VAN method

From Wikipedia, the free encyclopedia
Jump to: navigation, search

The VAN method is a controversial method for earthquake prediction based on the assumption that minerals under mechanical stress emit characteristic electrical signals. The name of the method derives from the surname initials of each of its inventors, Greek physicists Panayotis Varotsos, Caesar Alexopoulos and Kostas Nomikos. Currently (2010) the VAN team is part of the Solid Earth Physics Institute of the University of Athens, Greece and is headed by Professor Panayotis Varotsos.

Contents

[edit] Description of VAN

Prediction of earthquakes with this method is based on the detection, recording and evaluation of Seismic Electric Signals or SES. These electric signals have a fundamental frequency component of 1 Hz or less and an amplitude proportional to the magnitude of the earthquake.[1][2][3] According to the VAN team the SES are emitted by rocks under the stress caused by the movement of tectonic plates. They are attributed to the piezoelectric behaviour of some minerals, especially quartz, or to effects related to the behaviour of crystallographic defects under stress and they appear when the mechanical stress on rocks reaches a critical value, a few weeks before the earthquake.[4]

The seismic electric signals propagate with relatively low attenuation along the tectonic faults, due to the increased electrical conductivity caused either by the intrusion of ground water in them or by the ionic characteristics of the minerals.[5] These signals are detected at stations which consist of pairs of electrodes inserted into the ground, amplifiers and filters. They are then transmitted to the headquarters of the VAN team in Athens where they are recorded and evaluated. Currently the VAN team operates 9 stations, while in the past (1999) they could afford up to 17.[6] The VAN team claims that they are able to predict earthquakes of magnitude larger than 5, with an uncertainty of 0.7 units of magnitude and in a 2-hour to 11-day time window. The VAN stations have a degree of spatial selectivity. For example the station IOA, located near Ioannina, detects seismic electric signals which correspond to tectonic activity in Western Peloponnese and the Ionian Sea, while it does not detect signals related to tectonic activity around Ioannina.

The generation of electric signals by minerals under high stress leading to fracture has been confirmed with laboratory experiments.[7][8]

In recent years the VAN team has tried to improve the accuracy of the estimation of the time of the forthcoming earthquake by introducing the concept of natural time, a parameter which indicates the evolution of the process from the generation of the seismic electric signal to the fracture at the tectonic fault.[9][10][11][12]

The VAN method is also used for investigation of seismic electric signals in Japan.[13]

[edit] Criticism of VAN

The usefulness of the VAN method for prediction of earthquakes has been a matter of debate. Both positive and negative criticism on the VAN method is summarized in the 1996 book "A Critical Review of VAN", edited by Sir James Lighthill.[14] A very critical review of the methodology was published by Y. Y. Kagan of UCLA in 1997.[15]

VAN has claimed to have observed at a recording station in Athens a perfect record of a one-to-one correlation between SESs and earthquake of magnitude ≥ 2.9 which occurred 7 hours later in all of Greece.[16] However, it was later shown that the list of earthquake used for the correlation was false. Although VAN stated in their article that the list of earthquakes was that of the Bulletin of the National Observatory of Athens[2] (NOA) it was found that 37% of the earthquakes actually listed in the bulletin, including the largest one, were not in the list used by VAN for issuing their claim. In addition, 40% of the earthquake which VAN claimed had occurred were not in the NOA bulletin.[17]

Examining the probability of chance correlation of 22 claims of successful predictions by VAN[18] it was found that 74% were false, 9% correlated by chance, and for 14% the correlation was uncertain.[19] No event correlated at a probability greater than 85%, whereas the level required in statistics for accepting a hypothesis test as positive is 99%, sometimes relaxed to 95%.

None of the earthquakes which Van claimed were preceded by SESs generated an SES themselves and an analysis of the propagation properties of SESs in the Earth’s crust showed that it is impossible that signals with the amplitude reported by VAN could have been generated by small earthquakes and transmitted over the several hundred kilometers distances from the epicenter to the receiving station.[20][21]

VAN’s publications are characterized by a lack of addressing the problem of eliminating the many and strong sources of change in the magneto-electric field measured by them, such as telluric currents and neighbors of Varotsos turning on and off their television set in suburban Athens, by a lack of statistical testing of the validity of their hypothesis, by changing the parameters of the hypothesis constantly (the moving goal post technique), and by a belief that phenomena of rock physics seen in the laboratory can be assumed to take place in the Earth’s seismogenic crust.[22][23][24]

One inherent problem of the method is that, in order for any prediction to be useful, it has to predict a forthcoming earthquake with a reasonable accuracy with respect to timeframe, epicenter and magnitude. Otherwise, if the prediction is too vague, no feasible decision (such as to evacuate the population of a certain area for a given period of time) can be made. The VAN team have been arguing that, as the sensor rod network expands and its data processing technique is refined, its predictions will become increasingly useful.[citation needed]

Major opponents of VAN were the Greek seismologists Vassilis Papazachos and G. Stavrakakis. The debate between Papazachos and the VAN team has repeatedly caused public attention in their home country Greece and has been extensively discussed in the Greek media.[citation needed]

[edit] See also

[edit] References

  1. ^ Varotsos, P., Alexopoulos, K., and Nomicos, K. (1981). "Seismic electric currents". Proceedings of the Academy of Athens 56: 277–286. 
  2. ^ Varotsos, P., Alexopoulos, K., Nomicos, K., Papaioannou, G., Varotsou, M., Revelioti-Dologlou, E. (1981). "Determination of the epicenter of impending earthquakes from precursor changes of the telluric current". Proceedings of the Academy of Athens 56: 434–446. 
  3. ^ Varotsos, P., Alexopoulos, K., and Nomicos, K. (1982). "Electrotelluric precursors to earthquakes". Proceedings of the Academy of Athens 57: 341–363. 
  4. ^ P. Varotsos, K. Alexopoulos, K. Nomicos and M. Lazaridou (1986). "Earthquake prediction and electric signals". Nature 322 (6075): 120. doi:10.1038/322120a0. 
  5. ^ P. Varotsos, N. Sarlis, M. Lazaridou, and P. Kapiris (1998). "Transmission of stress induced electric signals". Journal of Applied Physics 83: 60–70. doi:10.1063/1.366702. 
  6. ^ P. Varotsos and M. Lazaridou (1991). "Latest aspects of earthquake Prediction in Greece based on Seismic Electric Signals. I". Tectonophysics 188: 322. 
  7. ^ V. Hadjicontis, C. Mavromatou, T. N. Antsygina and K. A. Chishko (2007). "Mechanism of electromagnetic emission in plastically deformed ionic crystals". Phys. Rev. B 76 (2): 024106. doi:10.1103/PhysRevB.76.024106. 
  8. ^ V. Hadjicontis, K. Eftaxias, and P. Varotsos (1988). "Thermodynamic properties of defects in crystals calculated on the basis of the bulk elastic data". Phys. Rev. B 37 (8): 4265–4266. doi:10.1103/PhysRevB.37.4265. 
  9. ^ P. Varotsos and M. Lazaridou (1991). "Latest aspects of earthquake Prediction in Greece based on Seismic Electric Signals. I". Tectonophysics 188 (3–4): 321–347. doi:10.1016/0040-1951(91)90462-2. 
  10. ^ P. Varotsos, K. Alexopoulos and M. Lazaridou (1993). "Latest aspects of earthquake prediction in Greece based on Seismic Electric Signals II". Tectonophysics 224: 1–37. doi:10.1016/0040-1951(93)90055-O. 
  11. ^ P. Varotsos, N. Sarlis, E. Skordas, and M. Lazaridou (2003). "Determination of the epicentral distance of an impending earthquake from the rise time of Seismic Electric Signals". Studying the Earth from Space 5: 3–5. 
  12. ^ P. Varotsos (2006). "What happened before the last five strong earthquakes in Greece". Proc. Jpn. Acad. Ser. B 82 (2): 86–91. doi:10.2183/pjab.82.86. 
  13. ^ Uyeda, S., M. Kamogawa, and H. Tanaka (2009). "Analysis of electrical activity and seismicity in the natural time domain for the volcanic-seismic swarm activity in 2000 in the Izu Island region, Japan". J. Geophys. Res. 114: B02310. doi:10.1029/2007JB005332.  [1]
  14. ^ Sir James Lighthill, ed. (1996). A Critical Review of VAN - Earthquake Prediction from Seismic Electrical Signals. London, UK: World Scientific Publishing Co Pte Ltd. ISBN 978-9810226701. http://www.worldscibooks.com/engineering/3006.html. 
  15. ^ Yan Y. Kagan (1997). "Special section-assessment of schemes for earthquake prediction; Are earthquakes predictable?". Geophys. J. Int. 131: 512. http://moho.ess.ucla.edu/~kagan/GJI_1997.pdf. 
  16. ^ Varotsos, P., Alexopoulos, K. & Nomicos, K. (1981). Seven-hour precursors to earthquakes determined from telluric currents, Praktika of the Academy of Athens, 56, 417-433.
  17. ^ Wyss, M. (1996). Inaccuracies in seismicity and magnitude data used by Varotsos and coworkers, Geophysical Research Letters, 23, 1299-1302.
  18. ^ Varotsos, P. & Lazaridou, M. (1991). Latest aspects of earthquake prediction in Greece based on seismic electric signals, Tectonophys., 188, 321-347.
  19. ^ Wyss, M. & Allmann, A. (1996). Probability of chance correlations of earthquakes with predictions in areas of heterogeneous seismicity rate: the VAN case, Geophysical Research Letters, 22, 1307-1310.
  20. ^ Bernard, P. (1992). Plausibility of long distance electrotelluric precursors to earthquakes, Journal of Geophysical Research, 97, 17531-17546.
  21. ^ Bernard, P. & LeMouel, J.L., (1996). On electrotelluric signals. in A critical review of VAN, pp. 118-154, ed. Lighthill, S. J. World Scientific, London.
  22. ^ Mulargia, F. & Gasperini, P. (1992). Analyzing the statistical validity of earthquake precursors. An application to the "VAN" method, Geophys. J. Int., 110, 32-44.
  23. ^ Mulargia, F. & Gasperini, P., (1996). Behind VAN: Tectonic stress changes or earthquake induced alertness? in A critical review of VAN, pp. 244-249, ed. Lighthill, S. J. World Scientific, London.
  24. ^ Wyss, M., (1996). Brief summary of some reasons why the VAN hypothesis for predicting earthquakes has to be rejected. in A critical review of VAN, pp. 250-266, ed. Lighthill, S. J. World Scientific, London.

[edit] Further reading

[edit] External links

Retrieved from "http://en.wikipedia.org/w/index.php?title=VAN_method&oldid=467584531"
Personal tools
Namespaces

Variants
Actions
Navigation
Interaction
Toolbox
Print/export
Languages