Thursday, 11 march 2010
"[SQUID] 2 system: Ultra Low Noise Underground Magnetometer for Earth-Ionosphere Interactions"
Georges WAYSAND(Université de Nice Sophia-Antipolis, Observatoire de la Côte d’Azur Laboratoire Souterrain bas Bruit de Rustrel-Pays d’Apt)
Each ground movement on Earth shakes the air column above it. When the acoustic wave reaches the ionosphere floor, charges are temporarily displaced, parallel to the acoustic excitation. An electric current is created giving birth to a magnetic signal. [SQUID]2 detects these signals in various situations. [SQUID]2 is a low Tc Superconducting QUantum Interferometer Device in a 3 axis magnetometer configuration inside a Shielding QUalified for Ionosphere Detection (noise level : 2fT/? Hz above 40Hz without µ metal). This set-up is buried below 518m of karst in the Low Noise Underground Laboratory of Rustrel-Pays d’Apt (France). The ionosphere response to P waves from quakes M>3 is a resonance mode of the ionosphere floor whose period is around 60 to 80 seconds. The same type of signal has been observed one hour before the Sichuan quake of May 2008, in time coincidence with observation of rainbow colored clouds in the surrounding area. For S and T Earth breathing modes of the Earth the ionosphere response is linear were and was observed during a magnetically quiet 72 hours time window with no quake M>5.2, Because the frequencies responses are so low wherever such an instrument is on Earth, it is always electromagnetically near the signal source . If one consider that instruments of this type allows also the observation at mid latitude of magnetic storms with a sensitivity at least equivalent to conventional polar magnetometer, it is worthwhile to discuss the feasibility of a world wide network of SQUID stations, even with more modest noise performance.
Seminario de Física TeóricaFacultad de Ciencias Universidad de Zaragoza