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Comment on: W. Hagag and H. Obermeyer, “Detection of active faults using EMR-Technique and Cerescope at Landau area in Central Upper Rhine Graben, SW Germany” by Hagag, W. and Obermeyer, H. (2016)
APPGEO-02911; No of Pages 2 Journal of Applied Geophysics xxx (2016) xxx–xxx
Contents lists available at ScienceDirect
Journal of Applied Geophysics journal homepage: www.elsevier.com/locate/jappgeo
Comment on: W. Hagag and H. Obermeyer, “Detection of active faults using EMR-Technique and Cerescope at Landau area in Central Upper Rhine Graben, SW Germany” by Hagag, W. and Obermeyer, H. (2016) Michael Krumbholz Geoscience Centre, Georg-August-University of Göttingen, Göttingen, Germany
A R T IC L E
IN F O
Article history: Received 19 December 2015 Received in revised form 30 January 2016 Accepted 1 February 2016 Available online xxxx Keywords: Comment EMR Method Cerescope
Comment: The study by Hagag and Obermeyer (2016) presents measurements of electromagnetic emissions recorded with a device called “Cerescope”. The emissions are claimed to originate from micro-cracks and are interpreted in terms of their significance for structural geology, i.e. horizontal-stress directions and the detection of active faults. Amongst others, Krumbholz (2010a) has been cited by Hagag and Obermeyer (2016) to have previously applied the EMR method. Nevertheless, the serious concerns about the applicability of the EMR method raised in this publication were not mentioned. This is my main critism of Hagag and Obermeyer (2016). The manuscript lacks a sound discussion of the origin of the signals that were picked up by the Cerescope and instead uses a very selective citation style when referring to the results of previous studies using the Cerescope. More precisely, it ignores the concerns made by Krumbholz (2010a,2010b), and Krumbholz et al. (2012). In addition, the interpretation of the data seems to be arbitrary in large parts. It is well accepted in the scientific community that brittle failure at micro- and nanoscale leads not only to acoustic, but also to electromagnetic emissions (e.g. Koktavy et al., 2004; Misra and Kumar, 2004). The applicability of the Cerescope, however, to record these electromagnetic emissions caused by micro cracking has never been proven! On the contrary, Krumbholz (2010a), and Krumbholz et al. (2012) showed in detail that all measurements taken with the Cerescope are compromised by artificial VLF transmissions and that the inbuilt filters of the Cerescope are not able to remove these VLF signals.
The argumentation of Krumbholz (2010a, 2010b) and Krumbholz et al. (2012) is based on a large number of “horizontal measurements” that were taken with the Cerescope over a large area and over a long period of time. It was shown that (1) horizontal measurements form a circular pattern around the strongest VLF transmitter (DHO38) in the study area, (2) the signal's intensity, when keeping the settings of the device constant, is a function of the distance to the VLF transmitter, (3) the number of measured transient single pulses per unit time corresponds to the broadcasting frequency of the VLF transmitter, and (4) sudden changes in the main directions determined during horizontal measurements correspond to the intermissions of the VLF signals of the transmitter DHO38. Having shed light on the origin of the signals recorded by the Cerescope, Krumbholz (2010a,2010b), and Krumbholz et al. (2012) discussed previous studies that used the Cerescope and demonstrated that "horizontal measurements" taken during this studies (e.g. Lichtenberger, 2006; Mallik et al., 2008) show solely the bearings to known VLF transmitters and that the “linear measurements” can only be attributed to the well-known VLF method. Thus, measuring the secondary VLF field that is induced at places of higher electric conductivity (i.e. faults), instead of providing the information whether a fault is active or not. In detail: (1) Regarding the polar plots by Hagag and Obermeyer (2016) that are supposed to show main-horizontal stress directions. From the presented polar plots of the horizontal measurements it seems to me extremely challenging to conclude a N- to NNEoriented main horizontal stress direction. Instead, plots 3, 7, and 10 might be interpreted to show an E–W main direction which would argue for the VLF transmitter DHO38 that is north of the study area as source of these signals. The authors should explain and show in more detail how they determined the N to NNE oriented main-horizontal stress direction, i.e. show it in the polar plots, rather than barely stating it. Did they lump the different measurements together? Why is no scale for the intensity provided in the polar plots and which parameter is shown? Furthermore, why are they not symmetric? Regarding the measurement procedure and assuming micro-cracks are emitters, one should expect a symmetric pattern. The same holds, however, for artificial VLF signals. In conclusion, the asymmetry is probably introduced by the wrong setup of the device that mutilated the “original” VLF
http://dx.doi.org/10.1016/j.jappgeo.2016.02.001 0926-9851/© 2016 Published by Elsevier B.V.
Please cite this article as: Krumbholz, M., Comment on: W. Hagag and H. Obermeyer, “Detection of active faults using EMR-Technique and Cerescope at Landau area in Central U..., Journal of Applied Geophysics (2016), http://dx.doi.org/10.1016/j.jappgeo.2016.02.001
2
M. Krumbholz / Journal of Applied Geophysics xxx (2016) xxx–xxx
signal(s) beyond recognition! Some of the horizontal measurements were taken above the identified faults (6, 7, 11) or in areas that show increased signal strengths which are claimed to belong to the recently-active faults. How do the authors explain that these horizontal measurements are not influenced by the “fault-related” signals? During some horizontal measurements (1, 2, 5, 6, 8, 9) no signals could be recorded! This should be explained by the authors in general and with special respect to their argumentation that the study area is strewn with active faults? Moreover, the horizontal measurement 4 was taken in the area claimed to be not suitable for the linear measurements, because of the high artificial noise. The authors are asked to explain how it was possible to carry out a horizontal measurement in this area.
faults and fractures, independent of type, are in the order of 0.01–0.0001. Using a very conservative approach, assuming the fault widths identified here are about 10 m and the aspect ratios are in the order of 0.01, the expected length of the faults is about 1 km. How does this agree with the presented fault map and the fact that the faults are not longer than a few hundred meters? To summarize: It was previously shown in detail that the Cerescope is not suitable to deliver the proposed information, because the recorded signals are controlled by artificial VLF transmissions (Krumbholz, 2010a, b; Krumbholz et al., 2012). The authors have disregarded this fact, i.e., their model lacks a profound base and in turn the proposed active fault set is only hypothetical. In consequence a discussion of the underlying cause for the fault formation is untenable. References
(2) Regarding the linear measurements by Hagag and Obermeyer (2016) which are supposed to show active faults. As mentioned above, fault detection with the Cerescope belongs to the well-known VLF method (Krumbholz, 2010a; Krumbholz et al., 2012) and is feasible, but it does not tell you whether a fault is active or not. Consequently, some of the peaks may indeed be caused by faults. In addition, the tracing of the faults (assuming each peak is caused by a fault) seems very arbitrary, i.e. for several faults the strike was interpreted from traversing the fault at one point only, e.g. profiles with faults: E6-F1; E4-F3; E2-F4, F6; and N4-F3, F4. Thus, prompting the question how the strike was determined. Peaks identified in more than one profile and interpreted to belong to the same faults show often extremely different “EMR patterns”, even when traversed by parallel profiles e.g. N6F3 and N7-F2; E1-F3 and E2-F5; E2-F1 and E3-F1. Given the small distances it is very unlikely that the width or infrastructure of the majority of the faults changes in such a dramatic manner. Moreover, taking the width of the “EMR signals” into account, and consider only those that are supposed to show (sub)vertical faults (e.g. E1-F3; E3-F1, F2; E5-F1) the EMR signal should give a reliable estimate of the width of the fault. According to the literature (e.g. Rubin, 1995; Odling et al., 2004) the thickness-length ratios of
Hagag, W., Obermeyer, H., 2016. Detection of active faults using EMR-Technique and Cerescope at Landau area in central Upper Rhine Graben, SW Germany. J. Appl. Geophys. 124, 117–129. Koktavy, P., Pavelka, J., Sikula, J., 2004. Characterization of acoustic and electromagnetic emission sources. Meas. Sci. Technol. 15, 973–977. Krumbholz, M., 2010a. Electromagnetic Radiation as a Tool to Determine Actual Crustal Stresses — Applications and Limitations Ph.D. thesis University of Göttingen, Germany, p. 151. Krumbholz, M., 2010b. Discussion: natural electromagnetic radiation (EMR) and its application in structural geology and neotectonics by R. O. Greiling and H. Obermeyer. J. Geol. Soc. India 76, 289–290. Krumbholz, M., Bock, M., Burchardt, S., Kelka, U., Vollbrecht, A., 2012. A critical discussion of the electromagnetic radiation (EMR) method to determine stress orientations within the crust. Solid Earth 3, 401–414. Lichtenberger, M., 2006. Bestimmen von Spannungen in der Lithosphäre aus geogener elektromagnetischer Strahlung Ph.D. thesis University of Heidelberg, Germany, p. 140. Mallik, J., Mathew, G., Angerer, T., Greiling, R.O., 2008. Determination of directions of horizontal principal stress and identification of active faults in Kachchh (India) by electromagnetic radiation (EMR). J. Geodyn. 45, 234–245. Misra, A., Kumar, A., 2004. Some basics of electromagnetic radiation during crack propagation in metals. Int. J. Fract. 127, 387–401. Odling, N.E., Harris, S.D., Knipe, R.J., 2004. Permeability scaling properties of fault damage zones in siliciclastic rocks. J. Struct. Geol. 26, 1727–1747. Rubin, A.M., 1995. Propagation of magma-filled cracks. Annu. Rev. Earth Planet. Sci. 23, 287–336.
Please cite this article as: Krumbholz, M., Comment on: W. Hagag and H. Obermeyer, “Detection of active faults using EMR-Technique and Cerescope at Landau area in Central U..., Journal of Applied Geophysics (2016), http://dx.doi.org/10.1016/j.jappgeo.2016.02.001
Contents lists available at ScienceDirect
Journal of Applied Geophysics journal homepage: www.elsevier.com/locate/jappgeo
Comment on: W. Hagag and H. Obermeyer, “Detection of active faults using EMR-Technique and Cerescope at Landau area in Central Upper Rhine Graben, SW Germany” by Hagag, W. and Obermeyer, H. (2016) Michael Krumbholz Geoscience Centre, Georg-August-University of Göttingen, Göttingen, Germany
A R T IC L E
IN F O
Article history: Received 19 December 2015 Received in revised form 30 January 2016 Accepted 1 February 2016 Available online xxxx Keywords: Comment EMR Method Cerescope
Comment: The study by Hagag and Obermeyer (2016) presents measurements of electromagnetic emissions recorded with a device called “Cerescope”. The emissions are claimed to originate from micro-cracks and are interpreted in terms of their significance for structural geology, i.e. horizontal-stress directions and the detection of active faults. Amongst others, Krumbholz (2010a) has been cited by Hagag and Obermeyer (2016) to have previously applied the EMR method. Nevertheless, the serious concerns about the applicability of the EMR method raised in this publication were not mentioned. This is my main critism of Hagag and Obermeyer (2016). The manuscript lacks a sound discussion of the origin of the signals that were picked up by the Cerescope and instead uses a very selective citation style when referring to the results of previous studies using the Cerescope. More precisely, it ignores the concerns made by Krumbholz (2010a,2010b), and Krumbholz et al. (2012). In addition, the interpretation of the data seems to be arbitrary in large parts. It is well accepted in the scientific community that brittle failure at micro- and nanoscale leads not only to acoustic, but also to electromagnetic emissions (e.g. Koktavy et al., 2004; Misra and Kumar, 2004). The applicability of the Cerescope, however, to record these electromagnetic emissions caused by micro cracking has never been proven! On the contrary, Krumbholz (2010a), and Krumbholz et al. (2012) showed in detail that all measurements taken with the Cerescope are compromised by artificial VLF transmissions and that the inbuilt filters of the Cerescope are not able to remove these VLF signals.
The argumentation of Krumbholz (2010a, 2010b) and Krumbholz et al. (2012) is based on a large number of “horizontal measurements” that were taken with the Cerescope over a large area and over a long period of time. It was shown that (1) horizontal measurements form a circular pattern around the strongest VLF transmitter (DHO38) in the study area, (2) the signal's intensity, when keeping the settings of the device constant, is a function of the distance to the VLF transmitter, (3) the number of measured transient single pulses per unit time corresponds to the broadcasting frequency of the VLF transmitter, and (4) sudden changes in the main directions determined during horizontal measurements correspond to the intermissions of the VLF signals of the transmitter DHO38. Having shed light on the origin of the signals recorded by the Cerescope, Krumbholz (2010a,2010b), and Krumbholz et al. (2012) discussed previous studies that used the Cerescope and demonstrated that "horizontal measurements" taken during this studies (e.g. Lichtenberger, 2006; Mallik et al., 2008) show solely the bearings to known VLF transmitters and that the “linear measurements” can only be attributed to the well-known VLF method. Thus, measuring the secondary VLF field that is induced at places of higher electric conductivity (i.e. faults), instead of providing the information whether a fault is active or not. In detail: (1) Regarding the polar plots by Hagag and Obermeyer (2016) that are supposed to show main-horizontal stress directions. From the presented polar plots of the horizontal measurements it seems to me extremely challenging to conclude a N- to NNEoriented main horizontal stress direction. Instead, plots 3, 7, and 10 might be interpreted to show an E–W main direction which would argue for the VLF transmitter DHO38 that is north of the study area as source of these signals. The authors should explain and show in more detail how they determined the N to NNE oriented main-horizontal stress direction, i.e. show it in the polar plots, rather than barely stating it. Did they lump the different measurements together? Why is no scale for the intensity provided in the polar plots and which parameter is shown? Furthermore, why are they not symmetric? Regarding the measurement procedure and assuming micro-cracks are emitters, one should expect a symmetric pattern. The same holds, however, for artificial VLF signals. In conclusion, the asymmetry is probably introduced by the wrong setup of the device that mutilated the “original” VLF
http://dx.doi.org/10.1016/j.jappgeo.2016.02.001 0926-9851/© 2016 Published by Elsevier B.V.
Please cite this article as: Krumbholz, M., Comment on: W. Hagag and H. Obermeyer, “Detection of active faults using EMR-Technique and Cerescope at Landau area in Central U..., Journal of Applied Geophysics (2016), http://dx.doi.org/10.1016/j.jappgeo.2016.02.001
2
M. Krumbholz / Journal of Applied Geophysics xxx (2016) xxx–xxx
signal(s) beyond recognition! Some of the horizontal measurements were taken above the identified faults (6, 7, 11) or in areas that show increased signal strengths which are claimed to belong to the recently-active faults. How do the authors explain that these horizontal measurements are not influenced by the “fault-related” signals? During some horizontal measurements (1, 2, 5, 6, 8, 9) no signals could be recorded! This should be explained by the authors in general and with special respect to their argumentation that the study area is strewn with active faults? Moreover, the horizontal measurement 4 was taken in the area claimed to be not suitable for the linear measurements, because of the high artificial noise. The authors are asked to explain how it was possible to carry out a horizontal measurement in this area.
faults and fractures, independent of type, are in the order of 0.01–0.0001. Using a very conservative approach, assuming the fault widths identified here are about 10 m and the aspect ratios are in the order of 0.01, the expected length of the faults is about 1 km. How does this agree with the presented fault map and the fact that the faults are not longer than a few hundred meters? To summarize: It was previously shown in detail that the Cerescope is not suitable to deliver the proposed information, because the recorded signals are controlled by artificial VLF transmissions (Krumbholz, 2010a, b; Krumbholz et al., 2012). The authors have disregarded this fact, i.e., their model lacks a profound base and in turn the proposed active fault set is only hypothetical. In consequence a discussion of the underlying cause for the fault formation is untenable. References
(2) Regarding the linear measurements by Hagag and Obermeyer (2016) which are supposed to show active faults. As mentioned above, fault detection with the Cerescope belongs to the well-known VLF method (Krumbholz, 2010a; Krumbholz et al., 2012) and is feasible, but it does not tell you whether a fault is active or not. Consequently, some of the peaks may indeed be caused by faults. In addition, the tracing of the faults (assuming each peak is caused by a fault) seems very arbitrary, i.e. for several faults the strike was interpreted from traversing the fault at one point only, e.g. profiles with faults: E6-F1; E4-F3; E2-F4, F6; and N4-F3, F4. Thus, prompting the question how the strike was determined. Peaks identified in more than one profile and interpreted to belong to the same faults show often extremely different “EMR patterns”, even when traversed by parallel profiles e.g. N6F3 and N7-F2; E1-F3 and E2-F5; E2-F1 and E3-F1. Given the small distances it is very unlikely that the width or infrastructure of the majority of the faults changes in such a dramatic manner. Moreover, taking the width of the “EMR signals” into account, and consider only those that are supposed to show (sub)vertical faults (e.g. E1-F3; E3-F1, F2; E5-F1) the EMR signal should give a reliable estimate of the width of the fault. According to the literature (e.g. Rubin, 1995; Odling et al., 2004) the thickness-length ratios of
Hagag, W., Obermeyer, H., 2016. Detection of active faults using EMR-Technique and Cerescope at Landau area in central Upper Rhine Graben, SW Germany. J. Appl. Geophys. 124, 117–129. Koktavy, P., Pavelka, J., Sikula, J., 2004. Characterization of acoustic and electromagnetic emission sources. Meas. Sci. Technol. 15, 973–977. Krumbholz, M., 2010a. Electromagnetic Radiation as a Tool to Determine Actual Crustal Stresses — Applications and Limitations Ph.D. thesis University of Göttingen, Germany, p. 151. Krumbholz, M., 2010b. Discussion: natural electromagnetic radiation (EMR) and its application in structural geology and neotectonics by R. O. Greiling and H. Obermeyer. J. Geol. Soc. India 76, 289–290. Krumbholz, M., Bock, M., Burchardt, S., Kelka, U., Vollbrecht, A., 2012. A critical discussion of the electromagnetic radiation (EMR) method to determine stress orientations within the crust. Solid Earth 3, 401–414. Lichtenberger, M., 2006. Bestimmen von Spannungen in der Lithosphäre aus geogener elektromagnetischer Strahlung Ph.D. thesis University of Heidelberg, Germany, p. 140. Mallik, J., Mathew, G., Angerer, T., Greiling, R.O., 2008. Determination of directions of horizontal principal stress and identification of active faults in Kachchh (India) by electromagnetic radiation (EMR). J. Geodyn. 45, 234–245. Misra, A., Kumar, A., 2004. Some basics of electromagnetic radiation during crack propagation in metals. Int. J. Fract. 127, 387–401. Odling, N.E., Harris, S.D., Knipe, R.J., 2004. Permeability scaling properties of fault damage zones in siliciclastic rocks. J. Struct. Geol. 26, 1727–1747. Rubin, A.M., 1995. Propagation of magma-filled cracks. Annu. Rev. Earth Planet. Sci. 23, 287–336.
Please cite this article as: Krumbholz, M., Comment on: W. Hagag and H. Obermeyer, “Detection of active faults using EMR-Technique and Cerescope at Landau area in Central U..., Journal of Applied Geophysics (2016), http://dx.doi.org/10.1016/j.jappgeo.2016.02.001