Shallow M5.7 Earthquake struck on Saturday Morning in the South Pacific Ocean 174km from Nuku‘alofa (Tonga).

Written by Earthquakelist.org on July 21st, 2023. Last updated September 19th, 2023.

In the morning of Saturday July 22nd, 2023, a shallow and significant MAG-5.7 earthquake hit in the South Pacific Ocean 174 kilometer from Nuku‘alofa, Tonga. Roughly 90 thousand people may have felt this earthquake.

Earthquake Summary

This earthquake hit under water in the South Pacific Ocean, 160 kilometers (99 mi) off the coast of Tonga, 174 kilometer south of Nuku‘alofa in Tongatapu. The center of this earthquake had a very shallow depth of 10 km. Shallow earthquakes usually have a larger impact than earthquakes deep in the earth.

Date and Time:	Jul 22, 2023 08:01AM (Tongatapu Time) - Jul 21, 2023 19:01 Universal Time.
Location:	174 km south of Nuku‘alofa, Tongatapu, Tonga. Coordinates 22°42'10"S 175°7'10"W.
Map:	Map of area around epicenter. Click to open in Google Maps.
Magnitude:	MAG 5.7 Detected by 25 stations. Maximum Error Range ±0.062 .
Depth:	10 km (6 mi) A very shallow depth.
Max. Intensity:	IV Light On the Modified Mercalli Scale.
Tsunami Risk:	Low tsunami risk Earthquakes under MAG-6.5 do not usually cause tsunami's. Always stay cautious - More info here.

Minimal impact predicted

Based on scientific estimates by the US Geographic Survey (USGS), the risk of high fatalities for this earthquake is classified at level GREEN (low). They expect an 65% likelyhood of between 0 and 1 fatalities, and a 96% chance that the number of fatalities falls no higher than 10.

The USGS classifies the economic impact of this earthquake at level GREEN (low). They expect an 65% likelyhood of between 0 and 1 million US Dollars in economic damage and impact, and a 96% chance that the economic impact of this earthquake falls no higher than 10 million USD.

Roughly 90 thousand people exposed to shaking

This earthquake may have been felt by around 90 thousand people. That is the expected population size of the area exposed to a level of shaking of II or higher on the Modified Mercalli scale according to the USGS.

Weak shaking and probably no damage may have been experienced by an estimated 85,770 people. At III, it is the highest MMI level this earthquake has caused. All exposure to shaking was within the borders of Tonga .

People	MMI Level	Shaking	Damage
0	I	Not noticable	None
0	II	Very weak	None
85,770	III	Weak	Probably none
0	IV	Light	Likely none
0	V	Moderate	Very light
0	VI	Strong	Light
0	VII	Very Strong	Moderate
0	VIII	Severe	Moderate to heavy
0	IX	Violent	Heavy
0	X	Extreme	Very heavy

Nearby towns and cities

This earthquake may have been felt in Tonga . Located 174 kilometer (108 mi) south of the epicenter of this earthquake, Nuku‘alofa (Tongatapu, Tonga) is the nearest significant population center. Nuku‘alofa experienced an earthquake intensity (MMI Scale) of roughly III. That level implies weak shaking and probably no damage.

Overview of nearby places

Cities and Towns around the epicenter of this earthquake.
Distance	Place	Intensity (MMI)
174 km (108 mi) N from epicenter	Nuku‘alofa Tongatapu, Tonga.	III Weak

Earthquake Intensity Map

The graph below overlays a map of the region around the epicenter with earthquake intensity data provided by the US Geographic Survey. The highest intensity level detected for this earthquake is III.

I Not felt

II Weak

III Weak

IV Light

V Moderate

VI Strong

VII Very Strong

VIII Severe

IX Violent

X Extreme

Earthquake Intensity Map based on Shakemap Data provided by USGS.

Aftershocks detected

After this earthquake struck, 1 smaller aftershock occurred. At a distance of 32 km (20 mi) west of this earthquake, an aftershock struck 5 mins later. It measured a magnitude of 4.9

This main shock was prefaced by 1 smaller foreshock. A 4.7 magnitude earthquake hit 3 days earlier nearby.

Overview of foreshocks and aftershocks

Detected MAG2.5+ earthquakes within within 100km (62 mi), that occurred in the three days before and after the main shock.
Classification	Magnitude	When	Where
Foreshock	M 4.7	3 days earlier Jul 19, 2023 08:51AM (Tongatapu Time)	24 km (15 mi) NE from Main Shock.
Main Shock This Earthquake	M 5.7	Jul 22, 2023 08:01AM (Tongatapu Time)	-
Aftershock	M 4.9	5 mins later Jul 22, 2023 08:06AM (Tongatapu Time)	32 km (20 mi) W from Main Shock.

More earthquakes coming?

The risk of aftershocks decreases rapidly over time. Usually, aftershocks are at least one order of magnitude lower than a main shock.

It's always adviced to be cautious of the risk of a larger shock following any significant earthquake, however this risk is fairly small. There is a roughly 94 percent change that no larger main shock will follow in the days following this earthquake.

Read: How to Stay Safe during an Earthquake (cdc.gov).

Earthquakes like this happen often in the region

Earthquakes of this strength are very common in the region. This is the strongest earthquake to hit since June 25th, 2023, when a 6.2 magnitude earthquake hit 160 km (100 mi) further south-southwest. An even stronger magnitude 7.2 earthquake struck on June 15th, 2023.

In total, 42 earthquakes with a magnitude of 5.7 or higher have been registered within 300km (186 mi) of this epicenter in the past 10 years. This comes down to an average of once every 3 months.

Low tsunami risk

DISCLAIMER: We strongly suggest to closely monitor advice from local authorities with regards to tsunami risks. Our analysis is based on automatically collected data from external sources, and these might contain mistakes. In addition, earthquakes can cause landslides that may lead to a tsunami, or be a followed by another, potentially stonger, earthquake.

Based on early data it appears this earthquake was not strong enough (lower than MAG-6.5) to be likely to cause destructive tsunami's. However this earthquake appeared to have hit at a shallow depth under sea, so stay cautious and monitor advice from local authorities.

Tsunami Risk Factors

Factor	Under Sea?	MAG-6.5 or stronger?	Shallow depth?
Explanation	Almost all tsunami's are caused by earthquakes with their epicenter under sea or very near the sea. However stay cautious in coastal areas as earthquakes on land may cause landslides into sea, potentially still causing a local tsunami.	Under MAG 6.5: Very unlikely to cause a tsunami. MAG 6.5 to 7.5: Destructive tsunami's do occur, but are uncommon. Likely to observe small sea level changes. MAG 7.6+: Earthquakes with these magnitudes might produce destructive tsunami's.	Most destructive tsunami's are caused by shallow earthquakes with a depth between 0 and 100km under the surface of the earth. Deeper tsunami's are unlikely to displace to ocean floor.
This Earthquake	This earthquake appears to have struck under the sea.	Not this earthquake. This earthquake had a magnitude of 5.7. Earthquakes of this strength are unlikely to trigger a tsunami.	This earthquake occurred at a depth of of 10 km (6 mi). Earthquakes this shallow could trigger a tsunami.

Sources

Last updated 19/09/23 12:57 (). This article is automatically generated based on available data. We keep checking multiple sources for additional information. This article gets updated as new details on this earthquake become available.