Using magnetic responses of natural magnetic systems to quantify geohazards.

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We know that geohazards such as earthquakes and volcanic eruptions, give rise to stresses, that generate measurable instantaneous magnetic signals, which can also be recorded by rocks. However, current accepted theories for how rocks respond to stress state that the stresses associated with these geohazards (~100 MPa) are too low to affect the magnetisation. Controlled laboratory experiments also suggest that these 'low' pressures are sufficient to generate magnetic signals. There is a clear mismatch between theory and observation. We have no accurate working model for the effect of stress on the magnetic response of minerals. If we can quantify the link between changes in stress and changes in rock magnetisations, then we can design valuable new tools for easy detection and monitoring of surface stresses. Why have we no working model for the effects of stress on the magnetic signal of minerals? Historically the effects of the induced pressures on the magnetic signal have been thought too small (< 1000 MPa) to alter or reset existing "stable" magnetic recordings (remanent magnetisations) in all but the most extreme impacts where heating also plays a significant role. For example, the impact crater that "killed the dinosaurs" - Chicxulub - is thought to have experienced pressures in excess of 60,000 MPa, i.e., 1 million times higher than a nuclear explosion. However, I show numerically as part of this proposal, that this assumption is incorrect. Using the latest state-of-the-art numerical micromagnetic model, I demonstrate in the case for support clearly that pressures of only ~200 MPa or lower are sufficient to affect "stable" magnetic recordings. Whilst 200 MPa is still a very high pressure, such pressures are very common in seismically active fault zones. It is the aim of this proposal to bridge this gap in understanding of the effect of stress on magnetic minerals, by experimentally verifying the numerical models. I will do this through a combination of three approaches: 1) extending the micromagnetic modelling which are on the nanometric scale, 2) experimental measurements on bulk samples on the centimetre scale, and 3) to the link the first two approaches together using Quantum Diamond Microscopy (QDM) done on the micron scale. With the new understanding, in the future I will apply for funding to quantify the magnetic signature of earthquakes by: (1) Determining the magnitude of stress-induced magnetic fields that might be used in early warning systems.(2) Developing a protocol for magnetically quantifying the palaeo-stress fields of palaeo-earthquakes.It is the QDM imaging which will be done in Utrecht and is key to the success of this research and for which the PI requests travel money as part of this proposal. These visits to Utrecht will be done as part of my sabbatical year. I plan to visit Utrecht University on a monthly basis for a about a week at a time starting in January 2023 for nine months to work on this project.