Effects of Heterogeneities on the Propagation, Scattering and Attenuation of Seismic Waves and the Characterization of Seismic Source.

1984 ◽  
Author(s):  
K. Aki ◽  
V. F. Cormier ◽  
M. N. Toksoz
Keyword(s):  
Seismic Waves ◽  
Seismic Source

The Qaanaaq airburst as an analog of seismic source in extraterrestrial atmospheres: seismic and infrasound investigation

2020 ◽  
Author(s):  
Foivos Karakostas ◽  
Nicholas Schmerr ◽  
Samuel Hop Bailey ◽  
Daniella Dellagiustina ◽  
Namrah Habib ◽  
...  
Keyword(s):  
Shock Wave ◽  
Wave Propagation ◽  
Solar System ◽  
Seismic Waves ◽  
Seismic Source ◽  
Shock Wave Propagation ◽  
Tectonic Activity ◽  
Seismic Sources ◽  
The Earth

<p>On July 25, 2018, a meteoroid-associated airburst occurred near the Qaanaaq town, in Greenland, at approximately 22:00 UTC (20:00 local time). The event generated seismic waves that were recorded by two stations of the Danish Seismological Network (TULEG and NEEM) and the bolide trajectory was consequently calculated by the NASA Center for Near-Earth Object Studies (CNEOS). The total impact energy, calculated by CNEOS was 2.1 kT of TNT and the brightest point on its trajectory corresponds to an altitude of around 43 km, at a distance of about 50 km S of the Qaanaaq town and 50 km N of the TULEG station and the Thule Air Force Base [1].</p> <p>An airburst occurring over the icy surface of Greenland is a rare terrestrial analog for regions of the Solar System, where both an atmosphere and an icy surface exist. In the past, a variety of works had indicated the presence of ice on Titan, the biggest moon of Saturn (e.g. [2] and more recently [3]) and more precisely, the icy composition of mountains which are formed by tectonic activity [4]. Titan has a relatively thick atmosphere, compared to those of other moons in the Solar System, composed mainly (94%) of nitrogen [5]. The characterization of atmospheric meteoroid-associated seismic sources for Titan has a particular interest, as it is found that, contrary to other moons of the solar system, the presence of craters on its surface is extremely low (only about 0.4% according to [3]). The reason for this low cratering of the surface is the presence of the thick atmosphere, into which many of the meteoroids are entirely ablated into dust. Therefore, a methodology for the characterization of airbursts as seismic sources and the modeling of the associated generated seismic waves is necessary for a future seismic experiment, as any recorded signal will either be a direct atmospheric wave (nonlinear shock wave, or linear acoustic wave) or a seismic wave generated through the coupling of the atmospheric and solid/ice part.<br /> <br />In the present study, our aim is to perform a seismic investigation of the Greenland ice shell with the use of the airburst-associated seismic source. The performed tasks into which this effort has been divided, include the application of a technique which approaches the bolide as an atmospheric seismic source, the calculation of the distance of shock wave propagation in the atmosphere, the description of the mechanism of generation of the seismic waves in the atmosphere and the solid-icy part.</p> <p>When the bolides enter the atmosphere of the Earth or that of any other body, shock waves are generated along the trajectory of the meteoroid. These waves are characterized by the overpressure that they generate, which create a clear pressure discontinuity in the atmosphere, referred to as the nonlinear part of the shock wave propagation. The propagation distance of this nonlinear wave is associated to the ratio of the meteoroid speed to the ambient sound speed, also known as the Mach number, as well as the physical diameter of the meteoroid. In this work, we compute this distance for the Earth case and for the known trajectory of the detected and examined bolide [1][6].</p> <p>The methodology developed in this study can serve the seismic investigation of structures covered by ice on planets or planetary bodies with a relatively thick atmosphere, where airbursts can occur due to the friction of the meteoroid with the ambient atmospheric material. An ideal example of this case are the icy mountains of Titan, which are known to be formed by tectonic activity on the Saturn’s moon [4]. The future Dragonfly mission to Titan will carry a seismometer as part of the DraGMet (Dragonfly Geophysics and Meteorology Package) payload [7]. Even if the primary goal of the mission is the characterization of the regolith properties, an eventual airburst and collection of seismic data near these mountainous icy structures, will be a great opportunity to investigate, through the identification of the associated waves and thus the investigation of the coupled seismic waves, the properties of this icy cover, its depth and composition.</p> <p>References: [1] https://cneos.jpl.nasa.gov/fireballs/ [2] Sohl, F. et al. (1995) Icarus, 115, 278–294 [3] Lopes R.M.C. et al. (2019) Nat Astron, [4] Radebaugh J. et al. (2007) Icarus, 192, 77-91, [5] Niemann H.B. et al. (2005) Nature, 438, 779–784 [6] Schmerr, N. et al. (2018) Abstract P21E-3406, AGU Fall Meeting 2018, Washington DC [7] Lorenz R. et al. (2018) Johns Hop- kins APL Technical Digest, 34, 3</p>

Local characterization of free-field ground motion and effects of wave passage

1980 ◽  
Vol 70 (6) ◽  
pp. 2229-2244
Author(s):  
J. E. Luco ◽  
D. A. Sotiropoulos
Keyword(s):  
Ground Motion ◽  
Seismic Waves ◽  
Plane Waves ◽  
Free Field ◽  
Seismic Source ◽  
Phase Velocities ◽  
Propagation Medium ◽  
Local Characterization ◽  
Wave Passage

abstract A simple model of the seismic source and of the propagation medium is used to obtain a local representation of the free-field ground motion in terms of a small number of equivalent dispersive plane waves. Numerical values for the equivalent phase velocities entering in the representation are presented for different epicentral distances and source depths. Based on the local characterization of the free-field motion, estimates of the magnitude of the effects of nonvertically incident seismic waves on the response of foundations and structures are presented.

scholarly journals On the point-source approximation of earthquake dynamics

2014 ◽  
Vol 57 (3) ◽  
Author(s):  
Andrea Bizzarri
Keyword(s):  
Point Source ◽  
Seismic Waves ◽  
Single Point ◽  
Seismic Source ◽  
Transition Process ◽  
Point Sources ◽  
Multiple Point ◽  
Earthquake Dynamics ◽  
Planar Fault ◽  
Source Models

<p>The focus on the present study is on the point-source approximation of a seismic source. First, we compare the synthetic motions on the free surface resulting from different analytical evolutions of the seismic source (the Gabor signal (G), the Bouchon ramp (B), the Cotton and Campillo ramp (CC), the Yoffe function (Y) and the Liu and Archuleta function (LA)). Our numerical experiments indicate that the CC and the Y functions produce synthetics with larger oscillations and correspondingly they have a higher frequency content. Moreover, the CC and the Y functions tend to produce higher peaks in the ground velocity (roughly of a factor of two). We have also found that the falloff at high frequencies is quite different: it roughly follows ω<span><sup>−2</sup></span> in the case of G and LA functions, it decays more faster than ω<span><sup>−2</sup></span> for the B function, while it is slow than ω<span><sup>−1</sup></span> for both the CC and the Y solutions. Then we perform a comparison of seismic waves resulting from 3-D extended ruptures (both supershear and subshear) obeying to different governing laws against those from a single point-source having the same features. It is shown that the point-source models tend to overestimate the ground motions and that they completely miss the Mach fronts emerging from the supershear transition process. When we compare the extended fault solutions against a multiple point-sources model the agreement becomes more significant, although relevant discrepancies still persist. Our results confirm that, and more importantly quantify how, the point-source approximation is unable to adequately describe the radiation emitted during a real world earthquake, even in the most idealized case of planar fault with homogeneous properties and embedded in a homogeneous, perfectly elastic medium.</p>

Fault Source Characterization of Probabilistic Seismic Hazard Analysis for the Sites of Offshore Wind Turbine in Taiwan

2015 ◽  
Vol 764-765 ◽  
pp. 1085-1089
Author(s):  
Cheng Yu Pan ◽  
Yuan Chieh Wu
Keyword(s):  
Wind Turbine ◽  
Seismic Design ◽  
Hazard Analysis ◽  
Active Faults ◽  
Seismic Source ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Source Characterization ◽  
Heavy Damage

During seismic hazards, offshore wind turbine structures do not have direct effects on people's safety; however, the seismic design is still important to prevent heavy damage on structure. The seismic design of offshore wind turbine has been discussed in some previous studies. Based on the result of those studies, we further modified the seismic source, especially on active faults in west foot hill zone. Of all the active faults in this area, we choose five which lie nearby the sites to make the modification. A logic tree has been set to avoid overlapping and derive an accurate recurrence model of the seismic source used in PSHA. This study is just a preliminary result of PSHA in wind turbine sites, Chunan and Chanbin, there are still several adjustments need to be done.

Modeling and interpretation of scattered waves in inter-stage DAS VSP survey

Geophysics ◽  
2020 ◽  
pp. 1-49
Author(s):  
Aleksei Titov ◽  
Gary Binder ◽  
Youfang Liu ◽  
Ge Jin ◽  
James Simmons ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Seismic Waves ◽  
Seismic Source ◽  
Cost Effective ◽  
Hydraulic Fractures ◽  
Zone Model ◽  
Low Velocity ◽  
Low Velocity Zone ◽  
Field Development ◽  
Velocity Zone

Optimization of well spacings and completions are key topics in research related to the development of unconventional reservoirs. In 2017, a vertical seismic profiling (VSP) survey using fiber-optic-based distributed acoustic sensing (DAS) technology was acquired. The data include a series of VSP surveys taken before and immediately following the hydraulic fracturing of each of 78 stages. Scattered seismic waves associated with hydraulic fractures are observed in the seismic waveforms. Kinematic traveltime analysis and full-wavefield modeling results indicate these scattered events are converted PS-waves. We tested three different models of fracture-induced velocity inhomogeneities that can cause scattering of seismic waves: single hydraulic fracture, low-velocity zone, and tip diffractors. We compare the results with the field observations and conclude that the low-velocity zone model has the best fit for the data. In this model, the low-velocity zone represents a stimulated rock volume (SRV). We propose a new approach that uses PS-waves converted by SRV to estimate the half-height of the SRV and the closure time of hydraulic fractures. This active seismic source approach has the potential for cost-effective real-time monitoring of hydraulic fracturing operations and can provide critical constraints on the optimization of unconventional field development.

scholarly journals Improving the characterization of the seismic source in Bebedouro, Paraná Basin, Brazil: further evidence of seismicity triggered by hydraulic stimulation in water wells

2017 ◽  
Vol 210 (2) ◽  
pp. 594-608 ◽  
Author(s):  
Gabriel Dicelis ◽  
Marcelo Assumpção ◽  
Renato Luiz Prado ◽  
Hans Agurto-Detzel ◽  
José Roberto Barbosa
Keyword(s):  
Seismic Source ◽  
Hydraulic Stimulation ◽  
Water Wells ◽  
Paraná Basin ◽  
Parana Basin

Shallow to very shallow, high‐resolution reflection seismic using a portable vibrator system

Geophysics ◽  
1998 ◽  
Vol 63 (4) ◽  
pp. 1295-1309 ◽  
Author(s):  
Ranajit Ghose ◽  
Vincent Nijhof ◽  
Jan Brouwer ◽  
Yoshikazu Matsubara ◽  
Yasuhiro Kaida ◽  
...  
Keyword(s):  
High Resolution ◽  
High Frequency ◽  
Seismic Waves ◽  
Soft Soil ◽  
Geophysical Methods ◽  
Seismic Source ◽  
P Wave ◽  
Nondestructive Technique ◽  
Buried Objects ◽  
Reflection Seismic

In shallow engineering‐geophysical applications, there is a lack of controlled, nondestructive, high‐resolution mapping tools, particularly for the target depth that ground‐penetrating radar cannot reach but which is too shallow for other conventional geophysical methods. For soft soil, this corresponds to a depth of 2 to 30 m. We have developed a portable, high‐frequency P-wave vibrator system that is capable of bridging this gap. As far as the important contribution of the seismic source is concerned, penetration and resolution can be individually controlled through easy modulation of the sweep signal generated by this electromagnetic vibrator. The feasibility of this system has been tested in shallow (10–50 m) to very shallow (0–10 m) applications. Seven field data sets representing varying geology, site conditions, and exploration targets are presented to illustrate the applicability. The first three examples show the potential of this portable vibrator source in shallow applications. Under favorable situations, a maximum resolution of about 20 cm for events located at 15–30 m depth could be achieved. Because high‐frequency seismic waves suffer from severe attenuation in the dry, unsaturated weathered zone, the penetration is relatively limited when the water table is deeper than 4–5 m. The fourth to seventh field examples illustrate very shallow applications at noisy, asphalt‐paved urban sites that are often encountered in civil, geotechnical, and environmental engineering projects. The prospecting targets were thin soil layers or small buried objects. On asphalt, the vibrator can produce high‐frequency energy easily. The fourth example shows high‐resolution delineation of very shallow soil structures. The last three examples present successful location of buried bodies—often small and closely spaced—in soft soil at depths of 0.5 to 5 m. We observe well‐defined reflection events of frequency exceeding 200 Hz. These results suggest that high‐frequency seismic reflection imaging using the portable vibrator system can indeed serve as a powerful, nondestructive technique for shallow to very shallow underground prospecting.

scholarly journals A source-synchronous filter for uncorrelated receiver traces from a swept-frequency seismic source

Geophysics ◽  
2016 ◽  
Vol 81 (5) ◽  
pp. P47-P55 ◽  
Author(s):  
Neal Lord ◽  
Herbert Wang ◽  
Dante Fratta
Keyword(s):  
Seismic Waves ◽  
Seismic Source ◽  
Propagation Delay ◽  
External Noise ◽  
Sweep Rate ◽  
Noise Sources ◽  
Frequency Domain Methods ◽  
Phase Alignment ◽  
Source Signal ◽  
Downhole Array

We have developed a novel algorithm to reduce noise in signals obtained from swept-frequency sources by removing out-of-band external noise sources and distortion caused from unwanted harmonics. The algorithm is designed to condition nonstationary signals for which traditional frequency-domain methods for removing noise have been less effective. The source synchronous filter (SSF) is a time-varying narrow band filter, which is synchronized with the frequency of the source signal at all times. Because the bandwidth of the filter needs to account for the source-to-receiver propagation delay and the sweep rate, SSF works best with slow sweep rates and moveout-adjusted waveforms to compensate for source-receiver delays. The SSF algorithm was applied to data collected during a field test at the University of California Santa Barbara’s Garner Valley downhole array site in Southern California. At the site, a 45 kN shaker was mounted on top of a one-story structure and swept from 0 to 10 Hz and back over 60 s (producing useful seismic waves greater than 1.6 Hz). The seismic data were captured with small accelerometer and geophone arrays and with a distributed acoustic sensing array, which is a fiber-optic-based technique for the monitoring of elastic waves. The result of the application of SSF on the field data is a set of undistorted and uncorrelated traces that can be used in different applications, such as measuring phase velocities of surface waves or applying convolution operations with the encoder source function to obtain traveltimes. The results from the SSF were used with a visual phase alignment tool to facilitate developing dispersion curves and as a prefilter to improve the interpretation of the data.

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