Ordinary Meeting

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"Seismic reflection data and space exploration" (Fowler ‘G’ award)

As we explore other planetary bodies, our understanding of their structure, formation, and resources becomes limited by our inability to properly examine their subsurface. Finding Earth analogues has proven critical to interpreting planetary surface features, so here I explore how we can use imagery of Earth’s subsurface to interpret that of other planetary bodies. In particular, I use seismic reflection data, which allows us to image Earth’s subsurface in unprecedented detail over broad areas and has arguably revolutionized our understanding of numerous geological disciplines. With these data, I focus on how we can study the 3D form and relationships of dykes, dyke-induced faults, and pit craters; these features are commonly observed and interpreted on other planetary bodies, and provide an important record of planetary processes.

Dykes are vertical sheets of magma, which can: (i) feed (fissure) eruptions at the surface; (ii) create cavities that overlying rock falls into, producing craters, termed pit craters, at the surface; or (iii) cause overlying rock to break, forming fractures (faults) that parallel and dip towards the underlying dyke. To-date, the surface expressions of these eruptions, pit craters, and dyke-induced faults have been used to infer subsurface processes on other planetary bodies by making assumptions regarding their 3D structure. However, even where these features are observed on Earth, our understanding of their 3D structure and formation remains limited, meaning we have yet to validate these assumptions. My colleague, Chris Jackson, and I have recently discovered a swarm of dykes, and associated dyke-induced faults and pit craters, imaged in 2D and 3D seismic reflection surveys offshore North-west Australia. These data allow us for the first time to: (i) map and quantify the structure of a dyke swarm in 3D; (ii) see the subsurface structure of pit craters and how they link to dykes, or faults; and (iii) measure the offset of rocks across dyke-induced faults in 3D, which we can use to reconstruct their growth and, thus, the injection history of associated dykes. Here, I discuss our findings and explore what they mean to our understanding of subsurface structure and processes on other planetary bodies.

Dr. Craig Magee (Leeds) 


Imaging solar coronal mass ejections in the heliosphere: From STEREO to Lagrange

A coronal mass ejection (CME) is a discrete eruption of up to 1012 kg of plasma from the solar atmosphere as a large magnetic structure expands out into the heliosphere. Discovered in the early 1970s, CMEs have been observed using coronagraphs – instruments that incorporate occulters to cover the solar disc in order to view the solar corona. Thus, for almost five decades we have imaged the eruption of CMEs as they cross the corona. However, it is well known that CMEs arriving at Earth can generate a range of adverse effects on human systems, perhaps most notably power generation, navigation and communications systems, and detecting CMEs leaving the corona and projecting their arrival at Earth is a bit like noting the weather systems leaving the USA eastern shores and waiting to see what will arrive at the UK some days later.

In recent years, the UK has led the development of instruments that can image CMEs as they cross the heliosphere, in particular with the pioneering Coriolis mission and, since 2007, with the Heliospheric Imagers aboard the NASA STEREO mission. This has resulted in a game-changer in terms of tracking CMEs and forecasting impacts at Earth, leading directly to the exploitation of the techniques for the upcoming ESA Lagrange space weather mission.


Professor Richard A Harrison MBE

Chief Scientist, RAL Space


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