Logarithmic measure of total seismic energy released. Each +1.0 unit = ~31× more energy. Governs wave amplitude and maximum possible intensity at all distances.

M4 — Light  ·  M6 — Strong  ·  M8 — Great  ·  M9+ — Mega

Vertical distance from surface to the rupture point. Shallow quakes (<70 km) concentrate energy near the surface → higher local intensity. Deep quakes spread energy wider but feel weaker nearby.

<70 km — Shallow (most destructive)
70–300 km — Intermediate depth
>300 km — Deep (less surface damage)

Controls how fast wave amplitude decays with distance. Formula: I = M − k·log₁₀(R). Higher k = faster decay. Reflects crustal rigidity and scattering properties.

Low k (0.5–1.2) — Efficient propagation, rigid crust
Standard (1.6–1.8) — Typical Japan crust
High k (2.5–3.0) — Highly attenuating crust

Soft sediment and reclaimed land amplify ground shaking by 2–4×. Tokyo's Kanto plain and coastal Osaka sit on thick sediment layers prone to amplification and liquefaction.

0.5–0.8 — Hard rock (mountain bedrock)
1.0 — Reference bedrock
1.5–2.5 — Stiff soil / shallow sediment
3.0–4.0 — Soft alluvial / reclaimed land

Type of tectonic movement along the fault. Affects directivity and vertical motion (tsunami risk).

Reverse/Thrust — Plates collide; one overrides the other. Strong vertical motion → tsunamis. Most of Japan's megaquakes.
Normal — Plates pull apart; crust sags and drops.
Strike-Slip — Horizontal sliding. Low tsunami risk.
Oblique — Mixed mechanism.

Compass direction the fault rupture propagates (0°=N, 90°=E, 180°=S). Cities in the forward rupture direction receive amplified shaking — a Doppler-like effect where wave energy piles up ahead of the moving rupture front.

Speed at which the rupture front propagates along the fault plane. Faster ruptures create stronger directivity and shorter, sharper shaking. Supershear ruptures (>3.5 km/s) generate anomalously large ground motions.

~2.5–2.8 km/s — Typical sub-Rayleigh
3.0–3.5 km/s — Fast rupture
>3.5 km/s — Supershear (rare, extreme)