M6.6 earthquake 89 km N of Saipan, Northern Mariana Islands

Saturday, February 5, 2005, 03:34:25 UTC · 16.011°N, 145.867°E

A magnitude 6.6 earthquake struck 89 km N of Saipan, Northern Mariana Islands on Saturday, February 5, 2005, 03:34:25 UTC, at a depth of 142.7 km (intermediate). USGS received 105 “Did You Feel It?” reports, with a maximum reported intensity of VI (strong). It is the strongest earthquake within 300 km since an M7.6 on April 5, 1990.

Magnitude: 6.6; Strong · mwc
Depth: 143 km; Intermediate
Felt reports: 105; 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

120 kilotons of TNT

That is about 8 times the Hiroshima bomb. It released about 251 times the energy of a magnitude 5.0.

Tectonic setting

115 km

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

Depth: intermediate

143 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
96950<br>0.128	V · Moderate	45	182 km
96929<br>0.236	III · Weak	13	322 km
96910<br>0.277	IV · Light	7	337 km
96913<br>0.277	IV · Light	7	334 km
96915<br>0.277	III · Weak	7	347 km
Garapan, Saipan, Northern Mariana Islands	V · Moderate	3	168 km
Capital Hill, Saipan, Northern Mariana Islands	VI · Strong	2	169 km
96952<br>0.320	V · Moderate	2	169 km
Yigo, Yigo, Guam	IV · Light	2	326 km
96911<br>0.320	IV · Light	2	331 km
Tamuning, Tamuning, Guam	II · Weak	2	335 km
Dandan, Saipan, Northern Mariana Islands	VI · Strong	1	173 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 4 M2.5+ earthquakes within 100 km in the following 30 days; the largest was M4.9 on February 25, 2005. 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 455 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 5 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:

1902M8.1
Agana
22 Sep 1902 · 222 km away · intensity IX
Severe damage ($5–24M)
1997M6.5
Guam
23 Apr 1997 · 248 km away · intensity VII
Limited damage (under $1M)
2002M6.5
Saipan
14 Aug 2002 · 215 km away
Limited damage (under $1M)
1975M6.1
Guam
1 Nov 1975 · 269 km away · intensity VII
Limited damage (under $1M)
1990M7.5
Saipan; Guam
5 Apr 1990 · 210 km away · intensity IV
tsunami

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

Nearby trackers