On Monday, 13 June, Christchurch was again rocked by earthquakes that caused damages and left people injured. Three significant events happened within two hours. At 1:00 UTC a mb5.0 event occured, followed by a Mw6.0 at 2:20 UTC and a M4.6 at 2:40 UTC. The strongest event caused instrumental intensities of up to VII close to the city. Update: Geonet reports a magnitude of 6.3.
Again, the PGA (peak ground acceleration) was extremely high, reaching 2g in the summer area! This is really, really extraordinary. This map provided by Geonet illustrates the PGAs measured:
Media report on environmental effects like liquefaction, landslides and rockfalls. The latest events are most likely aftershocks of the M6.3 earthquake that devastated Christchurch and left more than 180 people dead at 22 February, 2011 and of the M7.0 event in September last year.
Russia Today has a great video of the shaking and the environmental effects:
Monday’s M6.0 event was a strike-slip earthquake that occured 10 km NE of Christchurch in only 2 km depth. Here is a comparison of the moment tensor solutions provided by the EMSC:
It was located at the eastern end of the “inferred rupture of the 21 February 2011 M 6.1 earthquake” (USGS). This means that the fault system is quite long and that the stress release is still ongoing. The problem is, that such a long system could produce even stronger earthquakes if a large segment of the fault(s) ruptures at once, despite this seems not to be likely in the basin environment. The bad news is that more earthquakes can be expected. The good news is that already a lot of stress was released, probably decreasing the chance for an even stronger event. Apparently, the earthquakes happened at a fault that was not known before and does not have any surface expression. The New Zealand earthquake crisis is ongoing, and the number of questions rises.
- The Landslide Blog – Rockfalls from M=6.3 aftershock in Christchurch, New Zealand
- Ontario Geofish – NZ still believes these earthquakes are aftershocks of the M7.3
- Highly Allochthonous – More large aftershocks rattle Christchurch: will it ever end?
- Ontario Geofish – Terraforming earthquakes
- Geopedrados (Portugese) – Christchurch voltou a tremer depois de terramoto devastador em Fevereiro