Possible relationship between Seismic Electric Signals (SES) lead time and earthquake stress drop

Stress drop values for fourteen large earthquakes with MW ≥ 5.4 which occurred in Greece during the period 1983–2007 are available. All these earthquakes were preceded by Seismic Electric Signals (SES). An attempt has been made to investigate possible correlation between their stress drop values and the corresponding SES lead times. For the stress drop, we considered the Brune stress drop, ΔσB, estimated from far field body wave displacement source spectra and ΔσSB derived from the strong motion acceleration response spectra. The results show a relation may exist between Brune stress drop, ΔσB, and lead time which implies that earthquakes with higher stress drop values are preceded by SES with shorter lead time

Probability of chance correlations of earthquakes with predictions in areas of heterogeneous seismicity rate: The VAN case - Reply

All conclusions of Wyss and Allmann [1996] (hereafter cited as WA) are wrong, because their methodology is false. For example, WA’s main conclusion reads: ‘’the probability [P] that the observed correlations of [VAN] predictions with earthquakes (...11 out of 23 attempts) was due to chance is estimated as... 96%...” However, when following WA’s procedure exactly, and assuming that all 23 predictions (out of 23 attempts) are correct, we find a paradox, i.e., values of the probability P larger than unity. In view of this example, any further discussion on WA’s claims becomes unnecessary. However, we proceed to detailed replies, point by point, in order to show that WA have also made several mistakes and major misinterpretations of the true content of VAN’s statements. Characteristic examples of the various misinterpretations (and mistakes) made by WA include: (i) a direct comparison of predicted magnitude values with M(s);(PDE), while VAN had clearly stated that the magnitude values mentioned in the predictions correspond to M(s)(ATH), i.e., to M(L)+0.5. Such a comparison is not allowed because M(L)+0.5 significantly differs (i.e., on the average by 1.0 unit) from M(s)(PDE), (ii) an addition (or deletion) of critical wording to the VAN statements (and predictions) so that they distort VAN’s true meaning, (iii) the use of 22 day prediction time window in the large majority of predictions which, however, correspond to single SES (and hence to an 11 days prediction time window), (iv) an incorrect statement that Varotsos et al. [1993a,b] define the acceptable uncertainty as Delta M less than or equal to 1.0, while VAN repeatedly published that a prediction is accepted as successful only when Delta M less than or equal to 0.7, (v) an erroneous claim that when using SI-NOA ‘’12 out of 22 VAN predictions fail to conform to the error limits,” while the reader can easily check that only 6 (or 7) out of 23 cases deviate from the error limits. Furthermore, WA grossly overestimated the number of the earthquakes (EQs) that should have been predicted, i.e., while VAN clearly stated that predictions are issued only when the expected magnitude is larger than (or equal to) 5.0 units, WA erroneously demand that VAN should predict all EQs with M(s) greater than or equal to 4.3 or M(s) greater than or equal to 4.0. Hence they characterize as a ‘’missed earthquake” any event with M(s) greater than or equal to 4.3 (or M(s) greater than or equal to 4.0 respectively)for which prediction was not issued. Last but not least, we recall that Wyss and Baer [1981] published long term predictions in Greece (for the same time period discussed in this debate) -referring to expected EQs with magnitude 7.75- which turned out to be completely unsuccessful

Inaccuracies in seismicity and magnitude data used by Varotsos and co-workers - Reply

A direct comparison of the predicted magnitude values (M(pred)) to the actual magnitude values (M(EQ)) of the earthquakes (EQs) is allowed only when both values, i.e., M(pred) and MEQ, refer to the same scale. In view of the fact that the Seismological Institute of the National Observatory of Athens (SI-NOA) publicly announces as MEQ the M(L)+0.5 value (Where ML the local magnitude), VAN made it clear long ago, that the predicted values M(pred) (after a proper calibration) referred to M(L)+0.5. Therefore, a self-consistent evaluation of VAN-predictions should consist of a direct comparison of M,red with the actual M(L)+0.5. Unfortunately, Wyss [1996] confuses the discussion by proceeding to a direct comparison of M(pred) With M(s)(PDE); this is not allowed because the values of M(L)+0.5 exceed, on the average, M(s)(PDE) by 1.0 unit. An additional confusion arises from the fact that the relation suggested by Hamada [1993], i.e., M(L)+0.5=m(b)+0.3, is misinterpreted by Wyss as saying M(s)(PDE)=m(b)+0.3. These two alterations by Wyss reveal that his Figures 1 and 2 are erroneous. Wyss [1996] also criticizes VAN, because (in an early publication) Varotsos et al. [1981b] used the Preliminary Bulletin of SI-NOA, instead of the final one. First of all, the final bulletin could not be used by VAN at that time, because it appeared (more than one year) after the publication of the paper by Varotsos et al. [1981b]. Secondly, the correlation between SESs and EQs is evident,when we use consistently, either the preliminary, or the final bulletin of SI-NOA. On the other hand, Wyss [1996] claims that he could not find any correlation between EQs and SESs; we show that this is due to the fact that Wyss included, in his study, small EQs that occurred several hundreds km away from the measuring VAN station (i.e., in Albania, western Turkey, etc.), but he simultaneously deleted the small magnitude EQs that occurred very close to that station. Wyss’s procedure is, of course, not acceptable and hence his Appendix B is wrong. Furthermore, Wyss’s claim that VAN added 25% of events to the list, is shown to be untrue. Beyond the unusual fact that Wyss quotes ‘’VAN’s statements” that have never been published by VAN, the following is also noted: although Wyss [1996] uses quotation marks (in order to indicate that he reproduced exactly what VAN said), he adds critical wording to VAN statements and hence their true meaning is drastically changed. For example, Wyss states: ‘’Varotros et al. [l981a] had first formulated that SESs ‘’occurred a few minutes before each earthquake [related to that SES]” (Varotsos et al. [1981a]).” Thus, Wyss leads the reader to the wrong conclusion that VAN initially claimed that SES have a lead time of a few minutes, and that VAN changed it later. However, we show that this lead time (published by VAN) referred to another the of precursor, and not to SES, but the words in brackets (which are added by Wyss) alter the true meaning of our statement