Preliminary magnitude of 7.2 - Vanuatu

[StevieTNZ]

Limited information at this time:

A powerful earthquake with a preliminary magnitude of 7.2 has struck off the north coast of Vanuatu.

The quake struck at 6.23pm (AEST) at a depth of 35km, the US Geological Survey said.

The earthquake epicentre is 81km from Port Olry and 407km from Port Vila, the South Pacific nation's capital.

http://www.9news.com.au/world/2016/...strikes-off-vanuatu#RLUVoLYwGDV21je9.99#9News

A large 7.2 quake has struck off the coast of the South Pacific islands of Vanuatu on Sunday and there's a possibility of tsunamis within 300km radius, the Pacific Tsunami Warning Centre has said.

The Ministry of Civil Defence and Emergency Management has issued a immediate statement stating that there's no tsunami threat to New Zealand.

http://www.stuff.co.nz/world/78508265/72-quake-has-struck-off-vanuatu

 

[Astronuc]

USGS reports M6.9 - 81km NNW of Port-Olry, Vanuatu
http://earthquake.usgs.gov/earthquakes/eventpage/us20005e8t#general_region
2016-04-03 08:23:53 (UTC)

Location: Lat 14.352 °S, Long 166.821 °E
Depth: 35.0 km (21.7 mi)

Followed by
M4.9 - 96km WSW of Sola, Vanuatu
http://earthquake.usgs.gov/earthquakes/eventpage/us20005eaz#general_region
2016-04-03 14:48:06 (UTC)

Location: Lat 14.213 °S, Long 166.721 °E
Depth: 35.8 km (22.2 mi) - close to the same depth as the larger quake

 

[davenn]

respectable event
Largest amplitude I have recorded in the last month

several of the aftershocks can also be seenDave

 

[Astronuc]

An aftershock near the Mag 6.9

M5.1 - 91km NNW of Port-Olry, Vanuatu
http://earthquake.usgs.gov/earthquakes/eventpage/us20005ecc#general_region
2016-04-03 18:18:58 (UTC)
Location: Lat 14.269 °S, Long 166.771 °E
Depth: 35.0 km (21.7 mi)

There are a number of smaller earthquakes in the southern part of Vanuatu, and eastward in Fiji and Tonga.

 

[Astronuc]

And two more

M4.9 - 79km NNW of Port-Olry, Vanuatu
http://earthquake.usgs.gov/earthquakes/eventpage/us20005eff#general_region
2016-04-04 08:22:03 (UTC)
Location: Lat 14.351 °S, Long 166.878 °E
Depth: 10.0 km (6.2 mi) = shallow

M5.3 - 103km NNW of Port-Olry, Vanuatu
http://earthquake.usgs.gov/earthquakes/eventpage/us20005egl#general_region
2016-04-04 13:23:12 (UTC)
Location: Lat 14.201 °S, Long 166.651 °E
Depth: 35.0 km (21.7 mi)And there is an earthquake in the Solomons
M5.0 - 101km ENE of Kirakira, Solomon Islands
http://earthquake.usgs.gov/earthquakes/eventpage/us20005egv#general_region
2016-04-04 13:35:27 (UTC)
Location: Lat 10.249 °S, Long 162.821 °E
Depth: 47.4 km (29.4 mi)

 

[davenn]

A M6.7 aftershock last nite just a little north of the M 6.9
2016-04-06 06:58:48 (UTC)

1. 2016-04-06 16:58:48

Nearby Places

• 105.0 km (65.2 mi) WSW of Sola, Vanuatu
• 171.0 km (106.3 mi) NNW of Luganville, Vanuatu

This was followed by a M 5.9

cheers
Dave

 

[Astronuc]

Nice swarm. I was wondering if we'd see another event of similar magnitude to the Mag 6.9.

A M6.7 aftershock last nite just a little north of the M 6.9
2016-04-06 06:58:48 (UTC)

Was your seismograph as active as when the Mag 6.9 hit?

Now, interestingly, they put the depth of the today's Mag 6.7 at 24 km, and the aftershocks at 35 km, which is the depth of the Mag 6.9.
http://earthquake.usgs.gov/earthquakes/eventpage/us20005fsi#general

That should be felt more strongly near the surface than the deeper ones.

 

[davenn]

Nice swarm. I was wondering if we'd see another event of similar magnitude to the Mag 6.9.

Was your seismograph as active as when the Mag 6.9 hit?

no, it was substantially less amplitude
Initially it was reported as a M 6.9 and I was sitting there looking at it and thinking, yeah right ! haha
if that is correct, then the previous event was really the M7.2 it was initially reported as or if it was 6.9
then this latest event was smaller. It took quite some time for it to be revised down to 6.7

Now, interestingly, they put the depth of the today's Mag 6.7 at 24 km, and the aftershocks at 35 km, which is the depth of the Mag 6.9.
http://earthquake.usgs.gov/earthquakes/eventpage/us20005fsi#general

not too much difference considering the physical area of the subducting slab affected, that would have been expected by events of that magnitude and also the accuracy error in calculating the depth

from a USGS page...

Depth
The depth where the earthquake begins to rupture. This depth may be relative to mean sea-level or the average elevation of the seismic stations which provided arrival-time data for the earthquake location. The choice of reference depth is dependent on the method used to locate the earthquake. Sometimes when depth is poorly constrained by available seismic data, the location program will set the depth at a fixed value. For example, 33 km is often used as a default depth for earthquakes determined to be shallow, but whose depth is not satisfactorily determined by the data, whereas default depths of 5 or 10 km are often used in mid-continental areas and on mid-ocean ridges since earthquakes in these areas are usually shallower than 33 km.

I cannot find anything specific for data accuracy eg +- 2%, 5% etc
The accuracy is really constrained by how many stations they can get good Pp-P arrival time data from

some papers here about depth calcs that readers may be interested in reading
http://search.usa.gov/search?utf8=✓&affiliate=usgs&sitelimit=http://earthquake.usgs.gov&query=depth+calculations
including this one ...
http://earthquake.usgs.gov/research/external/reports/G11AP20195.pdf

That should be felt more strongly near the surface than the deeper ones.

yup
shallow = stronger and felt over smaller area
deep = weaker but felt over a wider areaDave

 

[davenn]

And another large event ...

another M 6.7 just on the Nth side of the previous M 6.7

6.7 106km W of Sola, Vanuatu 2016-04-07 03:32:53 UTC

still coming in on my seismo...
http://www.sydneystormcity.com/seismograms.htm
Dave

 

[davenn]

updated map

 

[Astronuc]

And another large event ...

another M 6.7 just on the Nth side of the previous M 6.7

6.7 106km W of Sola, Vanuatu 2016-04-07 03:32:53 UTC

I just saw that - a second Mag 6.7 - 106km W of Sola, Vanuatu
http://earthquake.usgs.gov/earthquakes/eventpage/us20005fzn#general
Location: Lat 13.994°S, Long 166.571°E
Depth: 26.8 km (16.6 mi)

Rather than quieting down, it's picking up.

still coming in on my seismo...
http://www.sydneystormcity.com/seismograms.htm

Busy day!

Does it look like the activity is drifting northward along the plate boundary?

 

[davenn]

Does it look like the activity is drifting northward along the plate boundary?

seems to be the general trend at the moment. It will be interesting to see for how far it continues

 

[Astronuc]

A couple more today

M 4.8 - 110km WSW of Sola, Vanuatu
http://earthquake.usgs.gov/earthquakes/eventpage/us20005g6k#general
2016-04-07 17:52:32 UTC
Location: 14.109°S, 166.556°E
Depth: 33.8 km

M 4.9 - 114km W of Sola, Vanuatu
http://earthquake.usgs.gov/earthquakes/eventpage/us20005gav#general
2016-04-08 07:03:46 UTC
Location: 13.916°S, 166.494°E
Depth: 8.9 km

and one further south

M 4.9 - 101km SW of Port-Vila, Vanuatu
http://earthquake.usgs.gov/earthquakes/eventpage/us20005ggr#general
2016-04-08 19:05:20 UTC
Location: 18.269°S, 167.540°E
Depth: 26.5 km

 

[davenn]

Another 2 aftershock events from the north end of the Vanuatu Islands

A M 6.0
86km NW of Port-Olry, Vanuatu 2016-04-14, 12:17:05 UTC, 10.0 km deep

And a M 6.4
88km NW of Port-Olry, Vanuatu, 2016-04-14, 21:50:26 UTC, 10.0 km deep

Does it look like the activity is drifting northward along the plate boundary?

seems to be the general trend at the moment. It will be interesting to see for how far it continues

Well, that was interesting, these 2 latest events bucked the observed northwards trending pattern
and occurred to the south side of the activity zone, much closer to the coast on northern Santo (Island)

The seismogram of the second event, the M6.4, also was quite different to what is normally seen from the Vanuatu region ... as in the upper of the 2 events in the seismogram below
Vanuatu events typically have very "clean" seismograms, that is, clear P, S and Surface Wave arrivals
The M 6.4, the lower of the 2 recordings can be seen to be quite different and also has a significantly
longer coda to the trailing signal

Dave

 

[Astronuc]

A M 6.0
86km NW of Port-Olry, Vanuatu 2016-04-14, 12:17:05 UTC, 10.0 km deep

And a M 6.4
88km NW of Port-Olry, Vanuatu, 2016-04-14, 21:50:26 UTC, 10.0 km deep

Both pretty shallow

M6.0 - 86km NW of Port-Olry, Vanuatu
http://earthquake.usgs.gov/earthquakes/eventpage/us20005hzl#general

M6.4 - 88km NW of Port-Olry, Vanuatu
http://earthquake.usgs.gov/earthquakes/eventpage/us20005i6p#general

The M 6.4, the lower of the 2 recordings can be seen to be quite different and also has a significantly longer coda to the trailing signal

That's interesting. Could the Mag 6.4 have triggered a smaller event in the Mag 5 range during the subsequent 10-20 minutes, such that it was not separately detectable?

 

[davenn]

That's interesting. Could the Mag 6.4 have triggered a smaller event in the Mag 5 range during the subsequent 10-20 minutes, such that it was not separately detectable?

well DOH, I didn't notice that M 5.2 ... 111km NNW of Port-Olry, Vanuatu, 2016-04-14, 22:23:28, UTC10.0 km deep

that is going to add a bit more signal to the tail of the M 6.4D

 

[Astronuc]

M5.7 - 68km WNW of Port-Olry, Vanuatu - south of the others yesterday.
http://earthquake.usgs.gov/earthquakes/eventpage/us20005icn#general
2016-04-15 03:43:04 (UTC)
Location: Lat 14.849°S, Long 166.450°E
Depth: 10.0 km (6.2 mi) - shallow

So the activity is distributing along the New Hebrides Trench.

 

[davenn]

M5.7 - 68km WNW of Port-Olry, Vanuatu - south of the others yesterday.

I thought I posted a comment on this event, noting it closer to the coast
I remember writing it

dunno what happened to it ?Dave

 

[davenn]

my missing response was to this comment of yours several days ago before that M5.7

Does it look like the activity is drifting northward along the plate boundary?

it was along the lines of ...
Well this event to the south seems to be bucking the trendDave