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GPS detection of ionospheric perturbations following the January 17, 1994, Northridge Earthquake
Author(s) -
Calais Eric,
Minster J. Bernard
Publication year - 1995
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/95gl00168
Subject(s) - ionosphere , epicenter , geology , total electron content , seismology , global positioning system , geodesy , geophysics , depth sounding , tec , telecommunications , oceanography , computer science
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 waves are coupled to ionospheric gravity waves and induce variations in the ionospheric electron density. Using Global Positioning System (GPS) data recorded by the permanent GPS network operating in southern California, we computed ionospheric electron content time series for several days preceding and following the January 17, 1994, M w =6.7 Northridge earthquake. We observe an anomalous signal beginning several minutes after the earthquake with time delays that increase with distance from the epicenter. The signal frequency and phase velocity are consistent with results from numerical models of atmospheric‐ionospheric acoustic‐gravity waves excited by seismic sources as well as previous electromagnetic sounding results. We believe that these perturbations are caused by the ionospheric response to the strong ground displacement associated with the Northridge earthquake.