on WEWAK Post-Earthquake Risk Assessment
9-11 September 2002
Professor Hugh Davies, UPNG
An earthquake of moment magnitude (MW) 7.4, Richter magnitude (MR) 7.7,
occurred at4.45 am local time at an epicentre about 70 km west-northwest of
Wewak, at or near3oS 143oE. The earthquake was at relatively shallow depth (30
km depth reported byPort Moresby Geophysical Observatory) and was strongly felt
in the Wewak area. Theearthquake was of significantly greater magnitude than
that which caused adevastating tsunami at Aitape in 1998. A small tsunami was
At 11 am on 9 September this observer departed Port Moresby on aircraft
P2-PNG andarrived Wewak 12.40 pm. At 2.40 pm the observer departed Wewak on
helicopter P2-MTSin company of Minister Sir Peter Barter, Governor, East Sepik,
Mr Arthur Somare,and a TV cameraman representing RTA and EM TV. The party
returned to Wewak at about5.30 pm.On 10 September the observer visited sites
along the coast west of Wewak, by roadand foot, in the company of Governor East
Sepik Province, AAP journalist JimBaynes, and driver.On 11 September the
observer visited the Murik people's settlement at Namba 2Pasis in Wewak, and
returned to Port Moresby on P2-PNG, arriving 2 pm.
1. To ascertain whether any people are at risk of further damage or injury
following on from the earthquake of 9.9.02.
2. To talk with people, answer questions, and, as far as possible, reassure them
so that the element of panic following the earthquake and tsunami is minimized.
Please note that this is not a damage assessment report.
- Aerial inspection of selected localities, looking for indications of
unstable ground or slopes that might fail, and so might threaten villages or
- Visits to as many locations as possible, in the time available, to make
on-the-ground inspections of possible hazardous sites, and talk with people.
- Record details of damage, of earth movements and of tsunami wave run-up
heights in as many places as possible, in the time available.
inspected from the air (helicopter P2-MTS):
- Mussu Island western end and part of centre
- Kairiru island all coasts
- Yuo and Keresau Islands
- Walis and Tarawai Islands
- Mainland coastline from Dagua east to Wewak
inspected on the ground:
- Sup village on Mussu
- St Xavier College on Kairiru
- Koragur (or Korgur) village on north coast of Kairiru
- Yuo on south coast of Yuo Island
- Tarawai on west coast of Tarawai Island
- Walis on south coast of Walis Island
- Boiken Baja near Boiken on mainland
- But Mission on mainland
- Kauk village on mainland
- Dagua Mission on mainland
- Kwabun village, east of Boiken
- Katio hamlet on Hawain River
- Ubidnim village (one of the Yuo villages) at mouth of Hawain River
- Namba 2 Pasis (Murik people settlement) on Wewak peninsula
- Coast Highway from Wewak to Kauk turn-off (past But)
- No people were found to be at risk of further damage or injury arising
from the earthquake and tsunami.
- Where unstable conditions were recognized, for example at Koragur village,
people had already taken appropriate action. At Koragur, the coastal cliff
had become unstable and people already had marked off the unstable ground
and had made plans to relocate houses that were at risk.
- There appeared to have been uplift of about 30 cm along parts of the wave-cutplatform
and reefs along the coast of Kairiru, Mussu and Tarawai Islands. This
wasnoteworthy but presented no risk to people. Upward or downward movement
of theearth's crust at the time of a strong earthquake is a relatively
common phenomenon.The uplift needs to be checked again to ensure it was not
a temporary effect.
- Cracks developed in the ground on the beachfront at Kauk, and in and
nearUbidnim village. At these and other locations, the subsurface sediments
hadliquefied and had emerged up the cracks and in some cases squirted into
the air.Liquefaction of subsurface sediments at the time of a strong
earthquake is a commonphenomenon.
- A crack that is reportedly causing concern to people on Keresau Island was
notinspected, but should be inspected by a geologist. It is likely that it
will proveto be similar to those seen at Kauk and Ubidnim.
- The tsunami developed within minutes of the earthquake.
- Tsunami run-up height (the maximum height reached by the tsunami wave as
it cameashore) was in most places less than a metre, but was 1.5 m at Kauk,
and reportedly3-4 m in the bay immediately east of the point at Boiken
(location not visited bythis observer). Other observations of run-up height
are being tabulated and will bereported separately.
- The level of tsunami awareness in the coastal villages is high. People
knew ofthe danger of a tsunami following the strongly felt earthquake, and
moved inland.After the event, some islands people had left the islands for
the same reason.
- Almost all of the visible damage was caused by the earthquake, and not by
thetsunami. Typical damage was for bush-material houses to have collapsed or
to havetilted or twisted, and for tanks and water reticulation systems to
have been brokenor disrupted.
- Shallow water wells in some coastal villages became filled with sand, due
tothe liquefaction and movement of subsurface sediments.
- In most of the villages visited, about 10 percent of houses had collapsed
and afurther 20-30 percent were damaged. The damage was not greater in the
westernvillages, such as Kauk, as might have been expected in view of the
location of theepicentre on or close to longitude 143oE.
- Most or all deaths and injuries were caused by the collapse of houses, or
aspeople escaped from houses.
- Damage caused directly by the tsunami was reported in the bay immediately
eastof the point at Boiken; on the southwest coast of Mussu; and in Victoria
Bay onKairiru. None of these sites was visited by this observer.
- People from coastal villages and some of the islands have retreated inland
forfear of a tsunami. The people should be encouraged to return to their
villagesbecause the risk of a tsunami developing is no greater than it was
in the past.However, they should be encouraged to remain alert, as in the
past, and to moveinland in the event of any strongly felt earthquake.
- No new risks or hazards
The inspection carried out on 9-11 September indicated that in the aftermath
of theearthquake and tsunami no new risks or hazards are threatening the
- Further inspection
However, not all sites were visited and it is desirable that a further
inspectionbe made as soon as conveniently possible.
- Resume normal life
People who have voluntarily evacuated from the coast or islands should
beencouraged to return to their villages and resume normal life.
- Assistance needed
Some people in most villages are temporarily without shelter, or have houses
thatneed repair. In many villages water supplies have been disrupted. The
people needassistance with temporary cover (tent flies), building materials,
water containersand restoration of water supply reticulation systems, tanks
Professor of Geology
UNIVERSITY OF PAPUA NEW GUINEA
Telephone 3267173, 36267395, 3260268