Ionospheric disturbances triggered by the M_w 7.6 earthquake off the coast of El Salvador on 13 January 2001

A network of five ground-based receivers of the global positioning system (GPS) was use to detect seismo-ionospheric disturbances in the total electron content (TEC) triggered by the 13 January 2001 EI Salvador M_w 7.6 earthquake. We apply least square fitted analysis as well as beam forming and ray tracing methods to analyze the GPS TECs. Results show that the average speeds of the seismo-ionospheric disturbances traveling in the upper atmosphere and ionosphere lie between 360 and 570 m s^-1, and the disturbance origins on the ground derived by the two methods are near the epicenter reported by the U.S. Geological Survey (USGS).