Mapping the Impact of Non-Tectonic Forcing mechanisms on GNSS measured Coseismic Ionospheric Perturbations

International audienceGlobal Navigation Satellite System (GNSS) measured Total Electron Content (TEC) is now widely used to study the near and far-field coseismic ionospheric perturbations (CIP). The generation of near field (~500–600 km surrounding an epicenter) CIP is mainly attributed to the coseismic crustal deformation. The azimuthal distribution of near field CIP may contain information on the seismic/tectonic source characteristics of rupture propagation direction and thrust orientations. However, numerous studies cautioned that before deriving the listed source characteristics based on coseismic TEC signatures, the contribution of non-tectonic forcing mechanisms needs to be examined. These mechanisms which are operative at ionospheric altitudes are classified as the i) orientation between the geomagnetic field and tectonically induced atmospheric wave perturbations ii) orientation between the GNSS satellite line of sight (LOS) geometry and coseismic atmospheric wave perturbations and iii) ambient electron density gradients. So far, the combined effects of these mechanisms have not been quantified. We propose a 3D geometrical model, based on acoustic ray tracing in space and time to estimate the combined effects of non-tectonic forcing mechanisms on the manifestations of GNSS measured near field CIP. Further, this model is tested on earthquakes occurring at different latitudes with a view to quickly quantify the collective effects of these mechanisms. We presume that this simple and direct 3D model would induce and enhance a proper perception among the researchers about the tectonic source characteristics derived based on the corresponding ionospheric manifestations

Locating Surface Deformation Induced by Earthquakes Using GPS, GLONASS and Galileo Ionospheric Sounding from a Single Station

Monitoring earthquakes to rapidly forecast their consequences remains a challenging task, especially in areas far from seismic and geodetic networks. Large and shallow earthquakes induce disturbances in the ionospheric Total Electron Content (TEC). These disturbances are commonly detected using Global Navigation Satellite Systems (GNSS) stations that can sound the ionosphere at great distances. To address this instrumentation sparsity issue, we assess a single GNSS station\u27s ability to constrain the origin location of a coseismic ionospheric disturbance (CID) using observations of TEC. We develop a grid-search method that explores different trial origins (i.e. source locations) to determine which synthetic CID signal best matches the observed TEC time series. We confirm that a larger number of monitoring satellites enhances the opportunity to have the favorable geometrical coverage of satellites needed to resolve CID origins. We use TEC data acquired during two earthquakes having different moment magnitudes: a Mw 7.1 from Turkey and a Mw 7.8 from New Zealand. Using a well-placed multi-GNSS station we are able to retrieve the CID origin with an accuracy of 50 km and a theoretical precision of the same order. We conclude that a very sparse network of multi-GNSS stations can provide an independent estimate of the spatial distribution of large scale coseismic motions, including offshore areas 200–300 km from the coastline

The 15 January 2022 Hunga Tonga Eruption History as Inferred From Ionospheric Observations

International audienceOn 15 January 2022, the Hunga Tonga-Hunga Ha'apai submarine volcano erupted violently and triggered a giant atmospheric shock wave and tsunami. The exact mechanism of this extraordinary eruptive event, its size and magnitude are not well understood yet. In this work, we analyze data from the nearest ground-based receivers of Global Navigation Satellite System to explore the ionospheric total electron content (TEC) response to this event. We show that the ionospheric response consists of a giant TEC increase followed by a strong long-lasting depletion. We observe that the explosive event of 15 January 2022 began at 04:05:54UT and consisted of at least five explosions. Based on the ionospheric TEC data, we estimate the energy released during the main major explosion to be between 9 and 37 Megatons in trinitrotoluene equivalent. This is the first detailed analysis of the eruption sequence scenario and the timeline from ionospheric TEC observations

Discriminating the tectonic and non-tectonic contributions in the ionospheric signature of the 2011, M(w)7.1, dip-slip Van earthquake, Eastern Turkey

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, M-w=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

Imaging and modeling the ionospheric airglow response over Hawaii to the tsunami generated by the Tohoku earthquake of 11 March 2011

International audienceAlthough only centimeters in amplitude over the open ocean, tsunamis can generate appreciable wave amplitudes in the upper atmosphere, including the naturally occurring chemiluminescent airglow layers, due to the exponential decrease in density with altitude. Here, we present the first observation of the airglow tsunami signature, resulting from the 11 March 2011 Tohoku earthquake off the eastern coast of Japan. These images are taken using a wide‐angle camera system located at the top of the Haleakala Volcano on Maui, Hawaii. They are correlated with GPS measurements of the total electron content from Hawaii GPS stations and the Jason‐1 satellite. We find waves propagating in the airglow layer from the direction of the earthquake epicenter with a velocity that matches that of the ocean tsunami. The first ionospheric signature precedes the modeled ocean tsunami generated by the main shock by approximately one hour. These results demonstrate the utility of monitoring the Earth's airglow layers for tsunami detection and early warning

A New Crater Near InSight: Implications for Seismic Impact Detectability on Mars

International audienceA new 1.5 m diameter impact crater was discovered on Mars only ~40 km from the InSight lander. Context camera images constrained its formation between 21 February and 6 April 2019; follow‐up High Resolution Imaging Science Experiment images resolved the crater. During this time period, three seismic events were identified in InSight data. We derive expected seismic signal characteristics and use them to evaluate each of the seismic events. However, none of them can definitively be associated with this source. Atmospheric perturbations are generally expected to be generated during impacts; however, in this case, no signal could be identified as related to the known impact. Using scaling relationships based on the terrestrial and lunar analogs and numerical modeling, we predict the amplitude, peak frequency, and duration of the seismic signal that would have emanated from this impact. The predicted amplitude falls near the lowest levels of the measured seismometer noise for the predicted frequency. Hence, it is not surprising this impact event was not positively identified in the seismic data. Finding this crater was a lucky event as its formation this close to InSight has a probability of only ~0.2, and the odds of capturing it in before and after images are extremely low. We revisit impact‐seismic discriminators in light of real experience with a seismometer on the Martian surface. Using measured noise of the instrument, we revise our previous prediction of seismic impact detections downward, from ~a few to tens, to just ~2 per Earth year, still with an order of magnitude uncertainty