In the past week, there has been a series of earthquakes in the New Britain trench. The largest quakes are M = 6.7 & 6.8. Now we might call those foreshocks to today’s M = 7.5 earthquake de Cinco de Mayo. Historic Earthquakes of epicenter larger than M = 7 are plotted in grey. These are also plotted in more detail below.
Here is a map that shows the seismicity from the last month. The moment tensors for the three largest magnitude earthquakes are shown, as well as a brief explanatory graphic about what moment tensors reveal. Based on the regional tectonics, I would interpret these three earthquakes to be ~east-west compressional earthquakes, dipping to the north.
Based on the original magnitude and hypocentral depth (63 km), it seemed less likely that a tsunami may be generated from this earthquake. The depth is now 42 km, which promotes the likelihood of a tsunami. The 1992 Petrolia Earthquake was at about 10 km depth and produced a tsunami with an earthquake of magnitude 7.2.
Any tsunami from today’s earthquake would probably be local and not travel very far from the region. The PTWC issued a threat message stating that the waves may be 0.3 to 1 meters above the tide level in the Papua New Guinea region. Here is their forecast ETA for one location:
LOCATION REGION COORDINATES ETA(UTC)
KAVIENG PAPUA NEW GUINEA 2.5S 150.7E 0258 05/05
The depth estimate originally placed this earthquake beneath the slab depth based upon the Hayes et al. (2012) model. At first the depth was set at ~63 km and has since shallowed to 42 km and is now plotted further north (placing it closer to a depth that we might expect based on the Hayes slab model).
I have posted material about the recent and near recent (decadal) seismicity in the past:
- Here is a post regarding the foreshocks. 2015.05.03
- Here is a post summarizing the seismicity since 2000 AD. 2015.03.29
- Here is a post comparing the New Britain region with the adjacent Bougainville region. 2015.03.30