Kilometer-scale structure on the core-mantle boundary at the source of the Hawaiian mantle plume

The lowermost mantle right above the core-mantle boundary is highly heterogeneous containing multiple poorly understood seismic features visible across a wide range of length scales. The smallest but most extreme heterogeneities yet observed are 'Ultra-Low Velocity Zones' (ULVZ), several of which have recently been linked to the base of mantle plumes. We exploit seismic shear waves that diffract along the core-mantle boundary to provide new insight into these enigmatic structures. We demonstrate that these waves have a strong frequency-dependent sensitivity to structure at different length scales above the core-mantle boundary. We measure a rare core-diffracted signal refracted by a ULVZ at the base of the Hawaiian mantle plume at unprecedentedly high frequencies. This signal shows remarkably longer time delays at higher compared to lower frequencies, indicating extreme internal variability within the Hawaiian ULVZ. Utilizing the latest computational advances in 3D synthetic waveform modeling, we are able to model this high frequency signal and constrain high-resolution structure on the scale of kilometers at the core-mantle boundary, for the first time. Results reveal that the lowermost part of the Hawaiian ULVZ is extremely reduced in shear wave velocity, by up to -40%. This new observation suggests a chemically distinct ULVZ with increasing iron content towards the core-mantle boundary, which has implications for Earth’s early evolutionary history and core-mantle interaction.

High-Order Multipole and Binary Love Number Universal Relations

Using a data set of approximately 2 million phenomenological equations of state consistent with observational constraints, we construct new equation-of-state-insensitive universal relations that exist between the multipolar tidal deformability parameters of neutron stars, Λl, for several high-order multipoles (l=5,6,7,8), and we consider finite-size effects of these high-order multipoles in waveform modeling. We also confirm the existence of a universal relation between the radius of the 1.4M⊙ NS, R1.4 and the reduced tidal parameter of the binary, Λ˜, and the chirp mass. We extend this relation to a large number of chirp masses and to the radii of isolated NSs of different mass M, RM. We find that there is an optimal value of M for every M such that the uncertainty in the estimate of RM is minimized when using the relation. We discuss the utility and implications of these relations for the upcoming LIGO O4 run and third-generation detectors.

HYDRODYNAMIC AND BOUSSINESQ WAVE MODELING FOR THE N219 AMPHIBIOUS AIRCRAFT SEAPLANE DOCK DEVELOPMENT PLAN IN PANJANG ISLAND

The flight test of N219 Amphibious aircraft will be targeted in 2003/2024. For flight tests, these aircraft need a seaplane dock. One of the potential locations for the seaplane dock is Panjang Island at Seribu Islands. This study aims to know the characteristic of hydrodynamic and wave conditions and to determine whether Panjang Island is suitable for the seaplane dock. This study uses a modeling method with MIKE 21 FM HD-SW module and MIKE 21 Boussinesq Wave (BW) module. The bathymetry data were obtained from the Indonesian Navy Hydrographic and Oceanographic Center (Pushidrosal), tide data is generated from Tide Model Driver (TMD), wave and wind data from ECMWF. The result of surface elevation validation between hydrodynamic modeling and TMD is 92%. During the west monsoon and spring conditions, the difference in the largest and lowest current velocity is quite large (0.018-0.199 m/s), on the other hand, when the tides are in neap conditions (0.008-0.144 m/s). Meanwhile, during the east monsoon and spring conditions, the difference in the largest and lowest current velocities is quite large (0.02-0.193 m/s), on the other hand, when the tides are in neap conditions (0.008-0.146 m/s). The maximum wave height resulting from the 50-year return period waveform modeling between 1.139 - 1.474 m. Meanwhile, the significant wave heights between 0.679 - 0.741 with a significant wave period of 13.45 seconds. In general, the current and wave conditions of the two locations are suitable for the construction of the seaplane dock, except that the dominant wave heights are still above the requirements.

Source Characterization for Two Small Earthquakes in Dartmouth, Nova Scotia, Canada: Pushing the Limit of Single Station

A pair of small earthquakes (MN 2.4 and 2.6, Earthquakes Canada) hit the city of Dartmouth, Nova Scotia, Canada, in early March 2020. The events were recorded by three seismic stations within 200 km, but only one station (HAL, <10 km) is close enough to offer high-quality broadband signals. In this study, we explore their source parameters using the nearest station through waveform modeling. A nearby quarry blast (MN 2.0) with known Global Positioning System coordinates is adopted as a reference for regional velocity model building and location calibration. We first build a half-space velocity model by estimating the P-S travel-time difference of the blast and determine the near-surface velocity through full-waveform modeling (i.e., comparing a set of synthetic waveforms with the observed blast). The velocity model is then used to evaluate the pair of earthquakes, in which waveform fitting and Rg/S amplitude ratios suggest source depths of ∼0.7 km. The epicenters of these two earthquakes are situated in a recently constructed commercial development. Lastly, single-station template matching finds no similar earthquakes near the hypocenters of the two events in the past decade and only three aftershocks in the following four months. Taking advantage of a ground-truth blast and waveform modeling, our study demonstrates the potential to construct a detailed regional velocity model and determine accurate earthquake source parameters in regions where only a single station is available.

Synthetic seismic modeling and inversion for the Oldoinyo Lengai volcanic complex.

<p>What is the effect of crustal melt accumulation on the seismic wavefield? Can we reproduce the dispersion, scattering and associated stress-anisotropy with modeling tools? By performing numerical experiments of seismic wave propagation in a synthetic and geodynamically-consistent volcanic system we can test our ability to model the seismic wavefield and to reconstruct the target “magma chamber”.</p><p>We built a synthetic volcano based on recent seismic observations at the Oldoinyo Lengai volcanic complex. The velocity model  is based on a geodynamic model that provides shear modulus, Poisson's ratio, and density. The isotropic P- and S-wave velocities can be computed directly from these parameters. To test a more realistic depth dependence, we introduced a reference 1D velocity model for Northern Tanzania and expanded this to 3D. Then, we inserted variations in the rock parameters mimicking a magma chamber and resolved it using the Fast Marching Travel Time tomography code.</p><p>To further our understanding, we also added  3D anisotropy and random velocity fluctuations to the system, acting both as synthetic input for future applications and testing of seismic techniques (e.g., shear wave splitting analysis) and as noise for the travel time tomography. For the waveform modeling we used the velocity-deviatoric stress-isotropic pressure equations together with perfectly matched layers. Also, we encoded the boundary condition between solid and air in this formulation. The 25 receivers with their real geographic locations were placed for inversion sensitivity analysis. In particular, the ability to reconstruct the magma chamber and the effect of anisotropy and velocity fluctuations at frequencies up to 5 Hz are evaluated. The results are compared with a parallel forward modeling and inversion of synthetic MT data. To confirm our results and as an additional test, we also employ adjoint tomography based on spectral element method to implement a forward waveform modeling and inversion using the tools provided in the SPECFEM3D_Cartesian package.</p><p>The results present a better idea of how to construct a realistic synthetic volcano in the future. By combining multiple seismic forward models and inversion approaches, this study yields insights into the sensitivity of the seismic wavefield to geodynamically-consistent volcanic structures.</p>