West Valley Fault

The Big One.

A 7.2 Mw rupture along the eastern edge of Metro Manila. Set the magnitude and the hour, then pull the trigger and watch the city light up by shake intensity.

Magnitude

7.2 Mw

Deaths (est.)

—

Injuries

—

Buildings

—

MMI VI VII VIII IX X X+

Magnitude7.2 Mw

PHIVOLCS MMEIRS scenario: 7.2. For scale, Luzon 1990 was 7.8.

Time of dayDaytime

Night is worst — people asleep inside collapsing homes (×1.5 casualties).

District intensity (MMI)

How to use

Set the magnitude (5.0–8.0 Mw) and the hour, then hit ⚡ Rupture fault. Each district lights up by Modified Mercalli Intensity — the closer to the fault, the harder the shaking. Casualty and building-damage totals are calibrated to the PHIVOLCS scenario. Blue rings mark liquefaction-prone reclaimed ground.

Why 7.2 Mw is "The Big One"

The West Valley Fault runs north–south along the eastern edge of Metro Manila — through Marikina, Pasig, Taguig, Muntinlupa. PHIVOLCS estimates it ruptures roughly every 400 years. The last major rupture was around 1658. We are inside the window.

A 7.2 Mw rupture is the MMEIRS (2004) baseline: ~34,000 deaths, ~114,000 injuries, and 168,000 buildings heavily damaged across Metro Manila. Add fire spread on Day 1 and lifeline collapse over Days 2–14 and the toll only climbs.

Earthquake energy scales as 10^1.5·ΔM — every full magnitude unit releases about 32× the energy. A 7.2 carries ~32× the punch of a 6.2.

The Modified Mercalli Intensity (MMI) scale

VI — Strong: furniture moves, light damage.

VII — Very strong: negligible-to-slight damage in well-built structures, considerable in poorly built ones.

VIII — Severe: partial collapse common.

IX — Violent: general damage, foundations cracked.

X — Extreme: most masonry structures destroyed.

Distance from the fault dictates MMI. Marikina sits right on it (IX–X). Manila is ~15 km west (VIII). Malabon ~22 km (VII).

Liquefaction & secondary hazards

Reclaimed coastal areas — Roxas Blvd, Pasay, parts of Manila — sit on water-saturated sand. Under strong shaking the sand liquefies: buildings tilt or sink as the ground briefly behaves like fluid.

Then come the fires. Gas lines rupture, roads block, hydrants lose pressure. Tokyo 1923, San Francisco 1906, and Kobe 1995 all show fire causing 30–60% of post-quake deaths in dense cities.

Citations

JICA-MMDA (2004) — Earthquake Impact Reduction Study (MMEIRS); West Valley Fault M7.2 scenario, 33,500 fatalities, 168,000 wounded.
PHIVOLCS (2015) — West Valley Fault Atlas, recurrence interval ~400 yrs.
Daligdig & Besana (1993) — geological mapping of the Valley Fault System.
Wells & Coppersmith (1994) — empirical rupture-length / magnitude regressions, BSSA 84, 974.
Boore & Atkinson (2008) — ground-motion prediction equations for active crustal regions.

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