M6.8 earthquake 181 km WSW of Merizo Village, Guam

Friday, May 9, 2008, 21:51:29 UTC · 12.516°N, 143.181°E

A magnitude 6.8 earthquake struck 181 km WSW of Merizo Village, Guam on Friday, May 9, 2008, 21:51:29 UTC, at a depth of 76.0 km (intermediate). USGS received 55 “Did You Feel It?” reports, with a maximum reported intensity of VI (strong). It is the strongest earthquake within 300 km since an M7.1 on April 26, 2002.

Magnitude: 6.8; Strong · mwc
Depth: 76 km; Intermediate
Felt reports: 55; Max intensity VI
Est. shaking: —; No ShakeMap
PAGER alert: None; Not issued
Tsunami: No flag; USGS feed

Outlined circle: this earthquakeDashed circle: 100 km aftershock search area

In context

How big was it, and why here?

Energy released

239 kilotons of TNT

That is about 16 times the Hiroshima bomb. It released about 501 times the energy of a magnitude 5.0.

Tectonic setting

8 km

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

Depth: intermediate

76 km

Intermediate-depth earthquakes usually break inside a plate that is sinking into the mantle. Shaking spreads over a wide area but is gentler at the epicenter than a shallow quake of the same size.

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
96915<br>0.203	IV · Light	19	203 km
96929<br>0.242	IV · Light	12	233 km
96913<br>0.255	IV · Light	10	219 km
96910<br>0.311	IV · Light	3	214 km
96911<br>0.320	IV · Light	2	221 km
96952<br>0.320	III · Weak	2	413 km
96950<br>0.320	II · Weak	2	389 km
96928<br>0.330	VI · Strong	1	201 km
Barrigada, Barrigada, Guam	V · Moderate	1	218 km
Agana Heights, Agana Heights, Guam	V · Moderate	1	213 km
Tamuning, Tamuning, Guam	IV · Light	1	217 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 100 km

USGS lists 7 M2.5+ earthquakes within 100 km in the following 30 days; the largest was M5.1 on June 5, 2008. 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 557 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. The most severe:

1993M7.8
Tuman Bay, Apra Harbor
8 Aug 1993 · 183 km away · intensity IX
$250 million damagetsunami
1849M7.5
Guam
25 Jan 1849 · 166 km away · intensity IX
Severe damage ($5–24M)tsunami
1909M8.0
Guam
9 Dec 1909 · 197 km away · intensity VIII
Moderate damage ($1–5M)tsunami
1892M7.5
Guam
16 May 1892 · 166 km away · intensity VIII
Moderate damage ($1–5M)tsunami
2001M7.0
Guam
12 Oct 2001 · 196 km away · intensity VIII
Moderate damage ($1–5M)
1825
Ladrones Island
Apr 1825 · 166 km away · intensity VIII
Moderate damage ($1–5M)tsunami

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

Nearby trackers