Ionospheric acousitc and rayleigh waves detected by GPS following the 2005 Mw=7.2 northern California earthquake

The Mw= 7.2 earthquake occurred in northern California on June 15, 2005 as results of strike-slip fault. Dramatic ionospheric disturbances are detected by GNSS measurements collected by UNAVCO in the southeast of epicenter just about 10 minutes after the onset, while no obvious seismic ionospheric disturbance is observed in the northwest. Seismic ionospheric disturbances with two speed modes, i.e. 1.24km/s and 1.97 km/s are extracted from GPS TEC with different satellite elevation angles. Based on their occurrence epochs and propagation speeds, it is believed that the slow mode perturbation is the acoustic wave propagating horizontally at ionospheric height induced by the fault rupture in focal regions. Due to the relatively smaller earthquake for co-seismic ionospheric effects and good GPS ionospheric observation geometry, seismic ionospheric disturbances from acoustic wave at the ionospheric height and Rayleigh wave are distinguished clearly in near-field.