Talk by Prof. Philippe Lognonné from IPGP, France
avani goyal
Prof. Philippe Lognonné from the Institut de Physique du Globe de Paris (IPGP), France, is visiting IIT Bombay this week as part of a collaborative effort with the Pratham Student Satellite Team.
He is the head of the Planetary and Space geophysics team of IPGP and is a professor of Geophysics at the University of Paris Diderot. His research is related to long period seismology, the seismic coupling of solid earth with the atmosphere and ionosphere, as well as Planetary Geophysics and seismology.
The Pratham team has organized a talk by Prof. Lognonné titled "Observations and modeling of Tsunami and seismic waves signal in the Ionosphere with GPS, space altimeters and over-the-horizon radars". The abstract of the talk is given below.
Date: 9th February 2011 (Wednesday)
Time: 16:00 to 17:00
Venue: Aerospace Seminar Hall
Abstract: With the development of dense GPS networks, space altimeters, observations in the ionosphere of acoustic waves or gravity waves associated to either surface seismic waves or tsunami are common and reported almost systematically after quakes with magnitude larger than 7.5 or tsunamis with see surface amplitude of a few cm.
All these signals are associated to perturbations in the ionospheric electron density at altitude between 250 and 350 km for GPS and altimeters, while those related to Doppler or OTHR are related to the vertical electrons velocities at altitudes between 150 and 200 km. Above a frequency of 3mHz, the observed waves are either acoustic waves, generated by the vertical displacement of the Earth surface near the epicenter and propagating over regional distances (up to about one thousand km) in the atmosphere or acoustic-Rayleigh waves generated by the Rayleigh surface wave front at tele-seismic distance of several thousands km. The tsunami-induced gravity waves, observed also in the ionosphere are in contrary observed below 3 mHz and below the atmospheric cutoff.
The modeling of these waves requests not only the modeling of the solid-earth/atmosphere coupling problems but also the one of the atmosphere/ionosphere coupling. It is then mandatory to consider the variability in space and time of the atmosphere and ionosphere (e.g. density, temperature, ions and electron density), as well as magnetic field, in order to model the observed electronic content perturbations. We present several observations (2008 Wenchuan, 2004/2005 Sumatra-Andaman, 2003 Tokachi-Oki earthquakes) of seismic Rayleigh observation and of tsunami (2004 Sumatra-Andaman, 2006 Kuril, 2009 Samoa, 2010 Chile and last 25/10/2010 Sumatra) and confrontate these observations with modeling.
All recent tsunami have therefore been detected, as early as 30 min or even less in the ionosphere, with signal directly related to the see level height and a detection threshold of only 2 cm in see level change. We conclude by discussing the strategy for developing with space systems, OTHR and GPS networks, a worldwide system enabling to mitigate the tsunami risk by a worldwide observation system.
You are all cordially invited for the lecture.
Regards
Saptarshi Bandyopadhyay
--
Avani Goyal,
Overall co-ordinator, TechniC
Dept. of civil engineering,
IIT Bombay