Earthquake source parameter estimation using synthetic waveform modelling

Fault plane solutions and focal depths for three crustal events occurring in the Himalayan collision zone have been obtained using synthetic waveform modelling. Two crustal events with their epicenters in the Tibetan plateau show large component of normal faulting with east-west trading T-axes. The third event with It’s epicenter north of Main Boundary Thrust (MBT) shows reverse faulting with the nodal planes paralleling the local structural trend. All the three crustal events studied have occurred at shallow focal depths of less than 15 km. The Inferred source parameters of these events are discussed In the light of active tectonics of the region.

The Signature and Elimination of Sediment Reverberations on Submarine Receiver Functions: Imaging the Lithosphere of a Normal Ocean

<p>While the receiver function technique has been successfully applied to high-resolution imaging of sharp discontinuities within and across the lithosphere, it has been shown, however, that it suffers from severe limitations when applied to seafloor seismic recordings. This is because the water and sediment layer could strongly influence the receiver function traces, making detection and interpretation of crust and mantle layering difficult. This effect is often referred to as the singing phenomena in marine environments. Here, we show how one can silence this singing effect. We demonstrate, using analytical and synthetic waveform modeling, that this singing effect can be reversed using dereverberation filters tuned to match the elastic property of each layer. We apply the filter approach to high-quality earthquake records collected from the NoMelt seismic array deployed on normal, mature (~70 Ma) Pacific seafloor. An appropriate filter designed using the elastic properties of the underlying sediments, and obtained from prior studies, greatly improves the detection of Ps conversions generated from the moho (~8.6 km) and from a sharp discontinuity (<~ 5 km) across the lithosphere-asthenosphere transition (~72 km). Sensitivity tests show that the filter is robust to small errors in the sediment properties. Our analysis suggests that appropriately filtering out the sediment reverberations from ocean seismic data could make inferences on subsurface structure more robust. We expect that this study will enable high-resolution receiver function imaging of the base of the oceanic plate across a growing fleet of ocean bottom seismic arrays being deployed in the global oceans.</p>

Computer-assisted beat-pattern analysis and the flagellar waveforms of bovine spermatozoa

Obstructed by hurdles in information extraction, handling and processing, computer-assisted sperm analysis systems have typically not considered in detail the complex flagellar waveforms of spermatozoa, despite their defining role in cell motility. Recent developments in imaging techniques and data processing have produced significantly improved methods of waveform digitization. Here, we use these improvements to demonstrate that near-complete flagellar capture is realizable on the scale of hundreds of cells, and, further, that meaningful statistical comparisons of flagellar waveforms may be readily performed with widely available tools. Representing the advent of high-fidelity computer-assisted beat-pattern analysis, we show how such a statistical approach can distinguish between samples using complex flagellar beating patterns rather than crude summary statistics. Dimensionality-reduction techniques applied to entire samples also reveal qualitatively distinct components of the beat, and a novel data-driven methodology for the generation of representative synthetic waveform data is proposed.

Computer-assisted beat-pattern analysis and the flagellar waveforms of bovine spermatozoa

Plagued by hurdles in information extraction, handling, and processing, computer-assisted sperm analysis (CASA) systems have typically neglected the complex flagellar waveforms of spermatozoa, despite their defining role in cell motility. Recent developments in imaging techniques and data processing have produced significantly-improved methods of waveform digitisation. Here, we utilise these improvements to demonstrate that near-complete flagellar capture is realisable on the scale of hundreds of cells, and, further, that meaningful statistical comparisons of flagellar waveforms may be readily performed with widely-available tools. Representing the advent of high-fidelity computer-assisted beat-pattern analysis (CABA), we show how such a statistical approach can distinguish between samples using complex flagellar beating patterns rather than crude summary statistics. Dimensionality-reduction techniques applied to entire samples also reveal qualitatively-distinct components of the beat, and a novel data-driven methodology for the generation of representative synthetic waveform data is proposed.

Optimal mode decomposition for unsteady flows

A new method, herein referred to as optimal mode decomposition (OMD), of finding a linear model to describe the evolution of a fluid flow is presented. The method estimates the linear dynamics of a high-dimensional system which is first projected onto a subspace of a user-defined fixed rank. An iterative procedure is used to find the optimal combination of linear model and subspace that minimizes the system residual error. The OMD method is shown to be a generalization of dynamic mode decomposition (DMD), in which the subspace is not optimized but rather fixed to be the proper orthogonal decomposition (POD) modes. Furthermore, OMD is shown to provide an approximation to the Koopman modes and eigenvalues of the underlying system. A comparison between OMD and DMD is made using both a synthetic waveform and an experimental data set. The OMD technique is shown to have lower residual errors than DMD and is shown on a synthetic waveform to provide more accurate estimates of the system eigenvalues. This new method can be used with experimental and numerical data to calculate the ‘optimal’ low-order model with a user-defined rank that best captures the system dynamics of unsteady and turbulent flows.

Variability of ground motions in southern California—data from the 1995 to 1996 Ridgecrest sequence

Seismograms from the 1995 to 1996 Ridgecrest, California, earthquake sequence, recorded by the TriNet digital seismic network, provide high-quality waveforms from sites throughout southern California, including sites in markedly heterogeneous areas like the Los Angeles area sedimentary basins. Synthetic seismograms calculated by the reflectivity method with various 1D models are used as a baseline to measure the variability of amplitudes throughout southern California. Regardless of the model used, there is greater variability in the amplitudes from basin site records than from rock site records. Rock, soil, and basin sites are all rather insensitive to radiation pattern nodes at the three frequency bands investigated: 0.1 to 0.2 Hz, 0.2 to 0.4 Hz, and 0.4 to 0.8 Hz. This complicates the analysis because the nodes create singularity points in the distribution of ratios of observed and synthetic amplitudes. When stations near nodal planes are removed, the surface waves observed at most rock sites have peak amplitudes within a factor of 2 of synthetic waveform amplitudes. Peak amplitude of the surface waves observed at the soil and basin stations are more variable, with the bulk of the distribution of data/synthetic amplitude ratios less than 3 and a few outliers greater than 5. These outliers occur at the higher frequency bands. Soil and basin sites are also more often larger than the synthetics (higher median values). Most outliers can be explained by applying a water level of 50% to the radiation pattern. This reduces the scatter in the distributions to about the same extent as removing data within 10° of nodes. Thus, most of the outliers are sites that are insensitive to the nodes, not sites that are larger than the overall data distribution.