remain poorly constrained, despite their importance in the accurate location and characterization of regional earthquakes. On 29 August 2014, a moderate earthquake with magnitude 5.0, which generated high-quality Rayleigh wave data, occurred...
Article
Lithospheric inheritance is thought to affect the location and reactivation of tectonic structures through successive cycles of supercontinent formation and dispersal; however, its relation to neotectonic activity remains unclear. In northwestern Canada, abundant seismicity throughout the northern Canadian Cordillera (NCC) is geographically confine...
Article
Seismic anisotropy data are often used to resolve rock textures and deformation in the crust based on compilations of rock properties that may not be representative of the local geology. In this paper, we use teleseismic receiver functions jointly with in situ rock property data to constrain the seismic structure and anisotropy of the crust in the...
Article
The expanding fleet of broad-band ocean-bottom seismograph (OBS) stations is facilitating the study of the structure and seismicity of oceanic plates at regional scales. For continental studies, an important tool to characterize continental crust and mantle structure is the analysis of teleseismic P receiver functions. In the oceans, however, recei...
Article
More than a decade after the discovery of deep episodic slow slip and tremor, or slow earthquakes, at subduction zones, much research has been carried out to investigate the structural and seismic properties of the environment in which they occur. Slow earthquakes generally occur on the megathrust fault some distance downdip of the great earthquake...
Article
We use seismic waveform data from the Mendocino Experiment to detect low-frequency earthquakes (LFEs) beneath Northern California during the April 2008 tremor-and-slip episode. In southern Cascadia, 59 templates were generated using iterative network cross correlation and stacking and grouped into 34 distinct LFE families. The main front of tremor...
Article
The rheology of the Earth's crust controls the long-term and short-term strength and stability of plate boundary faults and depends on the architecture and physical properties of crustal materials. In this paper we examine the seismic structure and anisotropy of the crust around the San Andreas Fault (SAF) near Parkfield, California, using teleseis...
Article
The crystallographic preferred orientations (CPOs) were measured on a suite of samples representative of different structural depths along the West Cycladic Detachment System, Greece. Electron backscatter diffraction (EBSD) analyses were conducted on calcitic and mica schists, impure quartzites, and a blueschist, and the average seismic properties...
Article
We apply phase-weighted stacking (PWS) to the analysis of low-frequency earthquakes (LFEs) in the Parkfield, California, region and central Cascadia. The technique uses the coherence of the instantaneous phase among the stacked signals to enhance the signal-to-noise ratio (SNR) of the stack. We find that for picking LFE arrivals for the Parkfield,...
Article
Tectonic plate reorganization at a subduction zone edge is a fundamental process that controls oceanic plate fragmentation and capture. However, the various factors responsible for these processes remain elusive. We characterize seismic anisotropy of the upper mantle in the Explorer region at the northern limit of the Cascadia subduction zone from...
Article
Seismic and geodetic observations in subduction zone forearcs indicate that slow earthquakes, including episodic tremor and slip, recur at intervals of less than six months to more than two years. In Cascadia, slow slip is segmented along strike and tremor data show a gradation from large, infrequent slip episodes to small, frequent slip events wit...
Article
Groundwater use in California's San Joaquin Valley exceeds replenishment of the aquifer, leading to substantial diminution of this resource and rapid subsidence of the valley floor. The volume of groundwater lost over the past century and a half also represents a substantial reduction in mass and a large-scale unburdening of the lithosphere, with s...
Article
On 17 May 2013 at 1343 hours UTC, a magnitude m N = 5.2 earthquake occurred ∼4 km from the town of Ladysmith, Quebec, within the Western Quebec Seismic Zone (WQSZ). This event produced limited damage but represents the largest earthquake to occur along the southwest margin of the WQSZ since 1935, and provides important seismotectonic constraints of...
Article
Full-text available
Subduction zones can exhibit variable seismic behaviour, ranging from great earthquakes to slow slip. This variability may be linked to fault frictional properties, and the rheology and structure of the upper plate. The subduction zone beneath the Nicoya Peninsula, Costa Rica, is characterized by strong variations in fault-slip behaviour and a late...
Article
Full-text available
Identifying the sources of seismic anisotropy in subduction zone forearcs is key to understanding mantle deformation processes. Current models based on the interpretation of shear-wave splitting measurements favor the flow-induced alignment of olivine crystals around down-going slabs or the presence of foliated serpentine minerals due to subduction...
Article
The effective elastic thickness (Te)(Te) of the lithosphere controls the flexural response to transverse loading and can be used in conjunction with rheological models to remotely estimate surface heat flux of terrestrial planets. In the vast majority of studies, TeTe estimation is carried out in a two-step process: (1) the joint spectra (admittanc...
Article
Following the release of global continental effective elastic thickness (Te) maps obtained using different approaches, we now have the opportunity to provide better constraints on Te. We improve previous estimates of Te derived from thermo-rheological models of lithospheric strength (or Ter) using new equations that consider variations of the Young...
Article
We characterize lithospheric structure of the Moon from an inversion of gravity and topography data, and infer global heat flow distribution based on estimated effective elastic thickness (Te). Lithospheric parameters are estimated by comparing observed complex admittance and correlation spectra between gravity and topography calculated with a sphe...
Presentation
There is growing evidence that subducting oceanic crust is associated with a seismic low-velocity zone, with seismic properties varying downdip reflecting prograde metamorphic and dehydration reactions within the crust. In Cascadia, the downdip change in reflectivity of the slab delimits the basalt to eclogite reaction, where water is released into...
Article
In the Cascadia subduction zone, beneath southern Vancouver Island at 25-45 km depth, converted teleseismic waves reveal an similar to 5-km-thick landward-dipping layer with anomalously high Vp/Vs averaging 2.35 +/- 0.10 (2 sigma), interpreted as subducted oceanic crust of the Juan de Fuca plate. This layer is observed downdip of the inferred locke...
Article
We investigate relationships between deep moonquake source regions and lithospheric and crustal structure from a wavelet analysis of gravity and topography.
Article
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An approach integrating different data sets has been used to map out seismic-velocity ratios in the crust of western North America. High inferred quartz content correlates with tectonic deformation zones. See Letter p.353
Article
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Supercontinents episodically assemble and break up, in association with the closure and opening of ocean basins. During these cycles, continental margins are repeatedly weakened and deformed during subduction, orogeny and rifting, whereas continental cores tend to remain intact. It has therefore been suggested that deformation during supercontinent...
Article
Full-text available
The spectral relations (admittance and correlation) between gravity and topography are often used to obtain information on the density structure, flexural support, and heat flow of planetary lithospheres. Mapping spatial variations in these quantities requires spatiospectral analysis techniques. Here we describe the application of a directional, co...
Presentation
The spectral relations (admittance and correlation) between gravity and topography are often used to obtain information on the density structure, flexural support and heat flow of planetary lithospheres. Mapping spatial variations in these quantities requires spatio-spectral analysis techniques. Here we describe the application of a fully direction...
Presentation
The Wilson cycle of ocean basin closure and opening, leading to supercontinent assembly and breakup, implies that continental margins are repeatedly weakened by thermal rejuvenation and fault reactivation during subduction, orogeny and rifting, leaving continental cores un-deformed. Such partitioning of deformation has led to the hypothesis of tect...
Article
Full-text available
Episodic tremor and slip (ETS) events in subduction zones occur in the general vicinity of the plate boundary, downdip of the locked zone. In developing an understanding of the ETS phenomenon it is important to relate the spatial occurrence of nonvolcanic tremor to the principal structural elements within the subduction complex. In Cascadia, active...
Article
We investigate temporal variations in teleseismic receiver functions using 11 yr of data at station PKD near Parkfield, California, by stacking power spectral density (PSD) functions within 12-month windows. We find that PSD levels for both radial and transverse components drop by similar to 5 dB following the 2003 San Simeon (M 6.5) earthquake, wi...
Article
The strength and seismogenic behavior of subduction zone plate boundaries depend critically on pore fluid pressure. Integrated over time, large amounts of H2O are released from subducting plates by tectonic compaction at shallow depths and by metamorphic dehydration reactions at deeper depths. In the Cascadia subduction zone, beneath southern Vanco...
Article
As USArray continues its progression across the United States it leaves in its wake a swath of images providing snapshots of the crust, lithosphere, asthenosphere and deeper mantle. Efforts to constrain the structure at these multiple scales have used a variety of seismic techniques to target specific depth ranges or regions. There are some signifi...
Article
The past decade has witnessed the deployment of large numbers of broadband seismometers along the Cascadia forearc. A high density of sampling has permitted the mapping of subduction zone structure along and across strike using scattered teleseismic body waves. Forearc structural signatures across profiles sampling central Oregon, Puget Sound, and...