bodyType

customContents

entityId

entityUuid

articlePageQuery

filter

article

articleBaseAdvertisingInfoArticle

articleListArticle

articleSeoArticle

helpersCheckIsPostiesArticle

hooksArticleAcknowledgementGateOverlayArticle

hooksTrackPageViewArticle

hooksContentInterestArticle

articleLinkingDataContent

articleSchemaContent

liveArticle

advertZone

sentiment

contentLock

topics

types

sections

moreOnThisArticles

urlAlias

commentCount

sponsorType

authorLocations

authors

paywallTypes

corrections

displaySlideShow

multimediaEmbed

printHeadline

seriesContainer

socialHeadline

headline

flag

firstTopic

glossary

flattenTypeIds

publishedDate

additionalInfoBoxes

images

image

relatedLinks

relatedNewsletters

__typename

createdDate

sponsor

factSheets

series

disableOffPlatformContent

published

updatedDate

summary

subHeadline

body

keywords

copyrighted

customTimezone

liveContents

Dee Ninis

The death toll from Vanuatu’s earthquake disaster continued to rise this week, leading to urgent international search and rescue operations to assist those affected by the initial quake and its subsequent aftershocks.
On Tuesday afternoon, a powerful earthquake with a magnitude of 7.3 struck 30km (18.6 miles) off the west coast of Efate, the main island of Vanuatu. The quake, which occurred at a depth of just 50km (31 miles), caused significant damage to numerous buildings and injured dozens of people in Port Vila, the capital of the Pacific island nation.
Since the initial quake, there have been several aftershocks at nearly the same location, including a magnitude 5.5 on Wednesday morning, which has further exacerbated the devastation and injuries.
Based on previous experience, here’s what might happen next.

More aftershocks?
Measuring 7.3 in magnitude, the earthquake that hit Vanuatu is considered major.
The several aftershocks of magnitude 5 in the same area are typical of an aftershock sequence – the series of smaller earthquakes that tend to follow the large one, known as the mainshock.
For an earthquake of this magnitude, over 7, it is expected that there will be at least a few aftershocks in the range of magnitude 6 as well. In a typical aftershock sequence, there would be 10 times as many aftershocks in the magnitude 5 range, and 10 times as many again in magnitude 4, and so on.
This pattern can persist for weeks to several months, or even longer, with both the magnitude and frequency of earthquakes generally decreasing over time.

A bigger quake?
There is a very small chance that an earthquake larger than Tuesday’s 7.3 might still occur. If this were to happen, the initial earthquake would be considered a “foreshock”, meaning a smaller earthquake preceding a larger one.
However, this is not very common. Only about 5 per cent of the time does a major earthquake of this magnitude serve as a foreshock to an even larger event.
Vanuatu sits within the Ring of Fire – a belt of tectonic activity that surrounds the Pacific Ocean, thanks to a series of plate boundaries around the Pacific plate.
Its name originates from the numerous volcanoes that are formed through subduction, which occurs when one tectonic plate is forced beneath another.

The Pacific plate and the Australian plate converge to the immediate west of Vanuatu. The Australian Plate is being subducted, meaning it is sliding beneath the Pacific Plate at a rate of about 80 to 90 millimetres per year, which classifies it as a fast-moving plate boundary.
This plate boundary also includes the Solomon Islands, Fiji, Tonga, and extends south to New Zealand.
In regions prone to earthquakes due to subduction, it’s possible to have earthquakes with magnitudes exceeding 8. However, there have been no recorded earthquakes of this magnitude in the historical records for the region of Vanuatu.
While Tuesday’s earthquake will continue to produce aftershocks, these will be confined to the area surrounding the mainshock.
Of course, earthquakes elsewhere on the plate boundary are always possible, but these distant events won’t be as a result of Tuesday’s earthquake.


Is Vanuatu hit by earthquakes often?
Earthquakes are common in Vanuatu, due to the aforementioned Ring of Fire. Since 1990, there have been 11 earthquakes with a magnitude greater than 7 within 200km (124 miles) of Tuesday’s event.
In 2010, a 7.5 magnitude quake struck just 40km (25 miles) from Port Vila at a depth of 35km (22 miles), generating a small tsunami. However, no deaths or injuries were reported.
The last time an earthquake sequence had a significant death toll in Vanuatu was in November 1999, when a shallow quake of magnitude 7.5 occurred off the coast of the volcanic island Ambrym, triggering a tsunami.
At this particular plate boundary, earthquakes can be as deep as 300km (186 miles). Generally, the deeper the earthquake, the less damage it will cause, because it’s further away from the surface, resulting in weaker shaking.
That’s another reason why Tuesday’s earthquake near Port Vila was so damaging – it was reasonably shallow for a plate boundary region, and produced very strong ground shaking.
Dee Ninis is an earthquake scientist at Australia’s Monash University. This article was first published by The Conversation




Why Vanuatu should expect more aftershocks – and maybe another earthquake

Australia strikes US$118 million policing deal with China-friendly Solomon Islands

Vanuatu hit by deadly magnitude 7.4 earthquake as rescuers search Pacific island for survivors

Vanuatu earthquake death toll reaches 14, including 2 Chinese

Pacific nations

Members of Australia’s federal police and other rescue workers stand by a collapsed building in Port Vila, Vanuatu. Photo: Australian Federal Police via AP

A vehicle is trapped beneath a collapsed building following a strong earthquake in Port Vila, Vanuatu on December 17/ Photo: Jeremy Ellison/Reuters

A landslide after an earthquake of magnitude 7.3 hit Port Vila, Vanuatu. Photo: Xinhua

Rescuers at a collapsed building after an earthquake struck Port Vila, the capital city of Vanuatu. Photo: AFP

Members of Australia’s federal police and other rescuers stand by a collapsed building in Port Vila, Vanuatu. Photo: Australian Federal Police via AP

Rescuers inspect a collapsed building in Vanuatu’s capital Port Vila after a powerful earthquake hit the Pacific nation. Photo: Michael Thompson via AFP

A landslide is seen near an international shipping terminal in Port Vila, Vanuatu. Photo: Dan McGarry via AP

Vanuatu Red Cross Society volunteers and staff help with the clean up at Vila Central Hospital in Port Vila on Wednesday. Photo: Vanuatu Red Cross Society via AP

Buildings ‘pancaked’ in Vanuatu as 7.4 magnitude earthquake rocks Pacific nation

A severely damaged building housing the embassies of the US, Britain and New Zealand is seen after a powerful earthquake struck Port Vila, the capital city of Vanuatu, on Tuesday. Photo: AFP

A member of security personnel inspects a collapsed building in Vanuatu’s capital Port Vila on Tuesday. Photo: Facebook/Michael Thompson/AFP

A car is seen trapped underneath a collapsed building in Vanuatu’s capital Port Vila on Tuesday. Photo: Facebook/Michael Thompson/AFP

Vanuatu replaces pro-West PM Kalsakau, with Sato Kilman who wants closer Beijing ties, amid China-US rivalry in Pacific

Vanuatu parliament has elected Sato Kilman as prime minister. Photo: NurPhoto via Getty Images

Ishmael Kalsakau was replaced as Vanuatu’s PM on Monday. Photo: Monday

Japan urged to provide earthquake tips to tourists amid surge in travel cancellations

A man at his home destroyed by fire in the city of Wajima, Ishikawa prefecture on February 1, one month after a 7.5 magnitude earthquake struck the Noto region. Photo: AFP

A collapsed house in Osaki in Kagoshima Prefecture after a strong earthquake hit southwestern Japan on August 8. Photo: Kyodo

A supermarket sign in the Sumida district of Tokyo indicating a limit on bottled water sales after quake-related media reports caused customers to hoard essentials. Photo: AFP

People seek shelter after an earthquake with a magnitude of 7.1 hit Miyazaki, southwestern Japan, on August 8. Photo: Kyodo

Japan to build hospital ships to boost disaster response in coastal areas: ‘a huge help’

A port is wrecked in Anamizu, Ishikawa prefecture, on January 5, following a strong earthquake that jolted the Noto Peninsula and surrounding areas in central Japan on January 1. Photo: Kyodo

Debris from the January 1 Noto Peninsula earthquake piled up on a temporary waste disposal site in the Ishikawa prefecture city of Suzu, central Japan, six months after the disaster. Photo: Kyodo

This Week in Asia

Opinion

A powerful 7.3 magnitude earthquake struck off the west coast of Efate, the main island of Vanuatu, earlier this week


A powerful 7.3 magnitude earthquake struck off the west coast of Efate, the main island of Vanuatu, earlier this week.


Earthquakes

Vanuatu

Natural disasters

Chinese overseas

Expresses the views, ideas and conclusions of the author. (Eg. Enough of Crazy Rich Asians, think of crazy poor Hongkongers.)


Opinion | Why Vanuatu should expect more aftershocks – and maybe another earthquake

A powerful 7.3 magnitude earthquake struck off the west coast of Efate, the main island of Vanuatu, earlier this week

More aftershocks?