We collected gravity data on a slope in Avcılar where near the North Anatolian Fault Zone (NAFZ) . We think that, we can study or collected gravity data on any slope (there is a slope stability problem) and gravity value are affected by on that. However, we worry that why does the gravity change on the same measurement point in 7 days. The increasing value is approximately 38 mgal near to (NAFZ) in Turkey? The measurements were conducted with the CG-5 Scientrex device. The stress is increasing sharlpy or not? We asked it to you.? For the earhtquake prediction, Is these increasing is normal or not?
Sincerly.
Dr. Savas KARABULUT (Istanbul University)
I would be suspicious of these results, and suspect operator / instrument error and / or disturbance. Gravity is a constant, and there can not be (as far as I am aware) any plausible explanation for significant changes in local rock density over a 7 day period.
Tidal effects, groundwater level, instrument drift, inaccurate elevation survey, or operator error (poor or unstable levelling). Check all of these. Good luck!
Tim
An increase of 38 mgal is significant and indicates higher density. I would be skeptical of this measurement and work to rule out operator error and ensure accuracy of the location of measurement to make sure the data is valid. Location along the slope will be important since about 1/3 of a mgal of change can be expected for a meter in height. A hundred meters of fill represents a significant stress change, if the measurement is accurate. I would compare the result to a gravimetric base map to see if one or the other of the measurements compares better to help identify which measurement might be in error. If the data seems to be reliable, I would next work on developing a site model to match the results and investigate the local Bouger Anomaly magnitude and shape. Understanding how this measurement fits with other local data will help to pinpoint the cause of the increase or help you rule out the result as erroneous.
As all above have stated, tides, elevation, and groundwater are all part of the total gravity measurement at any point in the world. Since these can all change over time, they could be contributing to the change you are observing.
Having said that, I have not personally used the Scintrex CG-5 gravimeter. In looking at the manufacturer's brochure, I see that it is claiming all sorts of automated corrections. I would therefore be very suspicious of either operator or instrument error in this matter. I am supposing that the instrument reports the values used for all those automatic corrections. I would look very closely at all of them. I suspect that you might find a clue among them. I would especially look at the elevation that was used on the two different days.
Another question that arises based on the claimed precision of the instrument. I am wondering if there is a chance that you mean 35 milligals (mgals) or 35 microgals? A change of 35 microgals would be much easier to explain, and so much more likely.
Hello Savas KARABULUT,
from a distance is an analysis hardly reliably possible. First, you should check the device and the stored software in case of such enormous gravity changes in a very short time, in one place.This is also important because in the present state of science it is not possible to make a temporally and spatially accurate, reliable prediction of earthquakes and it is thereby possible, that you can come to wrong conclusions.
Anyway, I would recommend, choise a other method and switch to the radon method. This will have likely more successful for the examined area.
Your Michael Lersow
The gravity field change in case of Earth is connected to the changing in Earth interior (mantle, outer core)... In case of Earth the most shorter gravity changing can be observed in case of Earth Quakes...
http://onlinelibrary.wiley.com/doi/10.1029/2011GL049018/full
http://physicsworld.com/cws/article/news/2004/oct/14/earthquake-shakes-up-gravity
In case of quantum mechanics these changing are more smaller... example changing direction of photon,... Photon impact,...
Dear Savaş Karabulut.
When I have read to the answer I see that common oppinion is that 38 mgal significant mistake. The usage error or the instrumental error as the cause of the error is discussed. Do you have idea about the issues mentioned by the researchers?
First, it's quite clear which one Δg is determined. The second Newtonian axiom called the 2 properties of the mass which is to be inertial and gravitational. So a Δg can be caused only by a Δm. Whereby the Δm has arised, is unclear, speculative. One thing is clear, however, an earthquake, it can not have been, then even the measuring equipment probably would not have survived.
Now the question remains whether the measured Δg is an indicator for an announcement of an earthquake? Since the measured value seems to be more an outlier, it's obvious this monitoring with another measurement method to repeat, see Radon method. This investment is worthwhile because on such a difficult field of science for more safety it is ever good, to use comparative measurements, direct measurement, indirect measurement. The question is not trivial.
Good luck
Temperature variation alone from one measurement to another may cause a reading difference of tents of mGals. Beware.
I concur; 38 mgal is certainly an operator error, or the equipment is not properly calibrated, or the reading unit is not broken. It is about 100 times larger than any of the reasonable or unreasonable ideas posed by other respondents. When I was party chief on a Mobil Oil gravity crew in 1960 we had a calibration course that was run once a month and whenever the meter had been repaired. If the operator came up with a 38 mgal error he would be too ashamed to talk about it.
Dear Dr. Savas,
Well, as Dr. Matthew mentioned earlier, you have to be careful if its microGal and not MilliGal. 35 micro-Gal is very normal as this area is active and many underground density distribution can cause such changes for example: water, stress change, heat or magma movement, and so on (you know better than me about the geology and the hazards of this area). a CG-5 or CG-3 or even the latest CG-6 can have an accuracy of around 5-10 MicroGal over very stable stations. I ask you to check my latest book chapter on microgravity and its applications in geoscience (2018). Second: Operator expertise and elevation (GPS data) are very important to have good data (representative data). At the end, gravity (microgravity) is changing over time at any specific stations due to what I mentioned above. I always say to my students that taking good data is the most important step before anything else. You may read some nice books such as: Geodesy by Wolfgang Torge (deGruyter Edition) for basic steps. Also, you must take measurements at a quite area far from the study area (far from the gravity change causes) to have a better understanding of such increases (micro-Gal).
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