M7.4 earthquake in San Juan, Argentina

Wednesday, November 23, 1977, 09:26:24 UTC · 31.028°S, 67.767°W

A magnitude 7.4 earthquake struck in San Juan, Argentina on Wednesday, November 23, 1977, 09:26:24 UTC, at a depth of 13.0 km (shallow). No earthquake of this size or larger appears within 300 km in the USGS catalog since 1900.

Magnitude: 7.4; Major · ms
Depth: 13 km; Shallow
Felt reports: 0; Did You Feel It?
Est. shaking: IX; Violent (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

1.9 megatons of TNT

That is about 126 times the Hiroshima bomb. It released about 3,981 times the energy of a magnitude 5.0.

Tectonic setting

463 km

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

Depth: shallow

13 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 96 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M6.3 on November 24, 1977. 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 52 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 12 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 24,484 recorded deaths. The most severe:

1861
Mendoza, San Luiz
20 Mar 1861 · 220 km away · intensity IX
14,000 deathsExtreme damage ($25M+)tsunami
1944M6.9
San Juan Province
15 Jan 1944 · 86 km away · intensity IX
10,000 deaths$100 million damage
1920M6.7
Mendoza
17 Dec 1920 · 115 km away · intensity VIII
400 deathsSevere damage ($5–24M)
1977M7.5
San Juan Province: Mendoza
23 Nov 1977 · 12 km away · intensity IX
65 deaths$80 million damage
1899
La Rioja
12 Apr 1899 · 271 km away · intensity VIII
11 deathsModerate damage ($1–5M)
1952M6.8
San Juan
11 Jun 1952 · 99 km away · intensity VIII
5 deathsModerate damage ($1–5M)

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

Nearby trackers