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Seismic Event Dossier00:11 Local (16:11 UTC)(50y ago)

M 7.9 Earthquake Shariff Kabunsuan, Philippines

A magnitude 7.9 (MW) earthquake occurred on 1976-08-16, 00:11 local time (16:11 UTC) (50y ago), centered ⁨109 km S of Cotabato (Philippines)⁩. The hypocenter was located at a shallow depth of ⁨33 km⁩. Primary telemetry verified by ⁨USGS⁩.

Historical Landmark Earthquake

#29 of All Time

Curated Global Seismic Archive (1700–Present)

Top-100 Earthquakes

A magnitude 7.9 earthquake struck ⁨Shariff Kabunsuan, Philippines⁩ on August 16, 1976. Source: ⁨Cotabato Trench⁩. Documented deaths: 8,000.

Documented Fatalities8,000Source: NOAA NCEI Significant Earthquake Database
Fault KinematicsSubduction megathrust
Equivalent Energy10.68 Mt TNT

Magnitude

MW
M 7.9

10.68 Mt TNT

Depth

33 km
33 km

shallow (Shallow crustal)

PAGER Impact

red
> 1,000 fatalities

Injuries: > 5,000 · ~39.9M felt

Interactive Epicenter & Fault Map

6.26°N, 124.02°E

Situation Monitoring

Continuous verification
Multi-agency verification of casualties, tsunami alerts, and seismic sequence
Casualties
Damage assessment in progress
Tsunami Status
No tsunami threat
NOAA PTWC & regional buoys
Felt by
MMI III+
~39.9M exposed
~27.8M in strong shaking
Citizen Felt Reports
0
No felt reports submitted
Macroseismic DYFI verification
Primary Solution
USGS
USGS#usp0000hvbreviewed
1 agencies reporting
Fault
5 km
Cotabato Trench
Subduction Megathrust · ~15.0 mm/yr
Geological Setting
6.3°N
Mindanao Island & Trench
Continental / Inland crustal
Multi-agency seismic telemetry active. Awaiting wire headlines.

Seismic Activity & Aftershock Sequence

Timeline of foreshocks, main rupture, aftershocks and machine learning risk probability evolution.

M0.0M4.5M9.0100%50%0%NOWMainshockAug 17Aug 31Sep 14Sep 28Oct 11Oct 25Nov 8Nov 22Dec 5Dec 19M7.9M≥4.0 51%
Hover or tap a point to inspect aftershocks and risk probability curve.
<35 km (Shallow)35–70 km (Intermediate)>70 km (Deep)MainshockProjected (+24h–7d)

Agency Discrepancy Matrix (Cross-Network Verification)

Comparing multi-network solutions from primary and teleseismic monitoring agencies.

Network / SourceMagnitude (Scale & Diff)Depth & DiffEpicenter & Shift (Δd)ConsensusData
USGS
United States Geological Survey · Global / US
M7.9(Mw)Ref
33.0 kmRef
6.26°, 124.02°Origin
Authoritative

Why do agency magnitudes differ? Seismological agencies use different instrumentation networks, crustal velocity models, and mathematical magnitude scales (e.g. Moment Magnitude Mw vs Local Richter ML vs Surface Wave Ms). Differences of 0.1–0.3 are common and reflect physical observation geometry rather than errors.

Where it was felt

6 settlements

Shaking intensity is modelled from magnitude, depth and distance (GMPE attenuation), not reported by residents.

TownDistanceIntensity
Cotabato · Shariff Kabunsuan109 kmMMI VIII
General Santos · South Cotabato128 kmMMI VII
Pagadian · Zamboanga Del Sur186 kmMMI VII
Davao · Davao Del Sur201 kmMMI VII
Ozamis · Misamis Occidental210 kmMMI VII
Iligan · Lanao del Norte213 kmMMI VII

Tectonic setting

Nearest mapped active fault: Cotabato Trench, , 5 km away, slip rate ~15.0 mm/yr (GEM Global Active Faults).

Explore 20 Major Fault Systems
Focal MechanismThrust / Megathrust
Thrust / Megathrust — NP1 327°/24°/66°

Low-angle compressional rupture pushed the overriding plate up over the subducting slab.

Isometric 3D block model showing crustal displacement along the fault plane with slip vectors.

Nodal Plane 1327° / 24° / 66°
Nodal Plane 2173° / 68° / 104°
Scalar Moment M₀1.90 × 1021 N·m
Tensor SourceStewart & Cohn (1979)
Regional Seismic Profile

Mindanao Island & Trench

View live seismic monitoring, historical danger benchmarks, fault slip models and recurrence intervals for this zone.