Seminar Schedule
Calendar
Date
Feb 10
Alexis Cartwright-Taylor (Univ. of Edinburgh)
The how and when of catastrophic failure: insights from 4D in-situ x-ray microtomography with acoustic emissions
Localisation of structural damage (faults and fractures) along a distinct and emergent fault plane is the key driving mechanism for catastrophic failure in the brittle Earth. However, due to the speed at which stable crack growth transitions to dynamic rupture, the precise mechanisms involved in localisation as a pathway to fault formation remain unknown. Understanding these mechanisms is critical to understanding and forecasting earthquakes, including induced seismicity, landslides and volcanic eruptions, as well as failure of man-made materials and structures. We used time-resolved synchrotron x-ray microtomography to image in situ damage localisation and shear band formation at the micron scale. Furthermore, by controlling the rate of micro-fracturing events during a triaxial deformation experiment, we deliberately slowed the strain localisation process from seconds to minutes as failure approached, achieving bulk axial strain rates down to 10-7 s-1. This approach has enabled us to image directly processes that are normally too transient even for fast synchrotron imaging methods. Here, I present recently published results demonstrating the influence of material starting heterogeneity on damage localisation and the predictability of failure, as well as brand new results showing the micromechanics of quasi-static shear band formation in unprecedented detail.
Feb 17
Elvira Mulyukova (Yale University)
A dislocation and a grain boundary walk into a bar
Deformation at tectonic plate boundaries is governed by the mechanical properties of crustal and lithospheric rocks, which evolve through changes in the microstructure of their constituent minerals. Geological observations of microstructure can, therefore, provide measures of the rock's deformation conditions through various piezometers (e.g., the relationship between stress and grain size or dislocation density). However, grain size and dislocation density do not evolve independently, and thus their associated piezometers are unlikely to be decoupled. We present a new theoretical model coupling the evolution of grain boundaries and dislocations in a deforming rock and make a novel prediction that the equilibrium dislocation density at a given stress (the dislocation piezometer) can be non-unique, with co-existing deformation states or piezometric branches. One stable piezometric branch exists at high stress and large grain-size, for which the steady state dislocation density is large and dictated by stress, in agreement with experimental observations and earlier theoretical models. However, another stable branch exists at low stress and small grain-size, in which case dislocation density is small, weakly stress-dependent, and is governed by the balance between dislocation sinks and sources at grain boundaries. The contrast in dislocation density between grains of different sizes induces grain boundary migration from smaller grains into larger grains. Dislocation-induced grain boundary forces thus act in the opposite direction to those dictated by surface energy, for which grain boundaries migrate from larger grains into smaller ones. When forces due to surface and dislocation energies are balanced, the system reaches a stable microstructural equilibrium, thereby halting grain growth and helping preserve plate boundary weakness. When the forces are not in balance, unstable and oscillatory behavior can ensue, with oscillation periods on the order of decades. Finally, the new theory provides a microphysical model for transient rheological behavior, which is particularly relevant to tectonic activity in which deformation is relatively rapid and where the steady state flow laws are a poor approximation, such as during postseismic relaxation or postglacial rebound.
Feb 24
Yiduo Liu (Univ. of Houston)
Emeishan Large Igneous Province: Magma Storage System, Hidden Hotspot Track, and the Unusual Timing of the Capitanian Mass Extinction
Large igneous provinces (LIPs) are often associated with mass extinctions and are vital for life evolution on Earth. However, the precise relation between LIPs and their impacts on biodiversity is enigmatic as they can be asynchronous. If the environmental impacts are primarily related to sill emplacement, the structure of LIPs’ magma storage system becomes critical as it dictates the occurrence and timing of mass extinction. Here we use surface wave tomography to image the lithosphere under the Permian Emeishan Large Igneous Province (ELIP) in SW China. We find a NE-trending zone of high shear-wave velocity (Vs) and negative radial anisotropy (Vsv > Vsh) in the crust and lithosphere and interpret it as a mafic-ultramafic, dike-dominated magma storage system on the hidden hotspot track of the ELIP. An area of less-negative radial anisotropy, on the hotspot track but away from the eruption center, reflects an elevated proportion of sills emplaced at the incipient stage of the ELIP. Liberation of poisonous gases and mercury by the sills explains why the mid-Capitanian global biota crisis preceded the peak ELIP eruption by 2-3 million years.
March 3
Cailey Condit (Univ. of Washington)
Slow Earthquakes in Subduction Zones: Constraints from the Geologic, Petrologic, and Constituent Realms
Subduction zones host destructive megathrust earthquakes, one of the deadliest natural hazards on earth. Some subduction zones experience the recently recognized set of slip behaviors: episodic tremor and slow slip. These slow earthquakes may ultimately trigger megathrust events and play a key role in the slip budget of some subduction zones. However, we currently do not have a mechanistic understanding of how they occur. In this talk, I will show observations from the exhumed rock record, petrologic modeling, and analysis of constitutive relations to offer new constraints on the mechanisms of slow earthquakes. These results demonstrate the importance of frictional deformation made possible by elevated pore fluid pressures, and the role of metamorphic dehydration in supplying these fluids.
March 10
Alana Hinchey (Geological Survey of Newfoundland and Labrador)
Regional Bedrock Mapping: Implications on Tectonic Models
Although essential research elements and core field skill requirements have not changed, there have been some fundamental changes in the field of bedrock mapping over the last 20 years. A complex, multidisciplinary approach is required to unravel the evolution of complex tectonic regimes. We need to apply a full suite of analytical techniques to a map area, such as field mapping, structural analysis, lithogeochemistry, isotope geochemisty, petrography, and geochronology in order to decipher its lithological, structural, and metamorphic history. These changes have important implications on how we interpret the geology around us.
Examples from the Makkovik Province, Canada, are used to illustrate the implications and limitations of regional bedrock mapping on how tectonic models are created. With the advent of digital data capture systems and portable tablets the way data are collected, integrated and published have changed. These advances in technology allow the full integration of GIS into bedrock mapping. We now utilize digital geologic mapping to improve our field efficiency and problem solving capabilities. Basic digital mapping is just the beginning of new and evolving capabilities with true 3D mapping (i.e. mapping through a 3D interface as opposed to building a 3D model post field mapping). The integration of these new technologies into digital field workflows and 3D visualizations is transforming the practice of bedrock mapping by making it more accessible and visually realistic.
March 17
Amir Salaree (University of Michigan)
The curious case of unexpected tsunamis: A quest in nonlinearity
Tsunamis are typically modeled as energy propagation from finite underwater sources. Physical/Seismological assumptions such as geometrical spreading and attenuation usually improve our understanding of tsunami hazard via numerical simulations. However, such assumptions do not apply to “non-optical” features which would only be explained using nonlinear aspects of wave propagation. This caveat usually manifests itself in the form of “unexplained” or unexpected waves in tsunami studies.
A few interesting examples of such behavior are coseismic excitation of tsunamis by megathrust events on the other side of continents (e.g., tsunamis in the Sea of Japan and Gulf of Mexico from 2011 Tohoku and 2020 Oaxaca earthquakes, respectively), large tsunami amplitudes created by curved shorelines (e.g., higher tsunami hazard in central Cascadia), and ‘leakage’ of tsunami waves through narrow openings (e.g., propagation of Makran tsunamis into the Persian Gulf). Careful study of hydrodynamic tsunami simulations in such cases and efforts to improve the modeling of these phenomena can help us better understand the nonlinear nature of the physics behind the excitation and propagation of tsunamis.
March 24
CANCELLED
Min Chen (Michigan State University)
The Nature of Deep Earthquakes in the Western Pacific Subduction Zones
The nature of deep earthquakes has long been controversial because the source region is subjected to high pressures and temperatures that should inhibit the brittle failure necessary to generate seismic waves. Several mechanisms that may promote seismic deformation below 300 km depth include dehydration embrittlement, phase transformational faulting, and thermal runaway instabilities. The most referenced mechanism, phase transformational faulting, involves the breakdown of metastable olivine within the core of a cold subducting slab. In this talk, I will present our latest findings with full waveform modeling and inversion and b-value analysis of the deep earthquakes in Western Japan Subduction Zones. The nature of deep earthquakes will be inferred based on the following new observations, improved seismological definition of slab structure, the spatial relationships between deep slab interfaces and seismicity, and the mineralogical, stress, thermal properties of the slab that may control deep earthquake genesis.
March 31
Jessica Irving (University of Bristol)
Seismic impressions of Earth’s dynamic outer core
Thousands of kilometres beneath our feet, Earth's iron-rich fluid outer core was detected more than a century ago, but still hides many secrets. The outer core is slowly being consumed by the growing inner core as Earth ages and cools. Though it is vigorously convecting, generating Earth’s geodynamo, there may be compositional variations in the outer core which have implications for our understanding of its nature. In many ways, the core represents a giant experiment in the properties and processes of materials at high temperature and pressure, but one which we cannot control. Instead we can use different seismic techniques to probe the deepest fluid region of our planet. In this seminar I will present high-frequency body wave and low-frequency normal mode investigations into the outer core, and link seismological findings to our understanding of the composition and evolution of our planet’s deep interior.
April 7
Attreyee Ghosh (Indian Institute of Science)
The Curious Case of the Earth's Largest Gravity Low
If one looks at the gravity anomaly map of the Earth, what stands out is the circular "hole" that lies in the northern Indian Ocean, just south of the Indian peninsula. Measuring about 100 meters deep, this is the largest negative gravity/geoid anomaly on Earth. Various studies have attempted to explain this negative geoid anomaly mostly by invoking past subduction. Other studies have suggested that subducted slabs in the lower mantle coupled with hot, buoyant, low-velocity anomalies in the upper mantle are responsible for this geoid low. However, there is still no consensus regarding the source of the Indian Ocean geoid low and how it originated in the first place. In this talk I will show how we can explain the presence of this anomaly with the help of low-density material in the mid-to-upper mantle depths. This low density anomaly most likely originated from a plume rising along the edge of the African Large Low Shear Velocity Province (LLSVP).
April 14
Walid Ben Mansour (Washington University in St. Louis)
Thermochemical structure beneath Gondwana terranes from multi-observables probabilistic inversion
Knowledge of the present-day thermochemical structure (temperature and bulk composition) of the lithosphere and sub-lithospheric upper mantle is important for exploration workflows, understanding the evolution of topography, interpreting geophysical anomalies, and for deciphering the physicochemical interactions between the lithosphere and the underlying convecting mantle. In this presentation, we will show and discuss the latest results of a Multi-observable Thermochemical Tomography (MTT) beneath several cratonic domains. We will also discuss the benefits and limitations of this approach and also important implication on current cratonic mantle evolution.
April 21
Margarete Jadamec (State University of New York at Buffalo)
Slab Driven Lithosphere-Asthenosphere Decoupling in Subduction Zones
The coupling of lithospheric plates to the asthenosphere plays a major role in the process of plate tectonics. However, the nature of this coupling, in terms of asthenospheric viscosity magnitude, spatial variability in viscosity, as well as what drives that variability in space and time, remain outstanding questions in geodynamics. Two-dimensional and three-dimensional numerical simulations of subduction are presented to shed light on this process. Specifically, the models examine the effect of slab geometry, non-linear mantle rheology, and plate interface properties on predicted flow velocities and dynamically emergent asthenospheric viscosity. In addition, this seminar will address how frameworks from the computational fluid dynamics community can facilitate digital scholarship and online learning.
April 28
Samer Naif (Georgia Institute of Technology)
A long-lived melt channel of Galápagos plume origin at the base of the Cocos lithosphere
The Cocos Plate, located in the eastern equatorial Pacific Ocean, has long been a site of geoscience intrigue and discovery, having inspired several geophysical, geochemical, and seafloor drilling surveys over the last four decades. Here we focus on the portion of the Cocos Plate where a magnetotelluric (MT) survey imaged an electrically conductive channel at the lithosphere-asthenosphere boundary (LAB); the channel's high conductivity requires a partial melt interpretation. Yet the presence and mechanical stability of melts at the LAB is controversial and attracts healthy debate. This led us to wonder whether any seafloor evidence might exist to corroborate the melt channel inference from the MT data. To that end, we synthesized numerous datasets to piece together a 20-million-year saga of the Cocos Plate that indeed documents multiple episodes of intraplate volcanism. The results not only confirm the presence of the melt channel, but also indicate a water-rich melt composition consistent with a Galápagos plume source.
May 5
Marine Lasbleis (Université de Nantes)
Crystallization of planetary cores: insights from the Earth's inner core
The Earth is a peculiar planet in the solar system: it hosts life and possesses a very active interior. However, it is not the only rocky body to present evidence of internal dynamics: all the rocky planets - except Venus - and some moons have been shown to generate or to have generated a magnetic field.
The Earth's magnetic field is thought to be driven nowadays primarily by the crystallization of its most central part: the inner core. Understanding its structure and dynamics will provide a unique insight into the Earth's thermal, chemical and magnetic history.
In this talk, I will take you from the Earth's center to other planets in the solar system and beyond. I will present some of our results on the Earth's inner core that may help us understand planetary magnetic fields, and highlight topics where ones should be careful when using the Earth as a reference for other planets.
May 12
Simone Pilia (University of Cambridge)
Effects of subduction termination on the continental lithosphere - A geophysical extravaganza on northern Borneo
The fragment of continental lithosphere that is now northern Borneo bears the signature of diachronous opposed subduction systems that ceased in the late Miocene. Intriguingly, there are a number of surface features that cannot be explained by our current understanding of the subduction cycle. These features include the presence of Plio-Pleistocene OIB lavas, evidence of sudden subsidence and uplift, and peak exhumation rates of more than 7 mm/year from the latest Miocene to the Early Pliocene in Mt. Kinabalu, bringing the mountain to 4095 m height (towering over most peaks in southeast Asia). New results from the nBOSS (northern Borneo Orogeny Seismic Survey) experiment, coupled with geological observations and a new numerical simulation, provide an explanation to the surface evidence of post-subduction tectonics on the continental lithosphere.
May 19
Iris van Zelst (University of Leeds)
Modelling tsunamigenic earthquakes
Video
Earthquakes on large thrust faults in subduction zones can cause tsunamis with devastating consequences. Therefore, it is important to understand how these events nucleate, propagate, and generate tsunamis. In particular, a thorough understanding of the stress state of the relevant faults is necessary. As it is difficult to achieve this with the limited number of direct measurements of the conditions in subduction zones, many studies have attempted to use observations of earthquake and tsunami occurrence, or numerical modelling techniques to shed light on the tsunamigenic earthquake process. In this seminar, I present a modelling framework to study tsunamigenic earthquakes from the geodynamic subduction evolution and tectonic stress build-up to the dynamic earthquake rupture and propagation and inundation of the resulting tsunami. I apply this modelling framework to both megathrust and splay fault earthquakes and I show some examples of applying the 3D version of this modelling framework to a recent earthquake, such as the 2018 Palu, Sulawesi earthquake and tsunami. With this talk, I hope to convey how we can use complex modelling frameworks to study processes on different scales in an interdisciplinary manner and I hope to continue the discussion on tsunamigenic earthquakes in subduction zones with an interdisciplinary audience.
May 26
Anne Glerum (GFZ Helmholtz Centre Potsdam)
Continental rift interaction and the formation of rotating continental microplates
Similar to the microplates that form between overlapping mid-ocean ridges, rotating continental microplates can form between overlapping active continental rifts. In this talk, I will first discuss how the large Victoria microplate in the East African Rift System came to rotate counter-clockwise with respect to Africa, in striking contrast to its neighboring plates. Our numerical models indicate that the amount of Victoria's rotation is primarily controlled by the distribution of (i) stronger zones transmitting the drag of the major plates and (ii) weaker regions facilitating the rotation. The combination of this particular lithospheric strength distribution, the regional extension, and the oblique orientation of the preexisting weaknesses results in local predominantly normal faulting oblique to the regional and local extension directions. Second, I will present our investigations into the conditions for continental microplate formation, by modeling how approaching rift arms propagate and link from inception to continental break-up without pre-existing heterogeneities to guide them. How the rifts interact and connect depends on their offset and the crustal strength. The microplate-mode of interaction sheds light on the evolution of the Flemish cap and the Sao Paolo Plateau, regions along rifted margins interpreted as ancient continental microplates.
June 2
Katie Cooper (Washington State University)
Craton Stability: What’s Thickness (and shape) Got To Do With It
Cratons are long-lived regions on the Earth’s continents. They are the secret keepers of Earth’s history witnessing the planet’s tectonic progression without themselves experiencing active deformation. These regions could provide clues into the Earth’s evolution if we can understand what is driving their stability. One of the first-order observations of cratons is their thick lithosphere. Though discussions around craton stability primarily focus on buoyancy and rheology, thickness also plays a primary control on both the long-lived nature of stable cratons and the demise of destroyed cratons. In other words, craton stability is determined, in part, by the material properties of cratonic lithosphere, its thermal structure, and its relative strength in comparison to the material around it and the mantle below. The integrated strength of the cratonic lithosphere, which determines its relative stability, depends on its thickness. Correspondingly, the shape of a craton (or how its thickness varies over a lateral extent) should also play a role in its overall stability. In this talk, I will summarize the connections between craton thickness and (in)stability, the limits on craton thickness, and the consequences of long-lived, thick lithosphere. Finally, I will present new work demonstrating the stability of cratons also depends on their shape.
June 9
Susannah Dorfman (Michigan State University)
Deep Earth Redox: Iron and Carbon in the Lower Mantle
On a journey towards the center of the Earth, rock encounters not only higher pressures and temperatures, but also more reducing conditions; geodynamic cycling over Earth’s history has carried material from the reduced interior back up to the crust and atmosphere. A key constraint on redox chemistry taking place in the inaccessible deep mantle is experiments on redox-sensitive elements iron and carbon. I will review recent work on the host phases and speciation of Fe and C in the mantle, redox interactions between Fe and C, and how they change with depth. These experiments illuminate potential signatures of deep mantle chemistry that could be recorded e.g. in ultradeep diamonds and used for better understanding of the dynamics and evolution of our planet.
June 16
Min Chen (Michigan State University)
The Nature of Deep Earthquakes in the Western Pacific Subduction Zones
The nature of deep earthquakes has long been controversial because the source region is subjected to high pressures and temperatures that should inhibit the brittle failure necessary to generate seismic waves. Several mechanisms that may promote seismic deformation below 300 km depth include dehydration embrittlement, phase transformational faulting, and thermal runaway instabilities. The most referenced mechanism, phase transformational faulting, involves the breakdown of metastable olivine within the core of a cold subducting slab. In this talk, I will present our latest findings with full waveform modeling and inversion and b-value analysis of the deep earthquakes in Western Japan Subduction Zones. The nature of deep earthquakes will be inferred based on the following new observations, improved seismological definition of slab structure, the spatial relationships between deep slab interfaces and seismicity, and the mineralogical, stress, thermal properties of the slab that may control deep earthquake genesis.
June 23
Cancelled/Postponed
Zoë Mildon (University of Plymouth)
June 30
Ruijia Wang (University of New Mexico)
Complexity and Simplicity of Injection-induced earthquakes in the Raton Basin
Waste-water injection induced seismicity has been active in the Raton Basin for the past two decades, including several M>4.0 normal-faulting earthquakes. To characterize the injection-induced fault reactivation processes, we utilize the state-of-art techniques to automatically detect and locate the seismicity using two datasets: 1) 8 broadband stations available since 2016 with an averaged spacing of ~30 km and 2) 96 high-frequency nodal instruments that were deployed for one month in the southern section of the basin in the summer of 2018. The two catalogs with ~30,000 and ~10,000 earthquakes show consistent patterns: clustering into multiple fault systems ranging from N-S, NE-SW normal to oblique dip-slip regimes. Further focal mechanisms and finite fault analysis suggest high fault and stress heterogeneity in this injection setting. On the other hand, statistical behaviors of the clusters are generally comparable to tectonic sequences. The detailed fault structures and earthquake cycle statistics offer an observational base for future mechanical modeling and hazard mitigation.
Upcoming seminars
Ruijia Wang
(University of New Mexico)
June 30, 2021 at 11:00am EDT
(University of New Mexico)
June 30, 2021 at 11:00am EDT
Complexity and Simplicity of Injection-induced earthquakes in the Raton Basin
Waste-water injection induced seismicity has been active in the Raton Basin for the past two decades, including several M>4.0 normal-faulting earthquakes. To characterize the injection-induced fault reactivation processes, we utilize the state-of-art techniques to automatically detect and locate the seismicity using two datasets: 1) 8 broadband stations available since 2016 with an averaged spacing of ~30 km and 2) 96 high-frequency nodal instruments that were deployed for one month in the southern section of the basin in the summer of 2018. The two catalogs with ~30,000 and ~10,000 earthquakes show consistent patterns: clustering into multiple fault systems ranging from N-S, NE-SW normal to oblique dip-slip regimes. Further focal mechanisms and finite fault analysis suggest high fault and stress heterogeneity in this injection setting. On the other hand, statistical behaviors of the clusters are generally comparable to tectonic sequences. The detailed fault structures and earthquake cycle statistics offer an observational base for future mechanical modeling and hazard mitigation.
Past seminars
Ruijia Wang
(University of New Mexico)
June 30, 2021 at 11:00am EDT
(University of New Mexico)
June 30, 2021 at 11:00am EDT
Complexity and Simplicity of Injection-induced earthquakes in the Raton Basin
Waste-water injection induced seismicity has been active in the Raton Basin for the past two decades, including several M>4.0 normal-faulting earthquakes. To characterize the injection-induced fault reactivation processes, we utilize the state-of-art techniques to automatically detect and locate the seismicity using two datasets: 1) 8 broadband stations available since 2016 with an averaged spacing of ~30 km and 2) 96 high-frequency nodal instruments that were deployed for one month in the southern section of the basin in the summer of 2018. The two catalogs with ~30,000 and ~10,000 earthquakes show consistent patterns: clustering into multiple fault systems ranging from N-S, NE-SW normal to oblique dip-slip regimes. Further focal mechanisms and finite fault analysis suggest high fault and stress heterogeneity in this injection setting. On the other hand, statistical behaviors of the clusters are generally comparable to tectonic sequences. The detailed fault structures and earthquake cycle statistics offer an observational base for future mechanical modeling and hazard mitigation.
Min Chen
(Michigan State University)
June 16, 2021 at 11:00am EDT
(Michigan State University)
June 16, 2021 at 11:00am EDT
The Nature of Deep Earthquakes in the Western Pacific Subduction Zones
The nature of deep earthquakes has long been controversial because the source region is subjected to high pressures and temperatures that should inhibit the brittle failure necessary to generate seismic waves. Several mechanisms that may promote seismic deformation below 300 km depth include dehydration embrittlement, phase transformational faulting, and thermal runaway instabilities. The most referenced mechanism, phase transformational faulting, involves the breakdown of metastable olivine within the core of a cold subducting slab. In this talk, I will present our latest findings with full waveform modeling and inversion and b-value analysis of the deep earthquakes in Western Japan Subduction Zones. The nature of deep earthquakes will be inferred based on the following new observations, improved seismological definition of slab structure, the spatial relationships between deep slab interfaces and seismicity, and the mineralogical, stress, thermal properties of the slab that may control deep earthquake genesis.
Susannah Dorfman
(Michigan State University)
June 9, 2021 at 11:00am EDT
(Michigan State University)
June 9, 2021 at 11:00am EDT
Deep Earth Redox: Iron and Carbon in the Lower Mantle
On a journey towards the center of the Earth, rock encounters not only higher pressures and temperatures, but also more reducing conditions; geodynamic cycling over Earth’s history has carried material from the reduced interior back up to the crust and atmosphere. A key constraint on redox chemistry taking place in the inaccessible deep mantle is experiments on redox-sensitive elements iron and carbon. I will review recent work on the host phases and speciation of Fe and C in the mantle, redox interactions between Fe and C, and how they change with depth. These experiments illuminate potential signatures of deep mantle chemistry that could be recorded e.g. in ultradeep diamonds and used for better understanding of the dynamics and evolution of our planet.
Katie Cooper
(Washington State University)
June 2, 2021 at 11:00am EDT
(Washington State University)
June 2, 2021 at 11:00am EDT
Craton Stability: What's Thickness (and shape) Got To Do With It.
Cratons are long-lived regions on the Earth's continents. They are the secret keepers of Earth's history witnessing the planet's tectonic progression without themselves experiencing active deformation. These regions could provide clues into the Earth's evolution if we can understand what is driving their stability. One of the first-order observations of cratons is their thick lithosphere. Though discussions around craton stability primarily focus on buoyancy and rheology, thickness also plays a primary control on both the long-lived nature of stable cratons and the demise of destroyed cratons. In other words, craton stability is determined, in part, by the material properties of cratonic lithosphere, its thermal structure, and its relative strength in comparison to the material around it and the mantle below. The integrated strength of the cratonic lithosphere, which determines its relative stability, depends on its thickness. Correspondingly, the shape of a craton (or how its thickness varies over a lateral extent) should also play a role in its overall stability. In this talk, I will summarize the connections between craton thickness and (in)stability, the limits on craton thickness, and the consequences of long-lived, thick lithosphere. Finally, I will present new work demonstrating the stability of cratons also depends on their shape.
Anne Glerum
(GFZ Helmholtz Centre Potsdam)
May 26, 2021 at 11:00am EDT
(GFZ Helmholtz Centre Potsdam)
May 26, 2021 at 11:00am EDT
Continental rift interaction and the formation of rotating continental microplates
Similar to the microplates that form between overlapping mid-ocean ridges, rotating continental microplates can form between overlapping active continental rifts. In this talk, I will first discuss how the large Victoria microplate in the East African Rift System came to rotate counter-clockwise with respect to Africa, in striking contrast to its neighboring plates. Our numerical models indicate that the amount of Victoria's rotation is primarily controlled by the distribution of (i) stronger zones transmitting the drag of the major plates and (ii) weaker regions facilitating the rotation. The combination of this particular lithospheric strength distribution, the regional extension, and the oblique orientation of the preexisting weaknesses results in local predominantly normal faulting oblique to the regional and local extension directions. Second, I will present our investigations into the conditions for continental microplate formation, by modeling how approaching rift arms propagate and link from inception to continental break-up without pre-existing heterogeneities to guide them. How the rifts interact and connect depends on their offset and the crustal strength. The microplate-mode of interaction sheds light on the evolution of the Flemish cap and the Sao Paolo Plateau, regions along rifted margins interpreted as ancient continental microplates.
Iris van Zelst
(University of Leeds)
May 19, 2021 at 11:00am EDT
(University of Leeds)
May 19, 2021 at 11:00am EDT
Modelling tsunamigenic earthquakes
Earthquakes on large thrust faults in subduction zones can cause tsunamis with devastating consequences. Therefore, it is important to understand how these events nucleate, propagate, and generate tsunamis. In particular, a thorough understanding of the stress state of the relevant faults is necessary. As it is difficult to achieve this with the limited number of direct measurements of the conditions in subduction zones, many studies have attempted to use observations of earthquake and tsunami occurrence, or numerical modelling techniques to shed light on the tsunamigenic earthquake process. In this seminar, I present a modelling framework to study tsunamigenic earthquakes from the geodynamic subduction evolution and tectonic stress build-up to the dynamic earthquake rupture and propagation and inundation of the resulting tsunami. I apply this modelling framework to both megathrust and splay fault earthquakes and I show some examples of applying the 3D version of this modelling framework to a recent earthquake, such as the 2018 Palu, Sulawesi earthquake and tsunami. With this talk, I hope to convey how we can use complex modelling frameworks to study processes on different scales in an interdisciplinary manner and I hope to continue the discussion on tsunamigenic earthquakes in subduction zones with an interdisciplinary audience.
Simone Pilia
(University of Cambridge)
May 12, 2021 at 11:00am EDT
(University of Cambridge)
May 12, 2021 at 11:00am EDT
Effects of subduction termination on the continental lithosphere - A geophysical extravaganza on northern Borneo
The fragment of continental lithosphere that is now northern Borneo bears the signature of diachronous opposed subduction systems that ceased in the late Miocene. Intriguingly, there are a number of surface features that cannot be explained by our current understanding of the subduction cycle. These features include the presence of Plio-Pleistocene OIB lavas, evidence of sudden subsidence and uplift, and peak exhumation rates of more than 7 mm/year from the latest Miocene to the Early Pliocene in Mt. Kinabalu, bringing the mountain to 4095 m height (towering over most peaks in southeast Asia). New results from the nBOSS (northern Borneo Orogeny Seismic Survey) experiment, coupled with geological observations and a new numerical simulation, provide an explanation to the surface evidence of post-subduction tectonics on the continental lithosphere.
Marine Lasbleis
(Université de Nantes)
May 5, 2021 at 11:00am EDT
(Université de Nantes)
May 5, 2021 at 11:00am EDT
Crystallization of planetary cores: insights from the Earth's inner core
The Earth is a peculiar planet in the solar system: it hosts life and possesses a very active interior. However, it is not the only rocky body to present evidence of internal dynamics: all the rocky planets - except Venus - and some moons have been shown to generate or to have generated a magnetic field.
The Earth's magnetic field is thought to be driven nowadays primarily by the crystallization of its most central part: the inner core. Understanding its structure and dynamics will provide a unique insight into the Earth's thermal, chemical and magnetic history.
In this talk, I will take you from the Earth's center to other planets in the solar system and beyond. I will present some of our results on the Earth's inner core that may help us understand planetary magnetic fields, and highlight topics where ones should be careful when using the Earth as a reference for other planets.
Samer Naif
(Georgia Institute of Technology)
April 28, 2021 at 11:00am EDT
(Georgia Institute of Technology)
April 28, 2021 at 11:00am EDT
A long-lived melt channel of Galápagos plume origin at the base of the Cocos lithosphere
The Cocos Plate, located in the eastern equatorial Pacific Ocean, has long been a site of geoscience intrigue and discovery, having inspired several geophysical, geochemical, and seafloor drilling surveys over the last four decades. Here we focus on the portion of the Cocos Plate where a magnetotelluric (MT) survey imaged an electrically conductive channel at the lithosphere-asthenosphere boundary (LAB); the channel's high conductivity requires a partial melt interpretation. Yet the presence and mechanical stability of melts at the LAB is controversial and attracts healthy debate. This led us to wonder whether any seafloor evidence might exist to corroborate the melt channel inference from the MT data. To that end, we synthesized numerous datasets to piece together a 20-million-year saga of the Cocos Plate that indeed documents multiple episodes of intraplate volcanism. The results not only confirm the presence of the melt channel, but also indicate a water-rich melt composition consistent with a Galápagos plume source.
Margarete Jadamec
(State University of New York at Buffalo)
April 21, 2021 at 11:00am EDT
(State University of New York at Buffalo)
April 21, 2021 at 11:00am EDT
Slab Driven Lithosphere-Asthenosphere Decoupling in Subduction Zones
The coupling of lithospheric plates to the asthenosphere plays a major role in the process of plate tectonics. However, the nature of this coupling, in terms of asthenospheric viscosity magnitude, spatial variability in viscosity, as well as what drives that variability in space and time, remain outstanding questions in geodynamics. Two-dimensional and three-dimensional numerical simulations of subduction are presented to shed light on this process. Specifically, the models examine the effect of slab geometry, non-linear mantle rheology, and plate interface properties on predicted flow velocities and dynamically emergent asthenospheric viscosity. In addition, this seminar will address how frameworks from the computational fluid dynamics community can facilitate digital scholarship and online learning.
Walid Ben Mansour
(Washington University in St. Louis)
April 14, 2021 at 11:00am EDT
(Washington University in St. Louis)
April 14, 2021 at 11:00am EDT
Thermochemical structure beneath Gondwana terranes from multi-observables probabilistic inversion
Knowledge of the present-day thermochemical structure (temperature and bulk composition) of the lithosphere and sub-lithospheric upper mantle is important for exploration workflows, understanding the evolution of topography, interpreting geophysical anomalies, and for deciphering the physicochemical interactions between the lithosphere and the underlying convecting mantle. In this presentation, we will show and discuss the latest results of a Multi-observable Thermochemical Tomography (MTT) beneath several cratonic domains. We will also discuss the benefits and limitations of this approach and also important implication on current cratonic mantle evolution.
Attreyee Ghosh
(Indian Institute of Science)
April 7, 2021 at 11:00am EDT
(Indian Institute of Science)
April 7, 2021 at 11:00am EDT
The Curious Case of the Earth's Largest Gravity Low
If one looks at the gravity anomaly map of the Earth, what stands out is the circular "hole" that lies in the northern Indian Ocean, just south of the Indian peninsula. Measuring about 100 meters deep, this is the largest negative gravity/geoid anomaly on Earth. Various studies have attempted to explain this negative geoid anomaly mostly by invoking past subduction. Other studies have suggested that subducted slabs in the lower mantle coupled with hot, buoyant, low-velocity anomalies in the upper mantle are responsible for this geoid low. However, there is still no consensus regarding the source of the Indian Ocean geoid low and how it originated in the first place. In this talk I will show how we can explain the presence of this anomaly with the help of low-density material in the mid-to-upper mantle depths. This low density anomaly most likely originated from a plume rising along the edge of the African Large Low Shear Velocity Province (LLSVP).
Jessica Irving
(University of Bristol)
March 31, 2021 at 11:00am EDT
(University of Bristol)
March 31, 2021 at 11:00am EDT
Seismic impressions of Earth's dynamic outer core
Thousands of kilometres beneath our feet, Earth's iron-rich fluid outer core was detected more than a century ago, but still hides many secrets. The outer core is slowly being consumed by the growing inner core as Earth ages and cools. Though it is vigorously convecting, generating Earth?s geodynamo, there may be compositional variations in the outer core which have implications for our understanding of its nature. In many ways, the core represents a giant experiment in the properties and processes of materials at high temperature and pressure, but one which we cannot control. Instead we can use different seismic techniques to probe the deepest fluid region of our planet. In this seminar I will present high-frequency body wave and low-frequency normal mode investigations into the outer core, and link seismological findings to our understanding of the composition and evolution of our planet's deep interior.
CANCELLED:
Min Chen
(Michigan State University)
March 24, 2021 at 11:00am EDT
(Michigan State University)
March 24, 2021 at 11:00am EDT
The Nature of Deep Earthquakes in the Western Pacific Subduction Zones
The nature of deep earthquakes has long been controversial because the source region is subjected to high pressures and temperatures that should inhibit the brittle failure necessary to generate seismic waves. Several mechanisms that may promote seismic deformation below 300 km depth include dehydration embrittlement, phase transformational faulting, and thermal runaway instabilities. The most referenced mechanism, phase transformational faulting, involves the breakdown of metastable olivine within the core of a cold subducting slab. In this talk, I will present our latest findings with full waveform modeling and inversion and b-value analysis of the deep earthquakes in Western Japan Subduction Zones. The nature of deep earthquakes will be inferred based on the following new observations, improved seismological definition of slab structure, the spatial relationships between deep slab interfaces and seismicity, and the mineralogical, stress, thermal properties of the slab that may control deep earthquake genesis.
Amir Salaree
(University of Michigan)
March 17, 2021 at 11:00am EDT
(University of Michigan)
March 17, 2021 at 11:00am EDT
The curious case of unexpected tsunamis: A quest in nonlinearity
Tsunamis are typically modeled as energy propagation from finite underwater sources. Physical/Seismological assumptions such as geometrical spreading and attenuation usually improve our understanding of tsunami hazard via numerical simulations. However, such assumptions do not apply to “non-optical” features which would only be explained using nonlinear aspects of wave propagation. This caveat usually manifests itself in the form of “unexplained” or unexpected waves in tsunami studies.
A few interesting examples of such behavior are coseismic excitation of tsunamis by megathrust events on the other side of continents (e.g., tsunamis in the Sea of Japan and Gulf of Mexico from 2011 Tohoku and 2020 Oaxaca earthquakes, respectively), large tsunami amplitudes created by curved shorelines (e.g., higher tsunami hazard in central Cascadia), and ‘leakage’ of tsunami waves through narrow openings (e.g., propagation of Makran tsunamis into the Persian Gulf). Careful study of hydrodynamic tsunami simulations in such cases and efforts to improve the modeling of these phenomena can help us better understand the nonlinear nature of the physics behind the excitation and propagation of tsunamis.
Alana Hinchey
(Geological Survey of Newfoundland and Labrador)
March 10, 2021 at 11:00am EST
(Geological Survey of Newfoundland and Labrador)
March 10, 2021 at 11:00am EST
Regional Bedrock Mapping: Implications on Tectonic Models
Although essential research elements and core field skill requirements have not changed, there have been some fundamental changes in the field of bedrock mapping over the last 20 years. A complex, multidisciplinary approach is required to unravel the evolution of complex tectonic regimes. We need to apply a full suite of analytical techniques to a map area, such as field mapping, structural analysis, lithogeochemistry, isotope geochemisty, petrography, and geochronology in order to decipher its lithological, structural, and metamorphic history. These changes have important implications on how we interpret the geology around us.
Examples from the Makkovik Province, Canada, are used to illustrate the implications and limitations of regional bedrock mapping on how tectonic models are created. With the advent of digital data capture systems and portable tablets the way data are collected, integrated and published have changed. These advances in technology allow the full integration of GIS into bedrock mapping. We now utilize digital geologic mapping to improve our field efficiency and problem solving capabilities. Basic digital mapping is just the beginning of new and evolving capabilities with true 3D mapping (i.e. mapping through a 3D interface as opposed to building a 3D model post field mapping). The integration of these new technologies into digital field workflows and 3D visualizations is transforming the practice of bedrock mapping by making it more accessible and visually realistic.
Cailey Condit
(University of Washington)
March 3, 2021 at 11:00am EST
(University of Washington)
March 3, 2021 at 11:00am EST
Slow Earthquakes in Subduction Zones: Constraints from the Geologic, Petrologic, and Constituent Realms
Subduction zones host destructive megathrust earthquakes, one of the deadliest natural hazards on earth. Some subduction zones experience the recently recognized set of slip behaviors: episodic tremor and slow slip. These slow earthquakes may ultimately trigger megathrust events and play a key role in the slip budget of some subduction zones. However, we currently do not have a mechanistic understanding of how they occur. In this talk, I will show observations from the exhumed rock record, petrologic modeling, and analysis of constitutive relations to offer new constraints on the mechanisms of slow earthquakes. These results demonstrate the importance of frictional deformation made possible by elevated pore fluid pressures, and the role of metamorphic dehydration in supplying these fluids.
Yiduo Liu
(University of Houston)
Feb 24, 2021 at 11:00am EST
(University of Houston)
Feb 24, 2021 at 11:00am EST
Emeishan Large Igneous Province: Magma Storage System, Hidden Hotspot Track, and the Unusual Timing of the Capitanian Mass Extinction
Large igneous provinces (LIPs) are often associated with mass extinctions and are vital for life evolution on Earth. However, the precise relation between LIPs and their impacts on biodiversity is enigmatic as they can be asynchronous. If the environmental impacts are primarily related to sill emplacement, the structure of LIPs? magma storage system becomes critical as it dictates the occurrence and timing of mass extinction. Here we use surface wave tomography to image the lithosphere under the Permian Emeishan Large Igneous Province (ELIP) in SW China. We find a NE-trending zone of high shear-wave velocity (Vs) and negative radial anisotropy (Vsv > Vsh) in the crust and lithosphere and interpret it as a mafic-ultramafic, dike-dominated magma storage system on the hidden hotspot track of the ELIP. An area of less-negative radial anisotropy, on the hotspot track but away from the eruption center, reflects an elevated proportion of sills emplaced at the incipient stage of the ELIP. Liberation of poisonous gases and mercury by the sills explains why the mid-Capitanian global biota crisis preceded the peak ELIP eruption by 2-3 million years.
Elvira Mulyukova
(Yale University)
Feb 17, 2021 at 11:00am EST
(Yale University)
Feb 17, 2021 at 11:00am EST
A dislocation and a grain boundary walk into a bar
Deformation at tectonic plate boundaries is governed by the mechanical properties of crustal and lithospheric rocks, which evolve through changes in the microstructure of their constituent minerals. Geological observations of microstructure can, therefore, provide measures of the rock's deformation conditions through various piezometers (e.g., the relationship between stress and grain size or dislocation density). However, grain size and dislocation density do not evolve independently, and thus their associated piezometers are unlikely to be decoupled. We present a new theoretical model coupling the evolution of grain boundaries and dislocations in a deforming rock and make a novel prediction that the equilibrium dislocation density at a given stress (the dislocation piezometer) can be non-unique, with co-existing deformation states or piezometric branches. One stable piezometric branch exists at high stress and large grain-size, for which the steady state dislocation density is large and dictated by stress, in agreement with experimental observations and earlier theoretical models. However, another stable branch exists at low stress and small grain-size, in which case dislocation density is small, weakly stress-dependent, and is governed by the balance between dislocation sinks and sources at grain boundaries. The contrast in dislocation density between grains of different sizes induces grain boundary migration from smaller grains into larger grains. Dislocation-induced grain boundary forces thus act in the opposite direction to those dictated by surface energy, for which grain boundaries migrate from larger grains into smaller ones. When forces due to surface and dislocation energies are balanced, the system reaches a stable microstructural equilibrium, thereby halting grain growth and helping preserve plate boundary weakness. When the forces are not in balance, unstable and oscillatory behavior can ensue, with oscillation periods on the order of decades. Finally, the new theory provides a microphysical model for transient rheological behavior, which is particularly relevant to tectonic activity in which deformation is relatively rapid and where the steady state flow laws are a poor approximation, such as during postseismic relaxation or postglacial rebound.
Alexis Cartwright-Taylor
(University of Edinburgh)
Feb 10, 2021 at 11:00am EST
(University of Edinburgh)
Feb 10, 2021 at 11:00am EST
The how and when of catastrophic failure: insights from 4D in-situ x-ray microtomography with acoustic emissions
Abstract:
Localisation of structural damage (faults and fractures) along a distinct and emergent fault plane is the key driving mechanism for catastrophic failure in the brittle Earth. However, due to the speed at which stable crack growth transitions to dynamic rupture, the precise mechanisms involved in localisation as a pathway to fault formation remain unknown. Understanding these mechanisms is critical to understanding and forecasting earthquakes, including induced seismicity, landslides and volcanic eruptions, as well as failure of man-made materials and structures. We used time-resolved synchrotron x-ray microtomography to image in situ damage localisation and shear band formation at the micron scale. Furthermore, by controlling the rate of micro-fracturing events during a triaxial deformation experiment, we deliberately slowed the strain localisation process from seconds to minutes as failure approached, achieving bulk axial strain rates down to 10-7 s-1. This approach has enabled us to image directly processes that are normally too transient even for fast synchrotron imaging methods. Here, I present recently published results demonstrating the influence of material starting heterogeneity on damage localisation and the predictability of failure, as well as brand new results showing the micromechanics of quasi-static shear band formation in unprecedented detail.