Transmission and Reflection of Strongly Nonlinear SolitaryWaves at Granular Interfaces

The interaction of a solitary wave with an interface formed by two strongly nonlinear noncohesive granular lattices displays rich behavior, characterized by the breakdown of continuum equations of motion in the vicinity of the interface. By treating the solitary wave as a quasiparticle with an effective mass, we construct an intuitive (energy- and linear-momentum-conserving) discrete model to predict the amplitudes of the transmitted solitary waves generated when an incident solitary-wave front, parallel to the interface, moves from a denser to a lighter granular hexagonal lattice. Our findings are corroborated with simulations. We then successfully extend this model to oblique interfaces, where we find that the angle of refraction and reflection of a solitary wave follows, below a critical value, an analogue of Snell?s law in which the solitary-wave speed replaces the speed of sound, which is zero in the sonic vacuum.Fil: Tichler, A. M.. Universiteit Leide. Instituut-Lorentz for Theoretical Physics; Holanda; Shell Global Solutions International; Holanda;Fil: Gomez, Leopoldo Raimundo. Universidad Nacional del Sur; Consejo Nacional de Invest Cientifícas y Tecnicas. Centro Cientifico Tecnológico - CONICET - Bahia Blanca. Instituto de Fisica del Sur; Argentina;Fil: Upadhyaya, N.. Universiteit Leide. Instituut-Lorentz for Theoretical Physics; Holanda;Fil: Campman, X. Shell Global Solutions International; Holanda;Fil: Nesterenko, V. F.. University of California. Jacobs School of Engineering; Estados Unidos de América;Fil: Vitelli, V.. Universiteit Leide. Instituut-Lorentz for Theoretical Physics; Holanda

Capturing spatial variability in the regional Ground Motion Model of Groningen, the Netherlands

Long-term exploration of the Groningen gas field in the Netherlands led to induced seismicity. Over the past nine years, an increasingly sophisticated Ground Motion Model (GMM) has been developed to assess the site response and the related seismic hazard. The GMM output strongly depends on the shear-wave velocity (VS), among other input parameters. To date, VS model data from soil profiles (Kruiver et al., Bulletin of Earthquake Engineering, 15(9): 3555–3580, 2017; Netherlands Journal of Geosciences, 96(5): s215–s233, 2017) have been used in the GMM. Recently, new VS profiles above the Groningen gas field were constructed using ambient noise surface wave tomography. These so-called field VS data, even though spatially limited, provide an independent source of VS to check whether the level of spatial variability in the GMM is sufficient. Here, we compared amplification factors (AF) for two sites (Borgsweer and Loppersum) calculated with the model VS and the field VS (Chmiel et al., Geophysical Journal International, 218(3), 1781–1795, 2019 and new data). Our AF results over periods relevant for seismic risk (0.01–1.0 s) show that model and field VS profiles agree within the uncertainty range generally accepted in geo-engineering. In addition, we compared modelled spectral accelerations using either field VS or model VS in Loppersum to the recordings of an earthquake that occurred during the monitoring period (ML 3.4 Zeerijp on 8 January 2018). The modelled spectral accelerations at the surface for both field VS and model VS are coherent with the earthquake data for the resonance periods representative of most buildings in Groningen (T = 0.2 and 0.3 s). These results confirm that the currently used VS model in the GMM captures spatial variability in the site response and represents reliable input for the site response calculations

Dissipative Chaos in Semiconductor Superlattices

We consider the motion of ballistic electrons in a miniband of a semiconductor superlattice (SSL) under the influence of an external, time-periodic electric field. We use the semi-classical balance-equation approach which incorporates elastic and inelastic scattering (as dissipation) and the self-consistent field generated by the electron motion. The coupling of electrons in the miniband to the self-consistent field produces a cooperative nonlinear oscillatory mode which, when interacting with the oscillatory external field and the intrinsic Bloch-type oscillatory mode, can lead to complicated dynamics, including dissipative chaos. For a range of values of the dissipation parameters we determine the regions in the amplitude-frequency plane of the external field in which chaos can occur. Our results suggest that for terahertz external fields of the amplitudes achieved by present-day free electron lasers, chaos may be observable in SSLs. We clarify the nature of this novel nonlinear dynamics in the superlattice-external field system by exploring analogies to the Dicke model of an ensemble of two-level atoms coupled with a resonant cavity field and to Josephson junctions.Comment: 33 pages, 8 figure

Characteristics of seismic noise: Fundamental and higher mode energy observed in the northeast of the Netherlands

We study seismic noise recorded in the northeast of the Netherlands by beamforming and by using empirical Green’s functions obtained by seismic interferometry. From beamforming we found differences in noise directions in different frequency bands. The main source region for primary microseisms (0.05–0.08 Hz) is in the west-northwest direction, while the secondary microseisms (0.1–0.14 Hz) have a west-southwest back azimuth. Furthermore, we observed a fast (~4 km/s) arrival corresponding to the Rayleigh wave overtone. This arrival is also in the secondary microseism band (between 0.15 and 0.2 Hz), but has a west-northwest back azimuth. Both arrivals in the secondary microseism band gain in strength during winter, as does the average wave height in the North Atlantic.We measured phase velocity dispersion curves from both beamforming and noise cross-correlations, as well as group velocity from the latter. These are then jointly inverted for an average 1D S-wave model. The results show how the combination of different methods leads to a more complete characterization of the propagation modes and an improved knowledge of the subsurface, especially as the group velocity measurements increase the upper frequency limit of analysis, providing valuable information of the shallowest subsurface

Pipe attrition acoustic locator (PAAL) from multi-mode dispersion analysis

Multi-mode dispersion imaging shows that pure dispersion-free torsional waves are reflected at a pipe end and flexural wave modes are suppressed. This effect can be used to locate and assess internal damage. The end reflection coefficient of this single propagating mode decreases with increasing wear. The pipe damage is located from the travel time of the torsional wave component reflected from the damage point

What can E&P learn from seismology and vice versa - Introduction Part 1

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Introduction Part II

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Extraction of P-wave reflections from microseisms

The last few years there has been a growing number of body-wave observations in noise records. In 1973 Vinnik conjectured that P-waves would even be the dominant wavemode, at epicentral distances of about 40 degrees and onwards from an oceanic source. At arrays far from offshore storms, surface waves induced by nearby storms would not mask the body-wave signal and hence primarily P-waves would be recorded. We measured at such an array in Egypt and indeed found a large proportion of P-waves. At the same time, a new methodology is under development to characterize the lithosphere below an array of receivers, without active sources or local earthquakes. Instead, transmitted waves are used which are caused by distant sources. These sources may either be transient or more stationary. With this new methodology, called seismic interferometry, reflection responses are extracted from the coda of transmissions. Combining the two developments it is clear that there is a large potential for obtaining reflection responses from low-frequency noise. A potential practical advantage of using noise instead of earthquake responses would be that an array only needs to be deployed for a few days or weeks instead of months, to gather enough illumination. We used a few days of continuous noise, recorded with an array in the Abu Gharadig basin, Egypt. We split up the record in three distinct frequency bands and in many small time windows. Using array techniques and taking advantage of all three-component recordings we could unravel the dominant wavemodes arriving in each time window and in each frequency band. The recorded wavemodes, and hence the noise sources, varied significantly per frequency band, and -to a lesser extent- per time window. Primarily P-waves were detected on the vertical component for two of the three frequency bands. For these frequency bands, we only selected the time windows with a favorable illumination. By subsequently applying seismic interferometry, we retrieved P-wave reflection responses and delineated reflectors in the crust, the Moho and possibly the Lehmann discontinuity.GeotechnologyCivil Engineering and Geoscience