# Seismology Reference

## Magnitude (Mw/M)

BMKG primarily uses **Mw (Moment Magnitude)** for significant events. Magnitudes below 5.0 are often reported as **ML (Local Magnitude)**. BMKG's "autogempa" (automatic earthquake) threshold is typically **M5.0+**.

- **< 3.0:** Micro — Rarely felt.
- **3.0–3.9:** Minor — Felt by some, no damage.
- **4.0–4.9:** Light — Felt by most, shaking of indoor items.
- **5.0–5.9:** Moderate — Can cause damage to poorly constructed buildings.
- **6.0–6.9:** Strong — Destructive in populated areas.
- **7.0–7.9:** Major — Severe damage over large areas, possible tsunami.
- **8.0+:** Great — Devastating, major tsunami risk.

## MMI Scale (Modified Mercalli Intensity)

| MMI | Description |
|-----|-------------|
| **I** | Not felt. |
| **II** | Felt by persons at rest, upper floors. |
| **III** | Felt indoors, like vibration of a passing truck. |
| **IV** | Windows and doors rattle. Felt like heavy truck striking building. |
| **V** | Felt by nearly everyone; many awakened. Small objects displaced. |
| **VI** | Felt by all; many frightened. Damage slight. |
| **VII** | Difficult to stand. Damage to poorly built structures. |
| **VIII** | Damage to ordinary structures. Fall of chimneys, walls, monuments. |
| **IX** | General panic. Considerable damage to well-built structures. Ground cracking. |
| **X** | Most masonry destroyed. Landslides. Rails bent. |
| **XI** | Few structures remain standing. Broad fissures in ground. Pipelines destroyed. |
| **XII** | Total destruction. Objects thrown into air. Waves seen on ground surface. |

## Depth Classification

- **Shallow:** 0–70 km — Most destructive, most strongly felt at surface.
- **Intermediate:** 70–300 km — Moderate felt area, less surface damage.
- **Deep:** 300–700 km — Rarely felt at surface, wide but weak propagation.

## Tsunami

### Warning Criteria
BMKG issues tsunami warnings for **M7.0+ shallow earthquakes** (typically < 70 km depth) with epicenter near or under the ocean.

### Warning Levels
| Level | Indonesian Term | Expected Wave Height |
|-------|----------------|---------------------|
| Advisory | **Waspada** | 0.5–1 m |
| Watch | **Siaga** | 1–3 m |
| Warning | **Awas** | > 3 m |

### Timeline
- Warning issued within **5 minutes** of earthquake detection.
- Updates every 10–15 minutes as data refines.
- Warning typically expires after **2 hours** if no tsunami observed.

## Moment Tensor & Beach Ball

- **Strike-Slip (Geser):** Horizontal movement. Result of horizontal pressure.
- **Normal (Turun):** Vertical movement, blocks move apart.
- **Thrust/Reverse (Naik):** Vertical movement, blocks move toward each other (common in subduction zones).

## Indonesia Tectonic Context

Indonesia sits on the **Ring of Fire**, at the convergence of four major tectonic plates:
- **Indo-Australian Plate** — subducting beneath Eurasian Plate along the Sunda Trench.
- **Eurasian Plate** — hosts most of western Indonesia.
- **Philippine Sea Plate** — interacts in eastern Indonesia (Maluku, Papua).
- **Pacific Plate** — subducts near Papua and northern Maluku.

### Major Fault Zones
- **Megathrust Sunda** — Offshore Sumatra to Java, source of M8–9 megaquakes.
- **Sesar Sumatera (Sumatran Fault)** — 1,900 km strike-slip fault along Sumatra's spine.
- **Sesar Palu-Koro** — Central Sulawesi, source of 2018 M7.5 Palu earthquake.
- **Flores Back-Arc Thrust** — Active thrust zone north of Flores/NTT.
- **Banda Arc** — Complex subduction zone in eastern Indonesia.

## Weather Warning Severity (Nowcast/Cuaca)

### Severity Levels
| Severity | Description |
|----------|-------------|
| **Minor** | Minimal impact. |
| **Moderate** | Possible threat to life/property. |
| **Severe** | Significant threat to life/property. |
| **Extreme** | Extraordinary threat to life/property. |

### Urgency
- **Immediate** — Action should be taken now.
- **Expected** — Action should be taken soon (within 1 hour).
- **Future** — Action should be taken in the near future.

### Certainty
- **Observed** — Event has been observed/detected.
- **Likely** — High probability (> 75%).
- **Possible** — Event is possible but not certain.