arxiv: 2605.09405 · v1 · submitted 2026-05-10 · 📡 eess.SP

Recognition: 2 theorem links

· Lean Theorem

Subsurface Propagation Characteristics of Medium-Wave Electromagnetic Fields Revealed by Measurements in the Nanatsuo-guchi Quarry: Conceptual Framework of the Subground Wave and the Rainfall Model

Eiichi Shoji

Authors on Pith no claims yet

Pith reviewed 2026-05-12 04:35 UTC · model grok-4.3

classification 📡 eess.SP

keywords medium-wave propagationsubsurface electromagnetic fieldsquarry measurementsvertical magnetic componentsurface wave modelsunderground communication

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The pith

Medium-wave signals develop a vertical magnetic component that strengthens with depth inside an underground quarry.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper presents measurements of medium-wave radio broadcasts received deep inside a quarry, where local and distant MW signals remain detectable while FM signals attenuate rapidly near the entrance. Two-axis loop antenna rotations reveal a vertical magnetic field component (Hz) that increases with depth alongside the horizontal component (Hx), producing a reception sensitivity minimum near 40-50 degrees inclination. These patterns cannot be explained by standard Zenneck-Sommerfeld surface-wave models and instead indicate a composite electromagnetic field structure shaped by subsurface boundary conditions. The work supplies experimental evidence for MW field behavior in rock environments and points toward applications in subsurface communication.

Core claim

Field observations inside the Nanatsuo-guchi quarry show that medium-wave signals from a nearby 927 kHz station and a distant 693 kHz station are received at depth with both horizontal and vertical magnetic components. The vertical component grows with depth and produces systematic shifts in apparent arrival direction, while inclination measurements display a clear minimum near 40-50 degrees. These results are not accounted for by conventional surface-wave propagation and point to the formation of a characteristic electromagnetic field structure under subsurface boundary conditions.

What carries the argument

Two-axis rotation of loop antennas that separates and quantifies the horizontal (Hx) and vertical (Hz) magnetic field components, together with inclination sweeps that locate the 40-50 degree sensitivity minimum.

If this is right

Subsurface communication links at medium-wave frequencies can remain usable at depths where higher-frequency signals fail.
Disaster-resilient networks may use MW broadcasts to reach underground locations without relying on surface-wave assumptions.
Propagation models for rock environments must incorporate both horizontal and vertical field components to match observed angular and depth dependence.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

Similar composite field structures may appear in other confined rock spaces such as mines or tunnels, suggesting a general subsurface propagation regime.
The rainfall model referenced in the title could link moisture content to changes in the Hz component, offering a testable way to modulate the observed field structure.

Load-bearing premise

The measured signals travel through the rock medium rather than along undetected surface paths, quarry-wall reflections, or instrument artifacts.

What would settle it

A controlled test that blocks all surface paths while repeating the depth and inclination measurements, or a comparison showing that Hz vanishes when surface contributions are eliminated, would confirm whether the vertical component is generated inside the subsurface medium.

read the original abstract

This paper presents field observations of medium-wave (MW; 300 kHz-3 MHz) radio signals propagating in the subsurface rock environment of the Nanatsuo-guchi quarry, an underground Shakudani Ishi excavation site on Mt. Asuwayama in Fukui City, Japan. MW broadcast signals from a nearby local station (JOFG, 927 kHz, 5 kW), received mainly as a surface wave, and from a distant station (JOAB, 693 kHz, 500 kW), received via ionospheric reflection, were successfully received deep inside the quarry, whereas very-high-frequency frequency-modulated (FM) broadcast signals attenuated rapidly and became undetectable near the entrance. This contrasting behavior highlights the strong wavelength dependence of electromagnetic-wave propagation in subsurface environments. Two-axis rotation measurements were performed using loop antennas to analyze the arrival direction and angular dependence of the received signals. In addition to the horizontal magnetic field component (Hx), dominant near the ground surface, a vertical magnetic field component (Hz) was consistently observed inside the quarry. The relative contribution of Hz increased with depth and was accompanied by systematic variations in the apparent arrival direction. Inclination measurements further revealed a characteristic minimum in reception sensitivity near 40-50 degrees, suggesting a composite magnetic field structure involving both Hx and Hz. These observations cannot be fully explained by conventional surface-wave propagation models based on the Zenneck-Sommerfeld formulation, and instead suggest the formation of a characteristic electromagnetic field structure under subsurface boundary conditions. This study provides experimental evidence for previously unreported MW field behavior in underground spaces and offers new perspectives for subsurface communication and disaster-resilient information systems.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

The quarry measurements document MW signals persisting with a growing vertical H component, but do not rule out surface leakage or reflections as the cause.

read the letter

The main thing to know is that the authors took loop-antenna measurements inside a Japanese quarry and saw medium-wave broadcast signals remain detectable at depth while FM signals died out near the entrance, with the vertical magnetic component becoming more prominent farther in. That contrast and the reported 40-50 degree inclination minimum are the concrete observations here. They used standard two-axis rotations to track arrival direction and field tilt, which is a straightforward way to gather polarization data in the field. The work adds one more real-world data point to the thin literature on low-frequency signals in rock environments, and the wavelength dependence they note aligns with basic skin-depth expectations. The soft spots are more substantial. No signal-strength numbers, depth values, or uncertainty estimates appear, and there is no quantitative comparison against Zenneck-Sommerfeld predictions that include the actual quarry boundaries or possible air paths. The quarry layout makes undetected surface coupling or wall reflections plausible explanations for the tilted fields, yet nothing in the description excludes them. The new labels subground wave and rainfall model are introduced to interpret the results rather than derived from equations or simulations, leaving the central claim unsupported by the evidence shown. This paper is mainly useful to researchers who need empirical notes on subsurface radio for mining or disaster comms applications. A reader looking for a demonstrated new propagation mechanism will find the case incomplete. I would send it for peer review so referees can check the full dataset and methods; the raw observations have some value even if the framing requires tightening.

Referee Report

3 major / 2 minor

Summary. The paper reports field measurements of medium-wave (MW) broadcast signals (693 kHz and 927 kHz) successfully received at depth inside the Nanatsuo-guchi quarry, in contrast to rapid attenuation of FM signals near the entrance. Using two-axis loop-antenna rotations, the authors observe a vertical magnetic-field component (Hz) whose relative contribution increases with depth, accompanied by shifts in apparent arrival direction and a reception-sensitivity minimum near 40–50° inclination. They conclude that these features indicate a composite Hx+Hz field structure under subsurface boundary conditions that cannot be explained by conventional Zenneck-Sommerfeld surface-wave theory, and introduce the conceptual notions of a “subground wave” and “rainfall model.”

Significance. If the measurements can be shown to exclude surface leakage, wall reflections, and equipment artifacts, the work would supply rare in-situ data on MW propagation inside rock volumes and could inform subsurface communication or disaster-resilient systems. At present the absence of quantitative field values, error bars, statistical tests, or any comparison against geometry-aware surface-wave or ray-tracing predictions limits the result to a preliminary observation whose broader significance remains to be established.

major comments (3)

[Abstract / results on arrival direction] Abstract and results section on two-axis rotations: the central claim that the observed Hz component and depth trends “cannot be fully explained by conventional surface-wave propagation models based on the Zenneck-Sommerfeld formulation” is asserted without any explicit calculation, FDTD simulation, or comparison to predicted H-vector tilt that incorporates the quarry’s entrances, irregular walls, and finite depth at 693–927 kHz.
[Inclination measurements] Section describing inclination measurements: the reported sensitivity minimum near 40–50° is presented without error bars, repeated trials, or statistical significance testing, leaving open the possibility that the feature arises from local interference or antenna-pattern effects rather than a composite subsurface field structure.
[Depth-dependence results] Discussion of depth trends: no skin-depth estimates, attenuation-rate data, or quantitative comparison of received power versus depth are supplied, so the claim that the increasing Hz contribution indicates a new propagation mode rather than conventional multipath or near-surface coupling cannot be evaluated.

minor comments (2)

[Introduction / conceptual framework] The terms “Subground Wave” and “Rainfall Model” appear in the title and are invoked to interpret the data, yet receive no formal definition or derivation; a brief clarifying paragraph would improve readability.
[Abstract] The abstract states that FM signals “attenuated rapidly and became undetectable near the entrance,” but supplies no numerical attenuation values or exact distances; adding these would strengthen the wavelength-dependence contrast.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the constructive comments, which help clarify the preliminary nature of our field observations. We address each major point below and indicate planned revisions to the manuscript.

read point-by-point responses

Referee: [Abstract / results on arrival direction] Abstract and results section on two-axis rotations: the central claim that the observed Hz component and depth trends “cannot be fully explained by conventional surface-wave propagation models based on the Zenneck-Sommerfeld formulation” is asserted without any explicit calculation, FDTD simulation, or comparison to predicted H-vector tilt that incorporates the quarry’s entrances, irregular walls, and finite depth at 693–927 kHz.

Authors: We agree that the manuscript would benefit from explicit comparisons or simulations. The central claim rests on the empirical observation of a depth-increasing vertical Hz component, which is not expected under standard Zenneck-Sommerfeld surface-wave assumptions of dominant horizontal polarization. Detailed FDTD modeling of the irregular quarry geometry lies beyond the scope of this observational study. In revision we will add an explicit limitations paragraph stating that future geometry-aware modeling is required to confirm the interpretation. revision: partial
Referee: [Inclination measurements] Section describing inclination measurements: the reported sensitivity minimum near 40–50° is presented without error bars, repeated trials, or statistical significance testing, leaving open the possibility that the feature arises from local interference or antenna-pattern effects rather than a composite subsurface field structure.

Authors: The inclination data were acquired as single field measurements under time constraints. We acknowledge the lack of error bars, repeats, and statistical tests as a genuine limitation that leaves alternative explanations (local interference or antenna pattern) viable. In the revised manuscript we will describe the measurement protocol, qualify the 40–50° minimum as preliminary, and note that it is consistent with but not definitive proof of a composite Hx+Hz structure. revision: yes
Referee: [Depth-dependence results] Discussion of depth trends: no skin-depth estimates, attenuation-rate data, or quantitative comparison of received power versus depth are supplied, so the claim that the increasing Hz contribution indicates a new propagation mode rather than conventional multipath or near-surface coupling cannot be evaluated.

Authors: The study prioritizes qualitative polarization and arrival-direction trends over quantitative attenuation curves. Skin-depth estimates require site-specific rock conductivity data that were not measured. In revision we will insert approximate skin-depth values drawn from literature for typical rock at 693–927 kHz, add a short discussion of possible multipath contributions, and clarify that the observed Hz increase is presented as suggestive rather than conclusive evidence of a distinct mode. revision: partial

Circularity Check

0 steps flagged

No significant circularity in observational interpretation

full rationale

The paper reports field measurements of MW signals inside a quarry, notes the presence of an increasing Hz component with depth, and contrasts these with Zenneck-Sommerfeld surface-wave expectations. It introduces a conceptual framework (subground wave and rainfall model) to interpret the data. No equations, parameter fitting, self-citations, or deductive steps are described that reduce a claimed prediction or result to the inputs by construction. The central claims rest on direct experimental observations and qualitative contrast with prior theory rather than any self-referential derivation chain, making the presentation self-contained.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 2 invented entities

Abstract-only review provides no quantitative parameters, derivations, or explicit axioms. The subground wave and rainfall model are introduced conceptually to account for the observations.

invented entities (2)

Subground Wave no independent evidence
purpose: To describe the observed composite magnetic field structure and depth-dependent propagation of MW signals in subsurface rock
Conceptual framework proposed to explain measurements not captured by conventional surface-wave models
Rainfall Model no independent evidence
purpose: To link moisture or boundary conditions to the formation of the characteristic electromagnetic field structure
Mentioned in title as part of the conceptual framework but not detailed in abstract

pith-pipeline@v0.9.0 · 5618 in / 1263 out tokens · 43624 ms · 2026-05-12T04:35:06.692397+00:00 · methodology

discussion (0)

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

IndisputableMonolith/Foundation/RealityFromDistinction.lean reality_from_one_distinction unclear

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unclear
Relation between the paper passage and the cited Recognition theorem.

These observations cannot be fully explained by conventional surface-wave propagation models based on the Zenneck-Sommerfeld formulation, and instead suggest the formation of a characteristic electromagnetic field structure under subsurface boundary conditions.
IndisputableMonolith/Cost/FunctionalEquation.lean washburn_uniqueness_aczel unclear

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unclear
Relation between the paper passage and the cited Recognition theorem.

rainfall model... vertically polarized electric field (Ez) induces currents (J) ... generating the vertical magnetic field component (Hz)

What do these tags mean?

matches: The paper's claim is directly supported by a theorem in the formal canon.
supports: The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends: The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
uses: The paper appears to rely on the theorem as machinery.
contradicts: The paper's claim conflicts with a theorem or certificate in the canon.
unclear: Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.

Reference graph

Works this paper leans on

3 extracted references · 3 canonical work pages

[1]

Collin, R. E. (1992), Foundations for Microwave Engineering, 2nd ed., McGraw-Hill. Echizen Ishi Inc. Shakudani Ishi Village, Available at https://shakudani.net/ (Accessed March, 2026). GSI (2026), Control Point Results Browsing Service: Asuwayama Third-Order Triangulation Point, Available at https://service.gsi.go.jp/kijunten/app/map/ (Accessed May, 2026)...

work page doi:10.1109/jrproc.1936.227360 1992
[2]

(2016), The chemical compositions of Shakudani Ishi and Green Tuff in Fukui Prefecture, Central Japan, Bulletin of the Fukui City Museum of Natural History, 63, 17–26

Yoshizawa, Y. (2016), The chemical compositions of Shakudani Ishi and Green Tuff in Fukui Prefecture, Central Japan, Bulletin of the Fukui City Museum of Natural History, 63, 17–26. https://www.nature.museum.city.fukui.fukui.jp/shuppan/kenpou/63/63-17-26.pdf (Accessed March,

work page 2016
[3]

(1907), Über die Fortpflanzung ebener elektromagnetischer Wellen längs einer ebenen Leiterfläche und ihre Beziehung zur drahtlosen Telegraphie, Annalen der Physik, 328, 846–866

Zenneck, J. (1907), Über die Fortpflanzung ebener elektromagnetischer Wellen längs einer ebenen Leiterfläche und ihre Beziehung zur drahtlosen Telegraphie, Annalen der Physik, 328, 846–866. https://doi.org/10.1002/andp.19073281003

work page doi:10.1002/andp.19073281003 1907