scholarly journals Array data processing techniques applied to long-period shear waves at Fennoscandian seismograph stations

1969 ◽  
Vol 59 (5) ◽  
pp. 1863-1887
Author(s):  
James H. Whitcomb
Keyword(s):  
Data Processing ◽  
Velocity Ratio ◽  
Underground Explosion ◽  
High Signal ◽  
S Wave ◽  
Array Data ◽  
S Waves ◽  
Long Period ◽  
Normal Record ◽  
The Individual

abstract Array data processing is applied to long-period records of S waves at a network of five Fennoscandian seismograph stations (Uppsala, Umeå, Nurmijärvi, Kongsberg, Copenhagen) with a maximum separation of 1300 km. Records of five earthquakes and one underground explosion are included in the study. The S motion is resolved into SH and SV, and after appropriate time shifts the individual traces are summed, both directly and after weighting. In general, high signal correlation exists among the different stations involved resulting in more accurate time readings, especially for records which have amplitudes that are too small to be read normally. S-wave station residuals correlate with the general crustal type under each station. In addition, the Fennoscandian shield may have a higher SH/SV velocity ratio than the adjacent tectonic area to the northwest.SV-to-P conversion at the base of the crust can seriously interfere with picking the onset of Sin normal record reading. The study demonstrates that, for epicentral distances beyond about 30°, existing networks of seismograph stations can be successfully used for array processing of long-period arrivals, especially the S arrivals.

Normal moveout velocity ellipse in tilted orthorhombic media

Geophysics ◽  
2016 ◽  
Vol 81 (6) ◽  
pp. C319-C336 ◽  
Author(s):  
Yuriy Ivanov ◽  
Alexey Stovas
Keyword(s):  
Wave Mode ◽  
Initial Position ◽  
Orthorhombic Symmetry ◽  
Arbitrary Orientation ◽  
S Wave ◽  
Converted Wave ◽  
Slowness Surface ◽  
S Waves ◽  
Trade Offs ◽  
The Individual

Normal moveout (NMO) velocity is a commonly used tool in the seismic industry nowadays. In 3D surveys, the variation of the NMO velocity in a horizontal plane is elliptic in shape for the anisotropy or heterogeneity of any strength (apart from a few exotic cases). The NMO ellipse is used for Dix-type inversion and can provide important information on the strength of anisotropy and the orientation of the vertical symmetry planes, which can correspond, for example, to fractures’ orientation and compliances. To describe a vertically fractured finely layered medium (the fracture is orthogonal to the layering), an anisotropy of orthorhombic symmetry is commonly used. In areas with complicated geology and stress distribution, the orientation of the orthorhombic symmetry planes can be considerably altered from the initial position. We have derived the exact equations for the NMO ellipse in an elastic tilted orthorhombic layer with an arbitrary orientation of the symmetry planes. We have evaluated pure and converted wave modes and determined that the influence of the orientation upon the NMO ellipse for all the waves is strong. We have considered acoustic and ellipsoidal orthorhombic approximations of the NMO ellipse equations, which we used to develop a numerical inversion scheme. We determined that in the most general case of arbitrary orientation of the orthorhombic symmetry planes, the inversion results are unreliable due to significant trade-offs between the parameters. We have evaluated S-wave features such as point singularities (slowness surfaces of the split S-waves cross) and triplications (due to concaveness of the individual S-wave mode slowness surface) and their influence on the NMO ellipse.

Amplitude balancing in separating P- and S-waves in 2D and 3D elastic seismic data

Geophysics ◽  
2011 ◽  
Vol 76 (3) ◽  
pp. S103-S113 ◽  
Author(s):  
Robert Sun ◽  
George A. McMechan ◽  
Han-Hsiang Chuang
Keyword(s):  
Wave Amplitude ◽  
Amplitude Ratio ◽  
Velocity Ratio ◽  
Displacement Component ◽  
P Wave ◽  
Elastic Displacement ◽  
Reverse Time ◽  
S Wave ◽  
Near Surface ◽  
S Waves

The reflected P- and S-waves in elastic displacement component data recorded at the earth’s surface are separated by reverse-time (downward) extrapolation of the data in an elastic computational model, followed by calculations to give divergence (dilatation) and curl (rotation) at a selected reference depth. The surface data are then reconstructed by separate forward-time (upward) scalar extrapolations, from the reference depth, of the magnitude of the divergence and curl wavefields, and extraction of the separated P- and S-waves, respectively, at the top of the models. A P-wave amplitude will change by a factor that is inversely proportional to the P-velocity when it is transformed from displacement to divergence, and an S-wave amplitude will change by a factor that is inversely proportional to the S-velocity when it is transformed from displacement to curl. Consequently, the ratio of the P- to the S-wave amplitude (the P-S amplitude ratio) in the form of divergence and curl (postseparation) is different from that in the (preseparation) displacement form. This distortion can be eliminated by multiplying the separated S-wave (curl) by a relative balancing factor (which is the S- to P-velocity ratio); thus, the postseparation P-S amplitude ratio can be returned to that in the preseparation data. The absolute P- and S-wave amplitudes are also recoverable by multiplying them by a factor that depends on frequency, on the P-velocity α, and on the unit of α and is location-dependent if the near-surface P-velocity is not constant.

scholarly journals Measuring and crust-correcting finite-frequency travel time residuals – application to southwestern Scandinavia

2015 ◽  
Vol 7 (3) ◽  
pp. 1909-1939
Author(s):  
M. L. Kolstrup ◽  
V. Maupin
Keyword(s):  
Data Processing ◽  
Travel Time ◽  
Cross Correlation ◽  
Correlation Method ◽  
Ray Theory ◽  
Finite Frequency ◽  
S Wave ◽  
Low Velocity ◽  
Arrival Times ◽  
S Waves

Abstract. We present a data processing routine to compute relative finite-frequency travel time residuals using a combination of the Iterative Cross-Correlation and Stack (ICCS) algorithm and the MultiChannel Cross-Correlation method (MCCC). The routine has been tailored for robust measurement of P and S wave travel times in several frequency bands and for avoiding cycle-skipping problems at the shortest periods. We also investigate the adequacy of ray theory to calculate crustal corrections for finite-frequency regional tomography in normal continental settings with non-thinned crust. We find that ray theory is valid for both P and S waves at all relevant frequencies as long as the crust does not contain low-velocity layers associated with sediments at the surface. Reverberations in the sediments perturb the arrival times of the S waves and the long-period P waves significantly, and need to be accounted for in crustal corrections. The data processing routine and crustal corrections are illustated using data from a network in southwestern Scandinavia.

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>

scholarly journals Measuring and crust-correcting finite-frequency travel time residuals – application to southwestern Scandinavia

Solid Earth ◽  
2015 ◽  
Vol 6 (4) ◽  
pp. 1117-1130 ◽  
Author(s):  
M. L. Kolstrup ◽  
V. Maupin
Keyword(s):  
Data Processing ◽  
Travel Time ◽  
Cross Correlation ◽  
Correlation Method ◽  
Ray Theory ◽  
Finite Frequency ◽  
S Wave ◽  
Low Velocity ◽  
Arrival Times ◽  
S Waves

Abstract. We present a data-processing routine to compute relative finite-frequency travel time residuals using a combination of the Iterative Cross-Correlation and Stack (ICCS) algorithm and the Multi-Channel Cross-Correlation method (MCCC). The routine has been tailored for robust measurement of P- and S-wave travel times in several frequency bands and for avoiding cycle-skipping problems at the shortest periods. We also investigate the adequacy of ray theory to calculate crustal corrections for finite-frequency regional tomography in normal continental settings with non-thinned crust. We find that ray theory is valid for both P and S waves at all relevant frequencies as long as the crust does not contain low-velocity layers associated with sediments at the surface. Reverberations in the sediments perturb the arrival times of the S waves and the long-period P waves significantly, and need to be accounted for in crustal corrections. The data-processing routine and crustal corrections are illustrated using data from a~network in southwestern Scandinavia.

Adaptive decomposition of multicomponent ocean‐bottom seismic data into downgoing and upgoing P‐ and S‐waves

Geophysics ◽  
2003 ◽  
Vol 68 (3) ◽  
pp. 1091-1102 ◽  
Author(s):  
K. M. Schalkwijk ◽  
C. P. A. Wapenaar ◽  
D. J. Verschuur
Keyword(s):  
Ocean Bottom ◽  
S Wave ◽  
Depth Level ◽  
S Waves ◽  
Decomposition Scheme ◽  
Adaptive Decomposition ◽  
The Individual ◽  
Event Definition ◽  
Wavefield Decomposition ◽  
Shallow Water Depth

With wavefield decomposition, the recorded wavefield at a certain depth level can be separated into upgoing and downgoing wavefields as well as into P‐ and S‐waves. The medium parameters at the considered depth level (e.g., just below the ocean‐bottom) need to be known in order to be able to do a decomposition. In general, these parameters are unknown and, in addition, measurement‐related issues, such as geophone coupling and crosstalk between the different components, need to be dealt with. In order to apply decomposition to field data, an adaptive five‐stage decomposition scheme was developed in which these issues are addressed. In this study, the adaptive decomposition scheme is tested on a data example with a relatively shallow water depth (∼120 m), consisting recordings from of a full line of ocean‐bottom receivers. Although some of the individual stages in the decomposition scheme are more difficult to apply because of stronger interference between events compared to data acquired over deeper water, the end result is satisfying. Also, a good decomposition result is obtained for the S‐waves. The extension of the decomposition scheme to a complete line of ocean‐bottom cable data consists of a repeated application of the procedure for each receiver. The resulting decomposed upgoing P‐ and S‐wavefields are processed, yielding poststack time migrated images of the subsurface. Comparison with the images obtained from the original (i.e., not decomposed) measurements shows that wavefield decomposition just below the ocean bottom leads to a strong attenuation of multiply reflected events at the sea surface and better event definition in both P‐ and S‐wave sections. Other decomposition effects like improved angle‐dependent amplitudes cannot be evaluated in this way.

scholarly journals Body-wave amplitude and travel-time correlations across North America

1983 ◽  
Vol 73 (4) ◽  
pp. 1063-1076
Author(s):  
Thorne Lay ◽  
Donald V. Helmberger
Keyword(s):  
North America ◽  
Travel Time ◽  
Body Wave ◽  
Rocky Mountain ◽  
S Wave ◽  
Arrival Times ◽  
S Waves ◽  
Long Period ◽  
Amplitude Data ◽  
Short Period

abstract Relationships between travel-time and amplitude station anomalies are examined for short- and long-period SH waves and short-period P waves recorded at North American WWSSN and Canadian Seismic Network stations. Data for two azimuths of approach to North America are analyzed. To facilitate intercomparison of the data, the S-wave travel times and amplitudes are measured from the same records, and the amplitude data processing is similar for both P and S waves. Short-period P- and S-wave amplitudes have similar regional variations, being relatively low in the western tectonic region and enhanced in the shield and mid-continental regions. The east coast has intermediate amplitude anomalies and systematic, large azimuthal travel-time variations. There is a general correlation between diminished short-period amplitudes and late S-wave arrival times, and enhanced amplitudes and early arrivals. However, this correlation is not obvious within the eastern and western provinces separately, and the data are consistent with a step-like shift in amplitude level across the Rocky Mountain front. Long-period S waves show no overall correlation between amplitude and travel-time anomalies.

Travel-time curves and upper-mantle structure from long period S waves

1967 ◽  
Vol 57 (5) ◽  
pp. 1063-1092 ◽  
Author(s):  
Abou-Bakr K. Ibrahim ◽  
Otto W. Nuttli
Keyword(s):  
Travel Time ◽  
Upper Mantle ◽  
Earth Model ◽  
S Wave ◽  
Time Data ◽  
Low Velocity ◽  
S Waves ◽  
Long Period ◽  
Travel Time Data ◽  
Proposed Model

abstract Long-period S-wave travel-time data, including second and later arrivals, are presented for distances of 3° to 65° for focal depths of 33 and 120 km. Onset times were determined on the basis of particle motion diagrams and the product of the horizontal radial and vertical components of motion. Because the recording stations principally were LRSM units, the travel times represent data for an “average” United States earth model. An S-wave velocity distribution calculated for the upper mantle provides a satisfactory fit to the empirical travel-time data for focal depths of both 33 and 120 km. The proposed model contains a pronounced low-velocity layer at a depth of about 150-200 km, and secondary low-velocity layers at depths of 340-370 km and of 670-710 km. In addition, there are regions of rapidly increasing velocity beginning at depths of about 400 and 750 km, and constant velocity zones at 220-350 km and 400-670 km.

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