Modelling of the Total Electronic Content and magnetic field anomalies generated by the 2011 Tohoku-oki tsunami and associated acoustic-gravity waves,

International audienceIn 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

The GEMS (Geophysical Monitoring Station) SEISmometer

International audienc

The early evolution of Venus controled by hydrodynamic escape.

International audienc

Modeling of atmospheric-coupled Rayleigh waves on planets with atmosphere: From Earth observation to Mars and Venus perspectives

International audienceAcoustic coupling between solid Earth and atmosphere has been observed since the 1960s, first from ground-based seismic, pressure, and ionospheric sensors and since 20 years with various satellite measurements, including with global positioning system (GPS) satellites. This coupling leads to the excitation of the Rayleigh surface waves by local atmospheric sources such as large natural explosions from volcanoes, meteor atmospheric air-bursts, or artificial explosions. It contributes also in the continuous excitation of Rayleigh waves and associated normal modes by atmospheric winds and pressure fluctuations. The same coupling allows the observation of Rayleigh waves in the thermosphere most of the time through ionospheric monitoring with Doppler sounders or GPS. The authors review briefly in this paper observations made on Earth and describe the general frame of the theory enabling the computation of Rayleigh waves for models of telluric planets with atmosphere. The authors then focus on Mars and Venus and give in both cases the atmospheric properties of the Rayleigh normal modes and associated surface waves compared to Earth. The authors then conclude on the observation perspectives especially for Rayleigh waves excited by atmospheric sources on Mars and for remote ionospheric observations of Rayleigh waves excited by quakes on Venus

From Sumatra 2004 to Tohoku-Oki 2011: The systematic GPS detection of the ionospheric signature induced by tsunamigenic earthquakes

International audienceThe recent tsunamigenic earthquake in Tohoku (11 March 2011) strongly affirms, one more time after the Sumatra event (26 December 2004), the necessity to open new paradigms in oceanic monitoring. Detection of ionospheric anomalies following the Sumatra tsunami demonstrated that ionosphere is sensitive to the tsunami propagation. Observations supported by modeling proved that tsunamigenic ionospheric anomalies are deterministic and reproducible by numerical modeling via the ocean/neutral-atmosphere/ionosphere coupling mechanism. In essence, tsunami induces internal gravity waves propagating within the neutral atmosphere and detectable in the ionosphere. Most of the ionospheric anomalies produced by tsunamis were observed in the far field where the tsunami signature in the ionosphere is clearly identifiable. In this work, we highlight the early signature in the ionosphere produced by tsunamigenic earthquakes and observed by GPS, measuring the total electron content, close to the epicenter. We focus on the first hour after the seismic rupture. We demonstrate that acoustic-gravity waves generated at the epicenter by the direct vertical displacement of the source rupture and the gravity wave coupled with the tsunami can be discriminated with theoretical support. We illustrate the systematic nature of those perturbations showing several observations: nominally the ionospheric perturbation following the tsunamigenic earthquakes in Sumatra on 26 December 2004 and 12 September 2007; in Chile on 14 November 2007; in Samoa on 29 September 2009; and the recent catastrophic Tohoku-Oki event on 11 March 2011. Based on the analytical description, we provide tracks for further modeling efforts and clues for the interpretation of complex--and thus often misleading--observations. The routine detection of the early ionospheric anomalies following the rupture highlights the role of ionospheric sounding in the future ocean monitoring and tsunami detection

Large impacts detected by the Apollo seismometers: Impactor mass and source cutoff frequency estimations

International audienceMeteoroid impacts are important seismic sources on the Moon. As they continuously impact the Moon, they are a significant contribution to the lunar micro-seismic background noise. They also were associated with the most powerful seismic sources recorded by the Apollo seismic network. We study in this paper the largest impacts. We show that their masses can be estimated with a rather simple modeling technique and that high frequency seismic signals have reduced amplitudes due to a relatively low (about 1 s) corner frequency resulting from the duration of the impact process and the crater formation. If synthetic seismograms computed for a spherical model of the Moon are unable to match the waveforms of the observations, they nevertheless provide an approximate measure of the energy of seismic waves in the coda. The latter can then be used for an estimation of the mass of the impactors, when the velocity of the impactor is known. This method, for the artificial impacts of the LM and SIVB Apollo upper stages, allows us to retrieve the mass within 20% of relative error. The estimated mass of the largest impacts observed during the 7 years of activity of the Apollo seismic network provides an explanation for the non-detection of surface waves on the seismograms. The specifications of future Moon seismometers, in order to provide the detection of surface waves, are given in conclusion

Parameters of seismic source as deduced from 1 Hz ionospheric GPS data: Case study of the 2011 Tohoku-oki event,

International audienceFollowing 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

The Seismicity of Mars Observed by the NASA InSight Mission

International audienceThis Plenary Lecture summarizes the seismicity of Mars recorded by the NASA InSight mission, which landed on Elysium Planitia on 26 August 2018. Equipped with a highly sensitive seismometer, the lander has been successfully recording the seismicity of Mars for over three years. Different types of marsquakes have been identified, including low-frequency events with mantle-going phases and shallow high-frequency events characterized by crustal propagation. More recently, a few meteoric impacts have also been identified. Over a thousand events have been recorded, with magnitudes reaching up to M W 4.7. Here we review the techniques used by the MarsQuake Service to locate and characterize marsquakes and the active crustal processes in different areas of the red planet, and we discuss the different types of marsquakes