Reviewed by USGS41y ago
M4.6 earthquake east of the North Island of New Zealand
Thursday, October 3, 1985, 19:47:07 UTC · 35.206°S, 178.886°W
A magnitude 4.6 earthquake struck east of the North Island of New Zealand on Thursday, October 3, 1985, 19:47:07 UTC, at a depth of 33.0 km (shallow). It is the strongest earthquake within 300 km since an M5.0 on October 1, 1985.
- Magnitude
- 4.6
- Light · mb
- Depth
- 33 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
120 tons of TNT
That is about 1/126 of the Hiroshima bomb. A magnitude 5.0 releases about 4 times more energy.
Tectonic setting
8 km
from the nearest mapped plate boundary, between the Kermadec and Pacific plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.
Depth: shallow
33 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 4 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M5.4 on October 17, 1985. 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 211 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 6.9south of the Kermadec IslandsSeptember 26, 1985 · 61 km N of this epicenter
- 6.9south of the Kermadec IslandsJuly 11, 1943 · 298 km N of this epicenter
- 6.8south of the Kermadec IslandsJanuary 8, 1970 · 216 km W of this epicenter
- 6.7south of the Kermadec IslandsFebruary 13, 1949 · 214 km NE of this epicenter
- 6.6off the east coast of the North Island of New ZealandFebruary 13, 1938 · 169 km SW of this epicenter
- 6.6south of the Kermadec IslandsSeptember 1, 1937 · 275 km N of this epicenter
- 6.5south of the Kermadec IslandsOctober 14, 1947 · 254 km NE of this epicenter
- 6.5south of the Kermadec IslandsMay 27, 1942 · 270 km NE of this epicenter