HR: 0800h
AN: S11B-1023    [Abstracts]
TI: Reverse Modeling for Seismic Event Characterization
AU: * Gajewski, D
EM: gajewski@dkrz.de
AF: Inst. of Geophysics, Uni. of Hamburg , Bundesstr. 55, Hamburg, 20146 Germany
AU: Tessmer, E
EM: ekkehart.tessmer@dkrz.de
AF: Inst. of Geophysics, Uni. of Hamburg , Bundesstr. 55, Hamburg, 20146 Germany
AB: The localization of seismic events is of utmost importance in seismology. Current techniques rely on the fact, that the recorded event is detectable on most of the stations of a seismic array. Weak events, not visible in the individual seismogram of the array, are missed out. We present a new approach, were no picking of events in the seismograms of the recording array is required. The observed wavefield of the array is reversed in time and than considered as the boundary value for the reverse modelling using a pseudo spectral or finite difference approach. Assuming the correct velocity model, these reverse modeled wavefield focusses in the hypocenter of the seismic event. The origin time of the event is given by the time where maximum focussing is observed. The spatial extent of the focus resembles the resolution power of the recorded wavefield and the acquisition. This automatically provides the uncertainty of the localization with respect to the bandwith of the recorded data. The new method is particularly usefull for the upcoming large passive arrays since no picking is required. It has a great potential for localizing very weak events, not detectable in the individual seismogram, since the reverse modelling stacks the energy of all recorded traces and therefore enhances the signal to noise ratio. The method is demonstrated by 2-D and 3-D numerical case studies for a simple and a complex subsurface model which shows the potential of the new technique. Events with a S/N ratio smaller than 1 are considered as well as velocity errors and its influence on the localization. Velocity errors lead to unfocussed wavefields which may be used to update the velocity model similar to the migration velocity analysis in reflection seismology.
DE: 7230 Seismicity and seismotectonics
DE: 7200 SEISMOLOGY
DE: 7215 Earthquake parameters
SC: Seismology [S]
MN: 2004 AGU Fall Meeting