M7.7 earthquake 2 km ESE of San Agustín Loxicha, Mexico

Wednesday, November 29, 1978, 19:52:47 UTC · 16.010°N, 96.591°W

A magnitude 7.7 earthquake struck 2 km ESE of San Agustín Loxicha, Mexico on Wednesday, November 29, 1978, 19:52:47 UTC, at a depth of 18.0 km (shallow). It is the strongest earthquake within 300 km since an M8.0 on June 17, 1928.

Magnitude: 7.7; Major · ms
Depth: 18 km; Shallow
Felt reports: 0; Did You Feel It?
Est. shaking: VIII; Severe (ShakeMap)
PAGER alert: None; Not issued
Tsunami: No flag; USGS feed

Outlined circle: this earthquakeDashed circle: 200 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)

In context

How big was it, and why here?

Energy released

5.4 megatons of TNT

That is about 355 times the Hiroshima bomb. It released about 11,220 times the energy of a magnitude 5.0.

Tectonic setting

72 km

from the nearest mapped plate boundary, between the Cocos and North American plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.

Depth: shallow

18 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 200 km

USGS lists 27 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M5.7 on November 29, 1978. 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 139 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 48 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 721 recorded deaths. The most severe:

1973M6.2
Veracruz, Mexico City
28 Aug 1973 · 251 km away · intensity VII
527 deathsSevere damage ($5–24M)
1957M7.9
Acapulco,Mexico City
28 Jul 1957 · 273 km away · intensity VII
65 deaths$25 million damagetsunami
1937M7.2
Central, Puebla: Esperanza, Veracruz
26 Jul 1937 · 290 km away
34 deathsModerate damage ($1–5M)
1870M7.9
Oaxaca,Zanaguia,San Francisco Ozolotepec
11 May 1870 · 75 km away
24 deathsSevere damage ($5–24M)tsunami
1968M7.3
Oaxaca, Guerrero
2 Aug 1968 · 135 km away · intensity VII
18 deaths$2 million damagetsunami
1787M8.6
San Marcos, Oaxaca
28 Mar 1787 · 211 km away · intensity IX
11 deathsSevere damage ($5–24M)tsunami

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

Nearby trackers