JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 117, A02305, doi:10.1029/2011JA017036, 2012
Multi-instrument observation on co-seismic ionospheric effects
after great Tohoku earthquake
Y. Q. Hao,1 Z. Xiao,1,2 and D. H. Zhang1,2
Received 28 July 2011; revised 28 November 2011; accepted 28 November 2011; published 10 February 2012.
[1] In this paper, evidence of quake-excited infrasonic waves is provided first by a
multi-instrument observation of Japan’s Tohoku earthquake. The observations of co-seismic
infrasonic waves are as follows: 1, effects of surface oscillations are observed by local
infrasonic detector, and it seems these effects are due to surface oscillation-excited infrasonic
waves instead of direct influence of seismic vibration on the detector; 2, these local excited
infrasonic waves propagate upwards and correspond to ionospheric disturbances observed
by Doppler shift measurements and GPS/TEC; 3, interactions between electron density
variation and currents in the ionosphere caused by infrasonic waves manifest as disturbances
in the geomagnetic field observed via surface magnetogram; 4, within 4 hours after this
strong earthquake, disturbances in the ionosphere related to arrivals of Rayleigh waves were
observed by Doppler shift sounding three times over. Two of the arrivals were from epicenter
along the minor arc of the great circle (with the second arrival due to a Rayleigh wave
propagating completely around the planet) and the other one from the opposite direction.
All of these seismo-ionospheric effects observed by HF Doppler shift appear after local
arrivals of surface Rayleigh waves, with a time delay of 8–10 min. This is the time required
for infrasonic wave to propagate upwards to the ionosphere.
Citation: Hao, Y. Q., Z. Xiao, and D. H. Zhang (2012), Multi-instrument observation on co-seismic ionospheric effects after
great Tohoku earthquake, J. Geophys. Res., 117, A02305, doi:10.1029/2011JA017036.
1. Introduction
[2] One of the interesting topics in lithosphere-atmosphere–
ionosphere coupling study is the response of ionosphere to
earthquakes, either as precursors or as co-seismic and after
effects. It is important to study the ionospheric and atmospheric responses after an earthquake, as these phenomena
can provide greater insight into the lithosphere-atmosphere–
ionosphere coupling mechanisms. Ionospheric disturbances
during large earthquakes have been first found with the
Doppler sounding technique as the basal oscillation of the
ionosphere [Davies and Baker, 1965; Yuen et al., 1969].
In the past 20 years, there has been great concern toward
atmospheric disturbances excited by earthquake and tsunami
and their propagation around and upward [Afraimovich et al.,
2001; Ducic et al., 2003; Artru et al., 2004]. The great Sumatra
earthquake accompanied with tsunami led to many investigations on their effects using various measures such as HF
Doppler shift [Hao et al., 2006; Liu et al., 2006a], GPS/TEC
[Liu et al., 2006b; Astafyeva et al., 2009; Choosakul et al.,
2009], atmospheric infrasound wave [Le Pichon et al., 2005;
Mikumo et al., 2008] and geomagnetic records [Iyemori et al.,
2005; Hasbi et al., 2009]. Lastovicka et al. [2010] recently
1
Department of Geophysics, Peking University, Beijing, China.
State Key Laboratory of Space Weather, Center for Space Science and
Applied Research, Chinese Academy of Sciences, Beijing, China.
2
Copyright 2012 by the American Geophysical Union.
0148-0227/12/2011JA017036
studied the infrasonic waves during a relatively weak earthquake on European land and concluded that the infrasonic
oscillations (1–12 Hz) in the epicenter region appear to be
excited by the vertical seismic oscillations. Infrasonic oscillations observed at a distance of 155 km from the epicenter
appear to be seismically excited in situ and no infrasonic
effects of this earthquake were observed in the ionosphere due
to the low earthquake magnitude and infrasonic periods too
short to be capable of exciting ionospheric effects detectable
by the Doppler measuring system.
[3] On 11 March, 2011 at 0546UT, an magnitude 9.0
earthquake occurred near the east coast of Honshu, Japan
(Tohoku Earthquake) with epicenter located at (38.3N,
142.4E), initiating a great tsunami. Both earthquake accompanying surface shaking and tsunami would excite atmospheric waves. As a contrast to the work of Lastovicka
et al. [2010], in this paper multi-instrument data from HF
Doppler measurement, infrasound detector, seismic stations,
GPS/TEC and geomagnetic stations are used to make a
comprehensive study of the effects after this great Tohoku
earthquake. Results and new findings on the atmospheric
and ionospheric infrasonic waves and geomagnetic variations induced by the ionosphere disturbances are reported
and discussed.
2. Instruments and Database Description
[4] The locations of instruments used in this work and
their angular distances to the epicenter are listed in Table 1,
and Figure 1 shows the mutual relations of these stations.
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Table 1. Stations and Data Used in This Paper
Code
Location (Geographic)
Distance From Epicenter
Seismic Waveform
44.6 N, 129.6E
40.0 N, 116.2E
30.3 N, 109.5E
11.5°
20.6°
28.2°
Doppler Shift Sounding
37.6 N, 112.9E
23.2°
28.8 N, 111.8E
27.1°
SSL
TAY
SYS
Geomagnetic Field
40.7 N, 116.6E
37.7 N, 112.5E
18.3 N, 109.5E
20.0°
23.5°
34.9°
tsk2
mkta
usud
ccj2
aira
shao
twtf
pimo
36.1
35.7
36.1
27.1
31.8
31.1
25.0
14.6
GPS/TEC
N, 140.1E
N, 139.6E
N, 138.4E
N, 142.2E
N, 130.6E
N, 121.2E
N, 121.2E
N, 121.1E
2.9°
3.5°
3.9°
11.2°
11.6°
18.8°
22.4°
30.2°
MDJ
BJT
ENH
BCT(P1)a
BDTb
SZT(P2)a
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mentioned data are that their records are all continuous in
time which is beneficial in analyzing morphological features
and evolutions of disturbances.
3. Observations and Preliminary Results
a
The location and distance of Doppler sounding stations are not of the
receivers; instead, they are of the area where Doppler signals are reflected
(P1 and P2). Roughly, the reflection point is the middle between
transmitter and receiver.
b
Since BDT and BCT are only 30 km apart and the records during this
quake are almost identical, only records of BCT are used in the following.
[5] The seismograms are taken from the IC network of
IRIS Data Management Center (http://www.iris.edu), and
data of three stations (MDJ, BJT and ENH) are used; Magnetographs are from Beijing (SSL), Taiyuan (TAY) and
Sanya (SYS); GPS/TEC data were downloaded from International GNSS Service (IGS, http://igscb.jpl.nasa.gov) for a
few stations near or far away from the epicenter.
[6] Both equipments for ionospheric HF Doppler measurement and atmospheric infrasound detector are operated
by the ionospheric observatory of Peking University. An
infrasound detector is at the campus of the University,
Beijing. The data used are from the records of the HF
Doppler frequency shift observation stations at three sites:
the campus of the University (BDT), Changping, Beijing
(BCT) and Shengzhen, Guangdong (SZT). The sounding
system continuously receives a 10 MHz stabilized frequency
electromagnetic wave transmitted by the National Time
Service Center (35.0N, 109.5E) to detect the ionospheric
disturbances through the Doppler shift of this standard frequency. A brief introduction to our Doppler shift sounding
system and the works we have done based on the data is
given by Xiao et al. [2007] and Xiao et al. [2009]. This
sounding technique measures the Doppler shift of radio
wave frequency, and this shift is caused by ionospheric
variation along the phase path and mainly around the
reflecting point in the ionosphere. So in Figure 1 receiver
stations are not labeled. Instead, the reflecting points for
radio wave received at BCT and SZT are denoted by P1
and P2 respectively. As an approximation, P1 and P2 are
treated to be near the midpoints between the transmitter and
the receivers. The characteristics in common of all above
3.1. Records of Seismic Waves (Seismogram)
[7] When an earthquake occurs, the seismic waves propagate outward. The body waves (P- and S-waves) travel
through Earth’s interior, and the surface waves (Love and
Rayleigh waves) propagate on the surface. The speed of the
Rayleigh waves is relatively slow, however, they are confined in the shallow surface of the Earth, and therefore decay
more slowly with distance than the body waves do. Strong
earthquakes may generate Rayleigh waves that can travel
around the Earth several times before dissipation. A single
seismometer can record Rayleigh waves several times
coming from two directions (along the minor and major
great circle arc). Due to the different traveling distances, the
records of arrivals are temporally separated. As an example,
after the Sumatra-Andaman earthquake in 2004 Park et al.
[2005] compiled seismograms from many Global Seismograph Network (GSN) stations, showing evidence of multiple arrivals of Rayleigh waves to every station. As for this
Tohoku earthquake, the global seismogram map is available
for online access (http://www.iris.edu/hq/files/iris_n_ews/
images/Sendai_R_S.jpg). In section 3.2, we will show observations of special variations in the ionosphere after this great
earthquake, which are related to the Rayleigh waves circling
the Earth.
[8] In this paper, seismometer records are used to retrieve
the wavefields of Rayleigh wave. Among various channels
of seismometer, the VHZ channel (this is a special channel
of seismometers meaning very long period, high gain and for
Figure 1. Reference map showing the mutual relations of
the epicenter and stations used in this work. The epicenter
is denoted by a star, and the stations include seismic stations
for seismogram (filled diamond), geomagnetic stations (dot),
reflection points of Doppler sounding signal (open triangle),
and ground GPS receivers (circle).
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Figure 2. Several hours’ VHZ component seismograms at three stations displayed against angular distances from the epicenter. To show both large and small amplitudes of R1 to R5, they are shown in two
panels with different scales. The time of earthquake occurrence is marked with a vertical dash-dot line.
vertical orientation) measures the vertical displacement of
the Earth’s surface with a low sampling rate (0.1 Hz), which
is the most appropriate for our study. In Figure 2, VHZ
component at three GSN stations (MDJ, BJT and ENH) are
displayed against distance from the epicenter. The ground
motions are dominated by surface waves (Rayleigh waves),
which produced peak-to-peak amplitudes of about 1–10 cm
(see scale bars in Figure 2). The Rayleigh waves reached the
antipode about 1.5 hours after the earthquake initiation, and
circled the Earth in about 3 hours. As far as can be recognized in Figure 2, the Rayleigh waves sweep around the
world twice in 7 hours. So, the arrivals of Rayleigh waves at
each station were noted as R1 (Rayleigh wave that travels
along the minor great circle arc), R2 (along the major great
circle arc), R3 (travels in the same direction with R1, but with
an additional global circuit), R4 (the same as R2, with an
additional global circuit), and so on.
[9] The speed of the Rayleigh waves can be calculated
from their travel times and distance. As in Figure 2, the slop
rates of dashed lines are used to estimate speed, which lies in
3.2–3.6 km/s. This is well in agreement with the existing
conclusion about Rayleigh wave speed and is 10 times faster
than the atmospheric sound speed.
3.2. Doppler Shift Observations
[10] R1 is the first time of seismic waves to arrive at local
regions, and seismic waves at this time are with the largest
amplitude and excite atmospheric infrasonic waves which, in
turn, can be found by Doppler shift sounding when it goes
up into the ionosphere. Figure 3 shows the relations between
seismic VHZ component and corresponding ionospheric
Doppler shift. The traces presented include Doppler frequency shift of BCT(P1) and SZT(P2), as well as VHZ
component of BJT and ENH. To give a time-distance
Figure 3. Doppler shift sounding traces (at reflection points P1 and P2, respectively) around the arrival
time of R1. The seismic waveforms at BJT and ENH are plotted together, and all the traces are displayed
against distances from the epicenter.
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Figure 4. Same as Figure 3, shown are Doppler shift sounding traces around the arrival time of R2
and R3.
diagram, these traces are arranged by distance from the
epicenter. Same as in Figure 2, the dashed lines represent the
time-distance relationship of the traveling of Rayleigh
wavefront, therefore we can identify the exact arrival times
of Rayleigh waves at P1 and P2. It is clear that at P1 the
sudden ionospheric disturbance has a time delay of 6–8 min
from the arrival of R1 (BJT), and at P2 the time delay is
identical. This delay is the time required for infrasonic wave
propagating from surface up to a height of about 160 km in
the ionosphere.
[11] At P1 and P2, the disturbances both began with a time
delay of 6–8 min after the arrival of R1. The manifestations of
these disturbances are much blurred in the traces of Doppler
shift sounding. The peak-to-peak amplitudes are about 1 Hz
at both P1 and P2. Furthermore, at P1 the blurred trace has a
regular shape of wave packet, which has similar shape and
duration time with R1, implying that the disturbance in ionosphere is closely correlated to the seismic Rayleigh waves.
The similar time delay of 6–8 min at different local regions
indicates that through identical physical processes the disturbances were exited in the atmosphere wherever the Rayleigh waves arrived and propagate to ionospheric altitudes.
As we have suggested in previous work on the Sumantra
earthquake [Hao et al., 2006], infrasonic waves are generated
in the atmosphere locally after the Rayleigh waves arrive, and
then it takes 6–8 min for the infrasonic waves to propagate
upward to the ionosphere altitude above 160 km.
[12] By ionospheric Doppler shift sounding, this type of
disturbances related to R1 after several great earthquakes has
been observed before, such as the Sumatra earthquake in 2004
[e.g., Hao et al., 2006; Liu et al., 2006a]. However, great
earthquakes can drive surface Rayleigh waves which sweep
the Earth for several circuits, so R2 and R3 signals possibly
have sufficient amplitudes (already shown in Figure 2). For
this Tohoku earthquake, ionospheric disturbances related to
R2 and R3 are also observed, which are presented in Figure 4.
[13] The disturbances appear at about 8 min after arrivals
of R2 and R3 (marked by bold lines in Figure 4). The vertical
displacements of the Earth surface with R2 and R3 are much
weaker (1 cm, peak-to-peak) compared with R1 ( 10 cm).
The amplitudes of the Doppler shifts oscillation are less than
0.5 Hz peak-to-peak, also much smaller compared with the
amplitudes of those disturbances related to R1. In general, the
larger magnitude of source, the larger magnitude of Doppler
shift, but, it should be noticed that the relation is not linear,
there are lots of factors that determine the relationship.
[14] Also, R1 are wave packet with wide band frequency
components, while we can notice that the R2 and R3 signals
are quasiperiodic oscillations. This is because, after traveling
a long distance, the high frequency components have mostly
attenuated. Corresponding to quasiperiodic R2 and R3, the
variations of Doppler shift display as monochromatic oscillations of a single frequency, which are very different from
the disturbances after R1. With FFT analysis, we have
identified the oscillation frequency at 4.4–4.5 mHz (220–
230 s period), which reflect the infrasonic wave periods in
the atmosphere and ionosphere.
3.3. Geomagnetic Variations Induced
by Ionospheric Waves
[15] The ionospheric disturbances at 0600UT are believed
to be indirectly excited by the oscillation of the surface
under sub-ionospheric reflecting point where R1 arrived. At
the same time, local geomagnetic field varied clearly corresponding to the ionospheric disturbances.
[16] At SSL, TAY and SYS stations, fluxgate magnetometer
recorded sudden disturbances in D and Z components. The
appearing time of such sudden variations are delayed as the arc
distance from epicenter increases. In Figures 5 and 6, oblique
dashed lines showed the relation between arc distances and
arriving time of the Rayleigh wavefront with a speed of
3.6 km/s. As the arc distance increases, appearance of disturbed D, Z components delayed correspondingly. This indicates that the disturbances of D and Z components are the
signatures of the perturbations of ionospheric current, which,
in turn, is caused by infrasonic waves propagated from below.
[17] It should be noticed that TAY is located almost
exactly beneath the reflecting point P1. Compared with the
Doppler shift observation, the sudden disturbances of D and
Z component appeared at the same time as ionospheric
disturbance occurred. This is the evidence that BCT(P1)
observed Doppler shift and geomagnetic sudden variation
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Figure 5. Geomagnetic D component recorded at three stations (bottom, SSL; middle, TAY; top, SYS)
with background trend removed by subtracting running average. Also displayed are seismic waveforms at
MDJ to show the arrivals of R1 as a reference.
are caused by the same source. In other words, ionospheric
disturbances modulate the current so that simultaneous
changes of geomagnetic field are thus induced.
[18] As shown in Figure 7, the geomagnetic H component
at SSL and TAY also show concurrent variations of D and Z
components, but at smaller amplitudes. However, at
0615UT, the H component at SYS showed an unusual valley, which may be the manifestation of the same disturbances shown in Figures 5 and 6. It is worth mentioning
that SYS is at the lowest magnetic latitude of the three
geomagnetic stations, where the equatorial jet is strong.
[19] We compared spectra of Doppler shift record at P1
with magnetic field at TAY. The spectral results indicate that
FFT spectrums of seismic VHZ data at BJT (BJT/VHZ),
of Doppler shift data at P1 (P1/DOP) and of geomagnetic
D-component at TAY (TAY/D) all have a same peak of
frequency around 0.007 Hz, further indicating that these
geomagnetic variations are likely related to the Rayleigh
waves perturbing the ionosphere.
3.4. GPS/TEC
[20] About 10 min after the occurrence of the quake,
the GPS/TEC records around the epicenter nearby within
30 degrees of angular distance showed clear wave-like disturbances with a period in the range of 3–5 min (Figure 8).
The appearing times of TEC disturbances are later and later
as arc distance increases and amplitudes and time lasted
seem weaker and smaller, too. It is convenient to estimate
the traveling speed of the ionospheric disturbances according to the beginning time of sudden TEC variations. This
gives a phase speed about 3.6 km/s, which is close to that of
the seismic Rayleigh wave. Actually, by dense ground-based
GPS receivers, disturbance waves of different velocities
have been found after this Tohoku earthquake and tsunami
[Liu et al., 2011]. These velocities cover a wide range, from
hundreds to thousands of m/s, corresponding to different
sources including Rayleigh waves, acoustic gravity waves
and tsunami waves.
Figure 6. Same as Figure 5, but for geomagnetic Z component.
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Figure 7. Same as Figure 5, but for geomagnetic H component.
3.5. Infrasound Observation on the Surface in Beijing
[21] An infrasound detector is established at Peking University (Beijing) to monitor the low frequency oscillations in
the local atmosphere. During this great earthquake, the
detector monitored disturbances shown in Figure 9. In the
VHZ record of BJT station (top panel), the arrivals of seismic waves from the major shock (R1) and after shocks are
shown clearly between 0550UT and 0630UT. Meanwhile, in
the infrasound record (middle panel) atmospheric wave
signals appear simultaneously with the seismic wave arrivals, indicating local excitation of infrasonic waves. Besides,
an interesting thing is the third infrasound signal at 0810UT
which is a ‘N’ shape disturbance with the largest amplitude.
This signal appeared 2 hours and 20 min later after the major
shock. We think it could be an infrasonic wave excited near
epicenter and propagated horizontally to Beijing area. Using
GPS/TEC data Tsugawa et al. [2011] found an ‘ionospheric
epicenter’ which is consistent with areas of the tsunami
source, hence it is possible that this is also the real source
region of atmospheric waves. This region is about 170 km
from the epicenter in the southeast direction, so we estimate
that the infrasonic wave traveled 2400–2500 km to reach
Beijing, then the wave speed can be calculated at about 285–
300 m/s. This is consistent with the earlier study by Calais
and Minster [1995] who showed GPS/TEC time series of
ionospheric disturbances from the Northridge quake with
infrasonic speeds around 300 m/s. Following recent major
events, such as the 2004 Sumatra earthquake, co-seismic
atmospheric disturbances with similar speed have also been
found from infrasound detector observations [Le Pichon
et al., 2005; Mikumo et al., 2008].
[22] It is worth noting that the infrasound detector reveals
two categories of propagation channel for seismo-induced
Figure 8. GPS/TEC data with background trend removed by subtracting running average. These data are
from several ground receivers and displayed against angular distances of the sub-ionospheric point from
the epicenter.
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Figure 9. Infrasound detector records in Beijing and seismic records at BJT. Actually the distance
between the two instruments is only 10 km which can be reasonably omitted. (top) Seismogram, (middle)
original infrasound record, and (bottom) infrasound records after a band-pass filtering of period 3–20 min.
disturbances. The first one is related to the Rayleigh waves
traveling in the shallow part of the mantle, hence it has larger
speed and excite atmospheric waves locally which can be
coupled to the ionosphere. The resulting disturbances in the
ionosphere have been proved by multi-instrument observations presented above. The latter category is represented by
the atmospheric waves that propagate from the source region
(epicenter) through the atmosphere at much lower speed.
Besides the infrasonic waves observed by the infrasound
detector, also internal Gravity Waves (GWs) initiated by the
earthquake or tsunami were reported. Liu et al. [2011] observed
GWs in the ionosphere propagating at speeds from 180 to
300 m/s after the Tohoku earthquake. GWs in the ionosphere
induced by major earthquake/tsunami events were also reported by Galvan et al. [2011] and Rolland et al. [2011].
4. Summary and Discussion
[23] Japan’s Tohoku earthquake excited infrasound waves
that propagated both horizontally and upwards into the ionosphere. The main results of multi-instrument observations
are as follows:
[24] 1. Surface-oscillation-excited infrasonic waves were
observed in Beijing by local infrasound detector simultaneously when Rayleigh waves arrived, and it seems that
these wave are not possible due to direct influence of seismic
vibration on the detector since the infrasonic wave was also
detected when there were no local seismic vibrations (see the
fourth point in the following).
[25] 2. These infrasonic waves (excited by Rayleigh
waves) propagated upwards into the ionosphere, causing
disturbances in the ionosphere which can be detected by HF
Doppler shift measurements or as fluctuations of GPS/TEC.
These disturbances were observed both over epicenter area
and by some other GPS stations far away.
[26] 3. Interactions between electron density variation and
ionospheric current was manifested by geomagnetic field
disturbances measured by ground based magnetometers.
[27] 4. Infrasonic waves excited around epicenter or tsunami area propagated horizontally in the atmosphere and
were received by infrasound detector in Beijing two hours
and 20 min later at a distance of about 2400–2500 km from
their source region, thus the estimated speed of propagation
is 285–300 m/s.
[28] Many previous studies found infrasonic disturbances
in the ionosphere after great earthquakes, however, in this
paper both waves locally excited by surface oscillations
caused by quake-Rayleigh waves and infrasonic waves
directly coming from epicenter area through atmospheric
propagation, and accompanying geomagnetic disturbances
are all observed simultaneously by multi-instrument observations. It should be particularly emphasized that besides the
variations in the ionosphere related to the first arrival of
major shock (R1), quasiperiodic oscillations in the ionosphere are also observed following the second and third
arrival of seismic surface waves (R2 and R3), as shown in
Figure 4. And another observational fact worthy mentioning
is the long distance horizontal propagation in the atmosphere
from epicenter to Beijing. Guglielmi et al. [2006] has
reported that co-seismic magnetic oscillations were detected
for two times of arrival of seismic Love waves after the
Sumatra earthquake (corresponding to R1 and R2 in this
paper). However, compared to polarization method analysis
by Guglielmi et al. [2006], these kinds of weak variations
are better demonstrated by our Doppler sounding data, in
which the variations are shown in a straightforward manner.
The surface wave, especially high frequency component,
experiences much attenuation during its traveling around the
Earth, so R2 and R3 have much smaller amplitudes and lower
frequency than R1. Meanwhile, Doppler shifts during R2 and
R3 have much smaller amplitudes and lower frequency than
during R1 but with clearer sinusoidal forms. Although the
amplitudes are equivalent to a small earthquake (maybe of
magnitude Mw 5), R2 and R3 excited significant monochromatic infrasonic waves in the atmosphere and ionosphere. A possible reason is that R2 and R3 is close to the
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atmospheric duct resonance period, so the excitation is more
efficient. The period of resonance has been calculated and
simulated to be of 3–5 min [e.g., Shinagawa et al., 2007;
Watada and Kanamori, 2010], which are also confirmed by
the ionospheric quasiperiodic oscillations (with period of
220–230 s) in Figure 4.
[29] Lastovicka et al. [2010] investigated a very weak
earthquake with the epicenter on land of Europe, and it is
also a multi-instrument study. A comparison of their results
with conclusions in this paper is interesting because of a
sharp contrast of the after effects. First, they observed
infrasonic oscillations (1–12 Hz) in the epicenter region
appear to be excited by the vertical seismic oscillations; we
found the same phenomena around epicenter. Secondly, they
found infrasonic oscillations observed at a distance of
155 km from the epicenter appear to be seismically excited
in situ, they did not represent the infrasound coming from
the epicenter region, however, we not only observed infrasonic waves excited in situ, but also observed the infrasonic
waves propagated horizontally to Beijing from epicenter
2400–2500 km away. The third, they said that no infrasonic
effects of this earthquake were observed in the ionosphere
due to the low earthquake magnitude and too short periods
of excited infrasound to be capable to excite ionospheric
effects and to be identified by the Doppler measuring
system, while we clearly observed the Doppler shifts at
two locations. Finally, they said that the observed magnetic effects were rather the effects of seismic shaking
of magnetic sensor than real earthquake effects, but we
observed the geomagnetic effects by magnetogram and
proved a connection of geomagnetic disturbances with the
ionospheric electron variation due to earthquake excited
infrasonic waves. This contrast indicates that the lithosphereionosphere couplings are strongly dependent upon the
strength of ground activities.
[30] Acknowledgments. The facilities of the IRIS Data Management
System, and specifically the IRIS Data Management Center, were used
for access to the IC network (New China Digital Seismograph Network)
waveform data. The geomagnetic field data of TAY were from Institute
of Geophysics, China Earthquake Administration, and the data of SSL
and SYS were provided by Institute of Geology and Geophysics, Chinese
Academy of Sciences (through Chinese Meridian Project). The highly
precise GPS data were from IGS network. This work was jointly supported
by NSFC (40904036), China NIBRP (2011CB811405) and Project
Supported by the Specialized Research Fund for State Key Laboratories.
[31] Robert Lysak thanks the reviewers for their assistance in evaluating
this paper.
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Y. Q. Hao, Z. Xiao, and D. H. Zhang, Department of Geophysics, Peking
University, Beijing, 100871, China. ([email protected]; [email protected];
[email protected])
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