Temperature gradients in a low-shear-velocity province the lowermost mantle (D'' region) beneath central Pacific Ocean were inferred from observation of rapid S-wave velocity increase overlying decrease. These paired seismic discontinuities are attributed to phase change perovskite post-perovskite and then back as temperature increases with depth. Iron enrichment could explain occurrence several hundred kilometers above core-mantle boundary this warm, chemically distinct province. The double...

Anomalous boundary layer structure at the core‐mantle (CMB) is investigated using a global set of broadband SKS and SPdKS waves from permanent portable seismometer arrays. an wave that intersects CMB critical angle for ScP , thus initiating diffracted P ( diff ) along core entry exit locations. The waveshape timing data are analyzed relative to with some showing significant delays broadening. Broadband several hundred deep focus earthquakes were analyzed; retaining simple sources high...

Abstract We analyzed vertical component short‐period ScP waveforms for 26 earthquakes occurring in the Tonga‐Fiji trench recorded at Alice Springs Array central Australia. These show strong precursory and postcursory seismic arrivals consistent with ultralow‐velocity zone (ULVZ) layering beneath Coral Sea. used Viterbi sparse spike detection method to measure differential travel times amplitudes of postcursor arrival ScSP precursor SPcP relative . compare our measurements a database 340,000...

Abstract 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 than 58,000 radial component seismograms, which sample 56.9% by surface area. inference...

Abstract We investigate broadband SPdKS waveforms from earthquakes occurring beneath Myanmar. These paths sample the core–mantle boundary northwestern China. Waveform modeling shows that two ∼250 × 250 km wide ultra-low velocity zones (ULVZs) with a thickness of roughly 10 exist in region. The ULVZ models fitting these data have large S-wave drops 55% but relatively small 14% P-wave reductions. This is almost 4:1 S- to ratio and suggestive partial melt origin. ULVZs region Circum-Pacific...

Abstract Intermittent seismic discontinuities near 250–300 km depth beneath South America and the Pacific basin are detected with high‐resolution array methods that use SS PP precursors recorded at High Lava Plains Seismic Experiment EarthScope Transportable Array. The transformation of coesite to stishovite in an eclogite‐rich mantle composition produces a discontinuity 300 depth; lateral changes basalt fraction upper will thus produce intermittent discontinuity. sensitivity structure is...

Ultralow-velocity zones (ULVZs) are thin patches of material with strongly reduced seismic wave speeds situated on top the core–mantle boundary (CMB). A common phase used to detect ULVZs is SPdKS (SKPdS), an SKS a short diffracted P leg along CMB. Most previous efforts have examined ULVZ properties using 1-D waveform modelling approaches. We present results 2.5-D finite-difference algorithm PSVaxi allowing us better insight into structure and location. characterize waveforms based elastic...

Ultralow-velocity zones (ULVZs) at the core–mantle boundary (CMB) represent some of most preternatural features in Earth’s mantle. These likely contain partial melt, extremely high iron content ferropericlase, or combinations both. We analyzed a new collection 58,155 carefully processed and quality-controlled broadband recordings seismic phase SPdKS epicentral distance range from 106° to 115°. data sample 56.9% CMB by surface area. From these we searched for anomalous waveforms that are...

Geometric spreading of P n and S waves in a spherical Earth model is different than that classical headwaves frequency dependent.The behavior cannot be fully represented by frequency-independent power-law model, as commonly assumed.The lack an accurate representation geometric impedes our ability to characterize properties including anelasticity.We conduct numerical simulations quantify with constant mantle-lid velocities.Based on simulation results, we present new empirical...

We extended a high-order finite-difference scheme for the elastic SH-wave equation in axisymmetric media use on parallel computers with distributed memory architecture. Moreover, we derive an analytical description of implemented ring source and compare it quantitatively double couple source. The restriction to axisymmetry high performance PC networks allows computation synthetic seismograms at dominant periods down 2.5 s global mantle models. give our algorithm (SHaxi) its verification...

We collected a new data set of 1354 broadband SPdKS waveforms sampling the western Pacific Ocean region. These indicate that multiple ultralow‐velocity zones (ULVZs) exist in this compared these to 2.5‐D synthetic seismograms computed with PSVaxi method for suite 517 ULVZ models. The region beneath North and South Philippine Sea shows no evidence presence. Coral large which is approximately 700 × km lateral dimensions up 20 thick. Multiple small‐scale ULVZs 180 10 thick are inferred China...

Abstract We analyzed the resonance characteristics of a prominent natural arch in Canyonlands National Park, Mesa Arch, as measured from ambient seismic data. Evaluating spectral and polarization attributes, we distinguished first four resonant frequencies arch, 2.9, 6.0, 6.9, 8.5 Hz, well basic properties associated mode shapes. then affirmed experimental data using 3‐D numerical modal analysis, providing estimates material clarifying vibrational Monitoring over time, searched for shifts...

Abstract The natural modes of vibration bedrock landforms, as well the sources and effects stimulated resonance remain poorly understood. Here we show that seismic energy created by an induced earthquake artificial reservoir has spectral content coincident with a prominent rock bridge. We measured resonant frequencies Rainbow Bridge, Utah using data from two broadband seismometers placed on span, identified eight distinct vibrational between 1 6 Hz. A distant, produced local ground motion...

Summary We use an axisymmetric, spherical Earth finite difference algorithm to model SH-wave propagation through cross-sections of laterally varying lower mantle models beneath the Cocos Plate derived from recent data analyses. Synthetic seismograms with dominant periods as short 4 s are computed for several models: (1) a D″ reflector 264 km above core-mantle boundary S-wave velocity increases 0.9–2.6 per cent, based on localized structures 1-D double-array stacking method; (2) undulating...

The advent of large-scale cabled ocean observatories brought about the need to handle large amounts ocean-based data, continuously recorded at a high sampling rate over many years and made accessible in near-real time science community public. Ocean Networks Canada (ONC) commenced installing operating two regional on Canada’s Pacific Coast, VENUS inshore NEPTUNE offshore 2000s, later expanded include Atlantic Arctic 2010s. first data streams from instrument nodes started flowing February...

SUMMARY Ultra-low velocity zones (ULVZs) have been identified as regions of extremely low anomalies in the Earth's lowermost mantle using seismic observations from reflected, refracted and diffracted arrivals along side core–mantle boundary. Estimation ULVZ geometrical (i.e. shape size) elastic density) parameters with uncertainties is crucial understanding role ULVZs ongoing dynamic processes within mantle; however, these are still poorly known due to tradeoffs seismically resolved...

Using an unusually large earthquake near the big island of Hawaii, we study core mantle boundary (CMB) beneath north‐northeastern Pacific between Hawaii and North America. A dense sampling CMB is achieved using core‐reflected phase PcP recorded at a number high‐quality stations in America, including networks California, Oregon, Washington, Alaska, as well EarthScope's USArray stations. We apply adaptive stacking technique for optimal record alignment on specific phases (namely P )...

Abstract We analyzed 16,150 transverse component seismic recordings from 54 deep‐focus earthquakes in the South American and Caribbean regions recorded at broadband stations North America between 2005 2012. treated subgroups of within 3° radius geographical bins as arrays performed vespagram analysis. focused on S , ScS Scd arrivals collected data epicentral distance range 55° to 90°. In particular, we searched for D ″ discontinuity presence vespagrams a 25° by 35° (or 1520 2130 km) area...

Abstract Broadband USArray recordings of the 21 July 2007 western Brazil earthquake ( M w =6.0; depth = 633 km) include high‐amplitude signals about 40 s, 75 and 100 s after P wave arrival. They are consistent with S to conversions in mantle beneath northwestern South America. The signal at denoted as 1750 , has highest amplitude is formed 1,750 km based on slant‐stacking semblance analysis. Waveform modeling using axisymmetric, finite difference synthetics indicates that generated by a 10...

Abstract We analyzed new recordings of SPdKS seismic waveforms from a global set broadband seismograms and horizontal tiltmeters the Hi‐net array in Japan 26 earthquakes Central American region. The anomalous are consistent with presence at least three ultralow‐velocity zones (ULVZs), on core‐mantle boundary beneath northern Mexico southeastern United States. These ULVZs ring an area high wave speeds observed tomographic models that has long been associated past subduction. Waveform modeling...

Abstract Ultralow‐velocity zones (ULVZs) have been studied using a variety of seismic phases; however, their physical origin is still poorly understood. Short period ScP waveforms are extensively used to infer ULVZ properties because they may be sensitive all elastic moduli and thickness. However, additionally complicated by the effects path attenuation, coherent noise, source complexity. To address these complications, we developed hierarchical Bayesian inversion method that allows us...