Confounding Sequence of Big Quakes Rattle Santa Cruz Islands

Over the last few days, a sequence of large earthquakes has rattled the Santa Cruz Islands area, the last of which just occurred, is a 6.7. (EDIT: This quake has now been dropped to a 6.3) Now I don't know about you's but this sequence is somewhat unusual, in that it started in one area, then opened up again in another.

It also is unusual in the sense that with earthquakes like this we usually see a mainshock-aftershock sequence- which we have seen to a degree here. But with this latest, increased magnitude 6.7 something is amiss. I just have that sinking feeling.

And that feeling is it could be foreshocks to something bigger of course. Hopefully not, but wanted to make this thread to call note to this activity as potentially dangerous to the area.

MAP 6.3 2013/02/01 22:16:37 -10.997 165.403 34.2 SANTA CRUZ ISLANDS
MAP 6.0 2013/02/01 05:36:40 -11.090 165.538 9.4 SANTA CRUZ ISLANDS
MAP 4.9 2013/02/01 01:49:13 -10.985 165.476 29.8 SANTA CRUZ ISLANDS
MAP 4.8 2013/02/01 00:42:59 -11.056 165.481 9.9 SANTA CRUZ ISLANDS
MAP 5.1 2013/02/01 00:18:08 -11.034 165.334 10.7 SANTA CRUZ ISLANDS
MAP 4.6 2013/01/31 23:57:00 -10.990 165.478 10.0 SANTA CRUZ ISLANDS
MAP 4.9 2013/01/31 06:50:16 -10.418 166.251 35.0 SANTA CRUZ ISLANDS
MAP 5.1 2013/01/31 06:42:10 -10.713 166.386 35.2 SANTA CRUZ ISLANDS
MAP 5.4 2013/01/31 05:18:14 -10.567 166.446 45.7 SANTA CRUZ ISLANDS
MAP 5.0 2013/01/31 05:16:58 -10.502 166.201 25.0 SANTA CRUZ ISLANDS
MAP 5.6 2013/01/31 04:31:33 -10.934 165.418 32.9 SANTA CRUZ ISLANDS
MAP 5.6 2013/01/31 03:58:00 -10.680 166.391 35.1 SANTA CRUZ ISLANDS
MAP 6.2 2013/01/31 03:33:43 -10.628 166.382 9.2 SANTA CRUZ ISLANDS
MAP 4.6 2013/01/30 23:53:54 -10.565 166.438 15.0 SANTA CRUZ ISLANDS
MAP 6.0 2013/01/30 23:03:45 -10.518 166.486 10.0 SANTA CRUZ ISLANDS
MAP 5.1 2013/01/29 19:30:33 -11.206 165.355 24.7 SANTA CRUZ ISLANDS
MAP 4.9 2013/01/28 12:00:17 -11.070 165.368 35.0 SANTA CRUZ ISLANDS

earthquake.usgs.gov...

Big quakes have happened there before, and it is a known subduction zone. Some additional info from previous studies on bigger quakes occurring there:

Abstract

The source process of two large earthquakes that occurred in the Santa Cruz Islands subduction zone has been studied, one with a surface wave magnitude MS = 7.9 in 1966 and the other with MS = 7.7 in 1980. The seismic moment of the 1980 event estimated from long-period surface waves of Global Digital Seismograph Network (GDSN) and International Deployment of Accelerographs (IDA) records is 5.6 × 1027 dyn cm. Both of these events occurred at a shallow depth (i.e. between 20 and 40 km) with a similar thrust type focal mechanism with a strike (∼ 347°) parallel to the local trench axis, and they are located within 100 km in distance.

The 1966 event is a break of a single asperity which ruptured unilaterally to the north along the local trench strike and was truncated sharply at the northern boundary. This rupture pattern and the aftershock area expansion to the north indicate that there was a distinct barrier on the south of the 1966 source area. The major moment release of the 1980 event represents the rupture of this barrier. However, inversion of P-waves with an assumption of a constant focal mechanism failed to constrain the source process thereafter. In particular, the deconvolved source-time functions of the 1980 event do not show such a clear truncation as is observed in the 1966 source process, indicating that some unresolved features followed the peak of the moment release. Nevertheless, the 1-day aftershock area suggests that the rupture propagated to the north into the source area of the 1966 event.

We conclude that both earthquakes are subduction events between the Pacific and Indo-Australian plates; the 1966 event is a break of a single asperity and the 1980 event is a break of the remnant asperity which acted as a barrier for the 1966 source rupture. The subduction segmentation inferred from the intermediate-depth seismicity seems to control the mechanical condition of the subduction interface at shallow depths where the two large events took place. This interface created a barrier between the two source areas.

www.sciencedirect.com...

Im with you.... strange increase....
Stay tuned shall we

I have noticed an uptick in the earthquakes the last couple of days on my twitter feed, most say Santa Cruz. Seems something is going on in that area or on a nearby fault. Hopefully it's just a small cluster that will relax soon.

I noticed on my iPhone earthquake app that there were quite a few!!

I hope it's not a prelude to a larger one


Be safe people

Hm, watching the area closely.

At first I wouldn't have reached so far, but the 6s seem to be getting larger little by little.

Maybe it's all balancing itself out so a 8+ won't be necessary.

reply to post by TrueAmerican


Uh oh I saw this thread and thought let me look at it and if its authored by trueamerican . . . . uh oh
I see that it is - you have my attention.

You can dismiss this - I don't even know why or how it happens but - I sometimes
well I sometimes "know" when these things happen - I can't explain why or how I get a sort of nervous sinking feeling. I can only explain it as perhaps some humans are more in tune to subtle shifts in energy?

I don't know - I hope I am wrong when I get these spidey senses I come to ATS and scroll around the fragile earth threads and when I spot posts authored by trueamerican, I sort of feel validation to this strange sense I have that cannot be explained.

It does seem like its building. I wish there was more historical data for that subduction zone like we have for Japan and Cascadia. Good looking out, s n f.

Peace

Well I might point out that even with the reduced magnitude to 6.3 from 6.7, it makes all other previous quakes in the immediate area foreshocks. And that is a concern.

And just a while ago apparently aftershocks of 5.7 and 4.9 to that 6.3.

That perhaps is a good sign that the biggest rupture has occurred. We can hope.

I think another pretty big quake just hit again near santa cruz islands...could be PNG, not sure..

Waiting...

Looking like 5.7+ or so... Maybe 6...



I dunno bout that one, was pretty far from the stations I have access to... But seemed bigger, from the propagation...


I dunno, all this activity around the pacific plate has got me a little spooked...


EDIT AGAIN: This quake was two quakes, a 5.1 followed by a 6.1, the USGS just listed it. So I was not that far off.
earthquake.usgs.gov...

Problem is, a 6.1 is way too close to the maximum quake mag of the 6.3, MEANING: This thing ain't done yet.

ALERT EXTENDED

reply to post by TrueAmerican

Hm, the QVS program pop-up alerted me to a 5.1 at 18:54Z, and a 5.8 (or was it a 5.9?) at 18:58Z, I think it was. A pop-up alert a moment ago had just the 5.1, though, so I don't know if the second one was a false trigger or not.

Yep, it was 2 'quakes, the second was real, not a false trigger. So what you saw was probably this one:

6.1 66km WSW of Lata, Solomon Islands 2013-02-02 13:58:07 10.912°S 165.260°E 10.0
earthquake.usgs.gov...

And I agree, all of this big activity around this area is very eerie...

my earthquake app has been going for week there. Another one just hit 6.1 a moment ago.

as I said in the quake watch thread, I expect a big one down there within the next 2 weeks...

the absence of M

Originally posted by aLLeKs
as I said in the quake watch thread, I expect a big one down there within the next 2 weeks...

the absence of M

ANOTHER 6.3 has just occurred:
earthquake.usgs.gov...

Although I expect that to drop a bit, down to around 5.9 - 6.1.

And behind that now another is coming in, less strong, but still around 4.9- 5.2 or so.

EDIT: That next one was deemed to be a 5.3:
earthquake.usgs.gov...

This is not your typical mainshock aftershock sequence, because usually aftershocks remain 1+ magnitude down from the mainshock.

And the rupture appears to be spreading, if you look at the map:
earthquake.usgs.gov...

Here's a better view:

8.0 !!!

It's coming

Wow, I seriously hope that zone doesn't destabilize after that 8.0, and have a massive rupture....

Crappola.... Northern Australia had better watch out.

Originally posted by TrueAmerican
Wow, I seriously hope that zone doesn't destabilize after that 8.0, and have a massive rupture....

Crappola.... Northern Australia had better watch out.

what do you mean by rupture?

I see by the title of your thread this is a odd series of quakes, yes?

Jesus, that after shock was a 6.4- ON THE OTHER SIDE OF THE ZONE:


I'm definitely worried for that area folks, this could get real nasty...

Originally posted by TrueAmerican
Jesus, that after shock was a 6.4- ON THE OTHER SIDE OF THE ZONE:

I'm definitely worried for that area folks, this could get real nasty...

Hmm, that's wild.