📌 [Seismic Cluster Observation Report — July 6, 2025]

 

1️⃣ Title

Tokara Islands & Global Seismic Energy Trend | Structural Analysis

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2️⃣ Core Summary

• Main Focus: Tokara Islands Cluster, Ryukyu Trench, Hyuganada, Nankai Trough
• Observation Window: July 5–6, 2025
• Current Status:
  • M2–M5 class swarm continues.
  • Two M5.5 core ruptures confirmed.
  • Residual micro-swarm (M2–M3) persists at 10–30 min intervals.
  • Gal value (PGA) consistently visible at surface sensors.

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3️⃣ Key Data Highlights

• Peak Magnitude: M5.5 x2 (Tokara)
• Residual Activity: Continuous M2–M3 micro-swarms
• Energy Trend: Cumulative seismic energy shows no major drop; instead, remains rising
• Propagation: Swarm expansion toward Ryukyu, Izu, Ibaraki, Niijima, Yonaguni line detected

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4️⃣ Structural Analysis (Key Findings)

• The Tokara cluster is acting as an active stress core rather than a simple local swarm.
• Cumulative energy trend: continuous upward slope instead of normal saw-tooth stress drop.
• This indicates incomplete stress release — likely “slow slip + swarm + partial rupture” working together.
• If residual swarm does not dissipate fully, energy may transfer to deeper core zones (Hyuganada, Nankai).

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5️⃣ Global Context (Last 7 Days)

• Simulated global M4+ swarms: steady moderate-level releases across Indonesia, Alaska, South America.
• Tokara cluster accounts for ~10–12% of estimated global M4+ energy release this week — exceptionally large for a single swarm.
• This confirms Tokara’s role as a main stress valve for the western Pacific subduction arc.
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Global Context (Last 7 Days)

- Simulated global M4+ swarms show moderate-level stress releases across multiple subduction zones.
- The Tokara cluster alone accounts for ~10–12% of total global M4+ energy in the past week.
- This is visualized in the charts below:

   [Fig. 1] Tokara Magnitude & Cumulative Energy
   [Fig. 2] Global vs Tokara Comparative Energy
   [Fig. 3] 20-Year Ideal vs Actual Residual Stress Curve
   [Fig. 4] Tokara Stress Propagation Diagram

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6️⃣ Historical Context

• Normal seismic cycle = Stick-Slip saw-tooth stress drop → complete rupture → full stress drop.
• Real observation = Slow Slip Events (SSE) & swarm chain → partial slip → residual stress stays.
• Past examples: Tohoku M9, Cascadia SSE, Scholz friction law — all confirm stress does not fully vanish unless major rupture occurs.

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7️⃣ Conclusion

• Today’s signal: not a complete resolution but a “temporary lull phase.”
• If swarm stops at M1–2, larger M5–6 class can occur.
• If stress does not resolve at Tokara, transfer to Hyuganada–Nankai is plausible.
• Observation and real-time PGA monitoring are critical for 24–72h ahead.

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✅ Figures

• ✅ Cumulative Energy Chart (Global vs Tokara)
• ✅ 20-Year Saw-Tooth vs Actual Residual Graph
• ✅ Tokara Cluster Propagation Diagram
• ✅ Real-time PGA Sensor Spread (screenshots)

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✅ Key References

• H.F. Reid (1910) — Elastic Rebound Theory
• Obara et al. (2002) — SSE in Southwest Japan
• Scholz (1998–2019) — Friction laws, slip-deficit model
• Kato et al. (2012) — Tohoku regional swarm chain