Coseismic Ionospheric Disturbances Research Articles

Temporal and Spatial Ionospheric Variations of 20 April 2013 Earthquake in Yaan, China

In this letter, we investigate the ionospheric variations associated with the Yaan earthquake that occurred on April 20, 2013 in China by using the total electron content (TEC) derived from ground-based Global Positioning System observations and a global ionosphere map (GIM). Geomagnetic and solar activities are taken into account. First, we focus on the coseismic ionospheric disturbances of the earthquake. The time period of the variations is about 15 min after the seismic rupture, and the maximum amplitude is about 0.1 TEC units. We then examine the preseismic ionospheric anomalies by the TEC values from the GIM and the electron density $(Ne)$ values reconstructed by computerized ionospheric tomography. Temporal variations show that the TEC and $Ne$ values simultaneously increased on April 5–8, 2013, which are 12–15 days before. This increase is possibly related to the earthquake. Spatial analysis shows that anomalies tend to appear around the epicenter and their conjugate points.

Far-field coseismic ionospheric disturbances of Tohoku earthquake

A computer code has been developed to simulate the generation of infrasonic waves by a strong earthquake at a distance of 9000km from the epicenter, their propagation through the atmosphere and their effects in the ionosphere. We provide estimates of the perturbations in the ionosphere at the height (210–220km) where radiowaves at the sounding frequency (3.595MHz) of a continuous Doppler radar reflect. Ionospheric perturbations have a global character and amplitudes of 1.5–7.5% of ambient value. Perturbations exist for ~1h. The form of calculated ionospheric disturbances coincides with the experimental results. The correlation coefficient between calculated and experimental forms was from 0.68 to 0.9.

Virtual array beamforming of GPS TEC observations of coseismic ionospheric disturbances near the Geomagnetic South Pole triggered by teleseismic megathrusts

AbstractWe identified coseismic ionospheric disturbances (CID) in Antarctica generated by the 2010 Maule and the 2011 Tohoku‐Oki earthquakes analyzing total electron content (TEC) data with a modified beamforming technique. Beamforming in Antarctica, however, is not straightforward due to the effects of array deformation and atmospheric neutral wave‐ionospheric plasma coupling. We take these effects into account and present a method to invert for the seismically generated acoustic wave using TEC observations. The back azimuths, speeds, and waveforms obtained by the beamform are in excellent agreement with the hypothesis that the TEC signals are generated by the passage of Rayleigh waves from the Maule and Tohoku‐Oki earthquakes. The Tohoku‐Oki earthquake is ~12,500 km from Antarctica, making this the farthest observation of CIDs to date using GPS.

Ionospheric and geomagnetic disturbances caused by the 2008 Wenchuan earthquake: A revisit

AbstractPrevious works have shown that coseismic ionospheric disturbances (CIDs) after the tsunamigenic 2011 Tohoku earthquake (Tohoku EQ, Mw9.1) covered a vast area and were observed thousands of kilometers away from the epicenter. For the purpose of making a comprehensive comparison between powerful oceanic and inland EQs, we conduct a retrospective investigation of CIDs and geomagnetic responses to the 2008 Wenchuan EQ (Mw7.9) using a combination of techniques, total electron content, HF Doppler, and ground magnetometer. It is the very first study to present CIDs recorded by different techniques at co‐located sites and profiled with regard to changes of both ionospheric plasma and current (geomagnetic field) simultaneously. The integrated observation also shows that (1) in the Wenchuan case, most of the ionospheric and geomagnetic disturbances were observed within 1000 km distance which is far less than the Tohoku case; (2) two groups of CIDs were found with maximum amplitudes in the direction of azimuth 150° and 135°, respectively; and (3) the geomagnetic changes were only registered by three magnetometers located to the east and southeast of the epicenter. All the facts indicate that the main directional lobe of Wenchuan EQ energy propagation is to southeast and perpendicular to the direction of the fault rupture, but this kind of directivity is not that distinct in the Tohoku case. We suggest that the different fault slip (inland or submarine) affecting the way of couplings of lithosphere with atmosphere may contribute to the discrepancies between the two events.

Dichotomy in mode propagation of coseismic ionospheric disturbance: Observations from 11 April 2012 Indian Ocean earthquake

AbstractThe ionosphere response to the great intraplate Indian Ocean earthquake of 11 April 2012 (Mw 8.6) and its largest aftershock (Mw 8.2) is analyzed using GPS‐aided total electron content (TEC) measurements. Data from the dense GPS networks, SuGAr (Sumatran GPS Array) and the permanent Andaman‐Nicobar array, formed the near‐field observations at distances 250–1200 km from the epicenter. Stations such as IISC, DGAR, and few others provided measurements over 2000 km from the epicenter. The coseismic ionospheric disturbances (CIDs) with a propagation velocity of 930–1262 m/s, equals the speeds of the shock acoustic waves, arrive within 10–18 min after the earthquake occurrence. The observed phenomenon of CID splitting into two modes, north and south of the epicenter, is akin to the well‐documented effects of anisotropy on wave propagation. Closer to the epicenter, to its south, the propagation velocity of CID is ~1 km/s, and farther southeast of the network the velocity reduces to 500–600 m/s. In contrast, toward Andaman in the north, the CID propagation velocity increases to 2–3.5 km/s. The zenith angle of the line of sight between the GPS receiver and satellite appears to influence the amplitude of the TEC fluctuations. The anomalous azimuthal variation of the Rayleigh wave radiation pattern best explains the observed N‐S asymmetry of CID.

GPS detection of the coseismic ionospheric disturbances following the 12 May 2008 M7.9 Wenchuan earthquake in China

Here we report two cases of coseismic ionospheric disturbances observed through a GPS network in China after the great Wenchuan earthquake at 06:28 UT on 12 May, 2008. One is detected 7.9 min after the earthquake and had an intensive “N” shape oscillated waveform with a pronounced amplitude of about 1 TECU, which propagates approximately southward to the distance about 1000 km with the horizontal phase velocity of 600±84 m/s and the period of 9.5±1.3 min. The other is detected 8.5 min after the earthquake and has an oscillated waveform more like a positive pulse with an amplitude of about 0.5 TECU, which propagates eastward to the distance about 800 km with the horizontal phase velocity of 720±59 m/s and the period of 7.4±0.8 min. These two coseismic ionospheric disturbances are caused by the acoustic gravity waves excited by partial transformation of the acoustic waves originated from the energy release of the earthquake, somewhere near the epicenter. The directional preferences of these two coseismic ionospheric disturbances may be associated with the oblique geomagnetic field lines and the background winds filtering effect.

Coseismic ionospheric disturbance of the large strike-slip earthquakes in North Sumatra in 2012: Mw dependence of the disturbance amplitudes

We studied ionospheric responses to the 2012 April 11 Mw 8.6 North Sumatra earthquake using total electron content (TEC) measurements with the regional Global Navigation Satellite System network. This earthquake ruptured the oceanic lithosphere off the Indian Ocean coast of North Sumatra, and is known as the largest strike-slip earthquake ever recorded. Coseismic ionospheric disturbances (CIDs) with rapid TEC enhancement of a few TEC units propagated northward with a speed of acoustic waves (∼1 km s–1). Resonant atmospheric oscillation with a frequency ∼4 mHz have been found as monochromatic oscillation of TEC lasting for an hour after the main shock and the largest aftershock. We compared CID amplitudes of 21 earthquakes world-wide with moment magnitudes (Mw) 6.6–9.2. They roughly obeyed a law such that CID amplitude increases by two orders of magnitude for the Mw increase of three. The 2012 North Sumatra earthquakes slightly deviated negatively from the trend possibly reflecting their strike-slip mechanisms, that is small vertical crustal movements for their magnitudes.

Strike-slip earthquakes can also be detected in the ionosphere

It is generally assumed that co-seismic ionospheric disturbances are generated by large vertical static displacements of the ground during an earthquake. Consequently, it is expected that co-seismic ionospheric disturbances are only observable after earthquakes with a significant dip–slip component. Therefore, earthquakes dominated by strike-slip motion, i.e. with very little vertical co-seismic component, are not expected to generate ionospheric perturbations. In this work, we use total electron content (TEC) measurements from ground-based GNSS-receivers to study ionospheric response to six recent largest strike-slip earthquakes: the Mw7.8 Kunlun earthquake of 14 November 2001, the Mw8.1 Macquarie earthquake of 23 December 2004, the Sumatra earthquake doublet, Mw8.6 and Mw8.2, of 11 April 2012, the Mw7.7 Balochistan earthquake of 24 September 2013 and the Mw 7.7 Scotia Sea earthquake of 17 November 2013. We show that large strike-slip earthquakes generate large ionospheric perturbations of amplitude comparable with those induced by dip–slip earthquakes of equivalent magnitude. We consider that in the absence of significant vertical static co-seismic displacements of the ground, other seismological parameters (primarily the magnitude of co-seismic horizontal displacements, seismic fault dimensions, seismic slip) may contribute in generation of large-amplitude ionospheric perturbations.

Pattern and evolution of seismo‐ionospheric disturbances following the 2011 Tohoku earthquakes from GPS observations

AbstractGlobal Positioning System (GPS) has been widely used to sense crustal deformation and ionospheric anomalies, particularly seismic ionospheric disturbances. In March 2011, the earthquakes with magnitude of up to Mw = 9 occurred in Tohoku near the east coast of Honshu, Japan. The GPS Earth Observation Network (GEONET) in Japan with more than 1200 continuously operating stations provides a unique opportunity to study the detailed seismic ionospheric disturbances. In this paper, the pattern and evolution of seismic ionospheric disturbances following the Tohoku earthquakes are investigated by dense GEONET data, including amplitude, propagation pattern, direction, speed, and evolution. Maximal coseismic ionospheric disturbances are found with up to more than 4 TECU, and the disturbance period is around 10–20 min. The seismic ionospheric effects following the aftershocks are attenuated with the increase of the time and distance between the ionospheric pierce point and the epicenter of the main event, which last more than 2 h. Seismic ionospheric disturbance detected by GPS measurement is not only related to the main shock but also the giant aftershocks. Propagation velocities of the total electron content (TEC) disturbance show a decrease when it spreads 400–600 km away from the epicenter in the north‐western direction, where it is just near the west coast of Japan. Furthermore, the TEC disturbance also has obvious directional features. In the first half hour, the TEC disturbance in the southeast direction has the biggest amplitude, while the dominant direction is changed to northwest tens of minutes later. In addition, signals with higher frequencies are existed in seismic TEC variation at the epicenter region but do not appear in the far field.

Study of the 2013 Lushan M7.0 earthquake coseismic ionospheric disturbances

On April 20, 2013, an earthquake of M7.0 occurred in Lushan, Sichuan province, China. This paper investigates the coseismic ionospheric anomalies using GPS (Global Positioning System) data from 23 reference stations in Sichuan province that are a part of the Crustal Movement Observation Network of China (CMONOC). The recorded results show that a clear ionospheric anomaly occurred within 15min after the earthquake near the epicenter, and the occurrence time of the anomalies recorded by various stations is related to the distance from the epicenter. The maximum anomaly is 0.25 TECu, with a 2min duration and the distance of the recording station to the epicenter is 83km. Acoustic waves generated by the crustal vertical movement during the earthquake propagate up to the height of the ionosphere lead to the ionospheric anomaly, and the propagation speed of the acoustic wave is calculated as 0.72±0.04km/s based on the propagation time and propagation distance, consistent with the average speed of sound waves within a 0–450km atmospheric height.

Coseismic displacements and inospheric changes of the 2013 Ms7. 0 Lushan earthquake from GPS measurements

By inverting GPS data recorded at stations of the Crustal Movement Observation Network of China (CMONOC) near the 2013 Lushan M s7. 0 earthquake, we found a horizontal displacement of 22 mm at a site about 32 km SW of the epicenter and vertical displacements of as much as 12. 4 mm at several sites. The vertical displacements were generally uplift on the west side of the nearby Longmenshan fault zone and subsidence on the east side. We also found coseismic ionospheric disturbances about 0. 5 to 0. 9 TECU in amplitude that lasted for about one hour.

Ionospheric disturbances of the 2007 Bengkulu and the 2005 Nias earthquakes, Sumatra, observed with a regional GPS network

We studied ionospheric disturbances associated with the two large earthquakes in Sumatra, Indonesia, namely, the 2007 Bengkulu and the 2005 Nias earthquakes, by measuring the total electron contents (TEC) using a regional network of global positioning system (GPS) receivers. We first focus on coseismic ionospheric disturbances (CIDs) of the Bengkulu earthquake (Mw 8.5). They appeared 11–16 min after the earthquake and propagated northward as fast as ~0.7 km/s, consistent with the sound speed at the ionospheric F layer height. Resonant oscillation of TEC with a frequency of ~5 mHz continued for at least 30 min after the earthquake. The largest aftershock (Mw 7.9) also showed clear CIDs similar to the main shock. A CID propagating with the Rayleigh wave velocity was not observed, possibly because the station distribution did not favor the radiation pattern of the surface waves. This earthquake, which occurred during a period of quiet geomagnetic activity, also showed clear preseismic TEC anomalies similar to those before the 2011 Tohoku‐Oki earthquake. The positive and negative anomalies started 30–60 min before the earthquake to the north and the south of the fault region, respectively. On the other hand, we did not find any long‐term TEC anomalies within 4–5 days before the earthquake. Co‐ and preseismic ionospheric anomalies of the 2005 Nias earthquake (Mw 8.6) were, however, masked by strong plasma bubble signatures, and we could not even discuss the presence or absence of CIDs and preseismic TEC changes for this earthquake.

Propagation of large amplitude ionospheric disturbances with velocity dispersion observed by the SuperDARN Hokkaido radar after the 2011 off the Pacific coast of Tohoku Earthquake

Ionospheric responses to the 2011 off the Pacific coast of Tohoku Earthquake are studied using the SuperDARN Hokkaido radar, which is located at (43.5°N, 143.6°E) and which monitors the ionosphere over a wide horizontal area. The radar observed an oscillation of the vertical motion of the ionosphere with a period of about 1 to 2 min. The disturbance propagated northward, away from the epicenter with the velocity of about 6.2, 4.5, 3.9 and 3.5 km/s. The latter three values are basically consistent with the propagation of the Earth’s surface waves reported in several previous studies. The propagation velocities decreased with time, which has not been reported in previous studies for this propagation velocity range. The peak-to-peak amplitudes of Doppler velocities of ground/sea scatter echoes observed by the radar were up to 200 m/s, which is considerably larger than previously-reported values using HF Doppler measurements, although they are not extremely large for this historical earthquake (M = 9.0). This is the first time that ionospheric data have been obtained with high temporal (8 s) and spatial (22.5 km) resolutions following a giant earthquake, which enables us to discuss the detailed characteristics of the propagation of coseismic ionospheric disturbances.

Long-distance propagation of ionospheric disturbance generated by the 2011 off the Pacific coast of Tohoku Earthquake

Propagation of the initial ionospheric total electron content (TEC) disturbances generated by the 2011 off the Pacific coast of Tohoku Earthquake at 05:46:23 UT on March 11, 2011, was investigated with ground-based Global Positioning System (GPS) receivers in the east-Asian region. It was found that the initial ionospheric disturbance formed a zonal wave front after the earthquake occurrence. Four zonal wave fronts of this initial ionospheric disturbance were observed to travel southward from Japan to Taiwan with a velocity of about 1,000– 1,700 m/s. This study further found that the direction of the wave vector rotated from the south-southwest to the south-southeast as it traveled from Japan to Taiwan. The meridional propagation of the coseismic ionospheric disturbances is consistent with those observed after previous intense earthquakes. The temporal evolutions of initial ionospheric disturbances, after the earthquake, near the epicenter was observed in two-dimensions. The directivity of the disturbances was caused by a geomagnetic field effect.

Lower atmospheric anomalies following the 2008 Wenchuan Earthquake observed by GPS measurements

The Mw=8.0 Wenchuan Earthquake occurred on May 12, 2008 at the Longmen Shan fault, the western Sichuan Basin, China, killing more than ten thousand people in several cities and causing large economic losses. Global Positioning System (GPS) observations have provided unique insights on this event, including co-seismic ionospheric disturbances, co-/post-seismic crustal deformations and fault slip distributions. However, the processes and the driving mechanisms are still not clear, particularly possible seismo-lower atmospheric–ionospheric coupling behaviors. In this paper, the lower atmospheric (tropospheric) variations are investigated using the total zenith tropospheric delay (ZTD) from GPS measurements around this event. It has the first found co-seismic tropospheric anomalies during the mainshock with an increase and then a decrease, mainly in the zenith hydrostatic delay component (ZHD), while it is also supported by the same pattern of surface-observed atmospheric pressure changes at co-located GPS site that are driven by the ground-coupled air waves from ground vertical motion of seismic waves propagation. Therefore, the co-seismic tropospheric disturbances (CTD) indicate again the acoustic coupling effect of the atmosphere and the solid-Earth with air wave propagation from the ground to the top atmosphere.

Coseismic ionospheric disturbances triggered by the Chi‐Chi earthquake

At 17:47 UT on 20 September 1999, a large earthquake of magnitude Mw 7.6 struck the central Taiwan near a small town of Chi‐Chi. The ground‐based receivers of the global positioning system (GPS) in the Taiwan area detected coseismic ionospheric disturbances (CIDs) in the total electron content (TEC) triggered by the Chi‐Chi earthquake. When the CIDs travel away from the origin on the Earth surface and then propagate into the ionosphere, their amplitudes and periods generally become smaller and longer, respectively. Moreover, two global grid searches, adapting the ray‐tracing and the beam‐forming techniques, have been used to analyze the observed GPS TEC. We have not only estimated the average speed of the CIDs propagating in the atmosphere and ionosphere but also determined the location of CID origin on the Earth surface by using the two techniques. The results show that the observed CIDs result from shock‐acoustic waves triggered by sudden and large vertical motions of the Chi‐Chi earthquake.

Co-seismic ionospheric and deformation signals on the 2008 magnitude 8.0 Wenchuan Earthquake from GPS observations

The 8.0 magnitude Wenchuan Earthquake occurred at the Longmenshan Fault along the eastern boundary between the Tibetan Plateau and the western Sichuan Basin in southwestern China on 12 May 2008, killing tens of thousands of people in several cities along the western Sichuan Basin. In this paper, co-seismic ionospheric and deformation signals from the mainshock of this event are extracted from national global positioning system (GPS) network observations, which provide unique insights into this event. The co-seismic deformation moves towards the earthquake epicentre, and the largest magnitude reaches 2.3 m in Beichuan. The total moment of the co-seismic rupture is 2.4 × 1021 nm, equivalent to a magnitude of 8.1 and nearly identical to the seismological estimate. Furthermore, co-seismic ionospheric disturbances indicate a shock-acoustic wave propagation at a mean velocity of about 600 m s−1 towards the rupture direction.

Two‐mode long‐distance propagation of coseismic ionosphere disturbances

Using GPS total electron content (TEC) measurements, we analyzed ionosphere response to the great Kurile earthquake of 4 October 1994. High spatial resolution of the Japanese dense array of GPS receivers (GEONET) provided us the unique opportunity to observe the evolution of coseismic ionospheric disturbances (CID), which propagated for more than 1800 km away from the epicenter. Plotting a traveltime diagram for the CID and using an “array processing” technique within the approximation of a spherical CID wavefront, we observed a phenomenon of CID separation into two modes and we found that characteristics of the CID depend on the distance from the epicenter. The maximum of the CID amplitude was observed at ∼500 km from the epicenter. Within the first 600–700 km, the CID propagation velocity was about 1 km/s, which is equal to the sound speed at the height of the ionospheric F‐layer. Starting from ∼600 to 700 km out from the epicenter, the disturbance seems to divide into two separate perturbations, with each propagating at a different velocity, about 3 km/s for the one and about 600 m/s for the other. Apparently, the TEC response in the far‐field of the CID source is a mixture of signals that further “splits” into two modes because of the difference in their velocities. Our observations are in good agreement with the results of space‐time data processing in the approximation of a spherical wavefront of CID propagation.

Dependence of waveform of near-field coseismic ionospheric disturbances on focal mechanisms

AbstractUsing Total Electron Content (TEC) measurements with Global Positioning System we studied ionospheric responses to three large earthquakes that occurred in the Kuril Arc on 04 October 1994, 15 November 2006, and 13 January 2007. These earthquakes have different focal mechanisms, i.e. high-angle reverse, low-angle reverse, and normal faulting, respectively. TEC responses to the 2006 and 2007 events initiated with positive and negative changes, respectively. On the other hand, the initial TEC changes in the 1994 earthquake showed both positive and negative polarities depending on the azimuth around the focal area. Such a variety may reflect differences in coseismic vertical crustal displacements, which are dominated by uplift and subsidence in the 2006 and 2007 events, respectively, but included both in the 1994 event.

Determining the parameters of ionospheric perturbation caused by earthquakes using the quasi-optimum algorithm of spatiotemporal processing of TEC measurements

Abstract We present the quasi-optimum algorithm of localization of a source of coseismic ionospheric perturbation based on GPS receivers’ network data processing. The initial data of the algorithm are the series of variations of ionospheric total electron content (TEC), reconstructed using the measurements of the phase delays of GPS signals. In order to select the TEC increments caused by ionospheric perturbation due to the earthquake, the TEC series are filtered using a special procedure. The algorithm realizes coherent summation of all TEC series of GPS array reasoning from the maximization of the energy of the total signal of the ionospheric response to earthquake. The quasi-optimum algorithm allows determination of the perturbation propagation velocity as well as of the coordinates, height and “switch-on” time of a source of coseismic ionospheric disturbance without prior information about the perturbation form and the site and time of the main shock of earthquake. We used the algorithm for measuring the parameters of ionospheric perturbations which accompanied the earthquake in the vicinity of Hokkaido Island on September 25, 2003 and the earthquake near the south coast of Honshu Island on September 5, 2004. The results of these experiments show the high accuracy of the perturbation source coordinates estimation (33 km and 27 km respectively with reference of the earthquakes epicenters). The estimations of perturbations propagation velocity (820 ± 60 m/s and 460 ± 40 m/s), heights (340 ± 80 km and 370 ± 130 km) and “switch-on” delay (346 s and 507 s) of a source of the perturbation obtained in both experiments are in agreement with a theory according to which coseismic atmospheric disturbance propagates within a narrow cone of zenith angles up to ionospheric heights and then diverges in the form of a spherical wave with the radial velocity close to the speed of sound at these heights. It is also in agreement with the results of earlier researches.