2020-2021 Geophysics Seminar Series


  Location: Virtual Link in emails

Time: Tuesday afternoons (4-5 pm during school year, 4:30-5:30 for KEGS meeting, 3-4 pm during summer, unless otherwise noted)

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

In the fall: 10/27 (Johnson Ha), 11/24 (Yajing Liu), AGU Fall meeting (12/7-17); In the Spring: Sheri Molnar (March 30th)

Dates reserved for KEGS talks: 09/15 (Schouten,Furseth), 10/13, 11/10. Important Dates: 09/10: fall classes start; 11/9-13: fall reading week; 12/09: last day of fall classes; 01/11: spring classes start; 02/15-19: spring reading week; 04/09: 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 (Tue 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: Computational and passive seismology applications towards urban seismic hazard analyses in Canada

Date/Time: March 30th, 2021, 4:10 pm
Speaker: Prof. Sheri Molnar
Affiliations: Department of Earth Sciences, Western University

Abstract: Earthquake site effects occur from the alteration of earthquake ground shaking (amplitude, frequency, duration) due to near surface ‘local’ ground conditions or the site geology. Shear wave speeds depend on the soils shear wave velocity and density and their subsurface measurement (modelling) is required for accurate local or urban-scale seismic hazard assessment. In the last two decades, two ‘hot topic’ areas of seismology have grown in significant use and popularity: passive and computational seismology. Passive seismic methods involve placing seismic sensors on the ground surface and recording the ‘free’ background seismic noise wavefield for characterization of subsurface material properties. I will summarize my experiences of developing and implementing passive seismic methods as well as their application in urban seismic hazard prediction across Canada. At the same time, advancements in computational seismology have enabled full three-dimensional (3D) earthquake rupture simulations and waveform modelling. I will present my limited successes and ongoing urban seismic hazard application efforts in this area. I will then summarize how advancements of urban seismic hazard prediction across Canada from both passive and computational seismology research will potentially impact seismic design guidelines of the 2025 and/or 2030 national building code.


Past Talks

Title: Earthquakes in Cascadia (Physics Colloquium/Geophysics)

Date/Time: March 18th, 2021, 4 pm
Speaker: Prof. Michael Bostock
Affiliations: University of British Columbia

Abstract: Cascadia, comprising the U.S. Pacific Northwest and southwestern British Columbia, is a beautiful corner of the planet where spectacular coast mountain scenery borders the temperate Pacific Ocean. But this beauty belies a hidden hazard. The same forces that lift the coast mountains from the sea are responsible for one of the most powerful of natural disasters: earthquakes. In this talk, I will discuss several distinct classes of earthquake that occur in Cascadia and the seismic hazards they pose. This list includes the highly anticipated magnitude 9 "megathrust" event that could rupture the entire Cascadia plate boundary from offshore northern Vancouver Island to northern California. It also includes less predictable "crustal" earthquakes up to magnitude 7.5 that can occur on faults anywhere in the region, and deep "intraslab" earthquakes up to magnitude 7 directly beneath major population centers such as Seattle, Victoria and Vancouver. "Slow earthquakes" with magnitudes of up to 6.5 represent a more recently discovered class of tremor that goes essentially unnoticed by the general public but which occurs at regular ~14 month intervals below Vancouver Island. Although earth motion during slow earthquakes is too protracted to generate significant seismic waves, these events may serve as harbingers for the next megathrust event as they transfer stress updip along the Cascadia plate boundary.

Title: Statistical Mechanics for Erosion and Earthquakes (Physics Colloquium/Geophysics)

Date/Time: March 4th, 2021, 4 pm
Speaker: Prof. Victor Tsai
Affiliations: Brown University

Abstract: Earth processes like debris flows and earthquakes are important for shaping the Earth's surface and can also have destructive effects on human infrastructure and life. Attempts to understand these complex Earth processes usually follow application of deterministic Newtonian physics. However, such attempts often cannot explain the observed complexity, which can be important for understanding the associated hazards and emergent behavior. Here, we describe a statistical mechanics approach and show how its application to debris flows and earthquakes allows for improved understanding of the most destructive aspects of these energetic systems.

2020-2021 J. Tuzo Wilson Lecture: Arctic sea ice thickness: From submarine sonars to satellite photon-counting altimeters

Date/Time: Feburary, 24 2020, 4 pm
Speaker: Dr. Ron Kwok
Affiliations: University of Washington

Abstract: Alongside the widely reporteddecline in Arctic ice extent, there have also been dramatic losses insea ice thickness and volume. Instead of a relatively consistentrecord of sea ice coverage from satellite passive microwaveradiometers since the late seventies, assessments of large-scaledecadal changes in sea ice thickness and volume have depended onmeasurements from a variety of sources: submarine and airbornesurveys, and mapping with satellite altimetry. Even though there issometimes sparse sampling (in space and time), lack of consistency inmeasurement approaches and continuity in individual records, thesecombined thickness datasets broadly depict an ice cover that hasthinned everywhere. Why are sea ice thickness measurements sodifficult to obtain? In my talk, I will provide a brief descriptionof the nature of the ice cover, a short history of how we haveconstructed a record of sea ice thickness of the Arctic Ocean,current technologies for observing the ice thickness, and the changesin thickness and volume over the last half century.

ES seminar (Geophysics): 3D fault architecture controls the dynamism of earthquake swarms

Date/Time: Feburary 11th, 2021, NOON
Speaker: Zachary E. Ross

Abstract: The vibrant evolutionary patterns made by earthquake swarms are incompatible with standard, effectively two-dimensional models for general fault architecture. We leverage advances in earthquake monitoring with a deep-learning algorithm to image a fault zone hosting a 4-year-long swarm in southern California. We infer that fluids are naturally injected into the fault zone from below and diffuse through strike-parallel channels while triggering earthquakes. A permeability barrier initially limits up-dip swarm migration but ultimately is circumvented. This enables fluid migration within a shallower section of the fault with fundamentally different mechanical properties. Our observations provide high-resolution constraints on the processes by which swarms initiate, grow, and arrest. These findings illustrate how swarm evolution is strongly controlled by 3D variations in fault architecture.

UTM CPS Colloquium (Geophysics): How to rock the Earth without an earthquake

Date/Time: January 13th (WED), 2021, 3:10 pm (see Geophysics seminar email for link)
Speaker: Prof. Wenyuan Fan
Affiliations: Scripps Institution of Oceanography, UCSD

Abstract: In addition to earthquakes, seismometers record ground motions generated by various environmental surficial processes, the ocean, the atmosphere, and anthropogenic activities, and the continuous seismic records are mainly these non-earthquake signals. However, these signals are complex and difficult to interpret, leaving their source mechanisms poorly understood. Therefore, these signals are often considered as noise and have received limited observational or theoretical attention. Here, using ten years of continuous records from more than 2000 seismic stations spanning the whole U.S. continent and a novel surface wave detection method, we identify and locate various unusual environmental seismic sources. In this seminar, I will show the discovery of abundant submarine landslides in the Gulf of Mexico. Specifically, we find 85 previously unknown submarine landslides in the Gulf of Mexico. Ten of the 85 landslides occurred spontaneously without preceding earthquakes, while the remaining 75 occurred nearly instantaneously after the passage of surface waves from distant earthquakes, and hence were likely dynamically triggered by the earthquakes. I will also discuss a newly discovered geophysical phenomenon - stormquakes, involving the coupling of the atmosphere-ocean and solid Earth. We discovered that large storms such as hurricanes and Nor'easters can excite coherent transcontinental seismic surface waves as large as those excited by M3.5 earthquakes. These stormquakes are fundamentally different from previously reported atmosphere-ocean-solid Earth couplings that produce incoherent seismic noise. These discoveries suggest the richness of the continuous seismic wavefield and hint future research directions.

Title: Slow slip events along plate boundary faults

Date/Time: CANCELLED (rescheduled for next year)
Speaker: Prof. Yajing Liu
Affiliations: McGill University

Abstract: The discovery of episodic slow slip events (SSE), sometimes accompanied by low-frequency seismic tremors, along major plate boundary faults has revolutionized our understanding of the spectrum of fault slip in an earthquake cycle. SSEs involve a few mm to cm of displacement released over a few days to months updip or downdip of the seismogenic zone, and some exhibit quasi-periodic recurrence intervals of several months to years. In this talk, I will first discuss numerical modeling effort, in the framework of rate-state friction, to understand the physical mechanism of SSEs and their relationship to subduction zone earthquakes, with a focus on the Cascadia margin. Episodic SSEs emerge spontaneously around friction stability transitional depths where pore pressure is near-lithostatic. SSE recurrence interval is largely controlled by the level of effective normal stress, and subduction fault geometry strongly influences along-strike slip segmentation. I will also present work on slow slip events in the context of continental and oceanic transform faults. In particular, using ocean bottom seismic observation and numerical modeling of earthquake sequences on the Gofar Transform Fault of East Pacific Rise, we found that strong dilatancy effect can stabilize seismic rupture propagation and result in rupture barriers where aseismic slip transients arise episodically. These aseismic/slow slip events may serve as a driving force for the abundant microseismicity detected on Gofar.

Title: 2020-2021 CSEG Distingished Lecture: Good Geoscience in Dire Places: Searching for Water in Humanitarian Crises

Date/Time: November 17th 2020, 4-5 pm
Speaker: Paul Bauman
Affiliations: Advisian

Abstract: The number of refugees and internally displaced persons (IDPs), worldwide, is about 80 million. Most refugees are fleeing water-stressed and conflict-torn countries such as South Sudan, Somalia, and Syria. Generally, the host countries for refugee populations are also arid or semi-arid, such as Kenya, Chad, and Jordan. In the marginal landscapes where refugee camps are usually sited, groundwater is often the only practical source of water for drinking, cooking, and sanitation. A lack of access to adequate water supplies is directly tied to increasing occurrences of cholera, dysentery, hepatitis, trachoma, and other diseases. Today, with Covid-19 outbreaks already occurring in overcrowded refugee camps, improving hygiene is critical. A well-targeted geophysical exploration program can make the difference between a successful water supply program and one doomed to failure. In this talk, I lead you on the geophysical search and then the discovery of water in a few of the refugee camps and conflict zones in East Africa. In each of these settings, the cause of human displacement is distinct, the geology and hydrogeology vary, the landscapes are strikingly different, but the need for water is equally desperate. In one of the largest refugee camps in the world, in the Turkana desert of Kenya, seismic and resistivity surveys helped to increase the water supply to the camp and, simultaneously, a previously unrecognized public health crisis was addressed. In Northern Uganda, in the devastation left behind by Joseph Kony and the Lord's Resistance Army, village water supplies were restored following geophysical surveys and hydrochemical testing. More importantly, the local Ugandan crews were trained to carry on with this technical work. Finally, in the midst of a civil war in the world's newest country, South Sudan, an emergency mission relying on resistivity surveys took advantage of a cessation of hostilities to find water in villages stranded by the conflict.

Title: Hydraulic fracturing in shale - the importance of anisotropy and geological structure

Date/Time:Oct 27, 2020, 4-5 pm
Speaker: Johnson Ha
Affiliations: Department of Civil & Mineral Engieering, University of Toronto

Abstract: The unconventional oil and gas industry in Canada is primed to have a significant role in the global supply chain. Investments made by liquified natural gas (LNG) Canada (a joint venture of LNG operators) to construct an LNG export facility in British Columbia to supply the Asian market will inevitably amplify Canada's role in the global supply chain. However, hydraulic fracturing production is currently on a steep learning curve and well performance is largely variable and difficult to predict. There are major technical, economic, social, and environmental challenges that the industry must overcome through improved fundamental understanding of the rock's behaviour. Our project proposes using reservoir-like laboratory experiments coupled with micro-hydro-mechanical based modelling to improve understanding of hydraulic fracturing mechanisms in shales. Lab-scale true triaxial hydraulic fracturing coupled with full geophysical imaging on Montney shale recovered from the reservoir were conducted at the University of Toronto. High-resolution imaging of the rock using X-ray computed tomography (CT) and serial sectioning of the sample coupled with machine learning image segmentation, has illuminated the importance of rock fabric and geological structures on the hydraulic fracturing process. The hybrid finite-discrete element method (FDEM) is the proposed tool to simulate the hydraulic fracturing process and can generate complex fractures based on sound mechanics principals. The combination of numerical models informed by controlled laboratory experiments will further the industry's understanding of hydraulic fracturing and bring the industry a step closer to resolving challenges that plague the industry.

UTM CPS Colloquium presents: Earthquakes in a laboratory by squeezing a 3 m rock

Date/Time:Sep 16th, 2020, 3-4 pm, Zoom link
Speaker: Prof. Greg McLaskey
Affiliations: Cornell University

Abstract: I describe sequences of magnitude -2.5 laboratory earthquakes generated on a 3-meter laboratory rock experiment that provide insights into how earthquakes begin and how earthquake ruptures stop. We slowly load the rock sample with up to 10 MN of force and wait for an instability—an earthquake—to spontaneously rupture the fault, which is the interface between two massive granite blocks. In the experiment, we measure the distribution of fault slip along the sample, as well as stress changes and ground motions. From slip sensor data, we image the initiation of the earthquakes and find that they begin as slow quasi-static slip on a localized region of the fault (the nucleation zone) that is about 1 m in size when it rapidly accelerates into a dynamic event. This information can aid in our understanding of how larger natural earthquakes initiate and how we should interpret foreshocks. Once the earthquake initiates, it ruptures as a shear crack that propagates close to the speed of sound in the granite (4 km/s). Unique to this large machine, some laboratory earthquakes stop before rupturing through the ends of the sample, and this allows us to study the stress conditions required to stop an earthquake rupture. I will also present some experiments where we trigger earthquakes by injecting fluid directly into the fault, and others where complex and unpredictable sequences of earthquakes can develop rather than highly periodic ruptures.

KEGS PRESENTS: Muon tomography for mineral exploration, and other applications in underground resources

Date/Time: Sep 15th, 2020, 4-5 pm, sign up
Speakers: Doug Schouten, Don Furseth

Abstract: Muon geotomography is a novel density measurement technique based on the attenuation of cosmic ray muons in the ground. Providing X-ray like density imaging and 3D tomography down to 1km deep, this technology has the potential to dramatically reduce drilling costs in exploring for a variety of deposits at the camp scale. It has also been demonstrated for underground monitoring applications, and has potential uses in oil & gas and geotechnical measurements. In this presentation, we will present the technology and describe some case studies performed by Ideon Technologies, Inc., and also discuss our HQ-sized borehole muon telescope that will be available in early 2021.