Generation of High-Frequency P and S Wave Radiation from Underground Explosions

2011 ◽  
Author(s):  
Charles G. Sammis
Keyword(s):  
High Frequency ◽  
Wave Radiation ◽  
S Wave

Average body-wave radiation coefficients

1984 ◽  
Vol 74 (5) ◽  
pp. 1615-1621
Author(s):  
David M. Boore ◽  
John Boatwright
Keyword(s):  
High Frequency ◽  
Body Wave ◽  
Strike Slip ◽  
Wave Radiation ◽  
Radiation Patterns ◽  
S Wave ◽  
P Waves ◽  
Effective Radiation ◽  
Average Body

Abstract Averages of P- and S-wave radiation patterns over all azimuths and various ranges of takeoff angles (corresponding to observations at teleseismic, regional, and near distances) have been computed for use in seismological applications requiring average radiation coefficients. Various fault orientations and averages of the squared, absolute, and logarithmic radiation patterns have been considered. Effective radiation patterns combining high-frequency direct and surfacere-flected waves from shallow faults have also been derived and used in the computation of average radiation coefficients at teleseismic distances. In most cases, the radiation coefficients are within a factor of 1.6 of the commonly used values of 0.52 and 0.63 for the rms of P- and S-wave radiation patterns, respectively, averaged over the whole focal sphere. The main exceptions to this conclusion are the coefficients for P waves at teleseismic distances from vertical strike-slip faults, which are at least a factor of 2.8 smaller than the commonly used value.

Spatial distribution of high-frequency energy radiation on the fault of the 1995 Hyogo-Ken Nanbu, Japan, earthquake (MW 6.9) on the basis of the seismogram envelope inversion

1999 ◽  
Vol 89 (1) ◽  
pp. 22-35 ◽  
Author(s):  
Hisashi Nakahara ◽  
Haruo Sato ◽  
Masakazu Ohtake ◽  
Takeshi Nishimura
Keyword(s):  
Spatial Distribution ◽  
Wave Energy ◽  
High Frequency ◽  
Fault Plane ◽  
Time Window ◽  
Source Region ◽  
Inversion Method ◽  
S Wave ◽  
Energy Radiation ◽  
Initial Rupture

Abstract We studied the generation and propagation of high-frequency (above 1 Hz) S-wave energy from the 1995 Hyogo-Ken Nanbu (Kobe), Japan, earthquake (MW 6.9) by analyzing seismogram envelopes of the mainshock and aftershocks. We first investigated the propagation characteristics of high-frequency S-wave energy in the heterogeneous lithosphere around the source region. By applying the multiple lapse time window analysis method to aftershock records, we estimated two parameters that quantitatively characterize the heterogeneity of the medium: the total scattering coefficient and the intrinsic absorption of the medium for S waves. Observed envelopes of aftershocks were well reproduced by the envelope Green functions synthesized based on the radiative transfer theory with the obtained parameters. Next, we applied the envelope inversion method to 13 strong-motion records of the mainshock. We divided the mainshock fault plane of 49 × 21 km into 21 subfaults of 7 × 7 km square and estimated the spatial distribution of the high-frequency energy radiation on that plane. The average constant rupture velocity and the duration of energy radiation for each subfault were determined by grid searching to be 3.0 km/sec and 5.0 sec, respectively. Energy radiated from the whole fault plane was estimated as 4.9 × 1014 J for 1 to 2 Hz, 3.3 × 1014 J for 2 to 4 Hz, 1.5 × 1014 J for 4 to 8 Hz, 8.9 × 1012 J for 8 to 16 Hz, and 9.8 × 1014 J in all four frequency bands. We found that strong energy was mainly radiated from three regions on the mainshock fault plane: around the initial rupture point, near the surface at Awaji Island, and a shallow portion beneath Kobe. We interpret that energetic portions were associated with rupture acceleration, a fault surface break, and rupture termination, respectively.

scholarly journals Capturing Regional Variations of Hard‐Rock Attenuation in Europe

2019 ◽  
Vol 109 (4) ◽  
pp. 1401-1418 ◽  
Author(s):  
Marco Pilz ◽  
Fabrice Cotton ◽  
Riccardo Zaccarelli ◽  
Dino Bindi
Keyword(s):  
High Frequency ◽  
Hard Rock ◽  
Epistemic Uncertainty ◽  
Ground Motions ◽  
Soft Soil ◽  
Coda Waves ◽  
Corner Frequency ◽  
S Wave ◽  
Empirical Parameter ◽  
Regional Variations

Abstract A proper assessment of seismic reference site conditions has important applications as they represent the basis on which ground motions and amplifications are generally computed. Besides accounting for the average S‐wave velocity over the uppermost 30 m (VS30), the parameterization of high‐frequency ground motions beyond source‐corner frequency received significant attention. κ, an empirical parameter introduced by Anderson and Hough (1984), is often used to represent the spectral decay of the acceleration spectrum at high frequencies. The lack of hard‐rock records and the poor understanding of the physics of κ introduced significant epistemic uncertainty in the final seismic hazard of recent projects. Thus, determining precise and accurate regional hard‐rock κ0 values is critical. We propose an alternative procedure for capturing the reference κ0 on regional scales by linking the well‐known high‐frequency attenuation parameter κ and the properties of multiple‐scattered coda waves. Using geological and geophysical data around more than 1300 stations for separating reference and soft soil sites and based on more than 10,000 crustal earthquake recordings, we observe that κ0 from multiple‐scattered coda waves seems to be independent of the soil type but correlated with the hard‐rock κ0, showing significant regional variations across Europe. The values range between 0.004 s for northern Europe and 0.020 s for the southern and southeastern parts. On the other hand, measuring κ (and correspondingly κ0) on the S‐wave window (as classically proposed), the results are strongly affected by transmitted (reflected, refracted, and scattered) waves included in the analyzed window biasing the proper assessment of κ0. This effect is more pronounced for soft soil sites. In this way, κ0coda can serve as a proxy for the regional hard‐rock κ0 at the reference sites.

Single-well S-wave imaging using multicomponent dipole acoustic-log data

Geophysics ◽  
2009 ◽  
Vol 74 (6) ◽  
pp. WCA211-WCA223 ◽  
Author(s):  
Xiao-Ming Tang ◽  
Douglas J. Patterson
Keyword(s):  
Field Data ◽  
Wave Radiation ◽  
Dipole Source ◽  
Directional Sensitivity ◽  
S Wave ◽  
Fracture Characterization ◽  
Processing Application ◽  
S Waves ◽  
Wave Imaging ◽  
Single Well

Single-well S-wave imaging has several attractive features because of its directional sensitivity and usefulness for fracture characterization. To provide a method for single-well acoustic imaging, we analyzed the effects of wave radiation, reflection, and borehole acoustic response on S-wave reflection measurements from a multicomponent dipole acoustic tool. A study of S-wave radiation from a dipole source and the wave’s reflection from a formation boundary shows that the S-waves generated by a dipole source in a borehole have a wide radiation pattern that allows imaging of reflectors at various dip angles crossing the borehole. More importantly, the azimuthal variation of the S-waves, in connection with the multicomponent nature of a cross-dipole tool, can determine the strike of the reflector. We used our theoretical foundation for borehole S-wave imaging to formulate an inversion procedure for field data processing. Application to field data validates the theoretical results and demonstrates the advantages of S-wave imaging. Application to near-borehole fracture imaging clearly demonstrates S-wave azimuthal sensitivity to fracture orientation.

Modeling guided waves to constrain the velocity structure of the oceanic crust in the subduction zone of eastern Alaska

2020 ◽  
Author(s):  
Xiaoyu Guan ◽  
Yuanze Zhou ◽  
Takashi Furumura
Keyword(s):  
Subduction Zone ◽  
Oceanic Crust ◽  
High Frequency ◽  
Subduction Zones ◽  
Guided Waves ◽  
Velocity Structure ◽  
Guided Wave ◽  
S Wave ◽  
Arrival Times ◽  
Velocity Models

<p>Fitting subduction zone guided waves with synthetics is an ideal choice for studying the velocity structure of the oceanic crust. After an earthquake occurs in subduction zones, seismic waves can be trapped in the low-velocity oceanic crust and propagated as guided waves. The arrival time and frequency characteristics of the guided waves can be used to image the velocity structure of the oceanic crust. The analysis and modeling based on guided wave observations provide a rare opportunity to understand the velocity structure of the oceanic crust and the variations in oceanic crustal materials during the subduction process.</p><p>High-frequency guided waves have been observed in the subduction zone of eastern Alaska. On several sections, observed seismograms recorded by seismic stations show low-frequency (<2Hz) onsets ahead of the main high-frequency (>2Hz) guided waves. Differences in the arrival times and dispersion characteristics of seismic phases are related to the velocity structure of the oceanic crust, and the characteristics of coda waves are related to the distribution of elongated scatters in the oceanic crust. Through fitting the observed broadband waveforms and synthetics modeled with the 2-D FDM (Finite Difference Method), we obtain the preferred oceanic crustal velocity models for several sections in the subduction zone of eastern Alaska. The preferred models can explain the seismic phase arrival times, dispersions, and coda characteristics in the observed waveforms. With the obtained P- and S- wave models of velocity structures on several sections, the material compositions they represent are deduced, and the variations of oceanic crustal materials during subducting can be understood. This provides new evidence for studying the details of the subduction process in the subduction zone of eastern Alaska.</p>

Consistent State Space Modelling of Hydrodynamic Memory

2020 ◽  
Author(s):  
Karl E. Kaasen
Keyword(s):  
Differential Equations ◽  
High Frequency ◽  
Radiation Force ◽  
Added Mass ◽  
Equation Model ◽  
Wave Radiation ◽  
Diffraction Radiation ◽  
Coupled Modes ◽  
Linear Differential ◽  
The Given

Abstract The conventional way to model hydrodynamic memory or radiation force is to use retardation functions. These functions are usually derived from frequency-dependent damping functions that are calculated by a diffraction-radiation code using potential theory. Calculating the retardation functions can be challenging due to lack of information at high frequency. In simulation of wave-driven vessel motion the retardation function is convolved with the velocity to give the wave radiation force, which is time-consuming. The paper describes how the memory effects can be modelled consistently by linear differential equations, such that coupled modes of motion share one set of poles. The coefficients of the differential equations are found by least squares fitting of a certain rational function to the numerical damping function. One advantage of this is that no assumption need to be made about the added mass at infinite frequency. Nor is any conditioning of the given data necessary. Using the fitted model in time-domain simulation is much quicker than using retardation functions. The method is applied to data representing the sway, roll and yaw motions of an FPSO of 238 m length. It was found that a sixth-order differential equation model fitted the given numeric radiation function well. It is shown how the high frequency asymptote for added mass can be estimated with high accuracy, which is valuable when it is not known in advance.

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