skip to content

Department of Earth Sciences

 
Subscribe to Earth Sciences talks feed
A collection of all the seminars going on at the Department, either on the downtown site, or out at the Bullard Laboratories
Updated: 50 min 52 sec ago

Wed 03 Mar 16:00: Faults in a poroelastic solid: Towards understanding the complex coupling of slip and pore-pressure changes

Wed, 24/02/2021 - 09:11
Faults in a poroelastic solid: Towards understanding the complex coupling of slip and pore-pressure changes

Slip on faults is often modeled or simulated assuming that the surrounding host rock is purely elastic. However, it is generally understood that the crust is a porous, fluid-filled medium and thus could be better described as poroelastic. Recently there has been considerable interest in the relationship between fault slip and changes in pore-pressure through various processes such as dilatancy and fluid-injection. Such investigations require treating the crust as poroelastic if the goal is to achieve a self-consistent framework for simulating the complex coupling of slip and pore-pressure changes with the surrounding host rock.

The talk will have two main parts. First, I will review the fundamental concepts and theories that enable us to simulate the entire spectrum of slip behavior on faults during the seismic cycle. Second, I will apply these concepts to analyze and simulate slip on a fault embedded in a poroelastic medium, where I account for the fully coupled dilatancy of the fault gouge. I start by using a linearized stability analysis to gain insight into this coupled and non-linear system. I identify a previously unknown stabilizing mechanism associated with the expansion of the fault through dilatancy. Further, I generalize the stability results of Segall and Rice (1995) to a poroelastic continuum. Finally, I show simulations using a novel spectral boundary integral formulation. I solve the coupled problem of a fault undergoing simultaneous pore-pressure changes from dilatancy and fluid injection. I systematically vary the injection rate but maintain a constant injection volume to investigate how different injection strategies affect the nucleation time of events. The results indicate that the nucleation time depends strongly on the injection rate, but the ultimate size of the earthquake only modestly depends on the injection rate for the simple injection strategy explored.

Add to your calendar or Include in your list

Wed 10 Mar 16:00: When climate loads the Earth: rheology from geodesy

Tue, 23/02/2021 - 11:18
When climate loads the Earth: rheology from geodesy

At timescales of seconds to minutes, encompassed by global seismological observations, Earth behaves as an almost perfectly elastic body displaying only slight attenuation of seismic waves as they propagate. In contrast, at the timescales of thousands to millions of years associated with major glacial episodes and planetary-scale deep Earth processes, Earth is dominated by the viscous deformation of its mantle which is overlain by a relatively thin lithosphere showing nearly elastic behavior only to depths of the order of several tens of kilometers. Between these end-member timescales, tidal deformation and postseismic relaxationstudies have revealed a transient rheological behavior that is neither purely elastic nor purely viscous. Today, emerging geodetic observing technologies and continuous improvements in data accuracy and coverage of measurements provide an unprecedented opportunity to study various transient processes and advance our understanding of Earth’s mechanical response across spatial and temporal scales.

In particular, accurate measurements of temporal changes in the Earth’s shape and rotation due to shifting hydrological, atmospherical and oceanic mass loads at its surface may bring new information on the Earth’s rheology at intermediate timescales. In this talk, I will discuss improvements in geodetic observations arising from innovative data analysis methods, as well as recent advances in probing Earth’s transient rheology using its response to surface mass redistribution over seasonal to decadal time scales. A time-dependent description of Earth’s rheology may, in turn, play a central role in better understanding processes deforming the solid Earth, and in monitoring temporal variations in terrestrial water storage.

Add to your calendar or Include in your list

Mon 01 Mar 17:00: The Energy Transition in industry and its impact on earth science careers

Tue, 23/02/2021 - 11:17
The Energy Transition in industry and its impact on earth science careers

The talk will look at the challenge of the energy transition for the oil and gas industry and the probable changes in il and gas demand. Even with flat or declining global demand there is likely to be demand for development both to replace production reduced by depletion of conventional fields as well as by the need to reduce the cardon intensity of production profiles. The possible development of oil prices and the probable growth in market share of low cost producers will be discussed. There will be new applications such as carbon capture and storage and production of hydrogen for difficult to decarbonise parts of the economy. There will be strong growth in demand for mined metals. There are changing opportunities for earth scientists of all backgrounds.

The session will be half presentation, half Q&A/discussion; attendees are encouraged to raise whatever subject they wish.

Add to your calendar or Include in your list

Wed 17 Feb 16:00: Bullard Lightning Talks

Thu, 11/02/2021 - 22:06
Bullard Lightning Talks

We’ll have a series of speakers giving 5 minute intro’s about what they’re up to at the moment.

Add to your calendar or Include in your list

Wed 17 Feb 16:00: Bullard Lightning Talks

Mon, 08/02/2021 - 20:41
Bullard Lightning Talks

We’ll have a series of speakers giving 5 minute intro’s about what they’re up to at the moment.

Add to your calendar or Include in your list

Mon 15 Feb 17:00: Predictive and invertible models of sediment geochemistry from catchment to continental scales

Mon, 08/02/2021 - 11:55
Predictive and invertible models of sediment geochemistry from catchment to continental scales

Sediments are weathered pieces of rocks that are mixed in rivers (mostly) and transported to basins, becoming sorted along the way. This conceptual understanding of sediment formation has been generally understood for many years, although recent updates to this understanding are still made (e.g. the importance of cation exchange). Here I will show how this conceptual understanding can be represented using quantitative schemes to make predictions about sedimentary geochemistry and improve our understanding of Earth’s surface. First, I demonstrate a statistical method to describe the major-element composition of sediments in terms of the composition of their protolith and how intensely they have been weathered. Applying this method to large compilations of sediment compositions allows us to reconstruct the composition of the Archean continents, and produce a Phanerozoic history of weathering intensity. Second, I show how modern-day river sediments can be reliably predicted using a simple mixture model of their source regions. Finally, I show how this mixing model can be ‘inverted’, allowing higher order river sediments to be ‘unmixed’ to produce geochemical maps of their source regions.

Add to your calendar or Include in your list

Mon 15 Feb 17:00: Predictive and invertible models of sediment geochemistry from catchment to continental scales

Mon, 08/02/2021 - 11:39
Predictive and invertible models of sediment geochemistry from catchment to continental scales

Sediments are weathered pieces of rocks that are mixed in rivers (mostly) and transported to basins, becoming sorted along the way. This conceptual understanding of sediment formation has been generally understood for many years, although recent updates to this understanding are still made (e.g. the importance of cation exchange). Here I will show how this conceptual understanding can be represented using quantitative schemes to make predictions about sedimentary geochemistry and improve our understanding of Earth’s surface. First, I demonstrate a statistical method to describe the major-element composition of sediments in terms of the composition of their protolith and how intensely they have been weathered. Applying this method to large compilations of sediment compositions allows us to reconstruct the composition of the Archean protolith, and produce a Phanerozoic history of weathering intensity. Second, I show how modern-day river sediments can be reliably predicted using a simple mixture model of their source regions. Finally, I show how this mixing model can be ‘inverted’, allowing higher order river sediments to be ‘unmixed’ to produce geochemical maps of their source regions.

Add to your calendar or Include in your list

Wed 17 Feb 16:00: Bullard Lightning Talks

Sun, 07/02/2021 - 12:05
Bullard Lightning Talks

We’ll have a series of speakers giving 5 minute intro’s about what they’re up to at the moment.

Add to your calendar or Include in your list

Thu 04 Mar 13:00: Refined eruptive history of Mount Pelée volcano and implications for tephra fallout hazard in Martinique

Fri, 05/02/2021 - 15:01
Refined eruptive history of Mount Pelée volcano and implications for tephra fallout hazard in Martinique

Mount Pelée volcano (Martinique) is one of the most active volcanoes in the Lesser Antilles arc with at least fifteen magmatic events in the last 5,000 years, including the deadliest eruption of the twentieth century in 1902. Our knowledge of the eruptions older than 5 ka is however very limited, thus reducing our capacity to predict the dynamics of future eruptions at Mount Pelée.

Two new extensive field studies performed in 2017 and 2019 in Martinique combined with carbon-dating measurements allow us identifying six new eruptions in the past 24 ka cal BP, including four Plinian and two Pelean eruptions. We reconstruct the dynamical evolution of the newly discovered Plinian eruptions of Bellefontaine (13.5 ka cal BP), Carbet (14 ka cal BP) and Etoile (21.5 ka cal BP) whose great interest stems from their unusual southward dispersal axis encompassing areas that are considered to be safe in current hazard maps. Using the 2-D ash dispersion HAZMAP model, we identify peculiar atmospheric circulations associated to a modification of the subtropical jet-stream path producing northerly winds over Martinique and thus spreading ash towards the most populated areas of the island.

This integrated approach, combining field studies and model predictions, allows us to build new volcanic hazard maps for tephra fallout in Martinique. Our method is based on 16 eruptive scenarios, consistent with the data retrieved from our stratigraphical records. Each scenario considers a different pair of deposit mass and mass discharge rate, and is given a probability of occurrence calculated from the complete eruptive history of the volcano. We use the ERA -5 database to consider the daily variability of winds. These new probability maps, as well as the predicted range of damages that could be expected at key infrastructures in Martinique, will be useful to revisit the emergency procedures as the volcanological observatory (OVSM) recently raised Mount Pelée volcano on alert level 2.

Add to your calendar or Include in your list

Thu 18 Feb 13:00: Looking Through the Sunda Arc: An Overview of Java’s Magmatism

Fri, 05/02/2021 - 14:59
Looking Through the Sunda Arc: An Overview of Java’s Magmatism

The Sunda arc is a simple-looking island arc at the western tip of Pacific Ring of Fire, extending from the Andaman islands in the North and Sumatra in the West to the small volcanic islands in the north of Savu Sea in the East. The current active arc is built on top of composite crustal blocks, and has been active since Miocene. This more recent style of activity occurred after the Cretaceous subduction period ceased, and arc activity shifted towards the north. Today, the Sunda Arc is one of the most active volcanic arcs in the world, with 95 Quaternary volcanic centers. The groundwork on Sunda arc magma geochemistry was laid in the 1970s (as early as 1973), and has now reached a new peak of data accumulation and complexity. This allows us to look through a large-scale systematics of arc geochemistry. Understanding this geochemical framework should provide an opportunity to understand the interplay between the three main subduction zone components (i.e., mantle source, subducting slab, and the overriding crust) and their role in the generation of magmas along Sunda arc. This talk will provide (1) an introduction to the general geochemical systematics along Sunda arc, followed by (2) a closer look into the across-arc chemical systematics in Central Java. In the first part I will briefly show you the geochemical variation of volcanics from along the arc to show the variable association with the underlying crustal blocks. In the second part I will highlight my recent work, which seeks to untangle the subduction contribution across Merapi-Muria volcanic line in Central Java, where the slab-mantle wedge interface goes deeper than the rest of the arc segments, using trace elements and radiogenic isotopes

Add to your calendar or Include in your list

Mon 08 Feb 17:00: Responsible sourcing of metals – geologists help get it right from the start!

Tue, 02/02/2021 - 10:45
Responsible sourcing of metals – geologists help get it right from the start!

Many of us buy fairtrade coffee, tea or bananas, but how many of us think about the origin of the raw materials in our manufactured goods? We may look for a forestry stewardship council tag on wooden furniture but are less likely to enquire about complex products such as cars or computers. With their thousands of components and long supply chains, responsible sourcing of these goods is difficult to assure but is just as important. Geologists sit right at the beginning of these supply chains and there is much that we can do to be involved in the responsible sourcing agenda, right from the very first stages of thinking about new potential ore deposits. Gemstones and gold in jewellery are the mineral commodities that make perhaps the closest analogy to tea and coffee. Companies use responsible sourcing as part of their brand image. For other minerals, public attention to a few high profile issues is accelerating the adoption of corporate ethics and governance schemes. It is often single high profile issues such as conflict minerals (‘blood diamonds and ‘coltan’) or child labour (cobalt) that are driving change. Responsible sourcing of minerals is gathering pace but there is no single ‘responsibly sourced’ badge. Quantitative comparison of the environmental impacts of mineral production from different deposit types via life cycle assessment (LCA) techniques is a really useful way to link right from the geology of a deposit to the manufacturing steps. The LCA technique can be applied during exploration, at the very first stages of mine design, so that deposits to be compared and production methods adjusted to reduce the environmental footprint. These data are also an important link to the circular economy. Metals are wonderfully sustainable materials if we can look after them well.

Add to your calendar or Include in your list

Fri 12 Feb 16:00: Scaling exoplanet topography

Mon, 01/02/2021 - 16:31
Scaling exoplanet topography

Abstract not available

Add to your calendar or Include in your list

Thu 25 Feb 15:00: Volatiles in Earth’s mantle: primordial or subducted? Insights from new generation nitrogen and sulfur isotope systematics

Wed, 27/01/2021 - 10:39
Volatiles in Earth’s mantle: primordial or subducted? Insights from new generation nitrogen and sulfur isotope systematics

Hydrothermal 15N15N abundances constrain the origins of mantle nitrogen

Nitrogen (N) is the main constituent of the Earth’s atmosphere, but its provenance in the Earth’s mantle is uncertain. In this presentation, we discuss nitrogen enrichments in multiple mantle reservoirs. We show that subduction may not be as important as previously thought to account for mantle nitrogen. We use the rare 15N15N isotopologue of N2 as a novel tracer of air contamination in volcanic gas effusions. By correcting for air contributions in the gases using this tracer, we derive new estimates for mantle 15N and N2/3He ratios from multiple volcanic regions. We focus on Yellowstone, a primitive hotspot, and the central American subduction zone. We show that subduction may cause elevated 15N and N2/3He values in a mantle source, as the result of the accumulation of surface-derived components. However, our 15N15N-based analysis requires the Yellowstone plume to have some of the lowest N2/3He ratio. This is inconsistent with subducted volatiles in this mantle source, and allows plume nitrogen to be a primordial component. This result opens the possibility that the budget of mantle volatiles was at least partly established during planetary formation, rather than exclusively reflecting subduction and tectonic plate activity.

Isotopic evidence of multiple sulfur sources delivered to the Samoan islands

Like nitrogen, sulfur isotopes can be used as a tool in placing constraints on crustal recycling and the nature of volatiles in primordial mantle reservoirs. Basalts from the Samoan islands sample contributions from all classical mantle endmembers, including extreme EM II and high 3He/4He components, as well as dilute contributions from the HIMU , EM I, and DM components. The geochemical heterogeneity of the Samoan islands provides an opportunity to test whether distinct S-isotope compositions are delivered to the Samoan mantle plume and whether they are linked to the various observed mantle components. Through high precision, quadruple S-isotope analyses of Samoan Basalts we observe unique S-isotope compositions linked to the HIMU , EM II, and EM I components at Samoa. We also use relationships between sulfur and tungsten isotopes to show that the primordial S-isotope composition of the mantle is within uncertainty of the convective mantle, suggesting S isotope compositions were well mixed within 60 Ma of Earth’s accretion.

Add to your calendar or Include in your list