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VAN method

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The VAN method is a method for earthquake prediction based on observations of Seismic Electric Signals (SES) correlated to earthquake events. The mechanism, methodology and statistical significance of these correlations are not well-constrained. The name of the method derives from the surname initials of each of the co-authors of the team's first paper, 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.

Description of VAN

Prediction of earthquakes with this method is based on the detection, recording and evaluation of Seismic Electric Signals or SES. These electrical 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.

There are several hypotheses put forth for to explain them:

  • They are perhaps attributed to the piezoelectric behaviour of some minerals, especially quartz, or
  • to effects related to the behaviour of crystallographic defects under stress. These may appear a few weeks before an earthquake, when the mechanical stress reaches a critical value.[4] The generation of electric signals by minerals under high stress leading to fracture has been confirmed with laboratory experiments.[5][6]
  • Alternately, the Chinese favor a mechanism which relies on the thermoelectric effect in magnetite.[7]
  • Finally, a mechanism has been proposed relying on the electrokinetic effect associated with the motion of groundwater during a change in pore pressure.[8]

While the groundwater mechanism (electrokinetic effect) may be consistent with signal detection tens or hundreds of kilometers away, the other mechanisms require a second mechanism to account for propagation:

  • In one model, 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.[9]
  • In the defect model, the presence of charge carriers and holes can be modeled as making an extensive circuit.[10]

Seismic electric signals are detected at stations which consist of pairs of electrodes (oriented NS and EW) 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. 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. Currently the VAN team operates 9 stations, while in the past (1999) they could afford up to 17.[11]

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, within a radius of 100 km, and in a 2-hour to 11-day time window. Several papers confirm this success rate, but the earthquake sample size is too small to make a statistically significant conclusion.[12] For example, there were eight M ≥ 5.5 earthquakes in Greece from January 1, 1984 through September 10, 1995, and the VAN network forecast six of these.[13]

Since 2001 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 puts weight on a process based on the ordering of events. Two terms, χ and Q, characterize each event. χ is defined as the k/N, where k is an integer (the k-th event) and N is the total number of events in the time sequence of data. Q is the energy released for each event. A related term, p, is the ratio Q/Q(total), and describes the fractional energy released. They introduce a term κ, defined as κ = [ Σ p(k) (k/N)^2 ] - [ Σ (k/N) pk ]^2, where κ is the variance in natural time, k is the event index, N is the number of events, Σ signifies summation, for k = 1 to N, and p(k) is the fractional quantity of energy for the k-th event. This variance puts extra weight on the energy term, p(k). Their current method detects SES as valid when κ = 0.070. Then seismic data are viewed for the site of the SES, starting new time series, with k now equal to zero. All the seismic events are noted, and the region is divided up as a Venn diagram with at least two seismic events per overlapping rectangle. When the distribution of κ for regions which include the most recent seismic event has its maximum at κ = 0.070, the critical seismic event is imminent, and a prediction is issued. Predictions can be found in arXiV. From 2001 to 2010, twenty five of the 28 major earthquakes in the region from N36 to N41 and E19 to E27 were successfully predicted. A summary of their work was published by the science publisher Springer in 2011, entitled "Natural Time Analysis: The New View of Time." Their prediction methodology is now in the mainstream.[14][15][16][17]

The VAN method has also been used for investigation of seismic electric signals in France[18] and in Japan.[19] Though not strictly a VAN methodology, China plans to launch a satellite in 2014 to compare changes in the ionosphere with ground-based seismic and electrical measurements, as ionospheric changes have been successfully charted as precedent to seismic phenomena.[20] The results of such a study could lend credence (or criticism) to the VAN method.

Criticisms 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.[21] A critical review of the statistical methodology was published by Y. Y. Kagan of UCLA in 1997.[22]

Regarding predictive success - 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.[23] 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 [4] (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.[24] Examining the probability of chance correlation of 22 claims of successful predictions by VAN of M > 4.0 from January 1, 1987 through November 30, 1989 [25] it was found that 74% were false, 9% correlated by chance, and for 14% the correlation was uncertain.[26] No event correlated at a probability greater than 85%, whereas the level required in statistics for accepting a hypothesis test as positive would more commonly be 95%.

Regarding mechanism - 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.[27][28] In effect, if the mechanism is based on piezoelectricity or electrical charging of crystal deformations with the signal traveling along faults, then none of the earthquakes which VAN claimed were preceded by SESs generated an SES themselves. There is also some doubt that phenomena of rock physics seen in the laboratory can be assumed to take place in the Earth’s seismogenic crust.

VAN’s publications are further weakened by not addressing the problem of eliminating the many and strong sources of change in the magneto-electric field measured by them, such as telluric currents from weather, and man-made signals, such as neighbors of Varotsos turning on and off their television set in suburban Athens.[citation needed] One critical paper clearly correlates an SES used by the VAN group with digital radio transmissions made from a military base.[29]

Most importantly, the method is hindered 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).[30][31][32]

Finally, 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. Errors of location for the VAN technique are presently less than or equal to 100 km, within a 2-hour to 11-day time frame, and of M > 5, with an uncertainty in M of < 0.7, all useful parameters - so this criticism seems unfounded.[33]

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]

See also

References

  1. ^ Varotsos, P., Alexopoulos, K., and Nomicos, K. (1981). "Seismic electric currents". Proceedings of the Academy of Athens. 56: 277–286.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  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.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  3. ^ Varotsos, P., Alexopoulos, K., and Nomicos, K. (1982). "Electrotelluric precursors to earthquakes". Proceedings of the Academy of Athens. 57: 341–363.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  4. ^ P. Varotsos, K. Alexopoulos, K. Nomicos and M. Lazaridou (1986). "Earthquake prediction and electric signals". Nature. 322 (6075): 120. Bibcode:1986Natur.322..120V. doi:10.1038/322120a0.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  5. ^ 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. Bibcode:2007PhRvB..76b4106H. doi:10.1103/PhysRevB.76.024106.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  6. ^ 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. Bibcode:1988PhRvB..37.4265H. doi:10.1103/PhysRevB.37.4265.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  7. ^ Shen, Xuhui, Xuemin Zhang, Lanwei Wang, Huaran Chen, Yun Wu, Shigeng Yuan, Junfeng Shen, Shufan Zhao, Jiadong Qian and Jianhai Ding (2011). "The earthquake-related disturbances in ionosphere and project of the first China seismo-electromagnetic satellite". Earthquake Science. 24 (6). Springer Science+Business Media: 639–650. Bibcode:2011EaSci..24..639S. doi:10.1007/s11589-011-0824-0.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  8. ^ N.I. Gershenzon, M.B. Gokhberg and S.L. Yunga (1993). "On the electromagnetic field of an earthquake focus". Physics of the Earth and Planetary Interiors. 77 (1–2): 13–19. Bibcode:1993PEPI...77...13G. doi:10.1016/0031-9201(93)90030-D.
  9. ^ P. Varotsos, N. Sarlis, M. Lazaridou, and P. Kapiris (1998). "Transmission of stress induced electric signals". Journal of Applied Physics. 83: 60–70. Bibcode:1998JAP....83...60V. doi:10.1063/1.366702.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  10. ^ F.T. Freund (1998). "Pre-earthquake signals – Part II: Flow of battery currents in the crust". Natural Hazards and Earth System Sciences. 7: 543–548. doi:10.5194/nhess-7-543-2007.{{cite journal}}: CS1 maint: unflagged free DOI (link)[1]
  11. ^ P. Varotsos and M. Lazaridou (1991). "Latest aspects of earthquake Prediction in Greece based on Seismic Electric Signals. I". Tectonophysics. 188: 322.
  12. ^ Kazuo Hamada (1993). "Statistical evaluation of the SES predictions issued in Greece: alarm and success rates". Tectonophysics. 224 (1–3): 203–210. Bibcode:1993Tectp.224..203H. doi:10.1016/0040-1951(93)90073-S.
  13. ^ S. Uyeda. "Introduction to the VAN method of earthquake prediction". 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 978-981-02-2670-1.
  14. ^ 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. Bibcode:1991Tectp.188..321V. doi:10.1016/0040-1951(91)90462-2.
  15. ^ 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. Bibcode:1993Tectp.224....1V. doi:10.1016/0040-1951(93)90055-O.
  16. ^ 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.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  17. ^ P. Varotsos (2006). "What happened before the last five strong earthquakes in Greece". Proc. Jpn. Acad. Ser. B. 82 (2): 86–91. Bibcode:2006PJAB...82...86V. doi:10.2183/pjab.82.86.
  18. ^ Christophe Maron, Gilles Baubron, Louis Herbreteau, Bernard Massinon (1993). "Experimental study of a VAN network in the French Alps". Tectonophysics. 224 (1–2): 51–81. Bibcode:1993Tectp.224...51M. doi:10.1016/0040-1951(93)90058-R.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  19. ^ 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. Bibcode:2009JGRB..11402310U. doi:10.1029/2007JB005332.{{cite journal}}: CS1 maint: multiple names: authors list (link) [2]
  20. ^ Shen, Xuhui, Xuemin Zhang, Lanwei Wang, Huaran Chen, Yun Wu, Shigeng Yuan, Junfeng Shen, Shufan Zhao, Jiadong Qian and Jianhai Ding (2011). "The earthquake-related disturbances in ionosphere and project of the first China seismo-electromagnetic satellite". Earthquake Science. 24: 639–650. Bibcode:2011EaSci..24..639S. doi:10.1007/s11589-011-0824-0.{{cite journal}}: CS1 maint: multiple names: authors list (link) [3]
  21. ^ 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 978-981-02-2670-1.
  22. ^ Yan Y. Kagan (1997). "Special section-assessment of schemes for earthquake prediction; Are earthquakes predictable?" (PDF). Geophys. J. Int. 131: 512.
  23. ^ 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.
  24. ^ Wyss, M. (1996). Inaccuracies in seismicity and magnitude data used by Varotsos and coworkers, Geophysical Research Letters, 23, 1299-1302.
  25. ^ Varotsos, P. & Lazaridou, M. (1991). Latest aspects of earthquake prediction in Greece based on seismic electric signals, Tectonophys., 188, 321-347.
  26. ^ 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.
  27. ^ Bernard, P. (1992). Plausibility of long distance electrotelluric precursors to earthquakes, Journal of Geophysical Research, 97, 17531-17546.
  28. ^ 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.
  29. ^ Pham, V. N.; Boyer, D.; Chouliaras, G.; Le Mouël, J. L.; Rossignol, J. C.; Stavrakakis, G. N. (1998). "Characteristics of electromagnetic noise in the Ioannina region (Greece); a possible origin for so called ``Seismic Electric Signal (SES)". Geophysical Research Letters. 25: 2229–2232. Bibcode:1998GeoRL..25.2229P. doi:10.1029/98GL01593.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  30. ^ Mulargia, F. & Gasperini, P. (1992). Analyzing the statistical validity of earthquake precursors. An application to the "VAN" method, Geophys. J. Int., 110, 32-44.
  31. ^ 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.
  32. ^ 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.
  33. ^ Kazuo Hamada (1993). "Statistical evaluation of the SES predictions issued in Greece: alarm and success rates". Tectonophysics 224 (1-3): 203-210. Bibcode 1993Tectp.224..203H. doi:10.1016/0040-1951(93)90073-S.

Further reading

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