HR: 0830h
AN: U51B-0009    [PDF]
TI: Differential Response Functions: A {\it ScS-S} Case Study
AU: * Lawrence, J F
EM: jfisher@levee.wustl.edu
AF: Washington University, Campus Box 1169 One Brookings Drive, St Louis, MO 63130 United States
AU: Wysession, M E
EM: michael@mantle.wustl.edu
AF: Washington University, Campus Box 1169 One Brookings Drive, St Louis, MO 63130 United States
AB: We develop and demonstrate the differential response function (DRF), which is a new class of waveform that corresponds to isolated earth responses. Differential response functions are easily calculated by solving for the transfer functions between particular pairs of seismic waves (e.g. {\it PcP-P, ScS-S, SS-S}, etc). We can model a localized earth response by comparing observed and synthetic DRFs. For example, we can isolate lower mantle structure by examining the {\it ScS/S} transfer function. Each seismic phase may be considered as a convolution of 5 functions: 1) seismic source, 2) near source structure, 3) mid path structure, 4) near receiver structure, and 5) instrument response function. In this case, the deconvolution of the {\it S} phase from the {\it ScS} phase effectively removes all functions but the lower mantle (mid-path) structural response. This is due to the similarity of the {\it ScS} and {\it S} paths through the upper mantle and crust. The remaining signal retains impulses corresponding to reflective interfaces, time shifts associated with velocity anomalies, and attenuation due to quality factor variations. Each of these observable variations in waveform results from the localized structure, with little outside contamination. In this study we produce synthetic {\it ScS-S} differential response functions to model several examples of divergent lower mantle earth response. We then compare several examples of real {\it ScS-S} differential response functions to the synthetics to isolate distinct structural models for several regions within the lowermost mantle. We observe changes in the shape and amplitude of the main pulse corresponding to the reflection from the core mantle boundary. We also observe the absence and presence of other secondary pulses corresponding to interfaces at other depths. Despite stringent signal-to-noise requirements, the DRF provides several advantages over differential measurement techniques and waveform modeling methods. The source, receiver, near source, and near receiver response functions do not contaminate the system, effectively isolating only the desired earth response. The DRF directly corresponds to seismic models, and therefore retains more information than traditional differential travel-time or differential attenuation studies.
UR: http://epsc.wustl.edu/seismology/jfisher/DRF/
DE: 7200 SEISMOLOGY
DE: 7203 Body wave propagation
DE: 7207 Core and mantle
DE: 7260 Theory and modeling
DE: 8180 Tomography
SC: U
MN: 2003 Fall Meeting