Geology Lessons To An Astrologer

Once again I find myself writing on a geology topic which has made recent news in the Indian media. I am referring to the belief held by some people that a particular alignment of the moon and planets is the cause of major earthquakes. This belief holds that plate tectonics and the earth's internal stresses play a minor role if at all. Astrology and the influence of the gravitational pull of the moon on our daily lives and now apparently the internal working of the earth is a topic that seems to fascinate a lot of people. The reaction I get when a discussion starts is a lot of head nodding and muttering that "there must be something to this" and occasionally a long confident but utterly nonsensical monologue on geology, gravity, tidal forces and earthquakes. Then how do you explain that the Bhuj earthquake took place during full moon? Coincidence is something that believers seem not to believe in.

I did some more searching for tidal triggering of quakes and found out that there has been some recent work that suggests a relation between tides and ocean tidal loading triggering small seismic shocks, but all these studies indicate that tectonic stresses play the major role and tidal stresses if at all a minor one. Researchers are suggesting that tides may raise the level of stress on faults and cause them to slip sooner than they would have. The earthquakes would have happened without the tides, but the additional tidal stresses may be helping it occur sooner. This is similar to the situation of reservoir induced seismicity, where the column of water in a reservoir may increase stresses on already critically stressed faults causing them to slip. So you cannot explain earthquakes as Mr. Dave is proposing by ignoring the tectonic setup. And in any case the mechanism Mr. Dave proposes for tides causing big earthquakes is not viable.

A while ago DNA had an interview with a Mr. Amit Dave who claims he can predict big earthquakes based on the alignment of planets. I criticized that article and pointed out the many mistakes and misunderstandings about geology that Mr. Dave 's theory was based on. I have gotten no substantive reply from him but he did leave a list of question for me in the comments section. Instead of replying to him in a comment I thought I would write a new post. Below is the list of questions:

A few question to MR.kher

(1) Does moon force depend on the body it is acting?
(2) How such a small force produce 4.5 mtrs of high tide in the oceans?
(3) can we observe high tide and low tides in a bucket full of water? why ?
(4) Does mass and volume of molten lava is more than that of waters in the oceans?
Now some questions to Plate Tectonics
(1) Why there are quakes at other than plate boundaries?
(2) How and why the initial two plates ie Laurasia and Gondwanaland
separated initially ? Due to heat currents or Due to Earth rotation?
Because magma will not solidify at the places where splitting forces are already there how did they separated ?
(1)Why there are major quakes allover the globe ,on different plate on a given date?
(2) Why some months are prone to major natural disasters Like May 2008?
(3)Why some of the major quakes have occured onf
full moon or new moon day. BOth Latur(30-09-1993) and Bhuj 26-01-2001)quakes are on full moon day
(4) How does plate tectonics explains pre shocks ?

It seems like a pretty confused and badly framed set of questions.

I'll lump the first two questions together:

(1) Does moon force depend on the body it is acting?
(2) How such a small force produce 4.5 mtrs of high tide in the oceans?

All objects on earth experience gravitational attraction to the moon. The moon's force is very small, about one ten millionth the gravitational pull of the earth. However, the water in the oceans is not rigid. It flows and the earth cannot hold on to it like it does to the rigid crust. The moon is able to pull at it and this gravitational pull along with the centrifugal force created by the earth's spin results in a piling up of water on the side of the earth facing the moon as well as on the side opposite it. Whether tides are 4.5 meters or less or more depends upon the location of the sun and the moon, the particular configuration of the coastline, depth of the ocean at that location and oceanic currents.

3) can we observe high tide and low tides in a bucket full of water? why ?

And do mentally unstable people become even more insane during full moon? And oh, did you hear about that Olympic swimmer who was dragged to the other end of the swimming pool by a low tide? All these are myths, tidal forces don't affect objects over small distances.

This is the key to understanding why large earthquakes cannot be caused by tidal forces acting alone on earth.

Tides are created not by just the gravitational pull of the moon but due to a difference in the gravitational pull of the moon across the body of the earth. The gravitational forces decrease with distance and so an object on the side of the earth closer to the moon will experience a slightly larger pull than an object at the center of the earth, which in turn will experience a slightly larger pull towards the moon than an object on the side of the earth facing away from the moon. The near side of the earth accelerates towards the moon a little faster than the center of the earth producing a tidal bulge on the near side. The solid earth bulges out only a little, maybe a few cm, but the more fluid water produces a bigger tidal bulge. Now the oceans on the far side are being pulled toward the moon less than the center of the earth. This difference causes the oceans to be "left behind" to form a second tidal bulge as the moon pulls the earth away from the oceans on the far side.

So small differences in the gravitational pull of the moon (and sun) realized across the body of the earth i.e over very large distances causes tides.

Now it is easier to understand why small bodies of water like that in buckets, swimming pools and lakes do not experience tides. It is because the water at different locations across these bodies is at the same distance from the moon and experiences no difference in gravitational pull.

4) Does mass and volume of molten lava is more than that of waters in the oceans?
At any one time the mass and volume of lava being produced is smaller than that of the water in the ocean. His theory of earthquakes depends upon tidal forces acting on molten material and causing it to disrupt the earth's crust. This is what DNA quote's him saying:

The earth consists of a thin upper crust and molten lava, magma. The inner crust is semi-solid and hot. Like tidal waves, this molten lava is also influenced by tidal currents. The moment the high tide pull is more, it breaks open the crust and earthquakes occur. If the crust breaks completely, it results in a volcanic eruption. Dave says the most potent quakes occur when the sun, Jupiter, Saturn, and the moon are in mutual potent positions like 0º, 90º, 180º, and 360º. The two planets change their direction of motion from direct to retrograde from time to time. The gravitational pull exerted on the earth by this movement induces a change in momentum, mass and velocity of the molten lava, creating disturbances.

According to him, in this imagined interior of the earth there is a uniform layer of molten material forming an ocean at depth just like the one on the surface. If the surface ocean experiences tides, then so does this subterranean magmatic ocean. High tides in this magmatic ocean will then exert pressure on the overlying solid crust causing it to rupture. The problem with this fantastic scenario is that the description of the interior of the earth is all wrong. There is no uniform layer of magma at depth. The earth's upper and lower crust is all solid and magma within it occurs as small discrete bodies localized along zones of melting mostly close to plate boundaries.

But wait.., what was it about small bodies of liquid and tidal forces? Yes that's right, the difference in lunar gravitational pull across these local bodies of magma will be small and they will experience no significant lunar tides, certainly not large enough to cause the surrounding crust to break.

Let's now take magma out of the picture. A lot of earthquakes are not associated with magmatism and Mr. Dave's theory fails to provide a mechanism to explain them. Can tidal forces cause solid earth to rupture causing earthquakes? This is not as unrealistic as it sounds. As the comet Shoemaker-Levy 9 accelerated towards Jupiter it broke up into pieces due to Jupiter's tidal forces. What happened was that the front of the comet accelerated towards Jupiter at a faster rate than the far side of the comet. This differential pull across its body caused it to split.

But the moon's gravitational pull is not that strong. Any differential pull due to moon's gravitational force felt by the solid rocks across the earth is easily overcome by the earth's own gravitational pull. Still lunar gravity does cause the solid earth to deform a little (solid earth tides), by just about 2 feet across its diameter. There is just not nearly enough differential gravitational pull across any local region of the earth (the swimming pool or bucket of water principle) which by itself can cause the crust to rupture. Earth tides if they do show a correlation to minor seismicity always act in concert with the regional tectonic stress field.

Now to Plate tectonics part of Mr. Dave's questionnaire

(1) Why there are quakes at other than plate boundaries?
Most earthquakes do take place at or near plate boundaries but there are plenty of examples of earthquakes in mid-plate locations far away from zones of plate interaction. The ultimate cause of these earthquakes can usually be traced to plate boundary stresses being propagated across the rigid crust leading to reactivation of weak crustal zones in mid plate areas. Crustal flow arising out of plate-plate collision zones can also form zones of deformation and earthquakes far away from plate boundaries. The recent Sichuan earthquake is a good example. The figure below depicts crustal flow patterns tracked by GPS measurements across and away from the Himalayan collisional zone.


Source: Continuous Deformation of the Tibetan Plateau from global positioning system data

I've explained how plate tectonics can ultimately explain this pattern of crustal flow, deformation and earthquakes in a previous post. Try explaining this using tidal forces.

(2) How and why the initial two plates i.e. Laurasia and Gondwanaland separated initially ? Due to heat currents or Due to Earth rotation? Because magma will not solidify at the places where splitting forces are already there how did they separated ?

The first part is easier to answer since I didn't really understand the second part! How do plates split apart, example Laurasia and Gondwanaland of Pangea fame. The best answer we have is due to mantle convection cells which bring hot material to the base of plates causing doming, weakening of the plate and finally rifting, eventually splitting the plate into two and creating a divergent plate margin. This mantle upwelling and the resultant decompression of the mantle material lowers the melting point of the mantle material causing melting. The melt does not force the plates apart, rather is a result of the rifting of plates.


Miscellaneous:

(1)Why there are major quakes allover the globe ,on different plate on a given date?
(2) Why some months are prone to major natural disasters Like May 2008?
(3)Why some of the major quakes have occured onf
full moon or new moon day. BOth Latur(30-09-1993) and Bhuj 26-01-2001)quakes are on full moon day
(4) How does plate tectonics explains pre shocks ?

All these can be answered in one thread. It also reveals a little of how Mr. Dave thinks. For example his fixation on dates is due to his blind faith that certain days are special because of a preferred alignment of the moon and planets. That's why his insistence on finding out if there is a relation between plates and dates!

Unlike a particular alignment of the moon and planets taking place on certain days, plate tectonics is not an event. It is an ongoing process taking place all the time, simultaneously all over the globe. The earth's plates are moving in different directions, jostling against, subducting underneath and sliding past other plates. This creates different stress fields on different plates and many times pre-shocks (which is nothing but a small earthquake preceding a big one in the same area) and large earthquakes on the same day. There is nothing special about these occasions. Rocks along faults situated on different plates may just happen to slip on the same day. A chance clustering of such events may make certain months seem more prone to earthquakes, but if one takes a large enough data set things even out.

Finally Mr. Dave left another comment on a previous post :

As you all have agreed that there could be major quakes in September 08 ,or for that matter in any month,why you people hesitate in giving three dates

He wants me to give him three random dates and check whether both of us have the same probability of success or failure. Scoring brownie points over each other using three data points is not how science works. This is his theory. The burden of proof is on him. If he want his work to be taken seriously then he will have to write up his results and present them for peer review. Inviting me to play a game of dice in the blogosphere is not the way to test a hypothesis.

Disclaimer Sept. 17: Contrary to some comments left on this post I did not predict the Sept 17 earthquake which occurred in the Satara district of Maharashtra. Nor did anyone else. Don't let people fool you otherwise. You have to give accurate location information (latitude and longitude) along with a hypothesis in terms of geological forces and stresses acting at that location why an earthquake is likely or imminent. Simply saying that an earthquake will occur on this day and time does not qualify as a prediction. The reason is that there are plenty of earthquakes occurring everyday on earth. On average about 10-11 earthquakes of 6-7 magnitude occur every month, 3 earthquakes of 5+ magnitude occur everyday and more than 20 earthquakes of 4+ magnitude occur everyday somewhere on earth. Without a location and a justification "predicting" an earthquake is easy!! :-)

I'll be writing a larger post on this later maybe in a couple of weeks. Do visit again.

Update: Was September 08 Earthquake Month?