M5.1 earthquake 7 km W of Sangay, Philippines

Monday, September 20, 1976, 15:04:45 UTC · 6.439°N, 123.974°E

A magnitude 5.1 earthquake struck 7 km W of Sangay, Philippines on Monday, September 20, 1976, 15:04:45 UTC, at a depth of 47.0 km (shallow). It is the strongest earthquake within 300 km since an M5.3 on September 11, 1976.

Magnitude: 5.1; Moderate · ms
Depth: 47 km; Shallow
Felt reports: 0; Did You Feel It?
Est. shaking: —; No ShakeMap
PAGER alert: None; Not issued
Tsunami: No flag; USGS feed

Outlined circle: this earthquakeDashed circle: 75 km aftershock search area

In context

How big was it, and why here?

Energy released

674 tons of TNT

That is about 1/22 of the Hiroshima bomb. It released about 1 times the energy of a magnitude 5.0.

Tectonic setting

362 km

from the nearest mapped plate boundary, between the Philippine Sea and Sunda plates. Earthquakes this far from a boundary happen on faults inside a plate, often less frequently but sometimes strongly.

Depth: shallow

47 km

Shallow earthquakes (under 70 km) produce the strongest surface shaking for their size, so they are the ones most likely to cause damage near the epicenter.

Did You Feel It?

Where it was felt

No “Did You Feel It?” reports have been published for this event yet. If you felt it, you can add your report on the USGS website.

I felt it — report to USGS ↗

USGS PAGER estimate

Who was exposed to shaking

USGS publishes PAGER impact estimates for significant earthquakes, usually within an hour. No PAGER estimate is available for this event.

After the main event

Aftershocks within 75 km

USGS lists 12 M2.5+ earthquakes within 75 km in the following 30 days; the largest was M6.0 on September 29, 1976. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.

Time after the mainshock on a logarithmic scale (first hours stretched), magnitude on the vertical axis. M2.5+ events from USGS.

Regional history

Past M5+ earthquakes within 300 km

USGS lists 201 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:

History · NOAA

Deadliest earthquakes in this area

NOAA’s significant-earthquake database lists 27 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 8,776 recorded deaths. The most severe:

1976M8.0
Mindanao: S
16 Aug 1976 · 21 km away · intensity VI
8,000 deaths$134 million damagetsunami
1955M7.4
Mindanao: Lanao,Ozamiz,Cotabato
31 Mar 1955 · 163 km away · intensity VIII
465 deaths$5 million damagetsunami
1913M7.8
Sangihe Island
14 Mar 1913 · 266 km away · intensity IX
138 deathsModerate damage ($1–5M)tsunami
1928M7.4
Cotabato,N Coast Of Illana Bay
19 Dec 1928 · 42 km away · intensity VII
97 deathsModerate damage ($1–5M)tsunami
1918M8.3
Mindanao: Cotabato
15 Aug 1918 · 100 km away · intensity X
52 deathsSevere damage ($5–24M)tsunami
1897M8.7
Mindanao, Zamboanga, Sulu, Isabela
21 Sep 1897 · 224 km away · intensity IX
13 deathsSevere damage ($5–24M)tsunami

NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.

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