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SiC optical nano-strain-meters for pico-detection in Geosciences (SiC nano for picoGeo)

Periodic Reporting for period 2 - SiC nano for PicoGeo (SiC optical nano-strain-meters for pico-detection in Geosciences (SiC nano for picoGeo))

Reporting period: 2020-11-01 to 2022-04-30

The project aims at the development of a radically new dynamic ground strain measurement technology with an ultra-high resolution of 10-12 that is about two order of magnitude better than the presently available technology. The new technology is based on the high performance 3C-SiC material with a high Young modulus (almost 3 times higher than silicon) that will enable the monitoring and detection of dynamic strain associated with geohazards, which pose significant risks to human life and infrastructure. Ultra small and slow strain transients preceding earthquakes and eruptions could be revealed and both new understanding of the volcano and of the seismology process can be obtained. Furthermore this new sensor will give the possibility of detecting for the first time both the strain gradient along the same hole and the strain along different axis. This will be a new result, not yet obtained, due to their large dimensions and the intrinsic isotropy of the actual detectors. This new sensor will also reduce the cost of the strain sensor of a factor 104 that will promote a large impulse in the physics study of both the volcanic areas and of the seismogenic faults. The project outcomes will have direct implications in forecasting volcanic eruptions and thus improve volcano-seismic crisis management. At the end of the project a start-up of one innovative frontier laboratory for advanced monitoring of dynamic strain associated to volcanic and seismic processes will be done. This “Pico strain Etna Lab” will be the starting point of a new network infrastructure that will control all the main volcanic regions and the main faults in Europe.
Dangerous phenomena associated with high risk situations for society, such as destructive earthquakes and volcanic eruptions, are characterized by ground deformation and strain. Therefore, in geodynamic studies it is fundamental to monitor strain to understand the processes that are predictive of these phenomena.The detection of strain preceding natural disasters is an open and critical challenge. The geophysical instruments with the best resolution are borehole strain-meters, which are high-resolution sensors that complement and highly improve modern deformation monitoring networks reaching a nominal resolution of 10-10 to 10-11. The goal of this project is to realize a high-resolution system at a lower cost using a Nano Optical Mechanical System (NOMS) realized with a high performing material: silicon carbide. This material has a Young modulus 2.5 times larger than silicon. It is possible to improve the mechanical properties and hence the NOMS sensitivity by reducing the defects density in this material with a compliance substrate. More accurate resolution means a higher frequency response. The small dimensions of the detector also allows for the instillation of different strain-meters in the same position, which will give new information about the volcanoes and the faults area. Final prototypes will be installed in one of the most active volcanoes in Europe: Etna, thus establishing the first “pico-strain volcanic lab”.
In the first year of the project the participants have developed the process of SiC growth of thin film on Si (111) and Si (100) and have realized different test structure to evaluate the stress and the mechanical parameters (Young modulus, Q factor,…) in different samples. At the same time some grow and characterization on thicker films grown on compliance substrates (Inverted Silicon Pyramids) has been performed to optimize the quality of the material. On this topic new smaller structures have been realized to improve the quality of thin films for the strain sensor applications. Regarding the WP3 activity, in this first year of the project it has been decided the locations of the three testing sites, all the authorizations for the first site drilling has been obtained and finally the first drilling both for the strain-meters and the seismometer installations has been performed before the winter.
The science-to-technology breakthrough of the present proposal will be the development of the innovative strain sensing technology illustrated in Fig. 1. The outcome of the proposed technology will be an optical fibre strain sensor with picostrain resolution (10-12), measurement band 0-100 Hz, temperature range -20-700 °C, suitable for remote, ultra high-resolution ground strain measurements to be applied in a wide spectrum of Geosciences’ purposes.
The new sensing technology will be obtained by the combining operating principles belonging to the fields of micromechanical resonators and distributed optical fibre sensors. The proposed device will be constituted by a vacuum-encapsulated SiC (silicon carbide) thin membrane resonator mounted on the termination of a multimode optical fiber (Fig. 1-a).
Natural geohazards, such as earthquakes and volcanic eruptions, are major concern for Society and their effects may profoundly impacts human life and Earth’s environment. At the territory of Italy, earthquakes represent a significant burden for the people’s life security and generate a considerable financial loss due to infrastructure damage. Recently, more than 250 persons died due to a magnitude M6 earthquake in the Central Italy. Continuous monitoring of the seismic activity of the faults of the Italian territory that go from the Alps to Sicily, of the faults of the Balkan peninsula and of the Anatolian one, with an efficient and affordable strain meter, would help safe human lives and reduce the financial burden by timely signalling and evacuation. Volcano eruptions also have a large impact on the Society with significant casualties and destructions of human infrastructures. More than 500 million people live within the potential exposure range of a volcano. The risk of catastrophic losses in future eruptions is significant given population growth, proximities of major cities to volcanoes, and the possibility of larger eruptions.