HISTORICAL TSUNAMI RECORDNovember 1, 1755

Major Ocean Tsunami Generated (Historical Record)

This undersea earthquake generated recorded tsunami waves across coastal and trans-oceanic sectors. Preserved in seismic archive for scientific reference — no active hazard exists.

Seismic Event Dossier•08:40 Local (09:40 UTC)(μόλις τώρα)

M 8.5 earthquake
North Atlantic Ocean (Portugal)

A magnitude 8.5 (MW) earthquake occurred on 1755-11-01, 08:40 local time (09:40 UTC) (μόλις τώρα), centered North Atlantic Ocean (254 km SW, Portugal). The hypocenter was located at a shallow depth of 20 km. Primary telemetry verified by USGS/ISC-GEM.

Historical Landmark Earthquake

#4 of All Time

Curated Global Seismic Archive (1700–Present)

Top-100 Earthquakes

A magnitude 8.5 earthquake struck ⁨North Atlantic Ocean (Portugal)⁩ on 1 Νοεμβρίου 1755. Source: ⁨Gorringe Bank Thrust⁩. Documented deaths: 50,000.

Documented Fatalities50,000Source: NOAA NCEI Significant Earthquake Database

Fault KinematicsThrust

Equivalent Energy84.80 Mt TNT

Μέγεθος

M 8.5

84.80 Mt TNT

Βάθος

20 km

shallow (Επιφανειακός φλοιικός)

Επίπτωση PAGER

red

60,000 fatalities

Τραυματίες: > 5,000 · ~51.4M αισθητός

Διαδραστικός χάρτης επικέντρου και ρηγμάτων

36.00°N, 11.00°W

Ρήγμα5 km

Gorringe Bank Thrust

Thrust · ~15.0 mm/yr

Felt byMMI III+

~51.4M exposed

~10.5M strong shaking

Primary SolutionUSGS/ISC-GEM

USGS/ISC-GEM#lisbon1755_benchmarkreviewed

1 agencies reporting

Setting36.0°N

Portugal

Offshore / Marine rupture

Seismic Activity & Aftershock Sequence

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

Hover or tap a point to inspect aftershocks and risk probability curve.

<35 χλμ (επιφανειακό)35–70 χλμ (ενδιάμεσο)>70 χλμ (βαθύ)Κύριος σεισμός

Situation Monitoring

Continuous verification

Multi-agency verification of casualties, tsunami alerts, and seismic sequence

Key facts so far

Casualties

None expected (offshore epicenter)

Zero exposed population

Tsunami Status

TSUNAMI WARNING

NOAA PTWC & regional buoys

Citizen Felt Reports

Not felt / offshore epicenter

Macroseismic DYFI verification

Aftershock Sequence

Monitoring

Aftershocks expected (Omori law)

LightGBM hazard model forecast

Multi-agency seismic telemetry active. Awaiting wire headlines.

Agency Discrepancy Matrix (Cross-Network Verification)

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

Network / Source	Magnitude (Scale & Diff)	Depth & Diff	Epicenter & Shift (Δd)	Consensus	Event ID / Data
USGS United States Geological Survey · Global / US	M8.5(Mw)Ref	20.0 kmRef	36.00°, -11.00°Origin	Authoritative	lisbon1755_benchmark

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

2 οικισμοί

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

Town	Distance	Intensity	Πληθυσμός
Portimão · Faro	254 km	MMI VII	61,226
Faro · Faro	297 km	MMI VII	41,355

Tectonic setting

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