Upper mantle structure from body-wave coda and amplitudes

Abstract

The last decade has seen a large increase in the amount of high-quality data from a growing number of digitally operating seismic stations. Both short- and long-period data are reported on a regular basis to central data centres. As global seismology is hampered by the unequal distribution of stations and earthquakes, extracting as much as possible information from the available data is important. However, only a relatively small part of the growing data volume is used on a more or less routine basis. New sources of information from the seismogram may add independent constraints on and provide a higher resolution of Earth structure. The most widely used parts of the seismogram are the P-wave travel time and the longperiod surface wave train. The travel time of the (mostly short-period) P-wave is used on a large scale to invert for Earth structure (Spakman 1991; Vandecar 1991; Van der Hilst & Engdahl 1991), Recently, also the S-wave travel time is used in tomographic inversions (e.g., Zielhuis 1988). On the low-frequency end of the spectrum, long-period surface wave forms are inverted for mantle velocity structure (e.g., Woodhouse & Dziewonski 1984; Snieder 1988). Recent studies include the long-period S-waves in the wave form modeling using modal summation (Nolet 1990: Zielhuis 1992). The results of Li & Tanimoto (1991) show that it is still prohibitively time-eonsuming to include also the long-period P-wave in this process. This leaves large parts of the seismogram unused in inversion procedures. Before these can be included in any inversion process, their information content and relation to Earth structure must be established (e.g.• wave propagation in a laterally homogeneous or heterogeneous Earth model). The main goal of the research presented in this thesis is to determine the information content of parts of the seismogram that are not frequently used and, if possible, to develop methods to extract this information.