M6.9 earthquake in Mariana Islands region

Friday, August 13, 2010, 21:19:34 UTC · 12.487°N, 141.474°E

A magnitude 6.9 earthquake struck in Mariana Islands region on Friday, August 13, 2010, 21:19:34 UTC, at a depth of 16.0 km (shallow). USGS received 9 “Did You Feel It?” reports, with a maximum reported intensity of I (not felt). It is the strongest earthquake within 300 km since an M7.0 on June 7, 1966.

Magnitude: 6.9; Strong · mwc
Depth: 16 km; Shallow
Felt reports: 9; Max intensity I
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

338 kilotons of TNT

That is about 22 times the Hiroshima bomb. It released about 708 times the energy of a magnitude 5.0.

Tectonic setting

150 km

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

Depth: shallow

16 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
Dededo, Dededo, Guam	I · Not felt	1	382 km
Talofofo, Talofofo, Guam	I · Not felt	1	368 km
Tamuning, Tamuning, Guam	I · Not felt	1	375 km
96913<br>0.330	I · Not felt	1	377 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 106 M2.5+ earthquakes within 100 km in the following 30 days; the largest was M6.6 on August 14, 2010. 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 412 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 7 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:

1849M7.5
Guam
25 Jan 1849 · 260 km away · intensity IX
Severe damage ($5–24M)tsunami
1892M7.5
Guam
16 May 1892 · 260 km away · intensity VIII
Moderate damage ($1–5M)tsunami
1825
Ladrones Island
Apr 1825 · 260 km away · intensity VIII
Moderate damage ($1–5M)tsunami
1834
Agana
May 1834 · 260 km away
Moderate damage ($1–5M)
1903
Guam
10 Feb 1903 · 260 km away · intensity VII
Limited damage (under $1M)tsunami
2010M6.9
Guam, Northern Mariana Islands
13 Aug 2010 · 0 km away
tsunami

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

Nearby trackers