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.

Relation between P- and S-wave corner frequencies in the seismic spectrum

1974 ◽  
Vol 64 (6) ◽  
pp. 1621-1627 ◽  
Author(s):  
J. C. Savage
Keyword(s):  
High Frequency ◽  
Body Wave ◽  
Fault Model ◽  
P Wave ◽  
Corner Frequency ◽  
Rupture Propagation ◽  
S Wave ◽  
P Waves ◽  
Fault Surface ◽  
S Waves

abstract A comprehensive set of body-wave spectra has been calculated for the Haskell fault model generalized to a circular fault surface. These spectra are used to show that in practice the P-wave corner frequency (ƒp) may exceed the S-wave corner frequency (ƒs) when near-sonic or transonic rupture propagation obtains. The explanation appears to be that in such cases ƒs is so large that it is not identified within the recorded band, but rather a secondary corner is mistaken for ƒs. As a consequence of failing to detect the true asymptotic trend, the high-frequency falloff of the spectrum with frequency is substantially less for S waves than for P waves. This explanation appears to be consistent with the demonstration by Molnar, Tucker, and Brune (1973) that ƒp may exceed ƒs.

P and S-wave displacements from kinematic dislocation models

1992 ◽  
Vol 82 (4) ◽  
pp. 1910-1926 ◽  
Author(s):  
R. R. Castro ◽  
J. G. Anderson ◽  
J. N. Brune
Keyword(s):  
Body Wave ◽  
Normal Component ◽  
Strong Motion ◽  
S Wave ◽  
P Waves ◽  
Planar Fault ◽  
Dislocation Models ◽  
Time Histories ◽  
Shear Slip ◽  
Echelon Fault

Abstract Numerical dislocation models based on Haskells (1969) formulation are used to estimate the amount of normal motion necessary to produce the high P/S spectral ratios observed from strong-motion records of the Guerrero, Mexico, subduction zone (Castro et al., 1991). While this depends on the nature of the assumed dislocations, a normal motion with amplitude of less than 10% of the amplitude of shear slip is sufficient to produce P/S values comparable with the observations. We model a planar fault with random patches distributed on the fault plane and a nonplanar fault in which a dilatational jog connects en-echelon fault segments (a structural system proposed by Sibson, 1985, 1989, which introduces normal motions on the fault that depend mainly on the geometry of the fault). For the planar fault model the magnitude of the normal motion is prescribed. Both models introduce complexity in both body-wave displacement time histories, although for the P waves this complexity is accentuated at higher frequencies (f > 1 Hz). For the nonplanar model, a jog with an angle of 10° introduces a normal component of 18% of the slip on the fault.

Seismicity of Mars

2020 ◽  
Author(s):  
Domenico Giardini ◽  
Philippe Lognonne ◽  
Bruce Banerdt ◽  
Maren Boese ◽  
Savas Ceylan ◽  
...  
Keyword(s):  
Internal Structure ◽  
High Frequency ◽  
Body Wave ◽  
Spectral Characteristics ◽  
S Wave ◽  
New Era ◽  
S Waves ◽  
Long Period ◽  
Seismic Experiment ◽  
Tectonic System

<p>NASA’s InSight mission deployed the Seismic Experiment for Interior Structure (SEIS) instrument on Mars, with the goal of detecting, discriminating, characterizing and locating the seismicity of Mars and study its internal structure, composition and dynamics. 44 years since the first attempt by the Viking missions, SEIS has revealed that Mars is seismically active. So far, the Marsquake Service (MQS) has identified 365 events that cannot be explained by local atmospheric or lander-induced vibrations, and are interpreted as marsquakes. We identify two families of marsquakes: (i) 35 events of magnitude MW=3-4, dominantly long period in nature, located below the crust and with waves traveling inside the mantle, and (ii) 330 high-frequency events of smaller magnitude and of closer distance, with waves trapped in the crust, exciting an ambient resonance at 2.4Hz. Two long period events with larger SNR and excellent P and S waves occurred on Sol 173 and 235, visible both on the VBB and the SP channels; the location of these events has been determined at distances of 26°-30° towards the East, close to the Cerberus Fossae tectonic system. Over ten additional long period events show consistent body-wave phases interpreted as P and S phases and can be aligned with distance using models of P and S propagation. Marsquakes have spectral characteristics similar to seismicity observed on the Earth and Moon. From the spectral characteristics of the recorded seismicity and the event distance, we constrain attenuation in the crust and mantle, and find indications of a potential low S-wave-velocity layer in the upper mantle. In contrast, the high-frequency events provide important constraints on the elastic and anelastic properties of the crust. The first seismic observations on Mars deliver key new knowledge on the internal structure, composition and dynamics of the red planet, opening a new era for planetary seismology. Here we review the seismicity detected so far on Mars, including location, distance, magnitude, magnitude-frequency distribution, tectonic context and possible seismic sources.</p>

Body wave radiation patterns from force applied within a half space

1966 ◽  
Vol 56 (1) ◽  
pp. 173-183 ◽  
Author(s):  
Indra N. Gupta
Keyword(s):  
Half Space ◽  
Body Wave ◽  
Elastic Half Space ◽  
Reciprocity Theorem ◽  
Numerical Results ◽  
Wave Radiation ◽  
Far Field ◽  
Radiation Patterns ◽  
Sh Waves ◽  
Vertical Displacements

abstract Expressions are derived for the horizontal and vertical displacements at an arbitrary depth within a homogeneous, isotropic, elastic half space when plane harmonic P, SV or SH waves are incident at any given angle. On the basis of the reciprocity theorem, these expressions represent also the far-field polar radiation patterns of P, SV and SH waves due to horizontal and vertical forces applied at a point within the half space. Numerical results for a few selected values of depth are shown for a solid half space.

Radiation pattern and seismic waves generated by a working roller‐cone drill bit

Geophysics ◽  
1992 ◽  
Vol 57 (10) ◽  
pp. 1319-1333 ◽  
Author(s):  
James W. Rector ◽  
Bob A. Hardage
Keyword(s):  
Radiation Pattern ◽  
Field Data ◽  
Body Wave ◽  
Drill String ◽  
Wave Radiation ◽  
Drill Bit ◽  
P Waves ◽  
The Earth ◽  
Working Roller ◽  
Cone Drill

The seismic body wave radiation pattern of a working roller‐cone drill bit can be characterized by theoretical modeling and field data examples. Our model of drill‐bit signal generation is a pseudo‐random series of bit‐tooth impacts that create both axial forces and tangential torques about the borehole axis. Each drill tooth impact creates an extensional wave that travels up the drill string and body waves that radiate into the earth. The model predicts that P‐waves radiate primarily along the axis of the borehole, and shear waves radiate primarily perpendicular to the borehole axis. In a vertical hole, the largest P‐waves will be recorded directly above and below the drill bit; whereas, the largest shear waves will be recorded in a horizontal plane containing the drill bit. In a deviated borehole, the radiation patterns should be rotated by the inclination angle of the drill bit. This proposed seismic body wave radiation pattern is investigated with field data examples. The presence of the drill string in the borehole creates other wave modes that are not typically observed when conventional vertical seismic profiles (VSPs) are conducted in fluid‐filled wells. For example, the extensional wave traveling up the drill string creates a head wave traveling away from the drill string, provided the formation velocities adjacent to the borehole are less than the drill‐string velocity. Likewise, when the extensional wave traveling up the drill string reaches the drill rig, some of the energy continues through the drill rig structure, re‐enters the earth, and travels away from the rig as ground roll or shallow refractions. Secondary events are radiated at the drill bit after they travel up the drill string, reflect off drill‐string discontinuities, and travel back down the drill string to the bit. Each of these drill‐bit arrivals has a characteristic moveout as a function of wellhead offset and drill‐bit depth. A knowledge of the radiation patterns and the wave modes generated by the drill bit is essential to interpreting drill‐bit wavefields.

Body wave radiation patterns from elementary sources within a half space

1967 ◽  
Vol 57 (4) ◽  
pp. 657-674
Author(s):  
I. N. Gupta
Keyword(s):  
Free Surface ◽  
Half Space ◽  
Body Wave ◽  
Point Sources ◽  
The Body ◽  
Wave Radiation ◽  
Seismic Sources ◽  
Vertical Force ◽  
Radiation Patterns ◽  
Double Couple

abstract The known expressions for the polar radiation patterns due to a horizontal or a vertical force, applied at a point within a uniform half space, are used to obtain the body wave radiation patterns from several other elementary seismic sources. Polar radiation patterns from seven elementary line sources, i.e., horizontal and vertical double forces without moment, horizontal and vertical single couples, center of dilatation, center of ratation, and double couple without moment, are first derived. Similar point sources in the three-dimensional space are also considered and the corresponding polar as well as azimuthal radiation patterns are obtained for P, SV, and SH waves. The results obtained include the effect of finite depth of the source below the free surface. Some of the results of Burridge et al for double-couple type seismic sources near a free surface are reproduced in a simple manner. For the elementary point sources considered here, the azimuthal radiation patterns for a uniform half-space are found to be identical with those for an infinite homogeneous medium. However the polar radiation patterns appear to be profoundly affected by the proximity of the free surface.

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