Geology Bites

Bruce Buffett is a Professor in the Department of Earth and Planetary Science at the University of California, Berkeley. He investigates the structure and motions within the Earth’s core by matching physics-based simulations of the core to the observed magnetic field of the Earth.

Go to geologybites.com for diagrams that support this podcast episode as well as more about the Geology Bites podcast series.

The Earth was formed just over 4.5 billion years ago. What happened just after it formed and what were conditions like then? John Valley reveals what we have managed to discover about our planet’s very distant past, and how we did it.

Knowing exactly where faults are located is important both for scientific reasons and for assessing how much damage a fault could inflict if it ruptured and caused an earthquake. In the podcast, Rufus Catchings describes how we can use natural and artificial sources of seismic waves to create high-resolution images of fault profiles. He also explains how faults can act as seismic waveguides, an effect that enables us to determine whether faults are connected to each other. In Napa, a famous wine-growing area near San Francisco, he used guided waves to determine that an active fault is actually ten times longer than previously thought. Rufus Catchings is a Research Geophysicist at the US Geological Survey (USGS). Over the past 40 years, he has studied many dozens of faults in California and elsewhere to pin down their precise locations and help assess the risks they pose.

As we wean ourselves away from fossil fuels and ramp up our reliance on alternatives, batteries become ever more important for two main reasons. First, we need grid-scale batteries to store excess electricity from time-varying sources such as wind and solar. Second, we use them to power electric vehicles, which we are now producing at the rate of about 15 million a year worldwide.

So far, the battery of choice is the lithium-ion battery. In addition to lithium, these rely on four metals — copper, nickel, cobalt, and manganese. In the podcast, Adam Simon explains the role these metals play in a battery. He then describes the geological context and origin of the economically viable deposits from which we extract these metals.

Simon is a professor of economic geology at the University of Michigan.

When plate tectonics was adopted in the 1960s and early '70s, researchers quickly mapped out plate movements. It seemed that plates moved as rigid caps about a pole on the Earth's surface. But since then, a lot of evidence has accumulated suggesting that plates are not, in fact, totally rigid. In fact, we can see them flex in response to stresses that are imposed on them. Such stresses can arise on plate boundaries, such as when two plates collide and one plate flexes down to subduct under the other. For example, we see a flexural bulge in Northern India where the Indian plate bends down under the Eurasian plate. Similar bulges are seen at subduction zones where the oceanic lithosphere flexes up before it bends down into a trench, such as off the eastern coast of Japan. Stresses can also be imposed in plate interiors when the plate is subjected to a load, such as a volcano or a sedimentary basin. An example of sediment loading occurs in river deltas, such as that of the Ganges in the Bay of Bengal.

Our guest today pioneered an ingenious method of determining the flexural strength of oceanic plates. The method uses the flexural sag of plates in response to the weight of seamounts, most of which were emplaced on their surfaces by mid-ocean eruptions. His results suggest that less than half of an oceanic plate actually contributes to its elastic strength. The rest is brittle (top layer) or ductile on the relevant time scales (bottom layer).Tony Watts is Professor of Marine Geology and Geophysics at the University of Oxford and a Fellow of the Royal Society.

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