High-resolution teleseismic tomography of upper-mantle structure using ana priorithree-dimensional crustal model

Abstract

Summary The effect of an a priori known 3‐D crustal model in teleseismic tomography of upper‐mantle structure is investigated. We developed a 3‐D crustal P‐wave velocity model for the greater Alpine region, encompassing the central and western Alps and the northern Apennines, to estimate the crustal contribution to teleseismic traveltimes. The model is constructed by comparative use of published information from active and passive seismic surveys. The model components are chosen to represent the present large‐scale Alpine crustal structure and for their significant effect on the propagation of seismic wavefields. They are first‐order structures such as the crust–mantle boundary, sedimentary basins and the high‐velocity Ivrea body. Teleseismic traveltime residuals are calculated for a realistic distribution of azimuths and distances by coupling a finite‐difference technique to the IASP91 traveltime tables. Residuals are produced for a synthetic upper‐mantle model featuring two slab structures and the 3‐D crustal model on top of it. The crustal model produces traveltime residuals in the range between −0.7 and 1.5 s that vary strongly as a function of backazimuth and epicentral distance. We find that the non‐linear inversion of the synthetic residuals without correcting for the 3‐D crustal structure erroneously maps the crustal anomalies into the upper mantle. Correction of the residuals for crustal structure before inversion properly recovers the synthetic slab structures placed in the upper mantle. We conclude that with the increasing amount of high‐quality seismic traveltime data, correction for near‐surface structure is essential for increasing resolution in tomographic images of upper‐mantle structure.

Structural and sedimentary records of the Oligocene revolution in the Western Alpine arc

“…The lower crustal section yielded Eocene ZFT ages (Siegesmund et al, 2008) which mark the N-directed thrusting stage (Handy et al, 1999) over the oceanic (Sesia) and continental European crust (Briançonnais) during the continental subduction stage. The western boundary of the Ivrea body, corresponding to lithospheric mantle, trends approximately N-S beneath the southern part of the Western Alpine arc (Waldhauser et al, 2002;Kissling et al, 2006;Lardeaux et al, 2006), that is in strong discrepancy with the present arc shape. We propose that this N-S boundary which appears roughly rectilinear at ~15 km depth (Vernant et al, 2002;Schreiber et al, 2010) could be a relict of the western transform boundary of Adria during northward Eocene drift (WATZ, fig.…”

Thick-Skinned and Thin-Skinned Tectonics: A Global Perspective

“…The cross-section of Figure 14 is based on reflection seismic data of NRP20 (Central and Southern traverse; [134,135]), teleseismic tomography and controlled-source seismology [136][137][138]. Earthquake loci are from the SED catalogue (Swiss Seismological Service) and are projected from a swath of 25 km width onto the cross-section (see [139]).…”

“…The cross-section of the Western Alps displayed in Figure 21A is based on the geological interpretation of the seismic lines of ECORS/CROP [185][186][187][188][189], structural work by [190], and teleseismic studies carried out by [136][137][138]. Earthquake tomography by [191] revealed the lithosphere structure.…”

Constraining P-wave velocity variations in the upper mantle beneath Southeast Asia

“…One could calculate travel times through the 3D crustal model, subtract these from the observed times, ray-trace to the bottom of the 3D crust, and then solve for the structure beneath the crust while leaving the crustal model unchanged (e.g., Waldhauser et al, 2002;Weidle and Widiyantoro, 2005). While straightforward and intuitive, without an explicit method for confining crustal anomalies to the crust, the relatively large anomalies of the 3D crust can still smear into the upper mantle.…”