Co-seismic EM signals in magnetotelluric measurement—a case study during Bhuj earthquake (26th January 2001), India

et al. 2014

JGR Solid Earth

Studied in this article are the properties of the electromagnetic (EM) fields generated by an earthquake due to the motional induction effect, which arises from the motion of the conducting crust across the Earth's magnetic field. By solving the governing equations that couple the elastodynamic equations with Maxwell equations, we derive the seismoelectromagnetic wavefields excited by a single-point force and a double-couple source in a full space. Two types of EM disturbances can be generated, i.e., the coseismic EM field accompanying the seismic wave and the independently propagating EM wave which arrives much earlier than the seismic wave. Simulation of an M w 6.1 earthquake shows that at a receiving location where the seismic acceleration is on the order of 0.1 m/s 2 , the coseismic electric and magnetic fields are on the orders of 1 μV/m and 0.1 nT, respectively, agreeing with the EM data observed in 2008 M w 6.1 Qingchuan earthquake, China, and indicating that the motional induction effect is effective enough to generate observable EM signal. We also simulated the EM signals observed by Haines et al. (2007) which were called the Lorentz fields and cannot be explained by the electrokinetic effect. The result shows that the EM wave generated by a horizontal force can explain the data well, suggesting that the motional induction effect is responsible for the Lorentz fields. The motional induction effect is compared with the electrokinetic effect, showing the overall conclusion that the former dominates the mechanoelectric conversion under low-frequency and high-conductivity conditions while the latter dominates under high-frequency and low-conductivity conditions.

Section: Introductionsupporting

confidence: 68%

Induced electromagnetic field by seismic waves in Earth's magnetic field

Gao

et al. 2014

JGR Solid Earth

Terr. Atmos. Ocean. Sci.

“…We examining and comparing the magnetometer data at the 10 stations find that at each station, the z component generally yields the greatest co-seismic pulsation, and the duration of co-seismic magnetic pulsations is slightly longer than that of the co-seismic geophone fluctuations, except that those at CC last upto 1200 sec. This long lasting magnetic pulsation may result from a sufficiently strong medium heterogeneity, fluid-pressure gradient [most likely ground water (Abdul Azeez et al 2009)], and/or a finite faulting in porous media proposed by Ren et al (2012Ren et al ( , 2016. Nevertheless, the long lasting co-seismic pulsations appearing at the CC station might be due to the ground water and underground structure around Meishan fault being complex (Yen et al 2008;Ching et al 2011;Wilcox et al 2011).…”

Section: Experiments Setup and Observationmentioning

confidence: 97%

“…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).…”

Section: Experiments Setup and Observationmentioning

confidence: 99%

“…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.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Liu¹,

Chen²,

Wu³

et al. 2017

This paper utilizes 10 stations of co-located seismometer, QuakeFinder/infrasound to observe co-seismic signatures triggered by the 6 February 2016 M 6.6 Meinong Earthquake. Each QuakeFinder system consists of a 3-axes induction magnetometer, an air conductivity sensor, a geophone, and temperature/relative humidity sensors. There are no obvious charges in the positive/negative ions, the temperature, and the humidity, while the magnetometer, the geophone, and infrasound data detect clear co-seismic signatures, similar to seismic waves recorded by seismometers. The magnetometers register high-frequency pulsations, like seismic waves, and superimpose with low-frequency variations, which could be caused by the magnetometer shaking/tilting and/or the underground water level change, respectively, upon the arrival of seismic waves. The spectrum centering around 2.0 Hz of the co-seismic geophone fluctuations is similar to that of the seismic waves. However, the energy of co-seismic geophone fluctuations (also magnetometer pulsations) yields an exponential decay to the distance of a station to the epicenter, while the energy of the seismic waves is inversely proportional to the square of the distance. This suggests that the mechanisms for detecting seismic waves of the QuakeFinder system and seismometers are different. In general, the geophone and magnetometer/infrasound system are useful to record high-and low-frequency seismic waves, respectively.

“…In some cases, STADs could further travel into the ionosphere and interact with the ionized gas resulting in seismo-traveling ionospheric disturbances (STIDs) [see papers listed in Davies (1990)]. Meanwhile, scientists reported that co-seismic geomagnetic pulsations can result from instrument oscillations due to seismic waves (Li et al 2018) and regional geomagnetic field fluctuations induced by STIDs (Iyemori et al 1996(Iyemori et al , 2005Honkura et al 2002;Azeez et al 2009;Widarto et al 2009;Hao et al 2013;Gao et al 2014;Yen et al 2015;Liu et al 2016a). Due to the low sampling rate, co-seismic fluctuations in the geomagnetic field were hard to distinguish from the effect of magnetometer sensor oscillation (Breiner 1964;Eleman 1965), and therefore, high resolution (e.g., 1 Hz) observation are necessary for such researches (Iyemori et al 1996).…”

Section: Introductionmentioning

confidence: 99%

Co-seismic geomagnetic fluctuations and atmospheric disturbances during the 2018 M 6.2 Hualien Earthquake

Liu²,

Terr. Atmos. Ocean. Sci.

et al. 2019

The strong ground motion of 6 February 2018 M 6.2 Hualien Earthquake triggered a series of co-seismic geomagnetic fluctuations and seismo-traveling atmospheric disturbances (STADs) signatures in infrasonic waves and micro-pressures upon the seismic wave arrival. Networks of 9 QuakeFinder systems, 3 infrasound systems, 2 tiltmeters, 2 micro-barometers, and 11 co-located seismometers are used in this study. Each QuakeFinder system consists of a 3-axes induction magnetometer, an air conductivity sensor, a geophone, and temperature/relative humidity sensors. Co-seismic signatures clearly appear in the induction magnetometers, infrasound systems, and micro-barometers data. The magnetometers register both high-and lowfrequency pulsations. Geomagnetic fluctuations occur upon the seismic wave arrival but last a longer duration, while the STADs lag their co-located seismic waves by about 15 -45 s. The long-lasting fluctuations recorded by both induction and fluxgate magnetometers suggest that the ground/underground water motion play an important role, which is further conformed by low-frequency fluctuations in the tiltmeter data. In general, the amplitude of geomagnetic fluctuations decays as away from the epicenter. However, unusual large co-seismic geomagnetic fluctuations are detected over areas of the abnormal seismic intensity level and/or the magnetic underground structure with anomalously high susceptibilities.