Sensitivity Kernels of <i>PP</i> Precursor Traveltimes and Their Limitations for Imaging Topography of Discontinuities

Koroni, Maria; Paulssen, Hanneke; Trampert, Jeannot

doi:10.1029/2018gl081592

Cited by 9 publications

(6 citation statements)

References 53 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This may partly explain the poorer agreement between ray theory and measured traveltimes for P-waves than for S-waves, as the ray theoretical prediction does not account for the influence of shear wavespeed structure on the P-wave traveltimes (for example see expression 1). It also implies that linearised corrections for mantle structure may require the correction for shear wavespeed structure as well, similar to a conclusion made by [Koroni et al, 2019] for the, rather difficult to observe, PP precursors.…”

Section: Discussion and Concluding Remarkssupporting

confidence: 65%

Analysis of core-mantle boundary seismic waves using full\-waveform modelling and adjoint methods

Koroni¹,

Borgeaud²,

Fichtner³

et al. 2021

Preprint

Self Cite

View full text Add to dashboard Cite

Using spectral-element synthetic seismograms and adjoint methods, we present a finite-frequency sensitivity analysis of traveltimes of seismic waves interacting with the core-mantle boundary (CMB). We focus on reflected and refracted P and S waves that are recorded in seismograms computed using SPECFEM3D_GLOBE. The core-mantle boundary is the most abrupt internal discontinuity of the Earth, marking the solid-fluid boundary between mantle and outer core that strongly affects the dynamics of the Earth's interior. A lot of research has been dedicated to resolving the structure of the CMB interface, however, a high resolution image of topographic variations is still lacking, due to difficulties relating both to observations in seismograms and good understanding of lowermost mantle velocity structure. We select some of the most important and widely used seismic phases, namely ScS, SKS, SKKS, PcP, PKP, PKKP and PcS, given their path through mantle and core and their interactions with CMB. These seismic waves have been widely deployed by investigators, trying to comprehend CMB and lowermost mantle structure. Firstly, we use computed synthetic seismograms with a dominant period of T ≈11s for existing models of CMB topography and compare traveltime perturbations measured by cross-correlation to those predicted using ray theory. We find deviations from a perfect agreement between ray theoretical predictions of time shifts and those measured on synthetics with and without CMB topography. We find that these deviations are generally small when the background velocity model is 1-D, but become larger when a 3-D background model is used, indicating trade-offs between 3-D mantle structure and core-mantle boundary topography. Secondly, we calculate the Fréchet kernels of traveltimes with respect to shear and compressional wavespeeds and the boundary sensitivities with respect to the CMB interface. We observe that the overall sensitivity of the traveltimes is mostly due to volumetric velocity structure and that imprints of CMB on traveltimes are less pronounced. In general, higher frequency data is used for imaging CMB, but the intermediate frequency range used here is compatible with current computational capabilities and provides a first approach to an FWI modelling of deep Earth structure. Our study explains the difficulties relating to inferring CMB topography using traveltimes and provides a gallery of exact, finite-frequency sensitivity kernels. We conclude that imaging of CMB using full-waveform inversion (FWI) techniques and kernels as presented here can improve our understanding of deep Earth structure and trade-off between seismic velocities and boundary topography.

show abstract

Section: Discussion and Concluding Remarkssupporting

confidence: 65%

Analysis of core-mantle boundary seismic waves using full\-waveform modelling and adjoint methods

Koroni¹,

Borgeaud²,

Fichtner³

et al. 2021

Preprint

Self Cite

View full text Add to dashboard Cite

show abstract

“…Nonetheless, there are still some limitations of the FAPPWF algorithm, such as considering only the 1‐D model and lacking finite frequency effects (Koroni et al, 2019). In each simulation, our method can only deal with the 1‐D model, and not including the complexity of lateral heterogeneity.…”

Section: Discussionmentioning

confidence: 99%

“…In the synthesis, the PREM is used and the seismograms are filtered with 15-75 s. The incident waveform for FAPPWF use the P wave computed by AxiSEM, and the synthetic from FAPPWF are applied the Hilbert transform to account for the phase advance of π/2 (Paulssen & Stutzmann, 1996;Shearer, 2009). The synthetic waveforms computed from FAPPWF fail to match those from AxiSEM at distances of 80-100°, which are mainly affected by the interfering seismic phases (such as Pp410p and Pp660p) from multiples of conversion and reflection Koroni et al, 2019;Shearer, 1991), but the seismograms fit well at distances of 100-140°. Although FAPPWF is not able to produce the full waveform, the method shown in this paper is valid to discuss the differential time and amplitude ratio of PP and its precursors.…”

Section: Comparison Of Travel Time Correction and Synthetic Waveformsmentioning

confidence: 99%

Effects of Near‐Surface Complexities on Differential Travel Times and Amplitude Ratios Between PP and Its Precursors

et al. 2020

View full text Add to dashboard Cite

The characteristics of mantle discontinuities at depths of 410 and 660 km are important to study the mantle dynamics. With the advantage of global samplings, the differential travel times and the amplitude ratios of PP and its precursors (PdP) have been extensively used to estimate the topography and the impedance contrast of mantle discontinuities. According to previous studies, effects of large‐scale structures on the PP phase cannot be neglected. Theoretically, the complex near‐surface structure, including ocean layer and crustal heterogeneity, may complicate the PP phase. It is necessary to assess the uncertainties of waveform by taking into account the near‐surface complexities. Through the usage of an efficient algorithm for constructing synthetic seismograms, the effects of near‐surface structure on the differential travel times and the amplitude ratios between the PP and PdP are explored. We demonstrate that the crustal structure mainly affects PP‐PdP differential travel time with minor effects on the amplitude, while the ocean depth governs PP/PdP amplitude ratio rather than the travel time. Through incorporating the crust model, the anomalies of PP‐PdP travel time and PdP/PP amplitude ratio are globally mapped. A clear continent‐ocean pattern was observed in the measurements of differential times and amplitude ratios. Moreover, time shift caused by the near‐surface complexities may be wrongly attributed to the topography of mantle discontinuity and our tests show that the offset could be up to 15 km, which should be taken into account in future PP precursor studies.

show abstract

“…Plume anomalies are in general much smaller in lateral extent compared to slab anomalies, therefore, they are less well resolved due to limited spacial resolution in this study. In addition, linearized velocity corrections may have an impact (Koroni et al., 2019; Koroni & Trampert, 2016), therefore, we do not attempt to interpret weak plume anomalies at a global scale but only focus on the most prominent anomalies. The only significant plume‐like signature in the discontinuity models regardless of wave speed corrections is located south of Hess Rise.…”

Section: Resultsmentioning

confidence: 99%

Stagnant Slabs and Their Return Flows From Finite‐Frequency Tomography of the 410‐km and 660‐km Discontinuities

Guo

Zhou

2021

JGR Solid Earth

View full text Add to dashboard Cite

The movement of surface tectonic plates is generally considered to be driven by the pulling force associated with slab subduction (Forsyth & Uyeda, 1975). Upwellings at mid-ocean ridges are passive return flows in the shallow mantle in response to subduction at convergent plate boundaries. For example, seismic anomalies beneath the East Pacific Rise spreading centers are mostly confined in the uppermost 250 km (Webb & Forsyth, 1998). Subduction-driven convection has been well studied in the upper mantle while convective mass exchange in the mid mantle remains less clear. The mantle transition zone (MTZ) between the upper mantle and the lower mantle is bounded by two seismic discontinuities associated with pressure-induced mineral phase transitions, one from olivine to wadsleyite at about 410 km depth and a second one from ringwoodite to bridgmanite and ferropericlase at about 660 km depth (Anderson, 1967;Ringwood, 1969). The 660-km discontinuity is generally considered a possible barrier for whole mantle convection due to its negative Clapeyron slope (e.g., U. Christensen, 1995;Ringwood, 1994;Wada & King, 2015). In contrast, the Clapeyron slope of the 410-km discontinuity is positive. This predicts an anti-correlation between depth perturbations of the 410-km and the 660-km discontinuities for purely thermal anomalies in the MTZ (Bina

show abstract

Sensitivity Kernels of PP Precursor Traveltimes and Their Limitations for Imaging Topography of Discontinuities

Cited by 9 publications

References 53 publications

Analysis of core-mantle boundary seismic waves using full\-waveform modelling and adjoint methods

Analysis of core-mantle boundary seismic waves using full\-waveform modelling and adjoint methods

Effects of Near‐Surface Complexities on Differential Travel Times and Amplitude Ratios Between PP and Its Precursors

Stagnant Slabs and Their Return Flows From Finite‐Frequency Tomography of the 410‐km and 660‐km Discontinuities

Contact Info

Product

Resources

About