January 13, 1941 Earthquake: Bismarck Sea, Papua New Guinea

Reference #414:

1941, January 14, 16:27:38 UTC, 4.5S, 152.5E, magnitude 7.3. The strongest earthquake since 1916 occurred on the Gazelle Peninsula. It was accompanied by a thunderous roar. Its effects were investigated from the air and by land surveys and by questionnaires sent out by N. Fisher. At Rabaul, strong tremors lasted 2-3 minutes. According to some eyewitnesses, they were preceded by not very strong, nor very prolonged oscillations, but since it was night, it was difficult to establish the nature of the beginning of the oscillations.

The belt of strongest tremors cut across the peninsula from Ataliklikun Bay in a southeastern direction, on the whole coinciding with the corresponding diagonal trough. At Lamingi, at the upper reaches of the Warangoi River, & at other places in the watershed southwest of the trough, numerous avalanches, collapses, and swellings occurred, mainly in loose weathered volcanic formations & on steep slopes. Many streams were backed up by the resulting dams. In one of the small valleys, a loose layer measuring 400 X 500 m came down from the slope, baring the rocks to a height of 100 m; the resulting dam had a length of 400 m, a width of 14 m and a thickness of 12 m three weeks after the earthquake. After the earthquake, the dams burst; three children died in the resulting streams of water and mud in the Warangoi Valley.

Numerous cracks appeared in the surface of the ground in the Warangoi Valley. Here and there, mainly at places with a high ground water level, there were water, mud and sand gryphons. A number of new springs appeared which soon dried up. The cracking of the ground was caused both by its compaction, and probably by tectonic dislocations of the buried crystalline base. According to Fisher, the system of faults revived by the earthquake extended in a southeastern direction; the southwestern flank of the system apparently subsided, while the northeastern flank rose. This is indicated by the subsidence, by about 1 m, of the western section of the coast of Ataliklikun Bay, and by the slowing down somewhat of the streams to the northeast of the assumed faultline.

In the pleistoseismic zone, 15 European homes and a large number of huts of local residents were seriously damaged. However, only one old wooden frame home collapsed completely, while the others were simply shifted off their foundations, to which they were not firmly attached, and which themselves were weak. In addition, some homes rested on piles which stood unsecured on the ground. A child was killed by a falling beam in one of the homes.

Everywhere, reservoirs with water, especially those standing on high props, were smashed or burst in the regions of Rabaul, Kokopo and Beinings. Everywhere, dishes, furniture, etc. were overturned and smashed. In Blanche Bay and on North Coast, many stretches of steep shores, made up of loose material, deposited, in particular, during the volcanic eruptions of 1937, went under water.

The earthquake was felt in the eastern half of New Britain, over almost all of New Ireland and on the adjacent islands. At Ulamona and Namatanai, the tremors were moderate in force and not as prolonged as at Rabaul; at Talasea and Gasmata, they were weak, while the earthquake was not felt at all at Kavieng and on the Arawe Islands. The high-paint isoseismals, in Fisher's opinion, were somewhat extended in a northwestern direction.

The tilt meters installed a month before the earthquake at the Rabaul volcanological observatory registered a marked intensification in the rate of tilts, which stopped immediately after the shock. For several hours after the earthquake, aftershocks up to 5 degrees in intensity were felt at intervals of a few minutes. The frequency and force of the aftershocks then began to abate gradually, but they continued for more than a month.

The earthquake generated oscillations of the seiche type in Blanche Bay.