On the onset of ionospheric precursors 40 min before strong earthquakes

Abstract

Heki (2011) and Heki and Enomoto (2013) claimed that anomalous, yet similar, increases of ionospheric total electron content (TEC) started~40 min prior to the 2011 Tohoku-Oki, as well as before other M w > 8 earthquakes. The authors concluded that the reported TEC anomalies were likely related to the pending earthquakes, suggesting also that TEC monitoring may be useful for future earthquake prediction. Here we carefully examine the findings of Heki (2011) and Heki and Enomoto (2013) by performing new analyses of the same TEC data. Our interpretation is that the 40 min onset of the ionospheric precursors is an artifact induced by the definition of the reference line adopted in analyzing TEC variations. We also discuss this repeatability in the tectonic and geodynamic context of the earthquakes. By performing a Superimposed Epoch Analysis of TEC data, we show that, however, the TEC increase reported by Heki (2011) was not particularly anomalous. We conclude that the TEC precursors reported by Heki (2011) and Heki and Enomoto (2013) are not useful for developing short-term earthquake prediction capabilities.

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

“…If we assume that ULF magnetic seismogenic signals actually appear before earthquakes, there is no physical reason that the P anomalies must show periodicity in a restricted time range (e.g., 11–15 days) before the main shock. This hypothesis is highly questionable since earthquakes occurred in an area having a radius of 100 km were generated by different fault zones, and thus, it is unlikely that they might share similar precursory phases [see Masci et al ., ]. Still, what is the physical mechanism that would generate electromagnetic signals just a few days before the earthquake?…”

“…Journal of Geophysical Research: Space Physics 10.1002/2015JA021336 main shock. This hypothesis is highly questionable since earthquakes occurred in an area having a radius of 100 km were generated by different fault zones, and thus, it is unlikely that they might share similar precursory phases [see Masci et al, 2015]. Still, what is the physical mechanism that would generate electromagnetic signals just a few days before the earthquake?…”

“…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, 2009;Masci, 2010Masci, , 2011aMasci, , 2011bMasci, , 2012aMasci, , 2012cMasci, , 2013bMasci and De Luca, 2013;Masci and Thomas, 2013a, 2013b, 2015bMoldovan et al, 2012;Romanova et al, 2015;Thomas et al, 2009aThomas et al, , 2009b and ionospheric disturbances [see Foppiano et al, 2008;Masci, 2012dMasci, , 2013aThomas, 2014, 2015a;Masci et al, 2015;Thomas et al, 2012aThomas et al, , 2012b are reasonably related to instrumentation malfunction, to the analysis procedure, or to the normal geomagnetic activity in response to Sun-Earth interactions.…”

Three‐dimensional distribution of ionospheric anomalies prior to three large earthquakes in Chile

“…Apart from these coseismic disturbances, Heki [] found ionospheric electron enhancements starting ~40 min before the 2011 Tohoku‐oki earthquake ( M w 9.0), Japan, using a dense array of continuous GPS stations. Through debates between critical papers [ Kamogawa and Kakinami , ; Utada and Shimizu , ; Masci et al ., ] and replies to them [ Heki and Enomoto , , , ], Heki and Enomoto [] showed that the enhancements preceded eight past earthquakes with M w 8.2 or more. They found that the enhancements started about 20/40 min prior to M w 8/9 earthquakes and that the changes in vertical TEC (VTEC) rates depend on M w as well as background absolute VTEC.…”

Monitoring potential ionospheric changes caused by the Van earthquake (<i>M</i><sub>w</sub>7.2)

“…The ionosphere reacts to geomagnetic effect, solar activity, diurnal and seasonal effects, and earthquake, and these factors cause irregularities in the ionosphere (Namgaladze et al, 2012;Li and Parrot, 2018).…”