M6.3 earthquake 125 km SSE of Pangai, Tonga
A magnitude 6.3 earthquake struck 125 km SSE of Pangai, Tonga on Tue, Oct 18, 1983, 2:25 AM GMT+13 (13:25 UTC), 30 km (19 mi) below the surface.
Map
Where this earthquake was located, with the others nearby. Select one for its page.
The earthquake
- Magnitude
- 6.3 (Mw, moment), strong
- Magnitude from
- USGS National Earthquake Information Center
- Local time
- UTC
- 1983-10-17 13:25:21 UTC
- Depth
- 30.4 km (18.9 mi), shallow
- Epicenter
- 20.794° S, 173.758° W
- Region
- Tonga
- Tsunami flag
- No
- Status
- Reviewed by a seismologist
Magnitude estimates
Different scales measure different things and differ by a few tenths. The USGS marks one as preferred, and it is the one this page uses.
| Mag. | Scale | Computed by | Notes |
|---|---|---|---|
| 6.3 | Mw, moment | USGS National Earthquake Information Center | Preferred · Reviewed |
| 6.12 | Mw, moment | ISC-GEM global catalog | Final · ±0.1 |
| 6.1 | Mwc, centroid moment | Global CMT project | Preliminary |
What happened
The USGS’s account of the effects of this earthquake.
[FS]. FAULT PLANE SOLUTION: P-WAVES NP1:STRIKE=28;DIP=84;SLIP=90 NP2:STRIKE=208;DIP=6;SLIP=90 PRINCIPAL AXES: (T) PLG=51; AZM=298 (P) PLG=39; AZM=118 COMMENT: The focal mechanism is poorly controlled and corresponds to reverse faulting. The preferred fault plane is NP2. MOMENT TENSOR SOLUTION NO OF STA 9 SCALE 10**25 D-CM DEPTH 5 PRINCIPAL AXES: (T) VAL=3.61; PLG=50; AZM=293 (N) VAL=-0.21; PLG=11; AZM=36 (P) VAL=-3.40; PLG=38; AZM=135 BEST DOUBLE COUPLE:Mo=3.5*10**25 NP1:STRIKE=277;DIP=12;SLIP=152 NP2:STRIKE=35;DIP=84;SLIP=79 CENTROID, MOMENT TENSOR SOLUTION HARVARD EVENT-FILE NAME B101783A DATA USED: GDSN L.P. BODY WAVES: 17S, 38C, T=45 CENTROID LOCATION: ORIGIN TIME 13:25:24.8 0.3 LAT 20.61S 0.05;LON 173.69W 0.04 DEP 10.1 FIX;HALF-DURATION 4.3 MOMENT TENSOR; SCALE 10**25 D-CM MRR=0.70 0.03; MTT=-0.25 0.03 MFF=-0.45 0.04; MRT=0.31 0.08 MRF=1.74 0.09; MTF=-0.37 0.03 PRINCIPAL AXES: 1.(T) VAL=1.96;PLG=54;AZM=271 2.(N) -0.10; 9; 14 3.(P) -1.86; 34; 110 BEST DOUBLE COUPLE:M0=1.9*10**25 NP1:STRIKE=235;DIP=14;SLIP=132 NP2:Strike=12;Dip=80;Slip=81
From the USGS event page for usp0001z25. U.S. Geological Survey text and figures are in the public domain.
Did you feel it?
No one has reported feeling this quake to the USGS.
How well it is located
Reviewed by a seismologist.
- Depth from
- CONSTRAINED_BY_DEPTH_PHASES
Nearest places
Distance and direction from each place to the epicenter, with its forecast.
Nearby
Within 100 km, magnitude 3.3 and up: 5 in the 60 days after this one and 0 in the 30 days before it.
After
- 5.3113 km ENE of ‘Ohonua, Tonga · 15688 days ago · 70 km deep · 24 km away
- 4.4133 km ESE of Pangai, Tonga · 15648 days ago · 33 km deep · 90 km away
- 4.795 km SE of Pangai, Tonga · 15645 days ago · 33 km deep · 46 km away
- 5.283 km SE of Pangai, Tonga · 15644 days ago · 33 km deep · 42 km away
- 5.4129 km SE of Pangai, Tonga · 15642 days ago · 33 km deep · 18 km away
Earthquakes todayTonga earthquakesLive radar here
Sources
From the USGS Earthquake Hazards Program and its partner networks, event usp0001z25 (also filed as gcmtb101783a, gcmt19831017132522, iscgem566709). Read Fri, Oct 2, 2026, 3:25 AM UTC.