Classify Anomaly

Primary Decision Tree

Is there a significant anomaly (|z| ≥ 2.0)?
├─ NO → NORMAL (no event detected)
└─ YES → Check proxy coupling...
         │
         ├─ COUPLED (δ18O and δ13C both anomalous, same sign)
         │   └─ Coupling ratio < 2.0 → **SEISMIC CANDIDATE**
         │
         ├─ DECOUPLED (δ18O anomalous, δ13C normal or opposite)
         │   ├─ Volcanic correlation? → **VOLCANIC**
         │   └─ No volcanic correlation → **CLIMATIC** (drought/wet)
         │
         └─ δ13C ONLY anomalous (δ18O normal)
             └─ Check geogenic CO₂ sources → **SEISMIC CANDIDATE**

Proxy Rules

Coupling Ratio Calculation

Coupling ratio = |δ18O_z| / |δ13C_z|

< 2.0  → COUPLED (seismic)
2.0-3.0 → AMBIGUOUS
> 3.0  → DECOUPLED (climatic/volcanic)

Recovery Time Assessment

Temporal Shape (Mg/Ca)

Classification Output

## Anomaly Classification: [Date/Window]

### Input Metrics

| Metric | Value | Notes |
|--------|-------|-------|
| δ18O z-score | -2.46σ | Significant negative |
| δ13C z-score | +1.60σ | Marginal positive |
| Mg/Ca z-score | +2.25σ | Significant positive |
| Recovery time | 15 years | Extended |
| Coupling ratio | 1.54 | COUPLED |

### Discrimination Tests

| Test | Result | Interpretation |
|------|--------|----------------|
| δ18O significance | ✓ PASS | z ≤ -2.0 |
| δ13C coupling | ✓ PASS | Same direction, ratio < 2 |
| Mg/Ca elevation | ✓ PASS | Deep/old water signature |
| Recovery duration | ✓ PASS | > 10 years |
| Volcanic correlation | ✗ NONE | No major eruptions ±5 years |

### CLASSIFICATION: **SEISMIC CANDIDATE** (Tier 1)

**Confidence**: HIGH
**Evidence tier**: Tier 1 (multi-proxy)

**Rationale**:
- Coupled proxies (ratio 1.54) indicate Chiodini mechanism
- Elevated Mg/Ca confirms deep water mobilization
- Extended recovery (15 yr) rules out volcanic/climatic
- No volcanic forcing in time window

Evidence Tiers

Volcanic Correlation Check

When --date is provided, check against major eruptions:

If date ±5 years overlaps major eruption AND proxies are DECOUPLED → VOLCANIC

Output Classifications

CVSE (Compound Volcanic-Seismic Event) Criteria

All THREE must be present:

1. Volcanic forcing - Documented eruption in ice cores
2. Seismic signal - Mg/Ca or δ13C proxy confirmation
3. Hydrological expression - Documented floods or aquifer disruption

Known CVSEs:

• 1285 Italy (UE6 + earthquake + Genoa floods)
• 936 Belize (Eldgjá + seismic + global floods)
• 853 Pacific NW (Churchill VEI 6 + Cascadia S + drought)

Example Full Analysis

User: /classify-anomaly -3.77 -1.18 --date 1275 --recovery 3

Classification Analysis:

Input:
- δ18O z = -3.77σ (EXTREME NEGATIVE)
- δ13C z = -1.18σ (not significant)
- Date: ~1275 CE
- Recovery: 3 years

Tests:
- Coupling ratio: 3.77/1.18 = 3.19 → DECOUPLED
- Volcanic check: 1257 Samalas (59.42 Tg S) within 18 years
- Recovery: 3 years (volcanic range)

CLASSIFICATION: **VOLCANIC**

Rationale:
- Decoupled signature (δ18O >> δ13C)
- Temporal proximity to 1257 Samalas (largest eruption in 2000 years)
- Short recovery (3 yr) matches volcanic pattern
- NOT seismic despite extreme δ18O

This is the documented Samalas volcanic response at Yok Balum.

Important Notes

1. Missing δ13C - Use Mg/Ca as substitute coupling test
2. Uncertainty propagates - Single proxy = Tier 3 max
3. CVSE is rare - Requires ALL THREE components
4. Recovery time is diagnostic - "Order of magnitude gap" between volcanic (1-3 yr) and seismic (10-71 yr)
5. Update ANOMALY_CATALOG.md - After classification with approval