M7.8 earthquake 32 km S of Inarajan Village, Guam

Sunday, August 8, 1993, 08:34:24 UTC · 12.982°N, 144.801°E

A magnitude 7.8 earthquake struck 32 km S of Inarajan Village, Guam on Sunday, August 8, 1993, 08:34:24 UTC, at a depth of 59.3 km (shallow). USGS received 15 “Did You Feel It?” reports, with a maximum reported intensity of IX (violent). No earthquake of this size or larger appears within 300 km in the USGS catalog since 1900.

Magnitude: 7.8; Major · mw
Depth: 59 km; Shallow
Felt reports: 15; Max intensity IX
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

7.6 megatons of TNT

That is about 502 times the Hiroshima bomb. It released about 15,849 times the energy of a magnitude 5.0.

Tectonic setting

89 km

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

Depth: shallow

59 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

Reports sent by people to USGS, grouped by place (most reports first). Intensity uses the Modified Mercalli scale (I–X): what people felt, not the magnitude.

Place	Intensity	Reports	Distance
96912<br>0.320	VIII · Severe	2	88 km
96910<br>0.320	VIII · Severe	2	80 km
96929<br>0.320	VIII · Severe	2	88 km
96913<br>0.320	V · Moderate	2	80 km
96923<br>0.330	IX · Violent	1	79 km
Dededo, Dededo, Guam	IX · Violent	1	84 km
96928<br>0.330	IX · Violent	1	73 km
96925<br>0.330	VII · Very strong	1	79 km
96911<br>0.330	I · Not felt	1	83 km

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 109 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M6.2 on August 11, 1993. 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 339 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 9 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:

1993M7.8
Tuman Bay, Apra Harbor
8 Aug 1993 · 0 km away · intensity IX
$250 million damagetsunami
1849M7.5
Guam
25 Jan 1849 · 198 km away · intensity IX
Severe damage ($5–24M)tsunami
1909M8.0
Guam
9 Dec 1909 · 58 km away · intensity VIII
Moderate damage ($1–5M)tsunami
1892M7.5
Guam
16 May 1892 · 198 km away · intensity VIII
Moderate damage ($1–5M)tsunami
1825
Ladrones Island
Apr 1825 · 198 km away · intensity VIII
Moderate damage ($1–5M)tsunami
1834
Agana
May 1834 · 198 km away
Moderate damage ($1–5M)

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

Nearby trackers