GPS detection of ionospheric perturbations following the January 17, 1994, Northridge Earthquake

摘要: 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 coupled gravity induce variations electron density. Using Global Positioning System (GPS) data recorded by permanent GPS network operating southern California, we computed content time series for several days preceding following January 17, 1994, Mw=6.7 Northridge earthquake. We observe an anomalous signal beginning minutes after earthquake with delays increase distance from epicenter. The phase velocity consistent results numerical models of atmospheric-ionospheric acoustic-gravity excited seismic sources well previous electromagnetic sounding results. believe these perturbations caused response displacement associated