M4.9 earthquake 63 km S of San Agustín de Valle Fértil, Argentina

Monday, December 12, 1977, 16:02:34 UTC · 31.209°S, 67.498°W

A magnitude 4.9 earthquake struck 63 km S of San Agustín de Valle Fértil, Argentina on Monday, December 12, 1977, 16:02:34 UTC, at a depth of 46.0 km (shallow). It is the strongest earthquake within 300 km since an M5.3 on December 10, 1977.

Magnitude: 4.9; Light · mb
Depth: 46 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: 50 km aftershock search area

In context

How big was it, and why here?

Energy released

338 tons of TNT

That is about 1/45 of the Hiroshima bomb. A magnitude 5.0 releases about 1 times more energy.

Tectonic setting

488 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

46 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 50 km

USGS lists 9 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M5.7 on December 21, 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 106 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 13 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 · 215 km away · intensity IX
14,000 deathsExtreme damage ($25M+)tsunami
1944M6.9
San Juan Province
15 Jan 1944 · 100 km away · intensity IX
10,000 deaths$100 million damage
1920M6.7
Mendoza
17 Dec 1920 · 116 km away · intensity VIII
400 deathsSevere damage ($5–24M)
1977M7.5
San Juan Province: Mendoza
23 Nov 1977 · 34 km away · intensity IX
65 deaths$80 million damage
1899
La Rioja
12 Apr 1899 · 298 km away · intensity VIII
11 deathsModerate damage ($1–5M)
1952M6.8
San Juan
11 Jun 1952 · 107 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