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arxiv: 2606.19124 · v1 · pith:HTC2BYZ3new · submitted 2026-06-17 · ⚛️ physics.ins-det · astro-ph.IM· gr-qc

Prospects for Observing Gravity-gradient Noise and Earthquake Gravity Signals with CHRONOS

Mario Juvenal S. Onglao III , Yuki Inoue , Daiki Tanabe This is my paper

Pith reviewed 2026-06-26 18:44 UTC · model grok-4.3

classification ⚛️ physics.ins-det astro-ph.IMgr-qc
keywords gravity-gradient noiseNewtonian noiseearthquake gravitational signalsCHRONOStorsion-bar detectorsub-Hz regimeRayleigh wavesseismic gravity perturbations
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The pith

CHRONOS torsion-bar detector can register prompt gravitational signals from earthquakes up to 90 km away before seismic P-waves arrive.

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

The paper models gravity-gradient noise from Rayleigh-wave seismic fields, atmospheric infrasound, and transient mass redistribution during earthquakes, then projects these effects onto the response of the proposed CHRONOS cryogenic torsion-bar detector. Rayleigh-wave Newtonian noise emerges as the leading environmental term below 0.5 Hz, while atmospheric contributions remain far smaller across the band. For a representative Mw=5.2 event at 40 km the integrated sub-Hz signal-to-noise ratio reaches 3.62, with the strain amplitude intersecting the detector sensitivity curve between 0.2 and 0.6 Hz. The gravitational perturbation is predicted to precede the first seismic P-wave by several seconds. This turns an expected noise source for sub-Hz gravitational-wave searches into a measurable geophysical signal.

Core claim

CHRONOS reaches a peak strain sensitivity of order 10^{-18} Hz^{-1/2} near 2 Hz. When gravity-gradient contributions from Rayleigh-wave seismic fields, atmospheric infrasound fluctuations, and earthquake mass redistribution are projected onto its torsion-bar response, Rayleigh-wave Newtonian noise dominates below approximately 0.5 Hz. For a representative Mw=5.2 event, sources within roughly 90 km produce detectable signals; at 40 km the integrated sub-Hz signal-to-noise ratio is approximately 3.62, and the corresponding strain amplitude reaches the sensitivity curve in the 0.2-0.6 Hz interval. The gravitational signal arrives several seconds before the seismic P-wave, depending on propagati

What carries the argument

Projection of modeled gravity-gradient fluctuations from Rayleigh waves, atmosphere, and earthquake mass redistribution onto the CHRONOS torsion-bar response function.

Load-bearing premise

The models of transient mass redistribution during earthquakes and the functional form used to project Rayleigh-wave gravity gradients onto the torsion-bar response accurately represent real processes.

What would settle it

An actual sub-Hz strain measurement from a confirmed Mw=5.2 earthquake at 40 km distance that either reaches or falls short of an integrated SNR of 3.62 while intersecting the sensitivity curve between 0.2 and 0.6 Hz.

Figures

Figures reproduced from arXiv: 2606.19124 by Daiki Tanabe, Mario Juvenal S. Onglao III, Yuki Inoue.

Figure 1
Figure 1. Figure 1: Elliptical ground displacement induced by Rayleigh waves lead to ground mass density fluctuations and, [PITH_FULL_IMAGE:figures/full_fig_p005_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Drastic changes in ground distribution due to earthquakes produce a multitude of body waves and surface [PITH_FULL_IMAGE:figures/full_fig_p008_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Angular amplitude spectral density of gravity-gradient backgrounds from Rayleigh-wave (green) and [PITH_FULL_IMAGE:figures/full_fig_p009_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Calculated gravity-gradient background spectra for different detector depths ( [PITH_FULL_IMAGE:figures/full_fig_p010_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Projected strain sensitivity of CHRONOS overlaid with strain-equivalent prompt gravity signals [PITH_FULL_IMAGE:figures/full_fig_p011_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: SNRs and lead time of an Mw = 5.2 earthquake at various source distances. Increasing distance extends the duration between P-wave and prompt gravity signal arrival, increasing lead time while simultaneously reducing signal strength [PITH_FULL_IMAGE:figures/full_fig_p012_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Projected strain sensitivity of CHRONOS overlaid with strain-equivalent prompt gravity signals [PITH_FULL_IMAGE:figures/full_fig_p012_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: SNRs of various earthquake magnitudes at a fixed source distance of 50 km. The SNR increases with [PITH_FULL_IMAGE:figures/full_fig_p013_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: Minimum detectable moment magnitude as a function of source distance for SNR thresholds of 1, 3, and [PITH_FULL_IMAGE:figures/full_fig_p013_9.png] view at source ↗
Figure 10
Figure 10. Figure 10: (a) Historical earthquakes with moment magnitudes [PITH_FULL_IMAGE:figures/full_fig_p015_10.png] view at source ↗
Figure 11
Figure 11. Figure 11: Logarithmic SNR contour map as a function of earthquake moment magnitude and source–detector [PITH_FULL_IMAGE:figures/full_fig_p015_11.png] view at source ↗
read the original abstract

Ground-based gravitational-wave detectors operating in the sub-Hertz regime are expected to be strongly limited by environmental gravity-gradient fluctuations, commonly referred to as Newtonian Noise (NN). At the same time, this frequency band provides unique opportunities to probe terrestrial gravitational perturbations associated with seismic and atmospheric processes. In this work, we investigate the feasibility of using the proposed Cryogenic sub-Hz cROss torsion-bar detector with quantum NOn-demolition speed meter (CHRONOS) as a platform for studying gravity-gradient noise and detecting prompt gravitational signals from earthquakes. We model gravity-gradient contributions from Rayleigh-wave-induced seismic fields, atmospheric infrasound fluctuations, and transient mass redistribution during earthquakes, and project these onto the CHRONOS torsion-bar response. CHRONOS achieves a peak strain sensitivity of order ~1e-18 Hz^(-1/2) near ~2 Hz. Rayleigh-wave NN is found to be the dominant environmental contribution below approximately 0.5 Hz, while atmospheric NN remains several orders of magnitude smaller throughout the frequency range considered. We further assess the detectability of prompt gravitational signals from earthquakes. For a representative Mw = 5.2 event, sources within approximately 90 km may produce detectable signals. At 40 km distance, we obtain a signal-to-noise ratio (SNR) of approximately 3.62 integrated over the sub-Hz band, with a corresponding strain amplitude reaching the CHRONOS sensitivity curve around 0.2 to 0.6 Hz. The gravitational signal is expected to precede seismic P-wave arrival by several seconds, depending on the assumed propagation velocity. These results demonstrate the potential of CHRONOS to probe both gravity-gradient noise and transient geophysical gravity signals in the sub-Hertz regime.

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.

Referee Report

2 major / 1 minor

Summary. The manuscript models gravity-gradient noise contributions from Rayleigh-wave seismic fields, atmospheric infrasound, and transient mass redistribution during earthquakes, projecting them onto the response of the proposed CHRONOS torsion-bar detector. It concludes that Rayleigh NN dominates below ~0.5 Hz while atmospheric NN is negligible, and that for a representative Mw=5.2 earthquake, signals are detectable within ~90 km (with SNR~3.62 at 40 km in the sub-Hz band), preceding seismic P-wave arrival.

Significance. If the underlying models are accurate, the work identifies a dual-use opportunity for CHRONOS in both characterizing Newtonian noise and observing prompt geophysical gravity signals, which could inform sub-Hz detector design and early geophysical monitoring. The absence of explicit modeling details, however, limits the strength of this assessment.

major comments (2)
  1. [Abstract] Abstract and modeling description: the central SNR~3.62 claim at 40 km (and the 0.2–0.6 Hz crossing of the sensitivity curve) for Mw=5.2 rests on the modeled gravitational strain from transient mass redistribution and its projection onto the CHRONOS torsion-bar response. No explicit functional form, source density perturbation profile, time-scale assumptions, or validation against independent calculations (e.g., gravimeter records or moment-tensor methods) is supplied, rendering the detectability conclusion uninspectable.
  2. [Modeling description] Modeling of Rayleigh-wave NN and atmospheric contributions: the statement that Rayleigh NN is dominant below ~0.5 Hz while atmospheric NN is orders of magnitude smaller requires the specific transfer functions or response projections used to map these fields onto the torsion-bar strain; without these equations the dominance claim cannot be reproduced or stress-tested.
minor comments (1)
  1. [Abstract] Abstract: the detector acronym expansion contains inconsistent capitalization ('cROss', 'NOn-demolition') that should be standardized for clarity.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the detailed report and the recognition of the potential dual-use value of CHRONOS. We agree that the current manuscript lacks sufficient explicit modeling details to allow independent reproduction or validation of the SNR and dominance claims. We will therefore expand the modeling sections with the requested functional forms, profiles, transfer functions, and validation steps.

read point-by-point responses

  1. Referee: [Abstract] Abstract and modeling description: the central SNR~3.62 claim at 40 km (and the 0.2–0.6 Hz crossing of the sensitivity curve) for Mw=5.2 rests on the modeled gravitational strain from transient mass redistribution and its projection onto the CHRONOS torsion-bar response. No explicit functional form, source density perturbation profile, time-scale assumptions, or validation against independent calculations (e.g., gravimeter records or moment-tensor methods) is supplied, rendering the detectability conclusion uninspectable.

    Authors: We agree that the absence of these explicit elements renders the detectability claim difficult to inspect. In the revised manuscript we will add a dedicated subsection deriving the gravitational strain from the transient mass redistribution, including the explicit functional form for the density perturbation profile (based on a moment-tensor source with finite rupture duration), the assumed time-scale (rise time ~1–2 s for Mw 5.2), the projection onto the torsion-bar differential strain, and direct numerical comparisons against published gravimeter records for similar events and against standard moment-tensor gravity calculations. revision: yes

  2. Referee: [Modeling description] Modeling of Rayleigh-wave NN and atmospheric contributions: the statement that Rayleigh NN is dominant below ~0.5 Hz while atmospheric NN is orders of magnitude smaller requires the specific transfer functions or response projections used to map these fields onto the torsion-bar strain; without these equations the dominance claim cannot be reproduced or stress-tested.

    Authors: We concur that the transfer functions mapping the seismic and atmospheric fields onto the CHRONOS torsion-bar response must be shown explicitly. The revised version will include the full set of response functions: the Rayleigh-wave NN transfer function (incorporating the vertical and horizontal displacement gradients projected onto the bar torsion), the atmospheric infrasound NN transfer function (pressure-to-strain coupling via the bar geometry), and the resulting strain spectra that demonstrate Rayleigh NN dominance below ~0.5 Hz by more than two orders of magnitude. These will be derived from the standard Saulson-type formalism adapted to the torsion-bar geometry. revision: yes

Circularity Check

0 steps flagged

No significant circularity; projections rely on external models

full rationale

The paper describes modeling of gravity-gradient noise from Rayleigh waves, atmospheric infrasound, and transient earthquake mass redistribution, then projects these onto the CHRONOS torsion-bar response to obtain SNR values such as 3.62 at 40 km for Mw=5.2. No equations or steps in the provided text reduce these outputs by construction to fitted parameters from the same data, self-citations, or ansatzes. The derivation chain uses external geophysical inputs and remains independent of the reported detectability claims.

Axiom & Free-Parameter Ledger

3 free parameters · 2 axioms · 0 invented entities

The central claims rest on standard geophysical models of Rayleigh-wave gravity gradients, atmospheric pressure fluctuations, and earthquake mass redistribution; these are treated as domain assumptions rather than derived quantities. No new particles or forces are introduced. A small number of representative parameters (magnitude, distance, propagation speed) are chosen to illustrate the result.

free parameters (3)
  • earthquake magnitude = 5.2
    Representative Mw = 5.2 chosen for explicit SNR calculation
  • source distance
    40 km and 90 km distances used to report concrete SNR and horizon values
  • propagation velocity
    Used to compute time lead of gravity signal over P-wave; value not stated in abstract
axioms (2)
  • domain assumption Rayleigh-wave seismic fields produce the dominant gravity-gradient fluctuations below 0.5 Hz
    Invoked to rank environmental contributions and identify the limiting noise source
  • domain assumption Transient mass redistribution during an earthquake generates a prompt gravitational signal that can be projected onto the torsion-bar response
    Central modeling step required to obtain the reported SNR values

pith-pipeline@v0.9.1-grok · 5863 in / 1553 out tokens · 31882 ms · 2026-06-26T18:44:36.579271+00:00 · methodology

discussion (0)

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Reference graph

Works this paper leans on

27 extracted references · 4 canonical work pages · 1 internal anchor

  1. [1]

    Figure 9 provides a convenient summary of the accessible distance–magnitude parameter space for the prototype CHRONOS detector

    Regions above and to the left of each curve correspond to detectable events. Figure 9 provides a convenient summary of the accessible distance–magnitude parameter space for the prototype CHRONOS detector. Figure 9 illustrates the minimum detectable moment magnitude as a function of source–site 14 distance for three SNR thresholds (SNR = 1, 3, and 5) obtai...

    1995

  2. [2]

    B. P. Abbott, R. Abbott, T. D. Abbott,et al., Phys. Rev. Lett.116, 061102 (2016)

    2016

  3. [3]

    Buikema, C

    A. Buikema, C. Cahillane, G. Mansell,et al., Phys. Rev. D102, 062003 (2020)

    2020

  4. [4]

    Capote, W

    E. Capote, W. Jia, N. Aritomi,et al., Phys. Rev. D111, 062002 (2025)

    2025

  5. [5]

    Cosmic Explorer: The U.S. Contribution to Gravitational-Wave Astronomy beyond LIGO

    D. Reitze, R. X. Adhikari, S. Ballmer,et al., Cosmic explorer: the us contribution to gravitational-wave astronomy beyond ligo (2019), arXiv:1907.04833

    work page internal anchor Pith review Pith/arXiv arXiv 2019

  6. [6]

    Punturo, M

    M. Punturo, M. Abernathy, F. Acernese,et al., Class. Quantum Grav.27, 194002 (2010)

    2010

  7. [7]

    M. Ando, K. Ishidoshiro, K. Yamamoto,et al., Phys. Rev. Lett.105, 161101 (2010)

    2010

  8. [8]

    D. J. McManus, P. Forsyth, M. J. Yap,et al., Class. Quantum Grav.34, 135002 (2017)

    2017

  9. [9]

    Inoue, D

    Y. Inoue, D. Tanabe, and V. Kumar, Improving calibration accuracy with torque coupled gravity field calibrator for sub-hz gravitational wave observation in chronos (2026), accepted by PTEP(2026), arXiv:2602.19436 [gr-qc]

    work page arXiv 2026

  10. [10]

    Inoue, D

    Y. Inoue, D. Tanabe, M. A. Ismail,et al., Optical design and sensitivity optimization of cryogenic sub-hz cross torsion bar detector with quantum non-demolition speed meter (chronos) (2026), arXiv:2510.24780 [physics.ins-det]

    work page arXiv 2026

  11. [11]

    Tanabe, Y

    D. Tanabe, Y. Inoue, V. Kumar, M. Ma’arif, and T.-C. Yu, Classical and Quantum Gravity (2026), accepted by CQG(2026)

    2026

  12. [12]

    M. J. S. Onglao, H.-Y. Huang, Y. Inoue, V. Kumar, and D. Tanabe, inProceedings of the 44 th Samahang Pisika ng Pilipinas Physics Conference(Philippines, 2026) pp. SPP–2026–3A–02

    2026

  13. [13]

    Tanabe, H.-Y

    D. Tanabe, H.-Y. Huang, Y. Inoue, M. J. S. Onglao, and T.-C. Yu, inProceedings of the 44 th Samahang Pisika ng Pilipinas Physics Conference(Philippines, 2026) pp. SPP–2026–3A–03

    2026

  14. [14]

    Inoue, H.-Y

    Y. Inoue, H.-Y. Huang, V. Kumar, M. Onglao, D. Tanabe, and T.-C. Yu, inProceedings of the 44 th Samahang Pisika ng Pilipinas Physics Conference(Philippines, 2026) pp. SPP–2026–3A–06

    2026

  15. [15]

    Harms, B

    J. Harms, B. J. Slagmolen, R. X. Adhikari,et al., Phys. Rev. D88, 122003 (2013)

    2013

  16. [16]

    Coughlin, N

    M. Coughlin, N. Mukund, J. Harms, J. Driggers, R. Adhikari, and S. Mitra, Classical and Quantum Gravity33, 244001 (2016)

    2016

  17. [17]

    Harms and H

    J. Harms and H. J. Paik, Physical Review D92, 022001 (2015)

    2015

  18. [18]

    Inoue, M

    Y. Inoue, M. J. S. O. III, V. Kumar, and D. Tanabe, Chronos science program (2026), arXiv:2603.10070 [astro-ph.IM]

    work page arXiv 2026

  19. [19]

    Fiorucci, J

    D. Fiorucci, J. Harms, M. Barsuglia, I. Fiori, and F. Paoletti, Physical Review D97, 062003 (2018)

    2018

  20. [20]

    De Carlo, F

    M. De Carlo, F. Ardhuin, and A. Le Pichon, Geophysical Journal International221, 569 (2020), https://academic.oup.com/gji/article-pdf/221/1/569/32511019/ggaa015.pdf

    2020

  21. [21]

    M. L. Waite, Journal of Fluid Mechanics888, F1 (2020)

    2020

  22. [22]

    Harms, J.-P

    J. Harms, J.-P. Ampuero, M. Barsuglia,et al., Geophys. J. Int.201, 1416 (2015). 18

    2015

  23. [23]

    Thenhaus, S

    P. Thenhaus, S. Hanson, S. Algermissen,et al., inNatural Disaster Mitigation in the Philippines (Proceedings)(1994) pp. 71–98

    1994

  24. [24]

    Bormann, B

    P. Bormann, B. Engdahl, and R. Kind, inNew manual of seismological observatory practice 2 (NMSOP2)(Deutsches GeoForschungsZentrum GFZ, 2012) pp. 1–105

    2012

  25. [25]

    Tanimoto and A

    T. Tanimoto and A. Anderson, Progress in Earth and Planetary Science10, 56 (2023)

    2023

  26. [26]

    M. S. Longuet-Higgins, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences243, 1 (1950)

    1950

  27. [27]

    Central Weather Administration, Earthquake reports (2026), accessed: 2026-05-16

    2026