Geophysics

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New submissions for Thu, 9 May 24

[1]  arXiv:2405.05026 [pdf, other]

Title: An anti-noise seismic inversion method based on diffusion model

Authors: Yingtian Liu, Yong Li, Xingan Hao, Huating Li, Zhangquan Liao, Junheng Peng

Subjects: Geophysics (physics.geo-ph)

Seismic impedance inversion is one of the most important part of geophysical exploration. However, due to random noise, the traditional semi-supervised learning (SSL) methods lack generalization and stability. To solve this problem, some authors have proposed SSL methods with anti-noise function to improve noise robustness and inversion accuracy. However, such methods are often not ideal when faced with strong noise. In addition, Low-frequency impedance models can mitigate this problem, but creating accurate low-frequency models is difficult and error-prone when well-log data is sparse and subsurface structures are complex. To address those issues, we propose a novel deep learning inversion method called DSIM-USSL (Unsupervised and Semi-supervised joint Learning for Seismic Inversion based on diffusion model). Specifically, we are the first to introduce a diffusion model with strong noise tendency and construct a diffusion seismic inversion model (DSIM). In the reverse diffusion of DSIM, we design the encoder-decoder which combines CNN for capturing local features and GRU for global sequence modeling; and we choose U-net to learn the distribution of random noise, enhancing the generalization and stability of proposed method. Furthermore, to further improve generalization of the proposed method, a two-step training approach (USSL) is utilized. First, an unsupervised trained encoder-decoder is used as the initial network model in place of the traditional low-frequency wave impedance model that is difficult to accurately acquire. Then, the SSL is employed to further optimize the encoder-decoder model. Experimental results on the Marmousi2 model and field data demonstrate that the DSIM-USSL method achieves higher accuracy in the presence of seismic data with random noise, and maintains high stability even under strong noise conditions.

[2]  arXiv:2405.05122 [pdf, ps, other]

Title: Knowledge Gaps and Research Needs for Modeling CO2 Mineralization in the Basalt-CO2-Water System: A Review of Laboratory Experiments

Authors: Peng Lu, John Apps, Guanru Zhang, Alexander Gysi Chen Zhu

Subjects: Geophysics (physics.geo-ph)

Carbon capture and storage in basalt is being actively investigated as a scalable climate change mitigation option. Accurate geochemical modeling prediction of the extent and rate of CO2 mineralization is a critical component in assessing the local and global feasibility and efficacy of this strategy. In this study, we review basalt-CO2-water interaction experimental studies conducted during the last two decades to determine whether they provide useable information for geochemical modeling. Most of the cited experiments generate data on the temporal evolution of water composition, and a few provide identification of secondary precipitates and their compositions, offering empirical and semi-quantitative information about the reactivity of basalts and the likelihood of secondary carbonate mineralization at various temperatures, pHs, and pCO2 conditions. However, most experiments provide insufficient information on the properties and quantity of secondary minerals formed, prohibiting accurate mass balance calculations and hence more quantitative geochemical modeling studies. Primary Ca, Mg, and Fe-bearing minerals in basalt control the availability of major ions released into aqueous solution for carbonate precipitation, and many secondary minerals, i.e., smectites, Ca-Mg-Fe carbonates, and zeolites, provide sinks for the same major ions, some of which are difficult to quantify experimentally. Thus, we have a multi-source and multi-sink inverse mass balance problem with insufficient constraints on the bulk system in which the temporal evolution of major ions does not provide sufficient information on which mineral(s) dissolve or the sequence of dissolution and precipitation reactions. Going forward, we propose that future experimental work should focus on trace elements and multiple isotopic tracers and better characterize the solid reaction products with modern analytical instruments.

Cross-lists for Thu, 9 May 24

[3]  arXiv:2405.04500 (cross-list from astro-ph.EP) [pdf, ps, other]

Title: The Chemical Composition of Ryugu: Prospects as a Reference Material for Solar System Composition

Authors: Tetsuya Yokoyama, Nicolas Dauphas, Ryota Fukai, Tomohiro Usui, Shogo Tachibana, Maria Schönbächler, Henner Busemann, Masanao Abe, Toru Yada

Comments: 13 pages, 5 figures, 2 Tables

Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM); Geophysics (physics.geo-ph)

The Hayabusa 2 spacecraft sampled approximately 5.4 g of asteroid material from the Cb-type asteroid Ryugu. Initial analysis of the Ryugu materials revealed a mineralogical, chemical, and isotopic kinship to the CI chondrites. The pristine nature of Ryugu makes the returned samples ideal for constraining the composition of the Solar System. However, some elements (e.g., P, Ca, Mn, and rare earth elements) show large relative dispersions compared to the other elements in the returned materials studied so far, most likely due to the presence of aqueously formed secondary minerals (e.g., carbonates, phosphates) in Ryugu. Therefore, the estimation of the Solar System composition using currently available Ryugu data is challenging due to the so-called nugget effect of carbonates, phosphates, and possibly other accessory minerals. The nugget effect can be mitigated by analyzing a homogenized, relatively large amount of sample. We estimate that for approximately 0.1 g of Ryugu sample, the dispersion (2SD) of the bulk Mn/Cr and Rb/Sr ratios are +/-13% and +/-15%, respectively, while they will be improved to be better than +/-5% for approximately 1 g of homogenized Ryugu sample. To further constrain the Solar System composition and to evaluate if previous estimates based on CI chondrites stored in museums for decades to centuries are reliable, it is strongly recommended to determine the chemical and isotopic compositions of Ryugu using a homogenized sample prepared from relatively large (approx. 1 g) returned material. Determining Ryugu reference compositions will be used by multidisciplinary communities, including Earth and planetary sciences, astronomy, physics, and chemistry.

[4]  arXiv:2405.04908 (cross-list from astro-ph.HE) [pdf, other]

Title: Sedimentary rocks from Mediterranean drought in the Messinian age as a probe of the past cosmic ray flux

Authors: Lorenzo Caccianiga, Claudio Galelli, Lorenzo Apollonio, Federico Maria Mariani, Paolo Magnani, Alessandro Veutro

Comments: 6 pages, 2 figures. To be submitted to PRX

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Geophysics (physics.geo-ph)

We propose the use of natural minerals as detectors to study the past flux of cosmic rays. This novel application of the \textit{paleo-detector} technique requires a specific approach as it needs samples that have been exposed to secondary cosmic rays for a well defined period of time. We suggest here the use of the evaporites formed during the desiccation of the Mediterranean sea ${\sim}6$ Myr ago. These minerals have been created and exposed to the air or under a shallow water basin for ${\sim}500$ kyr before being quickly submerged again by a km-scale overburden of water. We show that, by looking at the damages left in the minerals by muons in cosmic ray showers, we could detect differences in the primary cosmic ray flux during that period, as the ones expected from nearby supernova explosions, below the percent-level. We show also that little to no background from radioactive contamination and other astroparticles is expected for this kind of analysis.

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