&
present
2021-2022 Geophysics Seminar Series

 

  Location: Virtual Links in emails

Time: Tuesday afternoons (4-5 pm during school year, 4-5 for KEGS Virtual meeting, 3-4 pm during summer, unless otherwise noted)

Summer Schedule (email liuqy@physics if you have any visitor who would like to give a talk):

06/07-08: NSERC-Energi-Simulation Symposium
06/11: KEGS PDAC Electromagnetic mini symposium
06/13-06/15 (in-person), 06/28-06/29 (online): PDAC 2022
06/14-06/16 IRIS 2022 SAGE/GAGE Community Science workshop
TBA: Remote Online Sessions for Emerging Seismologists (ROSES)
Xiaowen Liu (University of Toronto) July 19th (hybrid)
Bin He (U of Texas Dallas) July 26th (online only)
Kyubo Noh (University of Toronto) August 23rd (hybrid)


Dates reserved for KEGS talks: second Tuesday afternoon of the month
Important Dates: 09/09: fall classes start; 10/11: Thanksgiving; 11/8-12: fall reading week; 12/08: last day of fall classes; 01/10: spring classes start; 02/22-25: spring reading week; 04/08: last day of classes.

Other relevant seminar series at UofT: ES seminar (Thu noon), ES Rockfest (Fri 3pm, run by grads), Physics Colloquium (Thu 4pm), Brewer-Wilson Seminar (Fri noon, run by grads), Center for Global Change Science (CGCS) Seminars (every second Tue 4 pm), Centre for Research in Earth System Science Seminars (UTSC) (Friday 4pm), UTM CPS Colloquium (Wed 3-4 pm)
For a list of Geoscience events across GTA, check out the GTA Geoscience Events Calendar. Also check out the websites for Toronto Geological Discussion Group (TGDG), Canadian Exploration Geophysical Society (KEGS) and KEGS Foundation.

External webinars of interest: IRIS webinars (Youtube Channel), CIG webinars (Youtube Channel), AGU Webinars, SEG Near surface global lecturers, SEG ON DEMAND (you may need to be an SEG member to view)


Upcoming Talks

Title: Lithospheric Imaging from Continental Interior to Subduction Margin

Date/Time: Apr 26th, 2022, 4-5 pm
Speaker: Prof. Xiaotao Yang
Affiliations: Department of Earth Atmospheric, and Planetary Sciences, Purdue University

Abstract: The Earth’s lithosphere is complicated, three-dimensionally. In this talk, I will summarize my research achievements in understanding the evolution of the lithosphere, focusing on the intracratonic Illinois Basin and the convergent Aleutian-Alaska margin. Although cratons are relatively stable, basins and plateaus are commonly seen around the globe. Beneath the central and southeastern Illinois Basin area, we found an unusually thick crust (up to 62 km). This contrasts with what we expect for cratonic basins formed under horizontal stretching or lithospheric flexural subsidence. We proposed four hypotheses to explain the crustal thickening and origination of the Illinois Basin subsidence, with the preferred mechanism being an ancient magmatic event in > one billion years ago. The subduction of oceanic plates underneath the continent plate is a complicated, three-dimensional process. The geometry of the downgoing plate and the associated volcanic activity vary along the subduction margin. We utilize an advanced seismic imaging technique to construct a detailed seismic velocity model of the Aleutian-Alaska margin, from crust to the uppermost mantle. The velocity model reveals multiple downgoing slabs, with various seismic velocities, thicknesses, and dip angles. The imaged Pacific slab, Yakutat slab, and Wrangell slab correlate spatially with the Aleutian arc volcanoes, the Buzzard Creek-Jumbo Dome volcanoes, and the Wrangell volcanoes, respectively. There is no melt below the Denali volcanic gap based on our observations. Our findings demonstrate the combined role of the subducting slab and the overriding plate in controlling the variation of arc magmatism.


rule

Past Talks


Title: Induced earthquakes in western Canada: case studies and new understandings

Date/Time: March 29th, 2022, 4-5 pm
Speaker: Dr. Hongyu Yu
Affiliations: Pacific Geoscience Centre, Geological Survey of Canada

Abstract: Fluid injections during unconventional oil and gas productions could sometimes induce earthquakes. In western Canada, the number and magnitude of injection-induced earthquakes (IIE) have both increased drastically during past decades, which received a certain amount of concern from the public, regulators and scientific communities. A better understanding of IIE triggering process is thus urgently required to help mitigate the injection-related seismic hazards. This talk will introduce our novel findings from IIE studies in western Canada. I will first talk about the identification of a new class of IIE characterized by hybrid-frequency waveforms (EHW) in northeast BC. The source characteristics of EHW are identical to those of low-frequency earthquakes widely documented in plate boundary fault transition zones. EHW likely represent the manifestation of slow rupture transitioning from aseismic to seismic slip. The finding of EHW provides a critical observational evidence supporting the “aseismic slip loading” triggering mechanism. Next, I will show a clear case of Riedel shear structures (RSS) illuminated by IIE in western Alberta. RSS are often observed in the embryonic stage of strike-slip fault development. The temporal spatial relation between fluid injections and RSS suggest that long-term fluid injection can expedite the development of local fault systems. It is probably important to consider the dimension of local/regional RSS in the assessment of the overall seismic hazard due to fluid injections.


Title: Modular and flexible waveform modelling and inversion in two and three dimensions

Date/Time: March 22nd, 2022, 4:10-5 pm
Speaker: Dr. Michael Afanasiev
Affiliations: Mondaic software

Abstract: Recent years have witnessed the application of waveform inversion to new and exciting domains, ranging from non-destructive testing to global seismology. Each new application has the potential to bring with it novel wave propagation physics, spatial and temporal discretizations, and models of variable complexity, and adapting existing software to these novel applications has traditionally required a significant investment of time and effort. To combat these problems, we introduce Salvus: a scalable and flexible software suite designed for solving full-waveform forward and inverse problems. Based on a high order finite (spectral) element discretization, SalvusCompute solves wave propagation problems on fully unstructured quad/hex meshes in both 2 or 3 dimensions, and targets both CPU and GPU architectures. SalvusOpt extends this functionality to allow for the solution of full-waveform inverse problems on generic unstructured domains. A python-based meshing package, SalvusMesh, simplifies the generation and manipulation of regional to global scale Earth models (quad/hex), and SalvusFlow acts as a “machine abstraction layer” separating simulation descriptions from compute resources. Finally, SalvusProject acts as a workflow management framework, ensuring that long-running inversions remain tractable by saving a compressed representation of intermediate results. In this presentation both the design philosophy and technical details of the Salvus suite will be presented, along with some highlights of recent and ongoing research into multi-scale full-waveform inversion.


Title: The Ins and Outs of Terrestrial Planets: A Magnetic Field Perspective (2022 Tuzo Wilson Lecture)

Date/Time: Feb 23rd, 2022, 4:10-5 pm
Speaker: Prof. Catherine Johnson
Affiliations: Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia

Abstract: See 2022 Tuzo Wilson Lecture website for details


Title: Imaging fluids from lithospheric to reservoir scales with 3D electromagnetic methods

Date/Time: Feburary 22nd 2022, 4-5 pm
Speaker: Dr. Kristina Tietze (CANCELLED)
Affiliations: GFZ German Research Centre for Geosciences

Abstract: Presence of fluids alters stress distribution and lowers mechanical strength of rocks. Moreover, fluids transport minerals e.g. from the mantle into the crust and play an important role in the formation of mineral deposits. But fluids can also be direct targets, e.g. in geothermal or hydrocarbon reservoirs, groundwater exploration and management or at C02 storage sites. Thus, imaging the distribution of fluids is crucial to unravel current and past tectonic regimes as well as to understand and manage the prevalence of natural resources. Mapping the electrical resistivity structure is particularly useful in this respect as fluid phases and their remnants usually reduce electrical resistivity of rock formations. Electromagnetic (EM) measurements are capable of recovering the electrical resistivity structure from surface to mantle depths and may be one of the best means to image fluid networks over wide regions. In this talk, I will show examples from three different settings: At the San Andreas fault (SAF) near Parkfield, 2D and 3D magnetotelluric (MT) surveying with more than 250 sites revealed “along-strike” changes on fluid systems at lower crustal to upper mantle depths where the fault changes its mechanical behaviour from creeping to being locked and where the source region of non-volcanic tremors has been located. In South Australia, MT is used to uncover former tectonic processes along fossil margins and understand their relation to mineral deposits within a comparative study of various inversion schemes using a set of ~280 AusLAMP sites across the Gawler Craton. Based on four years of EM measurements across a producing oil field in Lower Saxony, Germany, I will show recent and cheap developments of hardware and surveying strategies that enable to increase sensitivity to reservoirs located at more than 500 m depth with surface measurements, achievements in measurement repeatability, and as numerical developments that allow consideration of infrastructure such as steel-cased wells in 3D EM modelling. EM methods are quite young compared to many other geophysical methods. Theoretical considerations and numerical concepts have experienced enormous development in recent decades, but practical applications are still relatively rare. I will conclude this presentation with an outlook on potential targets for EM exploration and monitoring and discuss developments needed improve imaging capabilities.
Bio:Kristina joined the German Research Centre for Geosciences (GFZ Potsdam, Germany) in 2007 after completing her Diploma studies in Geophysics at the Johann Wolfgang Goethe University, Frankfurt. As member of the Geo-Electromagnetics working group she focused on application and development of 3D modelling and inversion approaches for magnetotelluric (MT) data. In 2012, she received her PhD from Freie Universität Berlin and GFZ Potsdam for studies of the electrical conductivity structure along the San Andreas fault system with 3D MT inversion. From 2012-2017 she has been heading a project on developing controlled-source electromagnetic methods for monitoring of fluid flow in reservoirs at GFZ Potsdam. Between 2018-2019, she was a visiting researcher at the Geological Survey of South Australia and the University of Adelaide working on 3D inversion and modelling of MT data from the AusLAMP project. Since 2020, she is a senior researcher at GFZ Potsdam working on combining various electromagnetic methods.


KEGS Feb talk: The theory and practice of irregular sampling to increase information content in EM data acquisition

Date/Time: Feburary 8th, 2022, 4-5 pm
Speaker: Mengli Zhang
Affiliations: Center for Gravity, Electrical and Magnetic Studies (CGEM), Colorado School of Mines

Abstract: See KEGS website for details.


Title: The magnetic fields of Mercury and Ganymede

Date/Time: Feb 1st 2022, 4:10-5 pm
Speaker: Prof. Alain Plattner
Affiliations: University of Alabama

Abstract: Of the many planetary bodies in our solar system, including the moons of Jupiter and Saturn, only seven are known to have an active core magnetic field. We will discuss two of these planetary bodies: Mercury and Jupiter's moon Ganymede. Flybys of NASA's Galileo spacecraft two decades ago first detected Ganymede's core magnetic field. Spherical-harmonic analysis of this field led to conclusions that it may be generated in an extremely small fraction of the moon's core. A flyby of NASA's Juno spacecraft last June confirmed this interpretation. In this talk will discuss the limitations of the available data and propose alternative magnetic field models with substantially different interpretations for the magnetic source depth. For Mercury, magnetic data collected by NASA's MESSENGER spacecraft revealed that Mercury's core magnetic field is highly symmetric with respect to Mercury's rotation axis, but not symmetric with respect to the equator. This core field is sometimes described as an offset axial dipole, shifted towards the north pole of the planet by approximately 20% of Mercury's radius. We will discuss a weak non-axisymmetric field hidden beneath Mercury's offset axial dipole. This field spatially aligns with a topographic bulge and a deep-seated gravity anomaly, creating the challenge of how such a connection could be explained geophysically.


Title: Geophysical Sensing on Submarine Cables: A Cocktail for Two Communities

Date/Time: Jan 27th 2022, 2 pm (ES seminar)
Speaker: Prof.Zhongwen Zhan
Affiliations: Caltech

Abstract: The oceans present a major gap in geophysical instrumentation, hindering fundamental research on submarine earthquakes and the Earth’s interior structure, as well as effective earthquake and tsunami warning for offshore events. Emerging fiber-optic sensing technologies that can leverage submarine telecommunication cables present a new opportunity in filling the data gap. Marra et al. (2018) turned a 96 km long submarine cable into a sensitive seismic sensor using ultra-stable laser interferometry of a round-tripped signal. Another technology, Distributed Acoustic Sensing (DAS), interrogates intrinsic Rayleigh backscattering and converts tens of kilometers of dedicated fiber into thousands of seismic strainmeters on the seafloor (e.g., Lindsey et al., 2019; Sladen et al., 2019; Williams et al., 2019; Spica et al., 2020). Zhan et al. (2021) successfully sensed seismic and water waves over a 10,000 km long submarine cable connecting Los Angeles and Valparaiso, by monitoring the polarization of regular optical telecommunication channels. However, these new technologies have substantially different levels of sensitivity, coverage, spatial resolution, and scalability. In this talk, we advocate that strategic combinations of the different sensing techniques (including conventional geophysical networks) are necessary to provide the best coverage of the seafloor and benefit both the geophysics and oceanography communities. Furthermore, strategic collaborations with the telecommunication community without burdening their operation will be critical to the long term success.


2021-22 CSEG Distinguished Lecture: Geological storage of carbon and the role of Geophysics

Date/Time: January 25th 2022, 4-5 pm
Speaker: Don White
Affiliations: Geological Survey of Canada

Location:Zoom Link

Abstract: Global efforts to reduce anthropogenic carbon emissions to the atmosphere are gaining momentum. Geological storage of CO2 is recognized as an important component of most reduction strategies and can contribute to the sequestration of excess CO2 already in the atmosphere. However, to be effective, the quantity of CO2 to be stored must be larger – by several orders of magnitude – than current underground injection of waste fluids or gas storage. This will require new monitoring and storage protocols and geophysical methods will play an important role in all stages of CO2 storage projects including site selection, geological characterization and long-term monitoring. Canada is a world leader in implementing CO2 storage pilot projects and related studies. In 2015, the Aquistore CO2 Storage Project began injection of CO2 into a deep saline formation at ~3300 m depth utilizing the deepest well in Saskatchewan. The total of CO2 injected is approaching 400 kilotonnes. A variety of geophysical methods have been employed to track the subsurface spread of the CO2 plume and verify its containment within the reservoir. Time-lapse seismic imaging has proven effective for tracking the growth of the CO2 plume over the first 5 years. Passive seismic monitoring combined with continuous GPS measurements and InSAR surveillance has documented an absence of induced seismicity or related surface deformation. The site has acted as a natural testbed for developing other geophysical monitoring methods including electromagnetics, borehole gravity, and fibre-optic DAS (distributed acoustic sensing) systems. The knowledge developed at the Aquistore site will benefit future geological storage projects.


Title: Space-Time Monitoring of Groundwater via Seismic Interferometry

Date/Time: Nov. 23rd, 2021, 4-5 pm
Speaker: Dr. Shujuan Mao
Affiliations: MIT

Abstract: Extreme droughts plaguing the western U.S. raise a vital call for sustainable management of fresh water resources. A refined understanding about the structures and dynamics of underground aquifer systems is urgently needed. Here we present a novel approach for monitoring the spatiotemporal fluctuations of groundwater using seismological observations. By combining ambient noise interferometry and coda-wave imaging techniques, we are able to measure the space-time evolution of Relative Changes in Seismic Velocity (Δv/v) in the Coastal Los Angeles Basins during 2000-2020. We find Δv/v to recover the hydraulic head, illustrating the potential of leveraging seismometers to propel the temporal and spatial density of well measurements. Images of Δv/v seasonality agree with surface deformation inferred from InSAR, but also further enable the characterization of aquifers and their hydrology at different depths. Long-term Δv/v suggest that distinct trends (decline and recovery) of groundwater storage occurred in adjacent basins, due to anthropogenic pumping practices compounding the effect of climate change. This pilot application bridges the gap between seismology and hydrology, and shows the promise of using Δv/v to decipher underground hydrologic processes. We anticipate Δv/v to be a unique type of 4D, in-situ geodata, which will add new insights into various dynamic processes in Earth’s shallow subsurface.


Title: Geoelectrical Resistivity Survey for Geoenvironmental Investigation in Benin, Edo South, Nigeria

Date/Time: Nov. 16th, 2021, 4-5 pm
Speaker: Prof. Owens Alile
Affiliations: University of Benin, Department of Physics

Abstract: 3-Dimensional (3D) electrical resistivity survey was carried out by engaging a 2-Dimensional (2D) profile lines in the field, for geoenvironmental investigation at Otofure in Ovia North East LGA of Edo State, Nigeria. A total of fifteen (15) 2D survey lines were acquired in both parallel and orthogonal directions within and around the dumpsites. Both the Wenner alpha and Dipole Dipole arrays were engaged in the survey. Three parallel lines of 60m in length and 3 orthogonal lines of 100m in length forming a rectangular grid format, was adopted at the eastern edge of the site at a distance of 20m away from the dumpsite. Another 6 lines 3 parallel and 3 orthogonal of 100m each forming a square grid format, was conducted at the northern edge of the dumpsite. The length of the 2D traverses varies from 80m to 100m in length and the minimum electrode spacing ranged from 2.5m using the dipole dipole array and 5m interval using the wenner array. The 2D data was inverted using RES2DINV software. The 2D apparent resistivity data were collated into 3D data sets and inversion of the 3D data was done using RES3DINV to give the 3D depth slices. A volume rendering image processing technology Voxler 3D software was used to transform the data into understandable visual 3D block models. The results showed that the subsurface lithology composes of lateritic soil, sands, sandy clay and clay. The results correlated with three Borehole logs of the study area showing various layers. The topsoil, which consists of reddish brown laterite and sandy clay, has resistivity values between 80Ωm and 8500Ωm and its thickness varies between 0.01 m to 7.00 m. The second layer is thick sediments of clay and sandy clay, and has resistivity values between 120Ωm and 4000Ωm. Its thickness ranges between 2.00 m to 16.00 m. The 2D Inversion delineated contaminant plumes have low resistivity zones with resistivity values ranging between 10Ωm and 27Ωm from the ground surface to varying depths of 0 to 7m in profile 7, 8 and profile 9 suspected to be leachate. While profile 1 to 6 which is about 50m from the dumpsite and profile 10 to 15 which is about 100m from the dumpsite delineated contaminant plumes with resistivity zones ranging between 10Ωm to 30Ωm, at varying depths ranging from 7m to 15m below the surface which is suspected to be leachate from decomposed waste. There was no evidence of groundwater contamination as showed by the inversion model in all the profiles.



KEGS November Talk: Deep Learning as an alternative to downward continuation filters for structural interpretation

Date/Time: Nov, 9th 2021, 4-5 pm
Speaker: Jean-Philippe Paiement
Affiliations: Director, Global Consulting, Mira Geoscience

Abstract: Oftentimes when working with regional magnetic surveys from multiple sources, we encounter resolution continuity issues, which makes 2D interpretation more challenging. The loss in resolution of anomalies borders and lack of texture in the gridded data, can cause issues to the interpreter. This talk sets the basis of using currently available deep learning architecture to train a model for special resolution enhancement. Recent advancement in image processing and deep learning have led to the development of neural networks capable of increasing images resolution using and adversarial learning strategy (Wang, X et al., 2018). In this deep learning model, available high-resolution grids with their low-resolution counter parts are used to train an encoder-decoder network to reconstruct the high-resolution from their starting point. Once the network is sufficiently trained it is then possible to apply it to upscale low-resolution images without existing ground truth high resolution counter part. This approach uses Generative Adversarial Networks or GAN’s, a relatively new class of machine learning frameworks designed in 2014 (Goodfellow, I. et al). A generator network is used to construct images that are then passed through a discriminator network which tries to discriminate between real images and fake images produced by the generator. Given a training set, this technique learns to generate higher resolution data with the same statistics as the training set. Once the general model is trained on high-resolution/low-resolution pairs, it is possible to refine it to the area of interest and use it to upscale low resolution survey patches. This will help in refining anomaly edges and increase the accuracy of the structural interpretation conducted by the geologist. This approach is proposed as an alternative to the commonly used downward continuation filters used in the industry.


Title: Advancing Remote Sensing Techniques for Groundwater Science and Management

Date/Time: Nov, 2th 2021, 4-5 pm
Speaker: Seogi Kang
Affiliations: Stanford University

Abstract: Groundwater sustainability is at risk. With the latest mega-droughts, major reservoirs in western U.S.A. expose their bottom. Lack of surface water increases groundwater pumping particularly in highly-irrigated areas such as the Central Valley of California in U.S.A. For sustainable management of groundwater resources, it is necessary to image hydrogeology of the subsurface and monitor spatial and temporal changes of groundwater flow and storage. Traditional well- based approaches provide us useful data for this imaging and monitoring tasks but limited given the poor spatial coverage and density of water wells. The latest enhancement in remote sensing technology provides alternative ways for the imaging and monitoring of groundwater systems. Working with remote sensing data acquired in the Central Valley, in this presentation, I will first present how airborne electromagnetic (AEM) method can be utilized to image large-scale structure of groundwater systems. Then, I will present a potential of using the InSAR (interferometric synthetic aperture) deformation data as a tool for monitoring spatial and temporal changes of groundwater flow.

Bio: Dr. Kang completed his PhD in Geophysics at University of British Columbia, Canada, in 2018. His thesis work focused on computational electromagnetics and its application to mining problems. Currently, he is a Postdoctoral Researcher in the Geophysics Department at Stanford. His research focus is on advancing use of remote sensing methods for groundwater management and groundwater science. He continues to contribute to the development of open-source software, SimPEG, and educational resources, GeoSci.xyz, for geophysics.



UTM CPS Colloquium: Tracking water resources and constraining Earth structure with space geodesy

Date/Time: Oct 27th, 2021, 3-4 pm
Speaker: Prof. Hilary Martens
Affliations: Department of Geosciences, University of Montana

Abstract: see link above.

KEGS October Talk: Yaouré Gold Mine 3D seismic case history and recent hard rock processing and interpretation developments

Date/Time: Oct 12, 2021, 4-5 pm
Speaker: Andy Dyke (speaker), Kevin Jarvis and Greg Turner
Affiliations: HiSeis

Abstract: 3D seismic reflection is gaining acceptance as a tool for accelerating the discovery of additional resources within mineralized environments. In this talk we will show how this is being achieved at the Yaouré Gold Mine in Côte d’Ivoire. In addition, we will show some of the new approaches that are being applied both to: 1. Obtain higher fidelity images which more clearly and accurately represent the subsurface geology; and 2. Derive more intuitive volume-based interpretations showing the 3D distribution of key rock units.





rule