Optimizing data usage in regional body wave tomography by using asynchronous network data and relative sensitivity kernels: an example from Patagonia

SUMMARY A very frequent approach for studying lithospheric processes is to deploy temporary seismological networks in dedicated areas and to map the mantle structures with different approaches. One of them is the well-established relative traveltime body wave tomography. Different circumstances often lead to a non-uniform deployment of stations both in space and time, and a wish to combine data which have been acquired asynchronously. This is the situation in Patagonia where two distinct seismic experiments provide complementary seismic data over the region covering the Patagonia slab window. Combining these data in one regional relative body wave tomography is however problematic as the two data sets are a priori with respect to two different reference models. In this contribution, we show that the number of finite-frequency relative traveltime residuals varies very strongly from station to station for this data set, violating the assumption implicit in relative traveltime tomography of a unique reference model due to an even data distribution for all events. We demonstrate the superiority of the inversion using relative sensitivity kernels compared with a traditional approach with absolute kernels and event terms. A resolution test proves how this is crucial for resolving the important issue of the eastern extent of the slab window. In addition, we discuss potential issues related to interference of the direct phases with core phases when measuring finite-frequency traveltime residuals by cross-correlation of waveforms in necessarily relatively large time windows. We also briefly outline our preferred strategy for performing crustal correction, keeping in mind that finite-frequency residuals require frequency-dependent crustal corrections.