Observations of high-frequency scattered waves using dense arrays at Teide Volcano

1997 ◽  
Vol 87 (6) ◽  
pp. 1637-1647
Author(s):  
E. Del Pezzo ◽  
M. La Rocca ◽  
J. Ibanez
Keyword(s):  
Random Distribution ◽  
Great Part ◽  
Apparent Velocity ◽  
Frequency Range ◽  
Small Aperture ◽  
Analysis Techniques ◽  
Correlated Arrivals ◽  
Seismic Coda ◽  
The Time Domain ◽  
Teide Volcano

Abstract A study of the seismic coda of seven small earthquakes recorded on the Teide Volcano-Canary Islands (Spain) was carried out using a temporary, small-aperture, 12-station, seismic array. The purpose was to measure backazimuth, apparent velocity and the type of waves that compose the coda in the frequency range 4 to 6 Hz. We used the zero-lag cross-correlation (ZLC) method to obtain the components of the wave vector and three-component analysis techniques based on the covariance matrix of the signal in the time domain to investigate the polarization properties of the signals. The results show that a great part of the coda signals in the analyzed frequency range are almost uncorrelated, while a low number of isolated correlated arrivals show an apparent slowness between 2 × 10−3 and 2.5 × 10−4 sec/m and an almost random distribution of backazimuths. The correlated arrivals have been interpreted as generated by strong scatterers, probably related to the presence, in the study area, of surface topography irregularities (the volcanic cone and the caldera rim). The wave type varies from pure S-type waves to mixed surface waves with some Rayleigh components.

Detection and source parameterization of small-energy fireball events in Western Alps with ground-based infrasonic arrays

2021 ◽  
Author(s):  
Giacomo Belli ◽  
Emanuele Pace ◽  
Emanuele Marchetti
Keyword(s):  
Western Alps ◽  
Apparent Velocity ◽  
Array Analysis ◽  
Small Energy ◽  
Small Aperture ◽  
Energy Estimation ◽  
Trajectory Reconstruction ◽  
Tnt Equivalent ◽  
Back Azimuth ◽  
Aperture Arrays

Summary We present infrasound signals generated by four fireball events occurred in Western Alps between 2016 and 2019 and that were recorded by small aperture arrays at source-to receiver distances < 300 km. Signals consist in a series of short-lived infrasonic arrivals that are closely spaced in time. Each arrival is identified as a cluster of detections with constant wave parameters (back-azimuth and apparent velocity), that change however from cluster to cluster. These arrivals are likely generated by multiple infrasonic sources (fragmentations or hypersonic flow) along the entry trajectory. We developed a method, based on 2D ray-tracing and on the independent optically determined time of the event, to locate the source position of the multiple arrivals from a single infrasonic array data and to reconstruct the 3D trajectory of a meteoroid in the Earth's atmosphere. The trajectories derived from infrasound array analysis are in excellent agreement with trajectories reconstructed from eyewitnesses reports for the four fireballs. Results suggest that the trajectory reconstruction is possible for meteoroid entries located up to ∼300 km from the array, with an accuracy that depends on the source-to-receiver distance and on the signal-to-noise level. We also estimate the energy of the four fireballs using three different empirical laws, based both on period and amplitude of recorded infrasonic signals, and discuss their applicability for the energy estimation of small energy fireball events ($\le 1{\rm{kt\,\,TNT\,\,equivalent}}$).

A waveform inversion technique for measuring elastic wave attenuation in cylindrical bars

Geophysics ◽  
1992 ◽  
Vol 57 (6) ◽  
pp. 854-859 ◽  
Author(s):  
Xiao Ming Tang
Keyword(s):  
Elastic Wave ◽  
Wave Attenuation ◽  
Waveform Inversion ◽  
Finite Size ◽  
Low Frequency ◽  
Frequency Range ◽  
Multiple Reflections ◽  
Low Frequencies ◽  
The Time Domain ◽  
Attenuation Values

A new technique for measuring elastic wave attenuation in the frequency range of 10–150 kHz consists of measuring low‐frequency waveforms using two cylindrical bars of the same material but of different lengths. The attenuation is obtained through two steps. In the first, the waveform measured within the shorter bar is propagated to the length of the longer bar, and the distortion of the waveform due to the dispersion effect of the cylindrical waveguide is compensated. The second step is the inversion for the attenuation or Q of the bar material by minimizing the difference between the waveform propagated from the shorter bar and the waveform measured within the longer bar. The waveform inversion is performed in the time domain, and the waveforms can be appropriately truncated to avoid multiple reflections due to the finite size of the (shorter) sample, allowing attenuation to be measured at long wavelengths or low frequencies. The frequency range in which this technique operates fills the gap between the resonant bar measurement (∼10 kHz) and ultrasonic measurement (∼100–1000 kHz). By using the technique, attenuation values in a PVC (a highly attenuative) material and in Sierra White granite were measured in the frequency range of 40–140 kHz. The obtained attenuation values for the two materials are found to be reliable and consistent.

Sensitivity Analysis for the Steady-State Response of Damped Linear Elastodynamic Systems Subject to Periodic Loads

1990 ◽  
Author(s):  
Daniel A. Tortorelli
Keyword(s):  
Steady State ◽  
Vibration Amplitude ◽  
Equations Of Motion ◽  
Steady State Response ◽  
Analysis Techniques ◽  
Direct Differentiation ◽  
State Response ◽  
Need To Evaluate ◽  
The Time Domain ◽  
General Response

Abstract Adjoint and direct differentiation methods are used to formulate design sensitivities for the steady-state response of damped linear elastodynamic systems that are subject to periodic loads. Variations of a general response functional are expressed in explicit form with respect to design field perturbations. Modal analysis techniques which uncouple the equations of motion are used to perform the analyses. In this way, it is possible to obtain closed form relations for the sensitivity expressions. This eliminates the need to evaluate the adjoint response and psuedo response (these responses are associated with the adjoint and direct differentiation sensitivity problems) over the time domain. The sensitivities need not be numerically integrated over time, thus they are quickly computed. The methodology is valid for problems with proportional as well as non-proportional damping. In an example problem, sensitivities of steady-state vibration amplitude of a crankshaft subject to engine firing loads are evaluated with respect to the stiffness, inertial, and damping parameters which define the shaft. Both the adjoint and direct differentiation methods are used to compute the sensitivities. Finite difference sensitivity approximations are also calculated to validate the explicit sensitivity results.

Observations of Loma Prieta aftershocks from a dense array in Sunnyvale, California

1991 ◽  
Vol 81 (5) ◽  
pp. 1900-1922
Author(s):  
Arthur Frankel ◽  
Susan Hough ◽  
Paul Friberg ◽  
Robert Busby
Keyword(s):  
Surface Waves ◽  
Body Waves ◽  
Love Waves ◽  
Apparent Velocity ◽  
Dense Array ◽  
S Wave ◽  
Small Aperture ◽  
Long Period ◽  
Santa Clara Valley ◽  
Loma Prieta

Abstract A small aperture (≈300 m), four-station array was deployed in Sunnyvale, California for 5 days to record aftershocks of the Loma Prieta earthquake of October 1989. The purpose of the array was to study the seismic response of the alluvium-filled Santa Clara Valley and the role of surface waves in the seismic shaking of sedimentary basins. Strong-motion records of the Loma Prieta mainshock indicate that surface waves produced the peak velocities and displacements at some sites in the Santa Clara Valley. We use the recordings from the dense array to determine the apparent velocity and azimuth of propagation for various arrivals in the seismograms of four aftershocks with magnitudes between 3.6 and 4.4. Apparent velocities are generally observed to decrease with increasing time after the S wave in the seismograms. Phases arriving less than about 8 sec after the S wave have apparent velocities comparable to the S wave and appear to be body waves multiply reflected under the receiver site or reflected by crustal interfaces. For times 10 to 30 sec after the direct S wave, we observe long-period (1 to 6 sec) arrivals with apparent velocities decreasing from 2.5 to 0.8 km / sec. We interpret these arrivals to be surface waves and conclude that these surface waves produce the long duration of shaking observed on the aftershock records. Much of the energy in the 40 sec after the S-wave is coming approximately from the direction of the source, although some arrivals have backazimuths as much as 60° different from the backazimuths to the epicenters. Two of the aftershocks show arrivals coming from 30 to 40° more easterly than the epicenters. This energy may have been scattered from outcrops along the southeastern edge of the basin. In contrast, the deepest aftershock studied (d = 17 km) displays later arrivals with backazimuths 30 to 40° more westerly than the epicenter. A distinct arrival for one of the aftershocks propagates from the southwest, possibly scattered from the western edge of the basin. Synthetic seismograms derived from a plane-layered crustal model do not produce the long-period Love waves observed in the waveforms of the ML 4.4 aftershock. These Love waves may be generated by the conversion of incident S waves or Rayleigh waves near the edge of the basin.

Estimation of Direction of Wavefront Propagation and Slowness Using Time Domain Wavenumber Analysis in Small-Size Dense Seismic Arrays

2012 ◽  
Vol 479-481 ◽  
pp. 1186-1189
Author(s):  
Ping Liu ◽  
Hua Ma ◽  
Xue Wei Zhang ◽  
Xin Yu Sun ◽  
Fei Cao
Keyword(s):  
Time Domain ◽  
Seismic Array ◽  
Apparent Velocity ◽  
Seismic Signals ◽  
Analysis Method ◽  
Seismic Arrays ◽  
Wavefront Propagation ◽  
Pass Through ◽  
The Time Domain ◽  
Dense Seismic Array

The time domain wavenumber analysis method can directly delay and align signals before the superposition of signals in the time domain. In this paper, estimating the direction of wavefront propagation and the slowness for seismic signals which pass through the small-size dense seismic array is described in detail. The earthquake recorder sample adopted from US Geological Survey Parkfield Dense Seismograph Array (UPSAR array) of the U.S is used for analyzing. The results indicate that, the direction of wavefront propagation cannot be determined rashly only by the connecting line of the earthquake epicenter to the seismic array. The accuracy of the apparent velocity and the direction of wavefront propagation calculated using vertical seismic recorders is higher in West-East direction and in North-South direction.

scholarly journals Ultra Wideband Coplanar Waveguide Antenna with an Improved Gain using a Frequency Selective Surfaces (FSS)

2019 ◽  
Vol 8 (9S) ◽  
pp. 145-149
Keyword(s):  
Time Domain ◽  
Coplanar Waveguide ◽  
Unit Cell ◽  
Ultra Wideband ◽  
Frequency Range ◽  
Rectangular Slot ◽  
Improved Performance ◽  
Set Up ◽  
The Time Domain ◽  
Uwb Applications

In this article, an ultra-wideband FSS reflector has been proposed to enhance the gain of a CPW antenna for UWB applications. A CPW fed antenna having dimensions of 38mm×38mm×1.605mm and FSS unit cell having dimensions 14mm × 14mm × 1.605 mm are presented in the paper. A rectangular slot and stubs are interleaved at the outer edges of the patch for achieving desired characteristics of an ultra-wideband for the frequency range of 3.39 GHz to 12.9 GHz. Simulation results carried out using the CST microwave 2016 version in the time domain are presented for the proposed antenna. An FSS unit cell designed and simulated using periodic boundary conditions and floquet ports is presented. The combined setup of an array of FSS reflector behind the antenna has been simulated in the time domain. This set up shows an improved performance in terms of antenna’s gain. A maximum and minimum gain of 8.14 dB and 4.98 dB has been observed with the presence of FSS reflector behind the coplanar waveguide antenna. A significant improvement of 2.9 dB has been observed over the entire band of antenna’s operation

Site Specific Wave Characterisation for Marine Energy Applications

2010 ◽  
Author(s):  
Thomas Davey ◽  
Vengatesan Venugopal ◽  
David M. Ingram ◽  
Helen C. M. Smith
Keyword(s):  
Test Site ◽  
Resource Assessment ◽  
Energy Industry ◽  
Sea State ◽  
Shetland Islands ◽  
Analysis Techniques ◽  
Energy Applications ◽  
The North ◽  
Marine Energy ◽  
The Time Domain

In order to conduct effective resource assessment for the marine energy industry the applied analysis techniques must be consistent and practicable. It is therefore important to establish the parameters of interest when characterising a sea state. A number of parameters for describing the shape of individual waves in the time-domain are examined. These parameters are used to characterise wave records from three selected sites: The European Marine Energy Centre (EMEC), UK; The Wave Hub test site, UK and the North Alwyn platform east of the Shetland Islands.

A low-frequency passive seismic array experiment over an onshore oil field in Abu Dhabi, United Arab Emirates

Geophysics ◽  
2013 ◽  
Vol 78 (4) ◽  
pp. B159-B176 ◽  
Author(s):  
Mohammed Y. Ali ◽  
Braham Barkat ◽  
Karl A. Berteussen ◽  
James Small
Keyword(s):  
United Arab Emirates ◽  
Low Frequency ◽  
Oil Field ◽  
Body Waves ◽  
Anthropogenic Sources ◽  
Abu Dhabi ◽  
Apparent Velocity ◽  
Frequency Range ◽  
Passive Seismic ◽  
Oil Plant

A low-frequency passive seismic experiment using an array of 49 3C broadband seismometers was conducted over an onshore oil field in the emirate of Abu Dhabi in the United Arab Emirates. The aim of the experiment was to understand the characteristics and origins of the microseism (0.15–0.4 Hz) and microtremor (about 1–6 Hz) signals recorded, the latter having been reported as being a hydrocarbon indicator above several reservoirs in the region. The recorded array data were analyzed for their polarization, apparent velocities, and wavefront azimuths using various techniques, including spectral and time-frequency analyses, particle motion, H/V spectral ratios, and high-resolution frequency-wavenumber (f-k) analyses. In the frequency range of 0.15–0.4 Hz, the dominant feature observed consisted of double-frequency microseisms peaks generated by the nonlinear interactions of ocean waves with the shoreline along the coasts of the Arabian Sea and the Arabian Gulf. The f-k analyses confirmed that microtremor events in the frequency range of 2–3 Hz have an azimuth pointing toward a major oil pipeline and oil plant facilities to the west–southwest of the study area, as well as a motorway to the southeast. This would indicate that the microtremor events are probably caused by local sources, including the continuous movement of oil through the pipeline, the noise from oil plant facilities, as well as nearby traffic noise. This interpretation was confirmed by the polarization analysis performed on the data. The data also indicated that no clear correlation exists between the microtremor signal and local meteorological conditions. Although some body waves with an infinite apparent velocity generated by earthquakes were recorded, no other body waves that could have possibly been generated by hydrocarbon reservoirs were observed using the analyses techniques used in this study. Therefore, our results indicated that for the site under investigation, the microseism and the microtremor signals detected could not be related to the presence of hydrocarbon accumulations in the subsurface, but instead they may be attributed to local anthropogenic sources.

Sensitivity Analysis for the Steady-State Response of Damped Linear Elastodynamic Systems Subject to Periodic Loads

1993 ◽  
Vol 115 (4) ◽  
pp. 822-828 ◽  
Author(s):  
D. A. Tortorelli
Keyword(s):  
Steady State ◽  
Vibration Amplitude ◽  
Equations Of Motion ◽  
Steady State Response ◽  
Analysis Techniques ◽  
Direct Differentiation ◽  
State Response ◽  
Nonproportional Damping ◽  
The Time Domain ◽  
General Response

Adjoint and direct differentiation methods are used to formulate design sensitivities for the steady-state response of damped linear elastodynamic systems that are subject to period loads. Variations of a general response functional are expressed in explicit form with respect to design field perturbations. Modal analysis techniques which uncouple the equations of motion are used to perform the analyses. In this way, it is possible to obtain closed form relations for the sensitivity expressions. This eliminates the need to separately evaluate the adjoint response and psuedo response (these responses are associated with the adjoint and direct differentiation sensitivity problems) over the time domain. The sensitivities need not be numerically integrated over time, thus they are quickly computed. The methodology is valid for problems with proportional as well as nonproportional damping. In an example problem, sensitivities of steady-state vibration amplitude of a crankshaft subject to engine firing loads are evaluated with respect to the stiffness, inertial, and damping parameters which define the shaft. Both the adjoint and direct differentiation methods are used to compute the sensitivities. Finite difference sensitivity approximations are also calculated to validate the explicit sensitivity results.

Installation and Performance of the Albuquerque Seismological Laboratory Small-Aperture Posthole Array

2020 ◽  
Vol 91 (4) ◽  
pp. 2425-2437
Author(s):  
Robert E. Anthony ◽  
Adam T. Ringler ◽  
David C. Wilson ◽  
J. Zebulon Maharrey ◽  
Gary Gyure ◽  
...  
Keyword(s):  
Real Time ◽  
P Wave ◽  
Apparent Velocity ◽  
Fiber Optic Gyroscope ◽  
Time Data ◽  
Original Design ◽  
Small Aperture ◽  
Low Frequencies ◽  
Deep Earth Structure ◽  
And Performance

Abstract The Global Seismographic Network (GSN) has been used extensively by seismologists to characterize large earthquakes and image deep earth structure. Although the network’s original design goals have been met, the seismological community has suggested that the incorporation of small-aperture seismic arrays at select sites may improve performance of the network and enable new observations. As a pilot study for this concept, we have created a 500 m aperture, nine-element broadband seismic array around the GSN station ANMO (Albuquerque, New Mexico) at the U.S. Geological Survey Albuquerque Seismological Laboratory (ASL). The array was formed by supplementing the secondary borehole seismometer (90 m depth) at ANMO with eight additional 2.6 m posthole sites. Each station’s seismometer was oriented using a fiber optic gyroscope to within 2.0° of north. Data quality, particularly on the vertical components, is excellent with median power levels closely tracking the secondary sensor at ANMO at frequencies lower than 1 Hz. Horizontal component data are more variable at low frequencies (<0.02  Hz), with the type of installation and local geography appearing to strongly influence the amount of tilt-induced noise. Throughout the article, we pose several fundamental questions related to the variability and precision of seismic wavefield measurements that we seek to address with data from this array. In addition, we calculate the array response and show a few examples of using the array to obtain back azimuths of a local event and a continuous narrowband noise source. The apparent velocity of the event across the array is then used to infer the local P-wave velocity at the ASL. Near-real-time data collected from the array along with collocated meteorological, magnetic, and infrasound data are freely available in near-real time from the Incorporated Research Institutions for Seismology Data Management Center.

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