Small electric and magnetic signals observed before the arrival of seismic wave

Abstract

Electric and magnetic data were obtained above the focal area in association with the 1999 Izmit, Turkey earthquake. The acquired data are extremely important for studies of electromagnetic phenomena associated with earthquakes, which have attracted much attention even without clear physical understanding of their characteristics. We have already reported that large electric and magnetic variations observed during the earthquake were simply due to seismic waves through the mechanism of seismic dynamo effect, because they appeared neither before nor simultaneously with the origin time of the earthquake but a few seconds later, with the arrival of seismic wave. In this letter we show the result of our further analyses. Our detailed examination of the electric and magnetic data disclosed small signals appearing less than one second before the large signals associated with the seismic waves. It is not yet solved whether this observational fact is simply one aspect of the seismic dynamo effect or requires a new mechanism.

Remote Detection of the Electric Field Change Induced at the Seismic Wave Front from the Start of Fault Rupturing

“…Belov et al [8] detected associated electromagnetic fields about 10 seconds before the seismic wave arrival and 4 seconds after the origin time. The ULF band field changes were detected some 0.3-0.8 seconds before P wave arrival and about three seconds after the origin time during the Izmit earthquake [13,24] and between the P wave arrival and the origin time during the 1995 Hyogoken-Nanbu earthquake [11]. The VLF band pulse-like signals were detected about 1,000 km from the fault at about the origin time of the great earthquake east of Hokkaido on October 4, 1994 [10].…”

“…External causes are also discarded on large robustness to environmental noises of the present observation [33]. Moreover, the order estimation of the SES strength due to several causes [34,38] suggests that the dominant causes are the piezomagnetic effect [11,13,14,39] and/or the electrokinetic effect [7,[14][15][16][17][40][41][42][43][44][45] for small stress changes such at the seismic wave frequency (see the appendix).…”

“…The seismic wave speed is about 6 km/s for the primary (P) wave and 3.5 km/s for the secondary wave [1,2] in the upper crust. There have been many reports on the electromagnetic phenomena of earthquakes and volcanic eruptions (e.g., [3][4][5][6][7]), but only a few papers have dealt with the field observation of electromagnetic variation that started just after the rupture of the fault [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Belov et al [8] detected associated electromagnetic fields about 10 seconds before the seismic wave arrival and 4 seconds after the origin time.…”

Co-seismic signatures in magnetometer, geophone, and infrasound data during the Meinong Earthquake

“…Gershenzon et al (1993) found the earthquake magnitude dependence of co-seismic geomagnetic variations for piezomagnetic, electro-kinetic, and induction (dynamo) effects. Many scientists (Honkura et al 2002;Abdul Azeez et al 2009;Widarto et al 2009;Gao et al 2014) conducted observations and simulations, and proposed mechanism to explain co-seismic magnetic pulsations. We compare our results with these studies, and find our low-frequency magnetic pulsations most likely result from motions of ground water due to seismic waves (i.e., electro-kinetic effect) observed by Abdul Azeez et al (2009) and simulated by Ren et al (2012Ren et al ( , 2015Ren et al ( , 2016, while the high-frequency ones are due to shaking/tilting effects (i.e., magnetometer coil motion) reported by Widarto et al (2009) and Gao et al (2014).…”

“…Traditionally, seismometers (also geophones) record seismic waves monitoring the Earth's surface motion (Shearer 1999), and infrasound systems measure atmospheric pressure changes induced by the Earth's surface motion and/or seismic waves, mainly Rayleigh waves, on the ground (Mutschlecner and Whitaker 2005;Liu et al 2006Liu et al , 2010Liu et al , 2016a. Meanwhile, scientists report magnetic pulsations triggered by seismic waves (Iyemori et al 1996(Iyemori et al , 2005Honkura et al 2002;Abdul Azeez et al 2009;Widarto et al 2009;Hao et al 2013;Gao et al 2014;Yen et al 2015;Liu et al 2016a). However, in previous co-seismic geomagnetic variations observed in time scale of seconds were rare, because the amplitude is rather small.…”