Review Article: On the relation between the seismic activity and the Hurst exponent of the geomagnetic field at the time of the 2000 Izu swarm

Abstract

Many papers document the observation of earthquake-related precursory signatures in geomagnetic field data. However, the significance of these findings is ambiguous because the authors did not adequately take into account that these signals could have been generated by other sources, and the seismogenic origin of these signals have not been validated by comparison with independent datasets. Thus, they are not reliable examples of magnetic disturbances induced by the seismic activity. Hayakawa et al. (2004) claim that at the time of the 2000 Izu swarm the Hurst exponent of the Ultra-Low-Frequency (ULF: 0.001–10 Hz) band of the geomagnetic field varied in accord with the energy released by the seismicity. The present paper demonstrates that the behaviour of the Hurst exponent was insufficiently investigated and also misinterpreted by the authors. We clearly show that during the Izu swarm the changes of the Hurst exponent were strongly related to the level of global geomagnetic activity and not to the increase of the local seismic activity

Are there new findings in the search for ULF magnetic precursors to earthquakes?

“…The most commonly used methods to identify preearthquake ULF anomalies in geomagnetic field records are the so called spectral polarization ratio analysis [see, e.g., Hayakawa et al ., ] and fractal analysis [ Hayakawa et al ., ]. Fractal anomalies preceding earthquakes have been extensively discussed and denied as precursors by Masci [, ] and Masci and Thomas [, , ]. Reports of precursory signatures in the spectral polarization ratio were proved invalid as well [see, e.g., Masci , , , ; Masci and Thomas , ; Thomas et al ., ].…”

“…What is more important, this correspondence is not expected always and everywhere. Conversely, if it is shown that there is close correspondence between alleged ULF magnetic precursors and geomagnetic indices (e.g., Kp ) [see Masci , , , , , , ; Masci and Thomas , , ], this indicates that the magnetic changes are part of global geomagnetic field changes and cannot be described as earthquake‐related signals. Therefore, the real issue is not the poor correlation that Currie and Waters [] have found between local ULF magnetic changes and geomagnetic indices but the correspondence that many papers have shown between ULF magnetic changes claimed to be precursors of earthquakes and global geomagnetic activity changes.…”

“…Unfortunately, the scientific literature of the last two decades demonstrates the opposite. Changes in polarization ratio and fractal properties of the geomagnetic field identified as possible precursors of earthquakes have been recently reviewed in many papers [see, e.g., Masci , , , , , ; Masci and Thomas , , ] in which the authors have found a close correspondence between the reported preearthquake ULF magnetic changes and Kp (see section 3). This shows that the reported ULF changes do not have a local geological origin but have a global origin in response to Sun‐Earth interactions.…”

“…Thus, some researchers do not agree that magnetic changes observed prior to earthquakes had seismogenic origin. They have demonstrated that many published preearthquake ULF magnetic changes [see Campbell , ; Masci , , , , , , , ; Masci and De Luca , ; Masci and Thomas , , , ; Moldovan et al ., ; Romanova et al ., ; Thomas et al ., , ] and ionospheric disturbances [see Foppiano et al ., ; Masci , , ; Masci and Thomas , , ; Masci et al ., ; Thomas et al ., , ] are reasonably related to instrumentation malfunction, to the analysis procedure, or to the normal geomagnetic activity in response to Sun‐Earth interactions.…”

How does solar eclipse influence the complex behavior of midlatitude ionosphere? Two case studies

“…Hurst exponent ( H ) is estimated by the slope of the best fit line in log ( R n / S n ) versus log ( n ) representation of the R n / S n power law [see Masci and Thomas , ].…”