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+--- Thread: M7.8 New Zealand (/showthread.php?tid=569)
M7.8 New Zealand - Island Chris - 11-13-2016
There was a M7.8 earthquake in New Zealand today. Looks like the aftershocks extend over 160 km NE-SW. I can't find a focal mechanism on USGS, but there must be one. It is in an area where there are right-lateral faults with more or less that orientation. But it is also the south end of subduction and there is contraction farther south along the plate boundary Alpine fault.
OK, found the focal mechanism: is right-lateral.
A cnn.com reporter said it was good news that they increased the depth from 10 km to 22 (?). It is not good news for a strike-slip quake: it probably ruptured all the way to the surface or close to it. The deep (for strike-slip) hypocenter just means a larger area ruptured and the shaking may be worse, not better.
There was also a local 1.5 m tsunami:
http://ptwc.weather.gov/ptwc/text.php?id=pacific.TIBPAC.2016.11.13.1304
Chris
RE: strange distant foreshock pattern? - Island Chris - 11-14-2016
There is an animation part way down this link
http://www.cnn.com/2016/11/13/asia/new-zealand-earthquake/index.html
It shows quakes filling in on the North Island of New Zealand including along a line aligned with the quake.
The original source is:
http://quakesearch.geonet.org.nz/
I'm playing around with the parameters to see whether the CNN animation is correct for 48 hours.
Chris
RE: M7.8 New Zealand - Island Chris - 11-14-2016
I don't think the line of quakes on North Island aligned with the future rupture over a 48 period is accurate. I looked at M2 to M8.
Maybe I will try M1 to M8. It did not look nearly as dramatic.
On the other hand, the aftershocks look clustered near the E end of the rupture near the coast and offshore, 50 km SW of Wellington on the North Island. I went on a field trip almost 20 years ago along the Hope fault which runs through Wellington. I'd have to double check but I think it is a right-lateral fault. I also have not checked, but presumably stress changes would have driven it closer to failure, by a year or two???
Chris
RE: M7.8 New Zealand - Island Chris - 11-14-2016
(11-14-2016, 11:29 AM)Island Chris Wrote: Correction; I meant I went on field trip along the Wellington fault, not the Hope fault. The Hope fault is on South Island
RE: M7.8 New Zealand - Island Chris - 11-14-2016
Island Chris
The linked focal mechanism is more oblique with a thrust/reverse component than the one I saw earlier:
http://earthquake.usgs.gov/earthquakes/eventpage/us1000778i#moment-tensor
The dip on the NNE-striking plane is moderate. This is interesting for application to California if it holds up. I have published on California moderately-dipping strike-slip faults.
What is also interesting is that the M7.8 strike more northerly than the faults shown on this map of the Hope fault:
https://en.wikipedia.org/wiki/Hope_Fault
There is now a good summary on the USGS page:
http://earthquake.usgs.gov/earthquakes/eventpage/us1000778i#executive
Chris
RE: M7.8 New Zealand - Skywise - 11-15-2016
A New Zealand article on the quake with some good photos.
Day the earth cracked: Symmetrical fault lines on rolling farmland show impact of deadly earthquake
Brian
RE: M7.8 New Zealand - marc / berkeley - 11-15-2016
(11-13-2016, 08:21 PM)Island Chris Wrote: There was a M7.8 earthquake in New Zealand today. Looks like the aftershocks extend over 160 km NE-SW. I can't find a focal mechanism on USGS, but there must be one. It is in an area where there are right-lateral faults with more or less that orientation. But it is also the south end of subduction and there is contraction farther south along the plate boundary Alpine fault.The Moment Tensor solution looked mighty intereesting.
OK, found the focal mechanism: is right-lateral.
A cnn.com reporter said it was good news that they increased the depth from 10 km to 22 (?). It is not good news for a strike-slip quake: it probably ruptured all the way to the surface or close to it. The deep (for strike-slip) hypocenter just means a larger area ruptured and the shaking may be worse, not better.
There was also a local 1.5 m tsunami:
http://ptwc.weather.gov/ptwc/text.php?id=pacific.TIBPAC.2016.11.13.1304
Chris
Mostly thrust, but with a volcanic fluid component. Are we going to see magma?
That combined with the successive triggering along the faulting makes this event far more interesting than a typical strike-slip.
You can bet this will be one of the poster child at next months AGU!
RE: M7.8 New Zealand - Island Chris - 11-15-2016
marc / berkeley
I could be wrong but I think Moment tensor solutions look funny like that compared to other methods. It probably is not a volcanic signal. There are volcanoes and volcanic fields on the North Island but I don't think there are any in the area of the quake.
AGU does have late-breaking sessions for earthquakes where they relax the August deadlines for abstracts. I don't know if they can do this less than 1 month ahead of the meeting.
RE: M7.8 New Zealand - Skywise - 11-19-2016
(11-15-2016, 08:57 PM)marc / berkeley Wrote: The Moment Tensor solution looked mighty intereesting.
Mostly thrust, but with a volcanic fluid component. Are we going to see magma?
That combined with the successive triggering along the faulting makes this event far more interesting than a typical strike-slip.
You can bet this will be one of the poster child at next months AGU!
This was brought up on that "other board" several times many years ago, and I directed folks to the following document:
http://serc.carleton.edu/files/NAGTWorkshops/structure04/Focal_mechanism_primer.pdf
Specifically, look at page 9. The beach ball as you see it is most likely just showing the uncertainty in the focal mechanism solution.
Brian