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Title

Using cross-correlation to map the Transition Zone thickness beneath the Iberian Peninsula and Morocco

AuthorsBonatto, Luciana ; Schimmel, Martin ; Gallart Muset, Josep ; Morales, José
Issue Date3-Dec-2012
PublisherAmerican Geophysical Union
CitationAmerican Geophysical Union, Fall Meeting 2012, abstract: T23F-2745 (2012)
AbstractUpper mantle discontinuities are commonly studied through the detection of waves which have been converted/reflected at these discontinuities. In this work a novel processing approach which is leaned on receiver functions and which is based on cross-correlation and stacking techniques was implemented to search for weak amplitude upper mantle phases that arrive in the P-wave coda, such as P-to-s conversions. To add consistency and robustness to the detections, the new approach has been used together with receiver functions. This, also permits to bridge observation gaps due to break down of one of the techniques inherent to data characteristics. The aim of this work is to map the limits of the Transition Zone, which are the 410-km and 660-km depth discontinuities, beneath the Iberian Peninsula and north Africa. The new processing approach uses two independent cross-correlations (phase cross-correlation and cross-correlation geometrically normalized) and stacking techniques (phase weighted stack) in order to eliminate the source influence and to enhance coherent signals detected for the different events at individual stations. A pilot wavelet is selected from the vertical component, this wavelet contains the P phase and part of its coda with the later arriving depth phases. Converted and reflected phases are then detected by the cross-correlation of this pilot with the vertical and radial component of each recorded event, and the stacking of cross-correlograms for common conversion point areas. Cross-correlation provides relative travel times with respect to the P phase through its correlation maxima, and stacking enhances the signals which arrive consistently (near receiver conversions and reflections) and attenuates isolated depth phases such as near source reverberations and spurious arrivals. Slant stacks are used to correctly identify these coda signals. The described process was performed for teleseismic earthquakes registered in the seismic network of TopoIberia project. A total of 260 broad band seismic stations have been used which were deployed in Spain, Portugal and north Africa. We focus on the converted phases P410s and P660s, and map the corresponding discontinuities beneath Spain and north Africa. Clear P-to-s conversions at the 660 km depth discontinuity were detected beneath the studied region. The P410s phase is less well observed. Both discontinuities show topography which are within the expected depth variations observed in global studies. We will present maps of the Transition zone thickness and their interpretation using all available data.
URIhttp://hdl.handle.net/10261/172193
Appears in Collections:(ICTJA) Comunicaciones congresos
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