[1] Anomalous boundary layer structure at the core-mantle boundary (CMB) is investigated using a global set of broadband SKS and SPdKS waves from permanent and portable broadband seismometer arrays. SPdKS is an SKS wave that intersects the CMB at the critical angle for ScP, thus initiating a diffracted P wave (Pdiff) along the CMB at the core entry and exit locations. The waveshape and timing o...

[1] Between 105–115 degrees, the SKS waveform is complicated by the formation of SPdKS, a wave that has segments of P diffraction along the core mantle boundary. While previous studies have primarily focused on the moveout of SPdKS from SKS, we analyze the concomitant reduction of the SKS amplitude. Long-period SKKS/SKS amplitude ratios present a coherent global pattern. SKKS/ SKS is relatively...

[1] We collected a new data set of 1354 broadband SPdKS waveforms sampling the western Pacific Ocean region. These data indicate that multiple ultralow-velocity zones (ULVZs) exist in this region. We compared these data to 2.5-D synthetic seismograms computed with the PSVaxi method for a suite of 517 ULVZ models. The region beneath the North and South Philippine Sea shows no evidence for ULVZ p...

Qualitative and quantitative analysis of seismic waveforms sensitive to the core–mantle boundary (CMB) region reveal presence ultralow-velocity zones (ULVZs) that have a strong decrease in compressional (P) shear (S) wave velocity, an increase density within thin structures. However, understanding their physical origin relation other large-scale structures lowermost mantle are limited due incom...

The locations of ultralow-velocity zones (ULVZs) at the core-mantle boundary (CMB) have been linked to a variety features including hot spot volcanoes and large low-velocity province (LLVP) boundaries, yet only small portion CMB region has probed for ULVZ existence. Here we present new map lower mantle heterogeneity using global collection highly anomalous SPdKS recordings based on dataset more...

a r t i c l e i n f o Some regions of the Earth's lowermost mantle exhibit anomalous seismic properties within a thin zone, less than tens of kilometers in thickness, that directly overlies the core-mantle boundary (CMB). These regions have been dubbed Ultra-Low Velocity Zones (ULVZs) due to their greater than 10% drop in seismic velocities. High resolution seismic array studies have found smal...

Recent studies of the core-mantle boundary (CMB) have revealed some very anomalous tructures interpreted in terms of ultra low velocity zones (ULVZ). However, there remains considerable uncertainties about their physical descriptions or even if they occur above or below the CMB. They have only been detected in isolated situations using rather special techniques; these includes: distortions in S...