Reviewed by USGSNorthern Mariana Islands36y ago
M4.9 earthquake 123 km E of Saipan, Northern Mariana Islands
Tuesday, July 31, 1990, 22:27:48 UTC · 15.358°N, 146.890°E
A magnitude 4.9 earthquake struck 123 km E of Saipan, Northern Mariana Islands on Tuesday, July 31, 1990, 22:27:48 UTC, at a depth of 45.7 km (shallow). It is the strongest earthquake within 300 km since an M5.1 on July 26, 1990.
- 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
71 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
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 1 M2.5+ earthquake within 50 km in the following 30 days; the largest was M4.9 on August 30, 1990. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
Regional history
Past M5+ earthquakes within 300 km
USGS lists 270 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 7.6198 km E of Saipan, Northern Mariana IslandsApril 5, 1990 · 80 km E of this epicenter
- 7.5Mariana Islands regionJanuary 17, 1940 · 234 km NE of this epicenter
- 7.1233 km NE of Saipan, Northern Mariana IslandsJuly 2, 1949 · 144 km NE of this epicenter
- 7.0176 km ESE of San Jose Village, Northern Mariana IslandsMay 18, 1913 · 124 km S of this epicenter
- 7.032 km NNE of Yigo Village, GuamOctober 26, 1912 · 270 km SW of this epicenter
- 7.0233 km ESE of Saipan, Northern Mariana IslandsJune 14, 1942 · 130 km SE of this epicenter
- 6.6Mariana Islands regionSeptember 1, 1970 · 276 km N of this epicenter
- 6.6Alamagan region, Northern Mariana IslandsFebruary 10, 1921 · 272 km N of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 2 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 1975M6.1
Guam
1 Nov 1975 · 285 km away · intensity VII
Limited damage (under $1M)
- 1990M7.5
Saipan; Guam
5 Apr 1990 · 80 km away · intensity IV
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.