|Feb3-13, 10:42 AM||#1|
Change in Earth's axis and Rotation due to tectonic activity
Since the redistribution of mass in the Earth's surface can be caused by earthquakes, sometimes the Earth's rotation is increased or decreased by a small amount.
Recent series of quakes seem to be related. To me, this makes sense, since if plate "A" should move, then plate "B" would also move. Somehow a portion of that stress would be felt by all the plates, but wouldn't necessarily result in distant quakes, since the transmitted forces would certainly dimish over distance. So I have three questions about this:
(1) If an individual quake is big enough, could it cause some sort of chain reaction thru a large number of other tectonic plates resulting in, say, a week of global, huge quakes?
After some time, a new tectonic homeostasis would be reached, but it would be a rough week for everyone on Earth. So that's one question.
(2) Then I ask, if this global shaking and quaking were to happen, could the tectonic balance around the Earth's axis be changed so much that the inclination might also change?
Say, perhaps from 23.5 degrees to 24 degrees?
(3) And my third question would be regarding the Earth's core. Is it thought to be totally liquid, or does it have rotating solid chunks in it? What would be the relationship between tectonic activity on the surface, and the rotational stability of the core? How might this affect the Earth's rotation andaxis?
Stumbled across a related thread on this forum while taking a googol on earthquakes and the Earth's question. I thought it would ok to bump that old thread back to life. Apparently it's not ok to bump the old thread, so started this new one.
|Feb3-13, 12:28 PM||#2|
|Feb3-13, 01:19 PM||#3|
(1) I very much doubt it.
(2) Earthquakes can change the moment of inertia of the planet slightly, and so although the total angular momentum won't be changed, it might have subtle effects on the rotation axis.
(3) The inner core is solid. The outer core is liquid. Funnily enough the core can transfer small amounts of momentum to the mantle, which affect the length of day and wobbles in the rotation axis (nutations). These processes are not caused by (or causal to) tectonics at the surface.
|Feb4-13, 02:21 AM||#4|
Change in Earth's axis and Rotation due to tectonic activity
Two of the largest earthquakes in recorded history, or at least quake recording history ( the M9 offshore nthrn Sumatera and the M9.2 offshore NE Honshu) were 7 odd years apart not a few days or weeks.
Neither of these 2 HUGE events triggered a few days or a week of major events worldwide
In all the worldwide records I have of quakes in my database going back ~ 500 years or so, there is no evidence of anything like you are suggesting.
The only thing that might, emphasis on the word might, cause something like your scenario could be maybe the impact of a large asteroid or comet that could cause multiple large quakes on various plate boundaries around the world.
|Feb5-13, 10:45 AM||#5|
Thanks for the preliminary answers!
"Huge Earthquake Triggered Other Quakes Worldwide"
What I'm learning here is that there is a significant difference between the Earth's rotational axis, and the Earth's figure axis. This means that an asteroid, say, would have to whack us to change the axis of rotation. Quakes can change the figure axis. I'm not sure how that would be perceived, tho, because I don't quite understand the differences in the two axes.
My first question is partially answered:
(1) If an individual quake is big enough, could it cause some sort of chain reaction thru a large number of other tectonic plates resulting in, say, a week of global, huge quakes? (Which eventually settle down into a new homeostasis.)
Yes it could, but it would have to be a large quake. Which leads me to ask:
What is the largest quake that could occur on Earth, barring an asteroid strike?
Given that the tectonic plates are all connected on exactly the same planet, there must be some transmission of force between them, which I surmised above. I say "given", because <i>Nature</i> has given the initial nod to the idea that resulting forces travel thru the plates to cause quakes in different global locations.
|Feb5-13, 08:07 PM||#6|
They havent given any figures of other event sizes. I will have to look back through the records for that week or two following that quake. WHICH BTW wasnt just one event!!!
they couldnt even get that right in their article There was a M8.6 followed by a M 8.2 in the same area within a couple of hours. Both events had my recording system hitting the peak datacounts :)
there were no other major events in the 2 weeks following ( or months for that matter), which is what you were working on in your opening post ....
In fact 2012 was a VERY quiet year for quakes and it really struggled to meet the annual avg of 18 x M7.0 - 7.9 events
On average there is only one M8.0 + event per year worldwide and that average has held pretty well for at least the last 100 years of serious seismological studies
Some years we may get 2 events like the 2 last year ( stated above) other years there may not be an event that reaches M8
1) the stress that has built up over time --- longer period since last rupture, more accumulated stress
2) the length of the rupture, the longer the rupture the larger the event.
this is sub-goverened by 2 other things....
a) whether the rupture is bilateral ( rupture spreads along the fault in both directions from a central rupture point) or unilateral where the rupture starts at one end of a zone and moves primarily in a single direction along the fault boundary
b) The overall rupture length will be goverened by previous ruptures along that faultline/plate boundary. Their positions and rupture zones will determine the length of any new "seismic gap" where a future event can occur.
3) finally, there is only so much stress that can build up between 2 surfaces of a fault/boundary before the friction is overcome and the fault ruptures.
The fact that there has not been anything larger than ~ a M9.2 recorded gives an indication that thats probably pretty close to the limit :)
Its interesting to note that the 2 largest events to occur in the last ~ 20 years
The 2003 Sumatra and the 2011 Honshu events were both primarily unilateral and had huge rupture lengths, ~ 800 - 1000km
This was really observed, confirmed and studied after the Landers, sthrn California M7.3 event in 1992 that triggered several bursts of activity in central California and also much further north.
|Feb5-13, 09:31 PM||#7|
And speaking of M8 events for the year!!
An hour or so before writing this post, probably during my last post ramblings
we have had a M8.0 in the Santa Cruz Islands ( N of Vanuatu and SE of the main Solomon Is group)
I have been just awaiting for the possibility of this happening. The area became quite active last Friday and Saturday with a series of 5 x M6+ (all less than 6.5) and I said at the time to my wife I wonder if this will result in a major event?
Well Sunday through to Tuesday it went quiet, then today it started afresh with a M6.3 followed by the M8.0, a 6.4, a 6.6 and a mass of M5+'s
Magnitude Date Time Lat Long Depth Location
M5.6 2013/02/06 02:30:49 -10.822 164.980 32.5 SANTA CRUZ ISLANDS REGION
M5.3 2013/02/06 02:23:12 -10.963 165.402 28.3 SANTA CRUZ ISLANDS
M5.2 2013/02/06 02:18:15 -11.468 165.614 34.4 SANTA CRUZ ISLANDS
M5.2 2013/02/06 02:06:21 -10.597 165.363 10.0 SANTA CRUZ ISLANDS
M6.6 2013/02/06 01:54:15 -10.514 165.733 10.2 SANTA CRUZ ISLANDS
M5.7 2013/02/06 01:48:43 -11.628 165.937 10.0 SANTA CRUZ ISLANDS
M5.6 2013/02/06 01:33:37 -10.922 165.085 10.0 SANTA CRUZ ISLANDS
M6.4 2013/02/06 01:23:20 -11.232 164.921 10.1 SANTA CRUZ ISLANDS REGION
M5.6 2013/02/06 01:22:13 -11.366 165.768 10.1 SANTA CRUZ ISLANDS
M8.0 2013/02/06 01:12:27 -10.738 165.138 28.7 SANTA CRUZ ISLANDS
M5.3 2013/02/06 00:46:01 -10.871 165.029 9.5 SANTA CRUZ ISLANDS
M6.3 2013/02/06 00:07:23 -10.858 165.206 10.0 SANTA CRUZ ISLANDS
|Feb6-13, 06:29 AM||#8|
We are talking about a complex system that is driven by the release of heat from below. You seem to be suggesting that a series of large quakes could stop plate tectonics. I would say that that sounds absurd. Also, unless the stress is already loaded, I don't see how one large quake could trigger the next. And having the few places on Earth where big events can happen all loaded to near critical stress levels at the same time would be quite a coincidence!
|Feb6-13, 08:32 AM||#9|
Yep, the big one caused a tsunami which claimed lives:
Just heard news of another Mw 6.0.
Preliminary Earthquake Report
6 Feb 2013 13:54:57 UTC
7 Feb 2013 00:54:57 near epicenter
6 Feb 2013 13:54:57 standard time in your timezone
Location 10.838S 166.451E
Depth 31 km
496 km (308 miles) E (95 degrees) of Kira Kira, Solomon Islands
728 km (452 miles) ESE (103 degrees) of HONIARA, Solomon Islands
2112 km (1313 miles) E (96 degrees) of PORT MORESBY, Papua New Guinea
Location Uncertainty Horizontal: 15.1 km; Vertical 5.5 km
Parameters Nph = 326; Dmin = 728.7 km; Rmss = 1.03 seconds; Gp = 36°
Version = 9
Event ID us c000f2d8
|Feb6-13, 09:22 AM||#10|
You pointed out that "there were no other major events in the 2 weeks following" the Sumatra quake. It appears that they were related. It sounds like you have better access to data which would verify their relatedness.
I did wonder whether there could be "huge" quakes in my original question, but it sounds like that is thought to be relatively unlikely.
For example, Isaac Newton never observed a moonquake. We now know that such things do take place, thanks to a much longer time of observing the Moon. Clearly, on Earth, there are cycles which last longer than a hundred years, therefore the observation period for earthquakes cannot be said to be closed.
Do I understand your answer correctly?
Based on "only" a hundred years of observation, there have been no quakes of magnitude 10, and it is thought that a quake of magnitude 10 or greater is not likely. Even so, it is not currently known what the largest possible earthquake could be; the accurate measurement of all the stresses in the plates are not known; it is impossible at the present time to predict such an event or the size and distribution of subsequent events.
It is thought that a series of related quakes would probably not be "huge", or "major", based on current observations.
What, me worry?
Thanks for the answers.
|Feb6-13, 04:11 PM||#11|
this happens occassionally, the last one that springs to mind .. in the last 10 - 20 yrs was a double M8+ in the Kuril Islands. Again a short time apart and again on the same fault zone
maybe you overlooked it ?
and it isnt the longer time of observing the moon, the knowledge of moonquakes came very quickly after moon landings that placed seismometers there.
You have to understand that earthquake records go back several 1000 years.
The Chinese in particular were diligent record keepers
Stresses can be calculated because the relative plate motions on major boundaries around the world have beed relatively well defined
It doesnt tell us WHEN the next quake will happen, It can only tell us what segments of a fault/boundary are more likely to be the next quake location.
We just cant tell you which specific year day or hour that may be.
Keeping in mind that, particularly for oceanic boundaries, where historical quake data is lacking and stress calculations across such an area is difficult and the lack of funding/manpower to indepth study EVERY section of EVERY boundary. It is mainly the ones onland or close to shore where it may affect large populations that are the ones more likely to receive any study work
|Feb7-13, 08:55 AM||#12|
Thanks for the continued commentary.
Staying focused on the original questions, because I'm thinking I have answers, but want to verify:
Q#1) Recent series of quakes seem to be related. If an individual quake is big enough, could it cause some sort of chain reaction thru a large number of other tectonic plates resulting in, say, a week of global, huge quakes?
A#1) Yes, an individual quake can cause a chain reaction thru a number of unrelated tectonic plates.
While it is true that series of quakes can be related over long geographic distances, depending on fault lines, fault characteristics, the nature of a particular quake, and other factors; so far, there have been no major, or "huge" effects because of this relatedness.
As to the related and inferred question, "What could be the largest quake?", that is not known. So far over the last one hundred years, the largest observed quake has been 9.xx.
Q#2) If this global shaking and quaking were to happen, could the tectonic balance around the Earth's axis be changed so much that the inclination might also change?
A#2) Highly unlikely, based on current knowledge. The 9.xx Japanese quake was calculated by NASA to have moved the Earth's figure axis by 6.5 inches. The Earth's axis of rotation is 33 feet away from the figure axis. External disturbances are the only known things which could affect the Earth's rotational axis.
As a side issue, I'm guessing that the dinosaur asteroid of 65mya, since it hit the Yucutan near the equator, didn't change the Earth's axis of rotation significantly.
Q#3) Is the Earth's core thought to be totally liquid, or does it have rotating solid chunks in it? What would be the relationship between tectonic activity on the surface, and the rotational stability of the core? How might this affect the Earth's rotation andaxis?
A#3) The Earth's core is solid, and there is no evidence suggesting that there is any relationship between the core and the crust which would manifest as an earthquake.
It is impossible at the present time to predict the next earthquake or the size and distribution of subsequent quake events that would be dependent on that "next" earthquake.
Yes, the "amount of stress accumulating each year due to plate motion can be calculated", thanks to accurate GPS observations. This allows the experts to "make good educated 'guesses'" about future quakes, but it is still impossible to predict their occurence, which is the state of art at the moment.
It is not at all clear to me that "prediction", and "educated guesses" are the same thing. I make no judgements on the ability to predict quakes. It is well known that such a predictive capability could save many lives.
Question #4: What is the largest quake that is possible on Earth?
|Feb7-13, 01:44 PM||#13|
Those factors are what determine the largest size of quake. They are what limits the largest quakes to ~ Mw9.5. Its why we have never seen a Mw 9.5 or greater
I never said they were :) The ability of prediction of a quake is the ( as at the moment) the unattainable holy grail. That is... to be able to say that on a particular day of a particular week there going to be a big quake on xxx fault. The professionals have pretty much given up on that idea., and instead have focussed their activities on mitigating the consequences of large events ... better buildings, infrastructure, education of the population on how to protect themselves etc etc.
BUT as I said in an earlier post, predicting which sections of a plate boundary are most likely to produce a major event next is reasonably doable.
|Feb7-13, 02:04 PM||#14|
Question #4: What is the largest quake that is possible on Earth?
Answer #4: Since stress fields along accessible major plate boundaries can be "quite easily calculated these days" thanks to GPS; since the "amount of stress accumulating each year due to plate motion can [also] be calculated"; since "these accumulations of stress can be extrapolated to see how much stress can accumulate [over,] say... 100 years", and since "stresses can be calculated because the relative plate motions on major boundaries around the world have been relatively well defined"; and since no quakes greater than 9.5 have been observed in the last 100 years; we can say the following:
It is "likely" that the largest quake possible on Earth would be 9.5.
Is that a correct answer?
|Feb7-13, 02:37 PM||#15|
PS ... Another big aftershock from the Santa Cruz Islands ~ an hour ago Mw 6.6
still visible on my recorder for a few more hours ...
|Feb7-13, 02:49 PM||#16|
Let's hope we don't get a ten!
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