ionospheric gnss imagery of seismic source possibilities difficulties and challenges up to now the possibility to obtain images of seismic source from ionospheric global navigation satellite systems gnss measurements seismo ionospheric imagery has only been demonstrated for giant earthquakes with moment magnitude mw 9 0 in this work we discuss difficulties and restrictions of this method and we apply for the first time the seismo ionospheric imagery for smaller earthquakes the latter is done on the example of the mw7 4 sanriku oki earthquake of 9 march 2011 analysis of 1 hz data of total electron content tec shows that the first coseismic ionospheric disturbances cid occur 470 480 s after the earthquake as tec enhancement on the east northeast from the epicenter the location of these first cid arrivals corresponds to the location of the coseismic uplift that is known as the source of tsunamis our results confirm that despite several difficulties and limitations high rate ionospheric gnss data can be used for determining the seismic source parameters for both giant and smaller moderate earthquakes in addition to these seismo ionospheric applications we raise several fundamental questions on cid nature and evolution namely one of the most challenging queries can moderate earthquake generate shock acoustic waves plain language summary ionosphere is a layer of charged particles of the earth s atmosphere located at altitudes 60 800 km however despite being high above the earth s surface the ionosphere is sensible to numerous near ground geophysical events earthquakes tsunamis volcano eruptions etc acoustic and gravity waves emitted by these events propagate upward and generate atmospheric ionospheric perturbations ionospheric disturbances generated by earthquakes are known as coseismic ionospheric disturbances cid recently it has been suggested that analysis of cid and their first arrivals can provide information on the position and on the structure of seismic fault ruptured in earthquake this method is known as ionospheric imagery of seismic source however so far this method has been only applied to giant earthquakes mw 9 0 in this work for the first time we apply the ionospheric imagery for smaller earthquakes on the example of the m7 4 sanriku oki earthquake that occurred on 9 march 2011 in japan our results show that this method is applicable to smaller earthquakes and despite some difficulties it can indicate the position of coseismic uplift 8 min after the earthquake the uplift generates cid but also tsunamis therefore our method can be used as independent or complementary one for near real time tsunami warning systems

two mode ionospheric response and rayleigh wave group velocity distribution reckoned from gps measurement following mw 7 8 nepal earthquake on 25 april 2015 the coseismic induced ionospheric total electron content tec perturbations were analyzed following the mw 7 8 nepal earthquake 28 147 n 84 708 e depth 15 km that occurred on 25 april 2015 at 06 11 26 utc the ionospheric response is due to both the modes i e shock acoustic waves slow mode and rayleigh wave induced fast mode the continuous global positioning system gps data at about 60 sites from various gps networks have been used in the present study all the sites within epicentral distance of 2400 km and 70 170 azimuth recorded the rayleigh wave induced tec response while the sites within 400 2200 km in the same azimuth recorded the response from both the modes the maximum coseismic induced peak to peak tec amplitude is 1 2 total electron content unit 1 tecu 1016 el m 2 from hodochron plot the apparent rayleigh wave velocity has been determined as 2400 m s on the average and the acoustic wave velocity as 1180 m s both these waves being discernible beyond 1200 km of epicentral distance as also evident from hodochron plot and wavelet spectrographs we reckoned the rayleigh wave group velocities using ionospheric response at selected radial pairs of stations and validated the ionospheric response distribution seen mainly depending on the epicentral distance satellite geometry directivity of radiation pattern and the upper crustal heterogeneity this study highlights the characteristics of ionospheric response consequent to the 2015 nepal earthquake

dichotomy in mode propagation of coseismic ionospheric disturbance observations from 11 april 2012 indian ocean earthquake the 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

in situ pore pressures what is their significance and how can they be reliably measured the intergranular fluid pressure in a soil matrix pore pressure has fundamental influence on the engineering behaviour of soils often assumptions are made regarding pore pressures however in critical analyses direct measurement of pore pressures should be made this paper discusses the pore pressure measurements made at the ormen lange field pore pressure measurements using piezometers indicate pore pressures in excess of hydrostatic at the back wall of the slide and the stornese feature hydrostatic pressures have been identified on the north flank and in the basin of the slide dissipation tests performed during the field investigation did not yield reliable in situ pressure estimates the pore pressure measurements from the piezometers are consistent with the assumptions required in the theoretical slope stability analyses explaining the storegga slide mechanism as no standard commercially available technology for autonomous pore pressure monitoring exists the paper describes also the technical solutions designed and implemented for pore pressure monitoring at the ormen lange field

plate boundary observatory and related networks gps data analysis methods and geodetic products the geodesy advancing geosciences and earthscope gage facility global positioning system gps data analysis centers produce position times series velocities and other parameters for approximately two thousand continuously operating gps receivers spanning a quadrant of earth s surface encompassing the high arctic north america and caribbean the purpose of this review is to document the methodology for generating station positions and their evolution over time and to describe the requisite tradeoffs involved with combination of results gage gps analysis involves formal merging within a kalman filter of two independent loosely constrained solutions one is based on precise point positioning produced with the gps inferred positioning system orbit analysis simulation gipsy oasis software at central washington university cwu and the other is a network solution based on phase and range double differencing produced with the gps at mit gamit software at new mexico institute of mining and technology nmt the primary products generated are the position time series that show motions relative to a north america reference frame and secular motions of the stations represented in the velocity field the position time series themselves contain a multitude of signals in addition to the secular motions co seismic and post seismic signals seasonal signals from hydrology and transient events some understood and other not yet fully explained are all evident in the time series and ready for further analysis and interpretation we explore the impact of analysis assumptions on the reference frame realization and on the final solutions and we compare within the gage solutions and with others

southern california permanent gps geodetic array continuous measurements of regional crustal deformation between the 1992 landers and 1994 northridge earthquakes the southern california permanent gps geodetic array pgga was established in 1990 across the pacific north america plate boundary to continuously monitor crustal deformation we describe the development of the array and the time series of daily positions estimated for its first 10 sites in the 19 month period between the june 28 1992 mw 7 3 landers and january 17 1994 mw 6 7 northridge earthquakes we compare displacement rates at four site locations with those reported by feigl et al 1993 which were derived from an independent set of global positioning system gps and very long baseline interferometry vlbi measurements collected over nearly a decade prior to the landers earthquake the velocity differences for three sites 65 100 km from the earthquake s epicenter are of order of 3 5 mm yr and are systematically coupled with the corresponding directions of coseismic displacement the fourth site 300 km from the epicenter shows no significant velocity difference these observations suggest large scale postseismic deformation with a relaxation time of at least 800 days the statistical significance of our observations is complicated by our incomplete knowledge of the noise properties of the two data sets two possible noise models fit the pgga data equally well as described in the companion paper by zhang et al this issue the pre landers data are too sparse and heterogeneous to derive a reliable noise model under a fractal white noise model for the pgga data we find that the velocity differences for all three sites are statistically different at the 99 significance level a white noise plus flicker noise model results in significance levels of only 94 43 and 88 additional investigations of the pre landers data and analysis of longer spans of pgga data could have an important effect on the significance of these results and will be addressed in future work

three dimensional distribution of ionospheric anomalies prior to three large earthquakes in chile using regional global positioning system gps networks we studied three dimensional spatial structure of ionospheric total electron content tec anomalies preceding three recent large earthquakes in chile south america i e the 2010 maule mw8 8 the 2014 iquique mw8 2 and the 2015 illapel mw8 3 earthquakes both positive and negative tec anomalies with areal extent dependent on the earthquake magnitudes appeared simultaneously 20 40 minutes before the earthquakes for the two mid latitude earthquakes 2010 maule and 2015 illapel positive anomalies occurred to the north of the epicenters at altitudes 150 250 km the negative anomalies occurred further to the north at higher altitudes 200 500 km this lets the epicenter the positive and negative anomalies align parallel with the local geomagnetic field which is a typical structure of ionospheric anomalies occurring in response to positive surface electric charges

ionosonde tracking of infrasound wavefronts in the thermosphere launched by seismic waves after the 2010 m8 8 chile earthquake

a strategy for the observation of volcanism on earth from space heat strain topography and atmospheric emissions associated with volcanism are well observed by satellites orbiting the earth gravity and electromagnetic transients from volcanoes may also prove to be measurable from space the nature of eruptions means that the best strategy for measuring their dynamic properties remotely from space is to employ two modes with different spatial and temporal samplings eruption mode and background mode such observational programmes are best carried out at local or regional volcano observatories by coupling them with numerical models of volcanic processes eventually such models could become multi process operational forecast models that assimilate the remote and other observables to constrain their uncertainties the threat posed by very large magnitude explosive eruptions is global and best addressed by a spaceborne observational programme with a global remit

directivity and apparent velocity of the coseismic ionospheric disturbances observed with a dense gps array abstract coseismic disturbances in ionosphere have been observed after recent thrust earthquakes off the pacific coast of japan with a dense global positioning system array positive pulses in electron content as large as several times 10 15 electrons m 2 and as long as 4 5 min emerge 10 min after earthquakes and propagate horizontally with apparent velocity of 1 km s close to the sound velocity at the ionospheric height they may have been excited by coseismic uplifts of the sea surface initially as upward propagating compressive pulses of atmosphere which were gradually refracted to propagate horizontally in ionosphere the propagation has strong north south asymmetry and interaction between the movements of charged particles in acoustic waves and geomagnetic fields might have selectively attenuated the northward propagating disturbances

are there new findings in the search for ulf magnetic precursors to earthquakes moore 1964 in a letter published in nature reported disturbances in geomagnetic field data prior to the 27 march 1964 alaska earthquake after the publication of this report many papers have shown magnetic changes preceding earthquakes however a causal relationship between preearthquake magnetic changes and impending earthquakes has never been demonstrated as a consequence after 50 years magnetic disturbances in the geomagnetic field are still candidate precursory phenomena some researchers consider the investigation of ultra low frequency ulf 0 001 10 hz magnetic data the correct approach for identifying precursory signatures of earthquakes other researchers instead have recently reviewed many published ulf magnetic changes that preceded earthquakes and have shown that these are not actual precursors the recent studies by currie and waters 2014 and han et al 2014 aim to provide relevant new findings in the search for ulf magnetic precursory signals however in order to contribute to science alleged precursors must be shown to be valid and reproducible by objective testing here we will briefly discuss the state of the art in the search for ulf magnetic precursors paying special attention to the recent findings of currie and waters 2014 and han et al 2014 we do not see in these two reports significant evidence that may support the observation of precursory signatures of earthquakes in ulf magnetic records

ionospheric electron enhancement preceding the 2011 tohoku oki earthquake 1 the 2011 march 11 tohoku oki earthquake mw9 0 caused vast damages to the country large events beneath dense observation networks could bring breakthroughs to seismology and geodynamics and here i report one such finding the japanese dense network of global positioning system gps detected clear precursory positive anomaly of ionospheric total electron content tec around the focal region it started 40 minutes before the earthquake and reached nearly ten percent of the background tec it lasted until atmospheric waves arrived at the ionosphere similar preseismic tec anomalies with amplitudes dependent on magnitudes were seen in the 2010 chile earthquake mw8 8 and possibly in the 2004 sumatra andaman mw9 2 and the 1994 hokkaido toho oki mw8 3 earthquakes but not in smaller earthquakes

detection of ionospheric perturbations using a dense gps array in southern california 1 we present observations of high frequency ionospheric perturbations detected using global positioning system gps data from the southern california integrated gps network scign a densely spaced gps array of about 250 stations centered on the los angeles area we show examples of perturbations with 3 10 minute periods that may result from coupling between the ionosphere and neutral gravity waves generated in the lower atmosphere although the signal to noise ratio of the perturbations is relatively small we show how multi station array processing techniques can take advantage of the high spatial density of the measurements and the coherence of the signal over a region the size of the scign to considerably improve the detection capability

three dimensional ionospheric tomography of post seismic perturbations produced by the denali earthquake from gps data summary the coupling between the solid earth and its atmosphere is responsible for vertically propagating infrasonic waves generated by seismic surface waves these pressure waves are amplified as they propagate upward and produce perturbations of ionospheric electron density the electron density perturbations above california due to the seismic surface waves generated by the denali earthquake on 2002 november 3 have been imaged from gps data by a tomographic method the integrated electron content along gps ray paths presents a noise level that is lower in the acoustic wave frequency band than in the gravity wave frequency band therefore the filtered gps data from californian networks are inverted for a tomographic reconstruction of electron density perturbations in the acoustic frequency band the inversion is properly resolved only in a small number of areas due to the geometry of gps ray paths in these areas a wave propagating upward at 1 2 0 3 km s 1 and horizontally at 4 1 km s 1 is observed with a timing consistent with an infrasonic wave generated by the path of seismic surface waves the discrepancies between the observed electron density perturbation structure and the expected infrasonic wave can be explained by the poor resolution of the inverse problem or by a simple model of interactions between the neutral wave and the plasma future development of dense gps networks and the advent of the galileo system will overcome the resolution problems and allow us to relate ionospheric perturbations to the seismic signal such a relation can be used to constrain the source and propagation of seismic waves as well as upper atmosphere characteristics

coseismic traveling ionospheric disturbances during the mw 7 8 gorkha nepal earthquake on 25 april 2015 from ground and spaceborne observations coseismic travelling ionospheric disturbances ctids and their propagation characteristics during mw 7 8 gorkha earthquake in nepal on 25 april 2015 have been investigated using a suite of ground based gps receivers and broad band seismometers along with the space borne radio occultation observations over the indian subcontinent region depletion in vertical total electron content vtec a so called ionospheric hole is observed near the epicenter 9 11 minutes after the onset of earthquake a positive pulse preceding the depletion similar to n shaped perturbation propagating with an apparent velocity of 2 4 km s is observed on the south further the ctids in the southward direction are found to split in to fast 2 4 1 7 km s and slow 680 520 m s propagating modes at epicentral distances greater than 800 km however the velocities of fast mode ctids are significantly smaller than the surface rayleigh wave velocity 3 7 km s indicating that they are not the true imprint of rayleigh wave instead can probably be attributed to the superimposed wave front formed by the mixture of acoustic waves excited by main shock and propagating rayleigh wave the southward ctids are found to propagate at f2 region altitudes of 300 440 km captured by cosmic radio occultation observations the ctids with periods of 4 6 minutes are observed in all directions with significantly larger amplitudes and faster propagation velocities in south and east directions the observed azimuthal asymmetry in the amplitudes and velocities of ctids are discussed in terms of the alignment with geomagnetic field and nature of surface crustal deformation during the earthquake

ionospheric disturbances in the vicinity of the chelyabinsk meteoroid explosive disruption as inferred from dense gps observations the paper describes results of studying effects of total electron content tec variations triggered by the chelyabinsk meteoroid airburst as inferred from unique data of a dense gps network located around the final part of the meteoroid atmospheric path well pronounced tec disturbances with an average period of about 10 min and amplitude of 0 07 0 5 tecu total electron content unit 1 tecu 1016 el m 2 were detected these disturbances were initiated by an ionospheric source activated about 5 6 min after the airburst the disturbance velocity damping with time and distance from the airburst was revealed using a gps interferometric technique several modes of tec disturbances with propagation velocities ranging from 250 to 660 m s were distinguished through the distance time diagram analysis the estimated position of ionospheric source of tec disturbances is shifted 36 km southwestward from the airburst which is most likely to be associated with the conjoint influence of tec data errors damping and anisotropy of tid propagation velocity

ionospheric response to infrasonic acoustic waves generated by natural hazard events recent measurements of gps derived total electron content tec reveal acoustic wave periods of 1 4 min in the f region ionosphere following natural hazard events such as earthquakes severe weather and volcanoes here we simulate the ionospheric responses to infrasonic acoustic waves generated by vertical accelerations at the earth s surface or within the lower atmosphere using a compressible atmospheric dynamics model to perturb a multifluid ionospheric model response dependencies on wave source geometry and spectrum are investigated at middle low and equatorial latitudes results suggest constraints on wave amplitudes that are consistent with observations and that provide insight on the geographical variability of tec signatures and their dependence on the geometry of wave velocity field perturbations relative to the ambient geomagnetic field asymmetries of responses poleward and equatorward from the wave sources indicate that electron perturbations are enhanced on the equatorward side while field aligned currents are driven principally on the poleward side due to alignments of acoustic wave velocities parallel and perpendicular to field lines respectively acoustic wave driven tec perturbations are shown to have periods of 3 4 min which are consistent with the fraction of the spectrum that remains following strong dissipation throughout the thermosphere furthermore thermospheric acoustic waves couple with ion sound waves throughout the f region and topside ionosphere driving plasma disturbances with similar periods and faster phase speeds the associated magnetic perturbations of the simulated waves are calculated to be observable and may provide new observational insight in addition to that provided by gps tec measurements

an updated bouguer anomaly map of south central west africa a new bouguer gravity anomaly map compiled for western africa adds data for ghana guinea and liberia the new data add detail to a key part of the eburnean shield and assist in the development of a model of rifting at the time of the eburnean orogeny 2000 million years ago this model includes a framework for the deposition of the region s mineral deposits the model and existing field data can be used to guide future minerals exploration in the region

detecting atmospheric perturbations produced by venus quakes 1 the possibility to detect seismic activity on venus by using the mechanical coupling of the solid atmosphere system is investigated first the atmospheric attenuation of infrasonic waves produced by quakes is theoretically determined from a pure co2 atmospheric model demonstrating that frequencies below 0 1 hz are amplified by a factor of 10 000 above 120 km altitude with a simple quake model an upper limit of infrasonic adiabatic temperature and density perturbations above the source is estimated then we demonstrate that the temperature increase due to high altitude acoustic energy dissipation above a quake is large enough to be measured by remote sensing methods finally the expected post seismic effects are analyzed in the framework of the virtis instrument on board the esa venus express mission

the 2009 samoa and 2010 chile tsunamis as observed in the ionosphere using gps total electron content 1 ground based global positioning system gps measurements of ionospheric total electron content tec show variations consistent with atmospheric internal gravity waves caused by ocean tsunamis following two recent seismic events the samoa earthquake of 29 september 2009 and the chile earthquake of 27 february 2010 both earthquakes produced ocean tsunamis that were destructive to coastal communities near the epicenters and both were observed in tidal gauge and buoy measurements throughout the pacific ocean we observe fluctuations in tec correlated in time space and wave properties with these tsunamis using the jet propulsion laboratory s global ionospheric mapping software these tec measurements were band pass filtered to remove ionospheric tec variations with wavelengths and periods outside the typical range for tsunamis observable variations in tec appear correlated with the tsunamis in some locations hawaii and japan but not in others southern california or near the epicenters where variations are observed the typical amplitude tends to be 0 1 0 2 tec units for these events on the order of 1 of the background tec value these observations are compared to estimates of expected tsunami driven tec variations produced by embry riddle aeronautical university s spectral full wave model an atmosphere ionosphere coupled model and are found to be in good agreement significant tec variations are not always seen when a tsunami is present but in these two events the regions where a strong ocean tsunami was observed coincided with clear tec observations while a lack of clear tec observations coincided with smaller sea surface height amplitudes there exists the potential to apply these detection techniques to real time gps tec data providing estimates of tsunami speed and amplitude that may be useful for early warning systems

vertical midscale ionospheric disturbances caused by surface seismic waves based on irkutsk chirp ionosonde data in 2011 2016

ionospheric gps total electron content tec disturbances triggered by the 26 december 2004 indian ocean tsunami 1 tsunami ionospheric disturbances tids of the 26 december 2004 mw 9 3 sumatra earthquake are detected by the total electron content tec of ground based receivers of the global positioning system gps in the indian ocean area it is found that the tsunami waves triggered atmospheric disturbances near the sea surface which then traveled upward with an average velocity of about 730 m s 2700 km hr into the ionosphere and significantly disturbed the electron density within it results further show that the tids which have maximum height of about 8 6 17 2 km periods of 10 20 min and horizontal wavelengths of 120 240 km travel away from the epicenter with an average horizontal speed of about 700 km hr 190 m s in the ionosphere

discriminating the tectonic and non tectonic contributions in the ionospheric signature of the 2011 mw7 1 dip slip van earthquake eastern turkey 1 it has previously been suggested that ionospheric perturbations triggered by large dip slip earthquakes might offer additional source parameter information compared to the information gathered from land observations based on 3d modeling of gps and glonass derived total electron content signals recorded during the 2011 van earthquake thrust intra plate event mw 7 1 turkey we confirm that coseismic ionospheric signals do contain important information about the earthquake source namely its slip mode moreover we show that part of the ionospheric signal initial polarity and amplitude distribution is not related to the earthquake source but is instead controlled by the geomagnetic field and the geometry of the global navigation satellite system satellites constellation ignoring these non tectonic effects would lead to an incorrect description of the earthquake source thus our work emphasizes the added caution that should be used when analyzing ionospheric signals for earthquake source studies

ionospheric signature of surface mine blasts from global positioning system measurements sources such as atmospheric or buried explosions and shallow earthquakes are known to produce infrasonic pressure waves in the atmosphere because of the coupling between neutral particles and electrons at ionospheric altitudes these acoustic and gravity waves induce variations of the ionospheric electron density the global positioning system gps provides a way of directly measuring the total electron content in the ionosphere and therefore of detecting such perturbations in the upper atmosphere in july and august 1996 three large surface mine blasts 1 5 kt each were detonated at the black thunder coal mine in eastern wyoming as part of a seismic and acoustic monitoring experiment we deployed five dual frequency gps receivers at distances ranging from 50 to 200 km from the mine and were able to detect the ionospheric perturbation caused by the blasts the perturbation starts 10 to 15 min after the blast lasts for about 30 min and propagates with an apparent horizontal velocity of 1200 meters per second its amplitude reaches 3 x 10 exp 14 el per square meters in the 7 3 min period band a value close to the ionospheric perturbation caused by the m 6 7 northridge earthquake the small signal to noise ratio of the perturbation can be improved by slant stacking the electron content time series recorded by the different gps receivers taking into account the horizontal propagation of the perturbation the energy of the perturbation is concentrated in the 200 to 300 second period band a result consistent with previous observations and numerical model predictions the 300 second band probably corresponds to gravity modes and shorter periods to acoustic modes respectively using a 1 d stratified velocity model of the atmosphere we show that linear acoustic ray tracing fits arrival times at all gps receivers we interpret the perturbation as a direct acoustic wave caused by the explosion itself this study shows that even relatively small subsurface events can produce ionospheric perturbations that are above the detection threshold of the gps technique by sensing derivative signals which can be detected over a relatively broad region it appears that gps might be particularly useful for source characterization within the first acoustic quiet zone where infrasound would probably be ineffective this suggests that dual frequency gps monitoring could contribute to comprehensive nuclear test ban treaty verification

on the reported ionospheric precursor of the 1999 hector mine california earthquake 1 using global positioning system gps data from sites near the 16 oct 1999 hector mine california earthquake pulinets et al 2007 identified anomalous changes in the ionospheric total electron content tec starting one week prior to the earthquake pulinets 2007 suggested that precursory phenomena of this type could be useful for predicting earthquakes on the other hand and in a separate analysis afraimovich et al 2004 concluded that tec variations near the epicenter were controlled by solar and geomagnetic activity that were unrelated to the earthquake in an investigation of these very different results we examine tec time series of long duration from gps stations near and far from the epicenter of the hector mine earthquake and long before and long after the earthquake while we can reproduce the essential time series results of pulinets et al we find that the signal they identified as being anomalous is not actually anomalous instead it is just part of normal global scale tec variation we conclude that the tec anomaly reported by pulinets et al is unrelated to the hector mine earthquake

modelling of the total electronic content and magnetic field anomalies generated by the 2011 tohoku oki tsunami and associated acoustic gravity waves summary in this work numerical simulations of the atmospheric and ionospheric anomalies are performed for the tohoku oki tsunami 2011 march 11 the tsunami atmosphere ionosphere tai coupling mechanism via acoustic gravity waves agws is explored theoretically using the tai coupled model for the modelled tsunami wave as an input the coupled model simulates the wind density and temperature disturbances or anomalies in the atmosphere and electron density magnetic anomalies in the f region of the ionosphere also presented are the gps total electron content tec and ground based magnetometer measurements during the first hour of tsunami and good agreements are found between modelled and observed anomalies at first within 6 min from the tsunami origin the simulated wind anomaly at 250 km altitude and tec anomaly appear as the dipole shaped disturbances around the epicentre then as the concentric circular wave fronts radially moving away from the epicentre with the horizontal velocity 800 m s 1 after 12 min followed by the slow moving horizontal velocity 250 m s 1 wave disturbance after 30 min the detailed vertical horizontal propagation characteristics suggest that the anomalies appear before and after 30 min are associated with the acoustic and gravity waves respectively similar propagation characteristics are found from the gps tec and magnetic measurements presented here and also reported from recent studies the modelled magnetic anomaly in the f region ionosphere is found to have similar temporal variations with respect to the epicentre distance as that of the magnetic anomaly registered from the ground based magnetometers the high frequency component 10 min of the simulated wind tec and magnetic anomalies in the f region develops within 6 7 min after the initiation of the tsunami suggesting the importance of monitoring the high frequency atmospheric ionospheric anomalies for the early warning these anomalies are found to maximize across the epicentre in the direction opposite to the tsunami propagation suggesting that the large atmospheric ionospheric disturbances are excited in the region where tsunami does not travel

ionospheric anomalies immediately before mw7 0 8 0 earthquakes recent observations suggested that ionospheric anomalies appear immediately before large earthquakes with moment magnitudes mw of 8 2 or more do similar phenomena precede smaller earthquakes here we answer this question by analyzing vertical total electron contents vtec observed near the epicenters before and after 32 earthquakes with mw7 0 8 0 using data from nearby global navigation satellite systems stations to detect anomalies we defined the reference curves to fit the observed vtec and considered the departure from the curves as anomalies in estimating the reference curves we excluded time windows prescribed for individual earthquakes considering mw possibly affected by earthquakes we validated the method using synthetic vtec data assuming both preseismic coseismic and postseismic anomalies out of the 32 mw7 0 8 0 earthquakes eight earthquakes showed possible preseismic anomalies starting 10 20 min before earthquakes for earthquakes of this mw range we can observe preseismic ionospheric changes probably when the background vtec is large say 50 tecu total electron content unit 1 tecu 1016 el m 2 or more

ionospheric disturbances triggered by the 11 march 2011 m9 0 tohoku earthquake 1 an earthquake of magnitude 9 0 occurred near the east coast of honshu tohoku area japan producing overwhelming earth surface motions and inducing devastating tsunamis which then traveled into the ionosphere and significantly disturbed the electron density within it hereafter referred to as seismotraveling ionospheric disturbances stids the total electron content tec derived from nationwide gps receiving networks in japan and taiwan is employed to monitor stids triggered by seismic and tsunami waves of the tohoku earthquake the stids first appear as a disk shaped tec increase about 7 min after the earthquake occurrence centered at about 200 km east of the epicenter near the west edge of the japan trench fast propagating disturbances related to rayleigh waves quickly travel away from the epicenter along the main island of japan with a speed of 2 3 3 3 km s accompanied by sequences of concentric circular tec wavefronts and followed by circular ripples close to a tsunami speed of about 720 800 km h that travel away from the stid center these are the most remarkable stids ever observed where signatures of rayleigh waves tsunami waves etc simultaneously appear in the ionosphere

rayleigh wave signature in ionograms induced by strong earthquakes 1 after the magnitude 9 0 earthquake off the pacific coast of tohoku near the east coast of honshu japan which occurred on 11 march 2011 an unusual multiple cusp signature mcs was observed in ionograms at three ionosonde stations across japan to investigate the general characteristics of mcss we examined ionograms obtained during the period 1957 to 2011 from five ionosonde stations in japan after earthquakes with a seismic magnitude of 8 0 or greater a total of 43 such earthquakes occurred after 1957 as recorded in the database of the united states geological survey mcss were observed in 8 of 43 earthquakes allowing us to investigate the specific conditions of mcs appearance the appearance of mcss at different epicentral distances exhibits traveling characteristics at a velocity of 4 0 km s which is in the range of rayleigh waves there is a 7 min offset in delay time after the earthquake at each epicentral distance in the travel time diagram this offset is consistent with the propagation time of acoustic waves from the ground to the ionosphere launched by rayleigh waves mcss in ionograms provide a snapshot of vertical disturbances induced by a wave because the sweep time for the whole ionospheric echo traces is much shorter than the propagation time of acoustic waves the vertical scale of the disturbances is 10 30 km which corresponds to an acoustic wave period of 20 50 s at ionospheric heights

effects of rayleigh taylor instability and ionospheric plasma bubbles on the global navigation satellite system signal abstract ionospheric disturbances induced by various natural e g earthquakes volcanic eruption thunderstorms meteorite showers solar eclipses or anthropogenic e g nuclear explosions launching of space shuttles processes can be detected through change in total electron content tec in the f layer these ionospheric perturbations can be captured by worldwide expanding geodetic gnss networks mainly during the day time when the solar radiation ionizes the air molecules however during post sunset period strong ionospheric irregularities known as equatorial plasma bubbles epbs develop due to the classical configuration for the rayleigh taylor r t instability that diffracts navigation and communication signals here we use various instances of ionospheric disturbances triggered by natural processes e g earthquakes and volcanic eruption in the recent decade to investigate the spatiotemporal and seasonal effects of ionospheric irregularities on the gnss signals our study suggests that in the low latitudinal region e g sumatra mexico such ionospheric irregularities can mask the ionospheric perturbations due to the higher production rate of epbs hence detection of such co seismic tec anomaly becomes difficult however in the high latitudinal region e g iceland alaska due to the lower production rate of epbs ambient ionospheric irregularities are insignificant and hence coseismic tec anomalies can be captured even during night time we argue that the production rate of epbs further depends upon seasonal and longitudinal parameters on the globe

ionospheric response to earthquakes of different magnitudes larger quakes perturb the ionosphere stronger and longer recently it has been shown that the ionosphere is capable of showing images of seismic fault shortly after an earthquake this gives rise to the idea of retrieval of seismic information from ionospheric observations as the first step toward such inversion here we study distinctive features of ionospheric response to shallow earthquakes both submarine and inland of moment magnitudes mw7 2 9 1 using gps measurements of the ionospheric total electron content we show that 1 the amplitude of coseismic total electron content variations in the near field is larger after more powerful earthquakes and 2 stronger earthquakes m 7 9 are in general characterized by a longer negative phase in coseismic perturbations

detection and modeling of rayleigh wave induced patterns in the ionosphere 1 global positioning system gps allows the detection of ionospheric disturbances associated with the vertical displacements of most of the major shallow seismic events we describe a method to model the time and space distributions of rayleigh wave induced total electron content tec patterns detected by a dense gps array we highlight the conditions for which a part of the ionospheric pattern can be directly measured at teleseismic distance and above the epicenter in particular a satellite elevation angle lower than 40 is a favorable condition to detect rayleigh wave induced ionospheric waves the coupling between the solid earth and its atmosphere is modeled by computing the normal modes of the solid earth atmosphere system we show the dependency of the coupling efficiency on various atmospheric conditions by summation of the normal modes we model the atmospheric perturbation triggered by a given earthquake this shows that a part of the observation is a rayleigh induced radiation pattern and therefore characteristic of the seismic rupture through atmosphere ionosphere coupling we model the ionospheric perturbation after the description of the local geomagnetic field anisotropic effects we show how the observation geometry is strongly affecting the radiation pattern this study deals with the related data for two earthquakes with far field and near field observations using the japanese gps network geonet after the 12 may 2008 wenchuan earthquake china and after the 25 september 2003 tokachi oki earthquake japan respectively waveforms and patterns are compared with the observed tec perturbations providing a new step toward the use of ionospheric data in seismological applications

gps detection of ionospheric perturbations following the january 17 1994 northridge earthquake sources such as atmospheric or buried explosions and shallow earthquakes producing strong vertical ground displacements are known to produce pressure waves that propagate at infrasonic speeds in the atmosphere at ionospheric altitudes low frequency acoustic waves are coupled to ionospheric gravity waves and induce variations in the ionospheric electron density using global positioning system gps data recorded by the permanent gps network operating in southern california we computed ionospheric electron content time series for several days preceding and following the january 17 1994 mw 6 7 northridge earthquake we observe an anomalous signal beginning several minutes after the earthquake with time delays that increase with distance from the epicenter the signal frequency and phase velocity are consistent with results from numerical models of atmospheric ionospheric acoustic gravity waves excited by seismic sources as well as previous electromagnetic sounding results we believe that these perturbations are caused by the ionospheric response to the strong ground displacement associated with the northridge earthquake

two mode long distance propagation of coseismic ionosphere disturbances 1 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

seismo ionospheric observations modeling and backprojection of the 2016 kaikōura earthquake we processed global navigation satellite system gnss time series data to extract total electron content tec perturbations of the ionosphere caused by the kaik ura earthquake we used ray based modeling to infer which part of the earth s surface coupled significant energy from the solid earth into the atmosphere we compared modeled tec data with the observed time series data and determined that significant coupling occurred north northeast of the initial slip this work corroborates existing analysis made with geodetic and interferometric synthetic aperture radar insar data the tec data suggested that the initial rupture coupled some energy into the atmosphere but later surface displacements 60 s after the initiation caused more significant ionospheric perturbations using an array of gnss stations we were able to track the moveout of the acoustic wave through the ionosphere we used a method commonly used in seismological studies called backprojection to estimate the location of the source of the tec perturbation on earth s surface this is the first time that this method has been applied to tec data and the results are promising the backprojection results are slightly shifted in space from the known area of maximum uplift and we attribute this small discrepancy to the fact that we did not account for horizontal winds in the atmosphere nor the 3d heterogeneity of the real atmosphere in the travel time modeling

co seismic displacements of the 1994 northridge california earthquake the 17 january 1994 northridge california earthquake significantly deformed the earth s crust in the epicentral region displacements of 66 survey stations determined from global positioning system gps observations collected before and after the earthquake show that individual stations were uplifted by up to 417 5 mm and displaced horizontally by up to 216 3 mm using these displacements we estimate parameters of a uniform slip model fault geometry and slip are estimated independent of seismological information using monte carlo optimization techniques that minimize the model residuals the plane that best fits the geodetic data lies 1 to 2 km above the plane indicated by aftershock seismicity modeling for distributed slip on a coplanar yet larger model fault indicates that a high slip patch occurred up dip and northwest of the mainshock hypocenter and that less than 1 m of slip occurred in the uppermost 5 km of the crust this finding is consistent with the lack of clear surface rupture and with the notion that the intersection with the fault that ruptured in 1971 formed the up dip terminus of slip in the northridge earthquake displacements predicted by either of these simple models explain most of the variance in the data within 50 km of the epicenter on average however the scatter of the residuals is twice the data uncertainties and in some areas there is significant systematic misfit to either model the co seismic contributions of aftershocks are insufficient to explain this mismatch indicating that the source geometry is more complicated than a single rectangular plane

variations of ionospheric total electron content during the chi chi earthquake on 20 september1999 ut 21 septemberin local time lt a large earthquake mw 7 7 struck central taiwan nearthe small town of chi chi the greatest plasma frequency in the ionosphere fof2 observed by the chung li ionosonde 25 0 n 121 2 e reveals three clear precur sors at 1 3 and 4 days prior to the earthquake this paper examines the ionospheric total electron content tec ob served by a network of the global positioning system gps receivers in taiwan area it is found that variations in fof2 and overhead tec recorded at chung li have a similar ten dency combining the data of the network of 13 gps re ceivers time and spatial variations of tec prior to the chi chi earthquake are examined results show that the equa torial anomaly crest moves equatorward and its tec value significantly decreases 1 3 and 4 days before the earth quake a comparison between the disturbed and reference previous 15 day median days confirms that tec decreases significantly around the epicenter in the afternoons of these days finally possible mechanisms are proposed and dis cussed

multisite remote sensing for tsunami induced waves in the 2011 tohoku tsunamigenic earthquake ionospheric anomalies generated by tsunami induced gravity waves were observed by many types of instruments three digisondes and one doppler receiver located in east asia were applied to investigate the far field ionospheric response to the westward propagating gravity waves generated by the earthquake based on time period spectrum analysis oscillations between 20 and 36 min on the fo text f 2 critical frequency of f2 layer curves and doppler variations of each observation location were identified the horizontal group speed generation time and source location estimated with the ray tracing method all indicated that the periodic disturbances recorded by the four radio systems were gravity waves induced by the tsunami following the 2011 tohoku earthquake the plasma frequency variations at five fixed altitudes in the ionospheric f2 layer over i cheon were used to investigate the vertical propagation of the tsunami associated gravity waves the measured phase progression in the vertical direction was opposite that of the energy transport which further confirmed that the recorded waves were atmospheric gravity waves the use of multisite remote sensing for examining tsunami induced waves in the ionosphere may open new perspectives in oceanic monitoring and future tsunami warning systems

preseismic ionospheric anomalies detected before the 2016 kumamoto earthquake on 15 april 2016 the kumamoto earthquake mw 7 3 occurred in japan with no warning signals global navigation satellite system gnss receivers provide useful information on disturbances in the ionosphere by calculating the changes in total electron content tec which is the number of electrons in the ionosphere here we show our recently proposed correlation analysis of tec data which can detect the preseismic ionospheric anomalies from the public gnss data our method detected the ionospheric anomaly several tens of minutes before the 2016 kumamoto earthquake near its epicenter furthermore we gave an indicator to distinguish between the preseismic tec anomalies and the medium scale traveling ionospheric disturbances mstids by calculating the anomalous area rates these results support the hypothesis for existence of the preceding phenomena before large earthquakes

pattern and evolution of seismo ionospheric disturbances following the 2011 tohoku earthquakes from gps observations global 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

ionospheric disturbances triggered by the 25 april 2015 m7 8 gorkha earthquake nepal constraints from gps tec measurements the ionosphere response to the april 11 2015 mw 7 8 gorkha earthquake occurring in the himalayan arc is analysed using gps total electron content tec measurements from gps sites in nepal and india situated both close to and far from the epicentre in the near field the coseismic ionospheric disturbance cid following the earthquake rupture propagation arrive east of the epicentre within 5 7 min with a propagation velocity of 980 m s equal to the speed of the shock acoustic waves at the ionospheric heights and on to the west with a reduced speed of 650 m s within 8 11 min after the earthquake occurrence the phenomenon of cid splitting into two modes east and west of the epicentre is observed in the far field region up to epicentral distances of 2200 km rayleigh wave induced ionospheric disturbance are recorded with a propagation speed of 2 6 km s higher tec amplitude of 0 2 1 5 tecu is observed east of the epicentre compared to the west with 0 1 0 3 tecu the characteristics of this dip slip earthquake are well projected in the tec waveforms the ambient magnetic field in the mid latitudes prohibited the propagation of ionospheric disturbance in the northward direction in the present study the observed primary cid is essentially in congruence with the rupture propagation of the earthquake in e se direction

ionospheric and geomagnetic disturbances caused by the 2008 wenchuan earthquake a revisit previous 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

coseismic ionospheric disturbances triggered by the chi chi earthquake 1 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

infrasonic sounds excited by seismic waves of the 2011 tohoku oki earthquake as visualized in ionograms after the m 9 0 tohoku oki earthquake in 2011 strong deformation of ionogram echo traces forming multiple cusp signatures mcss were observed at three stations 790 1880 km from the epicenter the vertical structure of the ionospheric disturbances was determined by true height analysis and compared with broadband seismograph records at stations close to the ionosondes these ionospheric disturbances were caused by vertically propagating acoustic waves excited by the up down ground motion of seismic waves numerical simulations have shown that acoustic waves with a period of 15 40 s and amplitude of order 1 mm s at the ground level were sufficient to create mcss as sharp as those observed these acoustic wave parameters are consistent with the seismic records if the motion of the air mass on the ground level is assumed to be the same as the ground motion the travel time diagram of the seismic records along the line connecting the epicenter and ionosondes showed that the first mcs ionogram detected at each station was caused by p waves while the others were caused by rayleigh waves

analysis of tec measurements above active seismic regions abstract ionospheric perturbations by natural geophysical activity such as volcanic eruptions and earthquakes have been studied since the great alaskan earthquake in 1964 measurements made from the ground show a variation of the critical frequency of the ionosphere layers before and after the shock in this paper we present an experimental investigation of the electron density variations before earthquakes when the low altitude satellite topex poseidon is above active seismic regions fluctuations in the integrated electron density or tec total electron content between the satellite and the ground are measured to correct the altimetry measurement the satellite was launched on august 10 1992 and an analysis of the tec fluctuations above the main earthquakes ms 5 is performed up to the end of 1995 due to different constraints the number of earthquakes considered in this study is only 706 increases as well as decreases of tec are observed above some epicentres three events are detailed and a statistical study is performed with the doris data the corresponding number of tec perturbations correlated in space and in time up to 48 h before these earthquakes is 238 i e 34 of the cases a comparison is made with tec data randomly selected during the lifetime of the satellite and ionospheric perturbations are observed in 16 of the cases this study indicates that it is possible to use tec measurements to survey these phenomena

detection of ruptures of andaman fault segments in the 2004 great sumatra earthquake with coseismic ionospheric disturbances 1 near field coseismic perturbations of ionospheric total electron content tec caused by direct acoustic waves from focal regions can be observed with global positioning system gps they appear 10 15 min after the earthquake with typical periods of 4 5 min and propagate as fast as 1 km s toward directions allowed by ambient geomagnetic fields ionospheric disturbance associated with the 2004 december 26 great sumatra andaman earthquake was recorded with nine continuous gps receiving stations in indonesia and thailand here we explore the possibility to constrain the rupture process of the earthquake with the observed ionospheric disturbances we assumed linearly distributed point sources along the zone of coseismic uplift extending 1300 km from sumatra to the andaman islands that excited acoustic waves sequentially as the rupture propagate northward by 2 5 km s tec variations for several satellite receiver pairs were synthesized by simulating the propagation of acoustic waves from the ground to the ionosphere and by integrating the tec perturbations at intersections of line of sights and the ray paths the tec perturbations from individual point sources were combined using realistic ratios and the total disturbances were compared with the observed signals prescribed ratios based on geodetically inferred coseismic uplifts reproduced the observed signals fairly well similar calculation using a rupture propagation speed of 1 7 km s degraded the fit suppression of acoustic waves from the segments north of the nicobar islands also resulted in a poor fit which suggests that ruptures in the northern half of the fault were slow enough to be overlooked in short period seismograms but fast enough to excite atmospheric acoustic waves coseismic ionospheric disturbance could serve as a new indicator of faulting sensitive to ruptures with timescale up to 4 5 min

multi dimensional distribution of near field ionospheric disturbances produced by the 2015 mw7 8 nepal earthquake abstract ionospheric anomalies possibly associated with large earthquakes particularly coseismic ionospheric disturbances have been detected by global positioning system gps a large nepal earthquake with magnitude mw7 8 occurred on april 25 2015 in this paper we investigate the multi dimensional distribution of near field coseismic ionospheric disturbances cids using total electron content tec and computerized ionospheric tomography cit from regional gps observational data the results show significant ionospheric tec disturbances and interesting multi dimensional structures around the main shock regarding the tec changes coseismic ionospheric disturbances occur approximately 10 20 min after the earthquake northeast and northwest of epicentre the maximum ridge to trough amplitude of cids is up to approximately 0 90 tecu min propagation velocities of the tec disturbances are 1 27 0 06 km s and 1 91 0 38 km s it is believed that the ionospheric disturbances are triggered by acoustic and rayleigh waves tomographic results show that the three dimensional distribution of ionospheric disturbances obviously increases at an altitude of 300 km above the surrounding epicentre predominantly in the entire region between 200 km and 400 km significant ionospheric disturbances appear at 06 30 ut from tomographic images this study reveals characteristics of an ionospheric anomaly caused by the nepal earthquake

vertical structure of the ionospheric response following the m w 7 9 wenchuan earthquake on 12 may 2008 the response of the vertical ionospheric electron density structure to the mw 7 9 wenchuan earthquake on 12 may 2008 was recorded by the formosat 3 cosmic f3 c radio occultation ro precise orbit determination pod total electron content tec the horizontal propagation characteristics of the seismo traveling ionospheric disturbances were identified by combining ground based global navigation satellite system gnss tec data and ro tec data the postseismic ionospheric infrasound wavefront with wavelength of around 80 km at altitude of 150 350 km was scanned vertically by an individual ro tec profile a large amount of tec profiles around the epicenter from 0000 to 1200 ut provide evidence of continental earthquake induced vertical oscillations that lasted in the ionosphere for several hours ro observed vertical perturbations appear on both the southward and northward sides of the epicenter the vertical structure of the ionospheric oscillations with wavelength ranging from 10 to 80 km increased with altitude between 230 and 650 km

study of ionospheric response to the 4b flare on 28 october 2003 using international gps service network data 1 using the gps data from as many as 114 gps stations of the international gps service for geodynamics igs the morphological features of the ionospheric total electron content tec variations on the sunlit hemisphere during the 4b solar flare on 28 october 2003 is studied it is found that the strongest sudden increase of tec sitec happened during the flare and the magnitudes of sitec vary at regions with different local solar zenith angle sza in the northern hemisphere the tec enhancement is approximately symmetrical to the local noon and its value is usually greater than 14 tecu 1 tecu 1016 m2 if the sza is less than 60 on the whole as the sza increases the value of tec enhancement in the northern hemisphere decreases it is worth mentioning that even in the regions of sza between 90 and 100 the sitec was still seen from the temporal tec curves using a photochemical model the electron production rate over the sunlit boundary region is calculated and some obvious features of sitec over this region are analyzed in the polar region the effect of this flare on the ionosphere exceeds the effect of the ionospheric scintillations and it seems that the ionosphere in the northern polar region responses more sensitively to this flare in the end superimposed on the curves of the rate of tec change there are some small disturbances spikes synchronously appearing on all curves and thus indicating an existence of similar structures in the euv band of the flare

parameters of seismic source as deduced from 1 hz ionospheric gps data case study of the 2011 tohoku oki event following the first time ionospheric imaging of a seismic fault here we perform a case study on retrieval of parameters of the extended seismic source ruptured during the great m9 0 tohoku oki earthquake using 1 hz ionospheric gps data from the japanese network of gps receivers geonet and several gps satellites we analyze spatiotemporal characteristics of coseismic ionospheric perturbations and we obtain information on the dimensions and location of the sea surface uplift seismic source we further assess the criterion for the successful determination of seismic parameters from the ionosphere the detection is possible when the line of sights from satellites to receivers cross the ionosphere above the seismic fault region besides we demonstrate that the multisegment structure of the seismic fault of the tohoku oki earthquake can be seen in high rate ionospheric gps data overall our results show that under certain conditions ionospheric gps derived tec measurements could complement the currently working systems or independent ionospherically based system might be developed in the future

gnss ionospheric seismology recent observation evidences and characteristics abstract the detail and nature of earthquakes are still challenging from traditional technique observations e g seismometers and strong motion accelerographs nowadays the ionospheric total electron content tec can be obtained from ground based global navigation satellite systems gnss and space borne gnss radio occultation which can be used to investigate the seismo ionospheric disturbances and may provide insights on the earthquake in this paper gnss ionospheric seismology is presented and reviewed including methods observation results and characteristics case studies of the 2008 wenchuan earthquake and 2011 japan earthquake are presented using ground based gnss observations significant co post seismic ionospheric anomalies are found from continuous gnss observations near the epicenters showing that the seismic ionospheric total electron content tec disturbances were derived mainly from the main shock the detailed pattern and evolution of the ionospheric disturbance are revealed by denser gnss observations some simulations explore the nature of the ionospheric perturbation highlighting that acoustic gravity waves are generated close to the epicenter and that surface rayleigh waves and tsunamis generate in the atmosphere ionosphere acoustic and gravity waves respectively these waves are induced by solid earth ocean and atmosphere coupling at the ground or ocean interface with the atmosphere propagating upward until the ionosphere create strong perturbation in plasma density and plasma velocity

two dimensional simulation of ionospheric variations in the vicinity of the epicenter of the tohoku oki earthquake on 11 march 2011 1 unusual ionospheric variations were observed in the m9 0 tohoku oki earthquake on 11 march 2011 among various kinds of features in the ionosphere significant depletion of total electron content tec near the epicenter was observed after the earthquake although previous studies have suggested that the coseismic ionospheric variations are associated with atmospheric perturbation caused by vertical displacement of the sea surface the mechanism of the tec depletion has not been fully understood in this paper a two dimensional nonlinear nonhydrostatic compressible atmosphere ionosphere model is employed to investigate the ionospheric variations in the vicinity of the epicenter the simulation results reveal that an impulsive pressure pulse produced by a sudden uplift of the sea surface leads to local atmospheric expansion in the thermosphere and that the expansion of the thermosphere combined with the effect of inclined magnetic field lines in the ionosphere causes the sudden tec depletion above the epicenter region

geomagnetic dependence of ionospheric disturbances induced by tsunamigenic internal gravity waves summary a series of ionospheric anomalies following the sumatra tsunami has been recently reported in the literature these anomalies show the signature in the ionosphere of tsunami generated internal gravity waves igw propagating in the neutral atmosphere over the ocean all these anomalies observed in the total electron content tec measured by gps or altimeters show geographical heterogeneity in the perturbed tec amplitude and suggest a dependence on geomagnetic latitude this latitudinal dependence has been taken into account in the previous 3 d modelling used for the interpretation of the tec topex and jason data here we present an accurate description of the ocean atmosphere ionosphere coupling method and focus on the properties of the propagation of tsunamigenic igw in the neutral atmosphere and their interaction with the ionospheric plasma the analytical dependence on the geomagnetic field in the neutral plasma coupling discussed in detail and quantitative modelling is used to describe the propagation of a simple tsunami wave at the global scale what emphasize the role of geomagnetic field within the neutral plasma coupling at the equatorial and mid latitude regions the results presented here in terms of electron density and tec variations show a strong geometric dependance involving the magnetic field inclination and the propagative direction of the tsunami if the strongest electron density and tec perturbations are located around 15 0 and 15 north the structure and amplitude of the modelled perturbation changes in the two

ionospheric disturbances infrasound waves over the czech republic excited by the 2011 tohoku earthquake 1 a train of large amplitude infrasound wave packets was observed by multipoint continuous doppler sounding system in the ionosphere over the czech republic on 11 march 2011 it is shown that these infrasound wave packets originated from vertical motion of the ground surface that was caused by arrival of seismic waves generated by the strong tohoku earthquake the infrasound wave packets were observed in the ionosphere at heights of 210 220 km about 9 min after the detection of corresponding wave packets on the ground which is consistent with the calculated time for vertically propagating infrasound waves absolute values of cross correlation coefficients between ionospheric and ground measurements are typically higher than 0 9 for two wave packets 0 98 the individual wave packets recorded on the ground have different observed horizontal velocities and correspond to different types of seismic waves a comparison of vertical velocities of ground motion with oscillation velocities of air particles in the ionosphere indicates that almost 1 10 of the infrasound energy flux excited at the ground reached the altitudes of 210 220 km for wave periods longer than 30 s estimates of sound attenuation are performed it is also shown that it is necessary to consider the value of electron density gradient at the reflection height of the sounding radio wave and air plasma compression owing to the infrasound wave to get reasonable estimates of oscillation velocities of air particles from doppler shift frequencies

explosion energy of the 2004 eruption of the asama volcano central japan inferred from ionospheric disturbances 1 the japanese dense array of global positioning system recorded ionospheric disturbances as changes in total electron content 12 minutes after the september 1 2004 eruption of the asama volcano central japan the disturbance had a period of one and a quarter minutes and propagated as fast as 1 1 km s suggesting its origin as the acoustic wave generated by the explosion by comparing the disturbance amplitudes with those by a surface mine blast with a known energy the overall asama explosion energy is inferred to be about 2 1014 j

ionospheric response following the mw 7 8 gorkha earthquake on 25 april 2015 a detailed observation of the coseismic ionospheric disturbances cids after the mw 7 8 gorkha earthquake has been carried out using total electron content tec data from 333 gps stations this inland earthquake occurred on 25 april 2015 at a depth of 15 km following the quake at 6 11 ut groups of cids were observed from 06 18 to 07 00 ut the cids we observed could be classified into three groups cids related to gravity waves gws cids related to acoustic waves aws and cids related to seismic rayleigh surface waves the gw related cids traveled at a velocity of 500 m s they were mainly observed to the south and north of the epicenter within 600 km of the event with a maximum amplitude of 0 18 tecu the aw related cids traveled at a velocity of 700 1400 m s they could be observed for 1000 km in all directions from the epicenter with an amplitude of 0 3 tecu the cids related to rayleigh waves could be observed only to the east of the epicenter at a maximum distance of 1800 km they had an apparent velocity of 2 0 2 3 km s through comparing the seismogram data from iris to the tec data we found the azimuthal characteristics of the ground vibrations agree with the directivity of the cids related to rayleigh surface waves

detection of crustal deformation from the landers earthquake sequence using continuous geodetic measurements the measurement of crustal motions in technically active regions is being performed increasingly by the satellite based global positioning system gps 1 2 which offers considerable advantages over conventional geodetic techniques3 4 continuously operating gps arrays with ground based receivers spaced tens of kilometres apart have been established in central japan5 6 and southern california to monitor the spatial and temporal details of crustal deformation here we report the first measurements for a major earthquake by a continuously operating gps network the permanent gps geodetic array pgga 7 9 in southern california the landers magnitude afw of 7 3 and big bear mw 6 2 earthquakes of 28 june 1992 were monitored by daily observations ten weeks of measurements centred on the earthquake events indicate significant coseismic motion at all pgga sites significant post seismic motion at one site for two weeks after the earthquakes and no significant preseismic motion these measurements demonstrate the potential of gps monitoring for precise detection of precursory and aftershock seismic deformation in the near and far field

normal modes modelling of post seismic ionospheric oscillations since 1960 several experiments have shown strong perturbations of the ionosphere after earthquakes for the biggest quakes doppler ionospheric soundings have revealed displacements of several tens of meter of the ionized layers e and f an accurate modelling of these phenomena was however never described we present here synthetic displacements of such oscillations and compare it with experimental data realistic models of the atmosphere including viscosity are used as well as realistic earth and seismic source model these ionospheric oscillations are computed by normal modes summation taking explicitly into account the coupling between the solid earth and the open atmosphere they are associated to the rayleigh fundamental surface waves we obtain a good agreement between synthetics and observations so it should be possible to use this method to study the ionospheric post seismic perturbations and possibly the high altitude profile of the density and the viscosity of the atmosphere

investigation of ionospheric electron content variations before earthquakes in southern california 2003 2004 1 it has been proposed that earthquakes are preceded by electromagnetic signals detectable from ground and space based measurements ionospheric anomalies such as variations in the electron density a few days before earthquakes are one of the precursory signals proposed since global positioning system gps data can be used to measure the ionospheric total electron content tec the technique has received attention as a potential tool to detect ionospheric perturbations related to earthquakes here we analyze 2 years 2003 2004 of data from the southern california integrated gps network scign a dense network of 265 continuous gps stations centered on the los angeles basin for possible precursors this time period encompasses the december 2003 m6 6 san simeon and september 2004 m6 0 parkfield earthquakes we produce tec time series at all scign sites and apply three different statistical tests to detect anomalous tec signals preceding earthquakes we find anomalous tec signals but no statistically significant correlation in time or in space between these tec anomalies and the occurrence of earthquakes in southern california for the 2003 2004 period this result does not disprove the possibility of precursory phenomena but show the signal to noise ratio of a hypothetical tec precursor signature is too low to be detected by the analysis techniques employed here precursors may still be revealed for future large earthquakes in well instrumented areas such as california and japan if the tests can be developed into techniques that can better separate external influences from the actual tec signal

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

ionospheric f2 region perturbed by the 25 april 2015 nepal earthquake seismic waves can be detected in the earth s atmosphere and ionosphere however their impacts on ionospheric electron density ne structures near the altitude of peak ne hmf2 have not yet been fully determined due to the lack of sufficient observations sampled in the vertical direction here we apply a ground based global positioning system gps receiving network in asia as well as the space based gps occultation experiment on board the formosat 3 cosmic f3 c satellite to vertically scan the ionospheric ne structures which were perturbed by the magnitude mw7 8 nepal earthquake that occurred on 25 april 2015 the f3 c altitudinal ne profiles show that the nepal earthquake induced air perturbations penetrate into the ionosphere at supersonic speeds of approximately 800 m s and change the ne structure by 10 near hmf2 the vertical scale of the ne perturbation is 150 km while the hmf2 is uplifted by more than 30 km within 1 min those results reveal that the earthquake induced ground displacement should be considered as a significant force that perturbs the vertical ne structure of the ionosphere

ionospheric disturbances induced by a missile launched from north korea on 12 december 2012 1 ionospheric disturbances caused by a missile launched from north korea on 12 december 2012 were investigated by using the gps total electron content tec the spatial characteristic of the front edge of v shaped disturbances produced by missiles and rockets was first determined considering the launch direction and the height of estimated ionospheric points at which gps radio signal pierces the ionosphere the missile passed through the ionosphere at heights of 391 425 and 435 km at 0056 30 0057 00 and 0057 30 ut respectively the observed velocities of the missile were 2 8 and 3 2 km s at that time which was estimated from the traveling speed of the front edge of v shaped disturbances westward and eastward v shaped disturbances propagated at 1 8 2 6 km s the phase velocities of the westward and eastward v shaped disturbances were much faster than the speed of acoustic waves reported in previous studies suggesting that sources other than acoustic waves may have played an important role furthermore the plasma density depletion that is often observed following missile and rocket launches was not found this suggests that the depletion resulting from the missile s exhaust was not strong enough to be observed in the tec distribution in the topside ionosphere