Pascal Audet

• PhD
• Professor at University of Ottawa

The composition and structure of the mantle wedge corner (MWC) exert a primary control on seismogenic and fluid processes in subduction zone forearcs. Seismic evidence suggests widespread serpentinization of the MWC in Cascadia, but constraints on its internal structure and fabrics remain sparse. Here, we compile receiver function data for a line o...

The Canadian Cordillera is characterized by higher mean elevation and thinner crust compared to the adjacent craton to the east, in apparent contradiction with the Airy isostatic model. Roy Hyndman hypothesized that the high Cordillera elevations may be supported by an overall hot, low-density Cordilleran backarc mantle, but this idea has not been...

Geologically, the Arctic is one of the least-explored regions of Earth. Obtaining data in the high Arctic is logistically, economically, and environmentally expensive, but the township of Longyearbyen (population of 2617 as of 2024) at 78° N represents a relatively easily accessible gateway to Arctic geology and is home to The University Centre in...

Slow-slip events at global subduction zones relieve tectonic stress over days to years. Through slow-slip cycles, high fluid pressures observed at the top of subducting plates are thought to fluctuate, potentially due to the valving action of an impermeable layer near the plate interface. We model teleseismic scattering data at the Manawatu deep sl...

The Canadian Cordillera marks a transition region from the current plate boundary through the Phanerozoic Cordilleran orogen to the Precambrian cratons. Knowledge of the subsurface structure of western Canada has been greatly advanced by seismological investigations during the past two decades, pioneered by the Lithoprobe project and, more recently...

Seismic velocity models provide important constraints on Greenland’s deep structure, which, in turn, has profound implications for our understanding of the tectonic history of this region. However, the resolution of seismic models has been limited by a sparse network, particularly in northern and central Greenland. We address these limitations by g...

Geologically, the Arctic is one of the least explored regions of Earth. Its significance, in terms of indigenous populations, resource extraction, tourism, shipping and a rapidly changing climate, is increasing. The Arctic offers geological diversity encompassing onshore and offshore environments, include active subduction zones in Alaska, deep sed...

Slow slip events (SSEs) at subduction zones relieve tectonic stress over periods ranging from days to years. A pervasive feature in SSE regions worldwide is the presence of high fluid pressures in the subducting slab, which are thought to fluctuate during SSEs through the fault-valving action of an impermeable layer at the plate interface. Yet, geo...

We map the characteristic signature of the subducting Juan de Fuca and Gorda plates along the entire Cascadia forearc from northern Vancouver Island, Canada, to Cape Mendocino in northern California, USA, using teleseismic receiver functions. The subducting oceanic crustal complex, possibly including subcreted material, is parameterized by three ho...

We map the characteristic signature of the subducting Juan de Fuca and Gorda plates along the entire Cascadia forearc from northern Vancouver Island, Canada to Cape Mendocino in northern California, USA, using teleseismic receiver functions. The subducting oceanic crustal complex, possibly including subcreted material, is characterized by three hor...

The recent deployment of temporary broadband seismic networks, notably the EarthScope USArray-Transportable Array (TA), has drastically improved the station coverage across northwestern Canada over the last ten years, enabling application of high-resolution passive-source seismic methods (i.e., seismic tomography, receiver functions and core phase...

Temporal changes in seismic velocities are an important tool for tracking structural changes within the crust during transient deformation. While many geophysical processes span the crust, including volcanic unrest and large-magnitude earthquakes, existing methods for seismic monitoring are limited to the shallow subsurface. We present an approach...

Our understanding of the present‐day state and evolution of the Canadian and Alaskan mantle is hindered by a lack of absolute P‐wavespeed constraints that provide complementary sensitivity to composition in conjunction with existing S‐wavespeed models. Consequently, cratonic modification, orogenic history of western North America and complexities w...

This article introduces PyRaysum, a Python software for modeling ray-theoretical body-wave propagation in dipping and/or anisotropic layered media based on the popular Fortran code Raysum. We improve and expand upon Raysum in several ways: 1) we significantly reduce the overhead by avoiding I/O operations; 2) we implement automatic phase labeling t...

This article introduces PyRaysum, a Python software for modeling ray-theoretical body-wave propagation in dipping and/or anisotropic layered media based on the popular Fortran code Raysum. We improve and expand upon Raysum in several ways: 1) we significantly reduce the overhead by avoiding input/output operations; 2) we implement automatic phase l...

The Mackenzie Mountains (MMs) in the Yukon and Northwest Territories, Canada, are an enigmatic mountain range. They are currently uplifting (Leonard et al., 2008, https//doi.org/10.1029/2007JB005456), yet are about 700 km from the nearest plate boundary. Their arcuate shape is distinct and extends over 100 km eastward from the general trend of the...

Periodic directional and temporal measurements are common in seismology, and necessitate specific statistical analyses that are appropriate for circular quantities. In this work, we explore the use of a von Mises distribution as a representation of errors on circular seismological observations. Specifically, we automate the estimation of surface-wa...

Coastal British Columbia (BC), Canada, has the highest seismic hazard in the country due to convergent and transpressive deformation at offshore plate boundaries between the Pacific, Juan de Fuca (JdF) and North American (NA) plates. Further landward, the crust of the NA plate is made up of several geologically unique exotic terranes and is unusual...

The tectonics of southwestern Canada are dominated by the Cascadia subduction zone. The northern Cascadia backarc encompasses a > 400 km wide region of the Southern Canadian Cordillera. Geophysical observations, including seismic tomography and surface heat flow, show that the backarc is characterized by a hot, thin lithosphere (60–70 km). The east...

Slow slip events are observed in subduction zones globally, with a wide range of variations in behaviour, including the periodicity and magnitude of events. These variations are observed both within and across different subduction zones. Due to their role in controlling strain accumulation and potential nucleation of regular earthquakes, understand...

Plain Language Summary The Canadian Beaufort Sea continental margin (BSCM) of northwestern Canada may represent a unique location in the world where we observe a newly forming convergent margin, potentially representing a rare case of incipient subduction. We develop 3‐D seismic velocity models of the region from the crust to the uppermost mantle u...

The Canadian Beaufort Sea continental margin of northwestern Canada is a Cenozoic convergent margin, potentially representing a rare case of incipient subduction. Here, we produce P- and S-wave seismic velocity models of the crust and the uppermost mantle using recordings from regional earthquakes. Our models reveal a northwest-dipping very low-vel...

The production and preparation of data sets are essential steps in machine learning (ML) applications. With the increasing volume and scale of available ML techniques in seismology, annotating seismograms or seismic features has become time consuming and tedious for many researchers. Furthermore, most methods train and validate on unique data subse...

Accurate knowledge of Earth structure in Greenland and eastern Canada is important because both glacial isostatic adjustment and Greenland ice sheet evolution are dependent on this structure. Understanding how the ice sheet has responded to past climate change and our ability to accurately predict its future evolution for a given climate change dep...

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...

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...

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...

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 Cord...

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...

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...

The effective elastic thickness (Te) 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 Te variations over the Pacific Ocean from the inversion of the admittance between free‐air gravity anomaly and bathymetry d...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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....

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

This presentation was intended to present the concept of the Canadian Cordillera Array to the Canadian Tectonics community.

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...

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...

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...

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...

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...

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...

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...

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...

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,...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

We investigate relationships between deep moonquake source regions and lithospheric and crustal structure from a wavelet analysis of gravity and topography.

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

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...

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...