Yellowstone Volcanic-Seismic Activity Status (1984-2025)

Technical Brief for Government Reference on Earthquake Prediction

Prepared by: GU Institute of Earthquake Prediction (GUIEP) / GEPC Team

Date: 2025-12-29

Contact: Professor Jicheng GU / Boston, MA USA / gujicheng@guiep.org / +1.617.497.1108

Data source: USGS ComCat (FDSN Event Web Service). Query: center 44.615°N, -110.6°W; radius 80 km; Mc = 1.5 / 2.0 / 2.5; depth all (max observed ~13.01 km); 1984-2025; swarms retained.

Executive Summary

Using a consistent spatial window centered on Yellowstone (44.615°N, -110.6°W; radius 80 km), we analyzed the Seismicity Index S time series from 1984-2025 at multiple magnitude thresholds and time scales (annual/monthly/weekly). The analysis reveals a persistent long-term increase in seismic activity. This trend is evident even when smaller earthquakes are excluded (M≥2.0 and M≥2.5). This indicates that the observed intensification is not solely an artifact of small-event catalog completeness.

Importantly, the frequency-domain structure (FFT) does not currently show a sudden collapse of energy into a single dominant low-frequency “main peak.” This spectral signature often accompanies late-stage, near-critical volcanic instability. The current pattern is best described as an “elevated and gradually intensifying background state” of the shallow volcanic-hydrothermal-tectonic system, not evidence of an imminent eruption. We recommend continued integrated monitoring and propose quantitative trigger thresholds for escalation.

1. Data and Study Definition

Region: Circular window, 80 km radius, centered at 44.615°N, −110.6°W (Yellowstone). Depth: All cataloged depths in the dataset; observed maximum depth ~13.01 km (shallow system).

Time window: 1984-2025 (modern continuous monitoring era).

Magnitude thresholds (Mc): Primary runs at M≥1.5, with robustness tests at M≥2.0 and M≥2.5.

Swarms: Retained (no declustering). This is appropriate for volcanic systems where swarms are a key signal, not “noise.”

Method: We compute the Seismicity Index S(t) at annual/monthly/weekly resolutions and evaluate long-term trends and spectral properties via FFT.

2. Key Findings

2.1 Long-term Increase Persists Across Magnitude Thresholds

The annual S series shows a positive linear trend from 1984 to 2025 for all tested thresholds:

• M≥1.5: slope ≈ +0.012 / year

• M≥2.0: slope ≈ +0.0189 / year

• M≥2.5: slope ≈ +0.0079 / year

  
  

Interpretation: The persistence of the trend at M≥2.0 and M≥2.5 demonstrates that the intensification is not driven solely by the increasing detectability of very small earthquakes. The magnitude-threshold consistency supports a genuine increase in moderate event activity and/or underlying system energy release.

2.2 System Remains in an “Elevated Background” Spectral Regime

FFT analyses (annual and monthly) show distributed low-to-mid frequency energy without a single dominant low-frequency peak overwhelming the spectrum. This spectral pattern is consistent with a system where:

• Multiple processes contribute (tectonic stress, hydrothermal fluid migration, fracture opening/closing).

• The system may be gradually intensifying.

• However, it has not entered a near-critical “spectral convergence” stage.

  
  

Working hypothesis: A late-stage pre-eruptive regime often exhibits rapid spectral focusing (energy concentrating into one or a few dominant low-frequency modes), along with accelerating deformation and gas anomalies. Current spectra suggest we are earlier than such a stage.

3. Risk Interpretation (What This Does and Does Not Mean)

What the Results Support

• Yellowstone’s shallow volcanic-hydrothermal-tectonic system shows gradually increasing seismic activity intensity over multi-decade scales.

• The increase is robust against raising magnitude thresholds, making it less likely to be a catalog artifact.

  
  

What the Results Do NOT Claim

• This analysis alone does not indicate imminent eruption.

• Seismicity trends without corroborating deformation/gas/thermal indicators are insufficient to conclude an eruption is near.

  
  

Recommended risk statement:

“Elevated background activity with gradual intensification; continue enhanced integrated monitoring; no basis for imminent-eruption warning from seismicity alone at present.”

4. Proposed Monitoring Triggers for Escalation

We propose a two-tier threshold framework that is quantitative, auditable, and suitable for government decision support.

Tier A - Seismicity Index Acceleration Triggers (S-based)

Trigger A1 (Acceleration):

The 5-year rolling trend of annual S exceeds the long-term slope by ≥2× and persists ≥24 months (monthly series may be used for earlier detection).

Trigger A2 (Sustained elevation):

Annual S remains above the historical 90th percentile for ≥3 consecutive years (computed within the 1984-present baseline, and separately for M≥2.0 and M≥2.5).

Trigger A3 (Cross-threshold coherence):

Anomalies occur simultaneously in M≥2.0 and M≥2.5 series (not only in M≥1.5), indicating intensification across moderate events.

Tier B - Spectral Convergence Triggers (FFT-based)

Trigger B1 (Peak dominance):

The dominant low-frequency peak amplitude / median background amplitude exceeds a preset ratio (e.g., ≥3-5×) and remains elevated for ≥6-12 months (monthly analysis).

Trigger B2 (Spectral narrowing / increasing Q):

Energy becomes concentrated into one or few bands with decreasing bandwidth (objective metric: decreasing spectral entropy or increasing peak sharpness).

Tier C - Integrated Confirmation Triggers (multi-parameter)

Escalate only when seismic triggers (Tier A/B) coincide with independent anomalies:

• Deformation: Accelerating uplift/subsidence patterns (InSAR/GPS).

• Gas: Sustained changes in CO₂/SO₂/He ratios or flux.

• Thermal/hydrothermal: Persistent changes in heat output or hydrothermal activity.

• Migration: Systematic hypocenter migration patterns.

  
  

Policy guidance:

• Tier A alone → enhanced monitoring, technical briefings.

• Tier A + Tier B → elevated advisory level, interagency review.

• Tier A/B + Tier C → formal alert consideration.

  
  

5. Recommendations

1. Maintain routine monitoring while establishing an S-based dashboard updated monthly and quarterly.

2. Adopt the above trigger framework as a living protocol, refined as more data are accumulated.

3. Ensure intercomparison across magnitude thresholds (M≥1.5/2.0/2.5) to reduce catalog bias concerns.

4. Integrate seismic indicators with deformation and gas data to avoid false positives.

   
   

Technical Notes / Caveats

• Seismicity-only indicators are necessary but not sufficient for eruption warning.

• Very long “periods” inferred from FFT near the record length should not be overinterpreted; operational decisions should rely on shorter, well-resolved bands and on time-domain acceleration tests.

• The protocol is designed for risk staging and monitoring escalation, not for deterministic eruption timing at this stage.

  
  

Conclusion

In conclusion, our findings indicate a significant increase in seismic activity in the Yellowstone region. While this trend is concerning, it is essential to approach these results with caution. Continued monitoring and the implementation of our proposed triggers will enhance our understanding of the seismic landscape. This proactive approach is vital for ensuring safety and preparedness in earthquake-prone areas.

Figure 1. Annual Seismicity Index S, Yellowstone, 1984-2025, M≥1.5, 80 km radius window. Red line: annual S; dashed blue line: linear trend.

Figure 2. Annual Seismicity Index S, Yellowstone, 1984-2025, M≥2.0, 80 km radius window. Red line: annual S; dashed blue line: linear trend.

Figure 3. Annual Seismicity Index S, Yellowstone, 1984-2025, M≥2.5, 80 km radius window. Red line: annual S; dashed blue line: linear trend.

Figure 4a.: FFT-based amplitude/power spectra of annual S series (M≥2.5). Current spectra show distributed energy without dominance of a single low-frequency peak.

Figure 4b.: FFT-based amplitude/power spectra of monthly S series (M≥2.5). Current spectra show distributed energy without dominance of a single low-frequency peak.

Fig 5: Yellowstone Volcano area (from USGS).