Peru-Chile Could Experience Megathrust Quake as Six Quakes Over 6 Mag Strike Area

reply to post by JustMike

I have noticed over the years the Chileans always tend to have bigger events further offshore than the main Networks.
Its hard to say who is correct, being closer to the action you would think the Chileans would have a handle on location, but you just never know for sure.
I am writing up a page on the whole series right now, here are a couple of maps I have done regarding the location estimates for the first 2
although I put LDEO in there, they locate using increments of .25 degrees of lat/long and more often than not they are miles away from everyone else, so should only be used for the magnitude reading (Ms) rather than for accurate location, and depth is always 33km so disregard that.
M6.7 of 16/03/2014 network location estimates
M6.3 of 17/03/2014 network location estimates

TA, if this latest one holds up at 6.2Mw, you may need to change your topic title to
............ as 5 Large Quakes Strike Area

reply to post by muzzy

Thank you for that. Those maps are especially interesting. I guess if one were to figure an average location from all the ones plotted it would likely be pretty near the mark. Or put it this way, it's very unlikely that the true epicentre is all that far away.

As for the Chilean site's preference to place these larger events further off shore, that's one of those things that makes me go, “Hmm.” Unless everyone else is just consistently less accurate than they are (which seems a touch doubtful) I suspect their reason for doing it that way may not be discernible from a purely seismological perspective.

reply to post by JustMike


Depths offshore are notoriously difficult to calculate, and I am not surprised at all by the discrepancies between the agencies. We have the same problem up in Cascadia.

Muzzy, I can't edit the thread title, but yeah, if Justmike would or another mod, that would be appreciated. Change the 3 to 5, pretty simple edit.

In pulling a 30 day at USGS, I can't help but notice that the entire fault just about is exhibiting activity at shallow, mid, and deep points:


It doesn't take a scientist to envision that slab from the Nazca Plate subducting under South America, because one just need look at that map to see it. Just look at the quakes. Quakes on the left= shallow, quakes on the right= deep.

The big question is whether something far more sinister is brewing. The quakes all seem to fit the depth profiles of the slab. It could be ready to tear. Southern Chile coast and mid Peru coast all in danger at the moment, in my opinion.

And Muzzy, so let's see the new excel with this latest 6.3. Show us how normal that is.

reply to post by JustMike

Thats OK, was working on it anyway,
FWIW at the 72 hour mark (3 days, after the first 5.8) the depths were looking like this

Depth km = Number of
2-10 = 8
10-20 = 20
20-30 = 39 (6.7, 6.3)
30-40 = 68 (5.8)
40-50 = 74
55-60 = 2
Total=211

Source: Servicio Sismológico Universidad de Chile data

reply to post by TrueAmerican

I appreciate the difficulties with depths for offshore quakes. The variance is bothersome but it's a technically difficult issue to overcome. However they all have the depths as quite shallow and that's the main point of concern.

That 30-day map is pretty telling. Not often we see one for that part of the world with that much activity along such a long stretch of coast and near-coastal regions.

Re changing the title: due to moderating rules etc I can't do the title edit myself in this case. So I've put in a request to staff for someone else to do the title edit and also provided a note that can be dropped into your OP to explain why it was done. I'm hopeful it will be dealt with pretty soon.
ETA: Okay, all fixed. Zaphod took care of it.

reply to post by JustMike


Thanks Justmike and Zaphod, now the thread title is accurate to this point.

An important distinction here that should be noted. The original quake to spark these "aftershocks" was a 6.7. Now usually, one would expect to see aftershocks from that up to about 5.7, and more rarely, up to 6.0.

But the problem is, now, we not only have ONE aftershock that reached 6.3, but TWO. This leads me to believe that there is a higher possibility than normal that what we are seeing here is actually a long set of foreshocks. That's what I suspect. Again, let's hope I am wrong. I will be ecstatic if I am wrong! I WANT to be wrong. Because if I am right, people are going to die.

reply to post by TrueAmerican

I have to agree that this sequence of bigger quakes doesn't fit the classic definition of a mainshock-aftershock sequence. If there'd been that 6.7 and then just a bunch of mid to high mag 5s and maybe one just squeaking a 6 (which is still pushing the limits a bit as an aftershock), then okay, that wouldn't look too bad and would fit the classic pattern. But they're too big, really. Like you say, it's suggestive of foreshocks.

On the other hand, we can hope: things could quieten down again and there might not be a megathrust event in that region for years. Granted, the longer until it happens the more powerful it's likely to be, but some more years of relative quiet would still be good to see.

the Chileans aren't buying the 6.2 offer from the gringo's
5.7Ml or 5.8Mw



here is the latest map from their data
0-145hours (6 and a bit days) interactive map

reply to post by TrueAmerican

some parts of IRIS have the Mainshock at M7.0, that would maybe explain these low M6 high M5 aftershocks
not sure if this link will work, its a long one

and here too

muzzy
the Chileans aren't buying the 6.2 offer from the gringo's
5.7Ml or 5.8Mw

Yeah well I think the Chilean seismologists are full of gringo dung.

I went back to the data, and pulled raw from LVC.IU. I compared the station counts to each of the previous big quakes. I proclaim this quake to be a minimum of a 6.0 ML, and that's on an extremely conservative day- more conservative than the right wing neo-nazis that just took over Ukraine.

It is easily a 6.2, as the USGS has it, and very easily a 6.3, as EMSC has it. Yeah you're darn right the Chileans don't want another 6 point something showing up, because at this point, the population would be a lot more alarmed- as they should be.

I been doing this a long damn time, and that quake ain't no 5.8. Screw that.

reply to post by TrueAmerican


yeah you are probably right about the magnitude.
I see IRIS are stuck on 5.9, but no MT yet.
I rescaled the 4 graphs off C.GO01 Chusmiza, Chile Chilean National Seismic Network all to the same scale, adding _s.0004.png to the end of the image address instead of .png, and yes todays looks more like the 6.3 on the 17th. than the 5.8 on the 18th

reply to post by muzzy


Now why would you even pay attention to a network that can't even get the epicenter right on a map? Look at the map on your link to IRIS... That's not where that quake was. Not even close. Furthermore, that seismogram is from one of their lowest resolution instruments at location 00, 20 sps. The BHZ and HHZ channels from location 10 are 40 and 100 sps, respectively. Just stupid. Thanks, I'll never look at IRIS derived magnitudes ever again. I hate that place I swear. They're snobs to try and deal with. Been there done that. Screw em.

As to Mw magnitudes, let's just say that I've discovered some professional disagreements on what the shear modulus values should be for that location and depth. And that most definitely will affect the calculations.

I'd like to see excel values using the EMSC and USGS catalogs. The heck with those Chilean "experts" too. Hell, everything they have was probably gotten with the guidance of American scientists. Doesn't mean they know how to use them better than we do. I'll stick with the USGS, thanks. They've probably got more experience than all those other agencies combined- and yeah, I know the USGS has its warts too. But still.

reply to post by TrueAmerican

there is a reason we at QW call USGS "Useless", lets see in 7 days what they have got for that last 5.8, if they are still putting out lists for the public then ..........
As for Servicio Sismológico Nacional (GUC), they have been around since 1842, I think they know a thing or two about earthquakes.

Add another 6 to the count (though this could still be adjusted down)
M6.1 - 97km WNW of Iquique, Chile 2014-03-23 18:19:59 UTC

Well, what are you waiting for Muzzy, go find the lowest magnitude you can and add it to spreadsheet! So which agency has your particular favor today? Oh wait! Looks like USGS has the lowest magnitude today! Oh no! What are you going to do? Can't use their Mb of 6.0! Noooooooooooooo. Chile has 6.2 Mw. EMSC 6.3 Mw. Oh dear. What a terrible problem.

Ha. Even IRIS has 6.1 ML and 6.2 Mw.


lol, and where's Zaphod?

"Peru-Chile Could Experience Megathrust Quake as Six Quakes Over 6 Mag Strike Area"

Is there any end in sight? Foreshocks. But I just KNOW I'm wrong.

reply to post by TrueAmerican


www.youtube.com...

Tha above, first read during 2012, is what frightens me for this particular district. Could this be helping a more regular series of Quakes ?????

Forever ready to learn.

Thanks Masqua for the title edit.

So what if.

With this much energy being released along that fault, the sheer potential for triggering becomes greater. Stress redistributions lead me to believe that the areas north and south of the current activity are at more risk in the upcoming days and weeks. That's why I said mid-southern Chile coast, because that part of the fault could be triggered into reacting to all these 6+'s, four of which have been directly north of there.

But then there is also the mid to northern Peru coast, which shows a stubborn absence of quakes. It appears to be holding out, and not responding yet to the activity south of there. Most scientists at this point, even after all this activity, are probably expecting it to die down and cease completely. I mean that's what we normally see. But this thing keeps breaking the rules.

One explanation would be possible, if there is not a very big quake upcoming: that the original M 6.7 was misread and was really more like a 7.2. That would bring all these "aftershocks" more in line with historical norms, and reduce my "foreshock alarm meter."

I only wish the South Americans the best of luck. Earthquakes can be some scary events and with water on top of that... I wouldn't want to be there.
Buena suerte y Que Dios los bendiga a todos (Good luck and God bless you all)

uh oh... pretty good shock incoming near Peru... Estimate: 6.2 to 6.5... Hmm... wait....this could be telemetry error, not sure yet.... Not seeing it in Chile yet.... Hang on...


Yeah, pretty sure it's telemetry error... Now you see why I detest that network II... Grrr. Too many errors.


Yeah, I think station NNA just went on the fritz.