Estimates of short-period Q values and seismic moments from coda waves for earthquakes of the Beijing and Yun-nan regions of China

1984 ◽  
Vol 74 (4) ◽  
pp. 1189-1207
Author(s):  
Peishan Chen ◽  
Otto W. Nuttli ◽  
Wenhua Ye ◽  
Jiazheng Qin
Keyword(s):  
Wave Theory ◽  
Seismic Intensity ◽  
Body Waves ◽  
Wave Frequency ◽  
Coda Waves ◽  
Coda Wave ◽  
Master Curves ◽  
Beijing Area ◽  
Short Period ◽  
Simple Equations

Abstract Coda waves are used to determine the Q value of short-period waves in the Beijing area and in Yun-nan Province, China, and the seismic moments of the earthquakes studied. For the Beijing area the Q0, or 1-Hz value, is found to be approximately 400, with little or no indication of frequency dependence of Q for frequencies near 1 Hz in that region. For Yun-nan Province, the Q0 value is about 180, and the data suggest that Q(f) = Q0f0.2, where f is wave frequency. These values are in fairly good agreement with short-period Q estimates made for those regions by Chen and Nuttli (1984), on the basis of attenuation of seismic intensity values. Hermann's (1980) application of Aki's (1969) coda wave theory is extended, to provide simple equations for calculating master curves for coda wave studies. Two types of master curves provide independent estimates of Q0 and of the dependency of Q on wave frequency. For the data analyzed the two methods gave similar results. A third type of master curves gives estimates of the seismic moments of the earthquakes studied. The moments obtained by this means agree with values obtained by the conventional methods of analysis that use the spectrum of body waves or surface waves.

Sensitivity kernels for coda-wave interferometry in a three-dimensional scalar scattering media

2020 ◽  
Author(s):  
Andres Barajas ◽  
Ludovic Margerin ◽  
Michel Campillo
Keyword(s):  
Free Surface ◽  
Surface Waves ◽  
Mixed Boundary ◽  
Surrounding Medium ◽  
Body Waves ◽  
Coda Waves ◽  
Coda Wave ◽  
Scattering Media ◽  
The Impact ◽  
Coda Wave Interferometry

<p>The ambient seismic noise has proven to be a powerful tool to assess velocity changes within the ground using coda-wave interferometry (CWI). CWI is based on the analysis of small waveform changes in the coda of the signals. Localizing and imaging the source that generates changes can be done with the help of sensitivity kernels which contain information on how each part of the surrounding medium contributes to the overall waveform perturbation that is recorded at a receiver. Although progress has been made in the theory of sensitivity kernels in the case of a full elastic space,  the inclusion of a free surface has proven to be difficult. Indeed, the free surface couples body waves and surface waves, which affects the sensitivity of coda waves with respect to the full-space case. Furthermore, one expects the depth sensitivity of coda waves to be strongly dependent on the relative contribution of surface and body waves, which depends on the lapse-time, source-receiver distance and scattering properties of the medium. Using the Monte-Carlo method, we compute traveltime-sensitivity kernels in a 3D scalar problem that includes body and surface waves, based on a recent theoretical model that integrates both through a mixed boundary condition. From these results, we assess the impact of the depth of a velocity perturbation on the recorded signals at the surface. Our results will be compared with previous numerical approaches from the literature. </p>

Geometrical spreading function for short-period S and coda waves recorded in southern Spain

1993 ◽  
Vol 80 (1-2) ◽  
pp. 25-36 ◽  
Author(s):  
J.M. Ibáñez ◽  
E. Del Pezzo ◽  
G. Alguacil ◽  
F. De Miguel ◽  
J. Morales ◽  
...  
Keyword(s):  
Southern Spain ◽  
Coda Waves ◽  
Geometrical Spreading ◽  
Short Period ◽  
Spreading Function

The foreshock sequence of the 1986 Chalfant, California, earthquake

1988 ◽  
Vol 78 (1) ◽  
pp. 172-187
Author(s):  
Kenneth D. Smith ◽  
Keith F. Priestley
Keyword(s):  
Main Shock ◽  
Slip Surface ◽  
Body Waves ◽  
Aftershock Distribution ◽  
Time Period ◽  
Main Shocks ◽  
Short Period ◽  
Local Shear ◽  
Stress Drops ◽  
Foreshock Activity

Abstract The ML 6.4 Chalfant, California, earthquake of 21 July 1986 was preceded by an extensive foreshock sequence. Foreshock activity is characterized by shallow clustering activity, including 7 events greater than ML 3, beginning 18 days before the earthquake, an ML 5.7 foreshock 24 hr before the main shock that ruptured only in the upper 10 km of the crust, and an “off-fault” cluster of activity perpendicular to the slip surface of the ML 5.7 foreshock associated with the hypocenter of the main shock. The Chalfant sequence occurred within the local short-period network, and the spatial and temporal development of the foreshock sequence can be observed in detail. Seismicity of the July 1986 time period is largely confined to two nearly conjugate planes; one striking N30°E and dipping 60° to the northwest associated with the ML 5.7 foreshock and the other striking N25°W and dipping 70° to the southwest associated with the main shock. Focal mechanisms for the foreshock period fall into two classes in agreement with these two planes. Shallow clustering of earthquakes in July and the ML 5.7 principal foreshock occur at the intersection of the two planes at a depth of approximately 7 km. The seismic moments determined from inversion of the teleseismic body waves are 4.2 × 1025 and 2.5 × 1025 dyne-cm for the principal foreshock and the main shock, respectively. Slip areas for these two events can be estimated from the aftershock distribution and result in stress drops of 63 bars for the principal foreshock and 16 bars for the main shock. The main shock occurred within an “off-fault” cluster of earthquakes associated with the principal foreshock. This cluster of activity occurs at a predicted local shear stress high in relation to the slip surface of the 20 July earthquake, and this appears to be the triggering mechanism of the main shock. The shallow rupture depth of the principal foreshock indicates that this event was anomalous with respect to the character of main shocks in the region.

Coda Waves for Health Monitoring of Composites Under Low-Velocity Impact

2021 ◽  
Author(s):  
Subal Sharma ◽  
Vinay Dayal
Keyword(s):  
Ultrasonic Waves ◽  
Coda Waves ◽  
Low Velocity Impact ◽  
Coda Wave ◽  
Low Velocity ◽  
Fibrous Composite Material ◽  
Velocity Impact ◽  
Isotropic Composite ◽  
The Impact ◽  
Impact Damages

Abstract Coda waves have been shown to be sensitive to lab-controlled defects such as very small holes in fibrous composite material. In the real world, damages are subtler and more irregular. The main objective of this work is to investigate coda wave capability to detect low-velocity impact damages. The emphasis is to detect the presence of barely visible impact damages using ultrasonic waves. Detection of incipient damage state is important as it will grow over the life of the structure. Differential features, previously used in similar work, have been utilized to detect realistic impact damages on carbon fiber composites. Quasi-isotropic composite laminates were subjected to low-velocity impact energy ranging from 2J to 4.5J. Two differential features reported could be used detect the presence of damage. It is also observed that ply orientation can be a deterministic factor for indicating damages. The size and shape of the impact damage has been characterized using ultrasonic C-scans. Results indicate that coda waves can be used for the detection of damage due to low-velocity impact.

Short-period seismic noise

1967 ◽  
Vol 57 (1) ◽  
pp. 55-81
Author(s):  
E. J. Douze
Keyword(s):  
Surface Waves ◽  
Rayleigh Waves ◽  
Seismic Noise ◽  
Body Waves ◽  
Deep Hole ◽  
Period Range ◽  
Short Period ◽  
The Subject ◽  
Hole Arrays

abstract This report consists of a summary of the studies conducted on the subject of short-period (6.0-0.3 sec period) noise over a period of approximately three years. Information from deep-hole and surface arrays was used in an attempt to determine the types of waves of which the noise is composed. The theoretical behavior of higher-mode Rayleigh waves and of body waves as measured by surface and deep-hole arrays is described. Both surface and body waves are shown to exist in the noise. Surface waves generally predominate at the longer periods (of the period range discussed) while body waves appear at the shorter periods at quiet sites. Not all the data could be interpreted to define the wave types present.

Upper-mantle discontinuity from amplitude data of P′P′ and its precursors

1973 ◽  
Vol 63 (2) ◽  
pp. 587-597
Author(s):  
Ta-Liang Teng ◽  
James P. Tung
Keyword(s):  
Upper Mantle ◽  
Body Waves ◽  
P Wave ◽  
Specific Reference ◽  
Amplitude Data ◽  
Surface Displacements ◽  
Short Period ◽  
Mantle Velocity ◽  
Mantle Discontinuity ◽  
Upper Mantle Discontinuity

abstract Recent observations of P′P′ and its precursors, identified as reflections from within the Earth's upper mantle, are used to examine the structure of the uppermantle discontinuities with specific reference to the density, the S velocity, and the Q variations. The Haskell-Thomson matrix method is used to generate the complex reflection spectrum, which is then Fourier synthesized for a variety of upper-mantle velocity-density and Q models. Surface displacements are obtained for the appropriate recording instrument, permitting a direct comparison with the actual seismograms. If the identifications of the P′P′ precursors are correct, our proposed method yields the following: (1) a structure of Gutenberg-Bullen A type is not likely to produce observable P′P′ upper-mantle reflections, (2) in order that a P′P′ upper-mantle reflection is strong enough to be observed, first-order density and S-velocity discontinuities together with a P-wave discontinuity are needed at a depth of about 650 km, and (3) corresponding to a given uppermantle velocity-density model, an estimate can be made of the Q in the upper mantle for short-period seismic body waves.

Imaging the Ice Sheet and Uppermost Crustal Structures with a Dense Linear Seismic Array in the Larsemann Hills, Prydz Bay, East Antarctica

2021 ◽  
Author(s):  
Lei Fu ◽  
Jingxue Guo ◽  
Junlun Li ◽  
Bao Deng ◽  
Guofeng Liu ◽  
...  
Keyword(s):  
High Resolution ◽  
Ice Sheet ◽  
Velocity Model ◽  
Dispersion Curves ◽  
Body Waves ◽  
East Antarctica ◽  
Prydz Bay ◽  
Larsemann Hills ◽  
Geophysical Surveys ◽  
Short Period

Abstract Comprehensive geophysical surveys including magnetotelluric, seismic, and aerial gravity–magnetic surveys are essential for understanding the history of Antarctic tectonics. The ice sheet and uppermost structure derived from those geophysical methods are relatively low resolution. Although ice-penetrating radar can provide high-resolution reflectivity images of the ice sheet, it cannot provide constraints on subice physical properties, which are important for geological understanding of the Antarctic continent. To obtain high-resolution images of the ice sheet and uppermost crustal structure beneath the Larsemann Hills, Prydz Bay, East Antarctica, we conduct an ambient noise seismic experiment with 100 short-period seismometers spaced at 0.2 km intervals. Continuous seismic waveforms are recorded for one month at a 2 ms sampling rate. Empirical Green’s functions are extracted by cross correlating the seismic waveform of one station with that of another station, and dispersion curves are extracted using a new phase-shift method. A high-resolution shear-velocity model is derived by inverting the dispersion curves. Furthermore, body waves are enhanced using a set of processing techniques commonly used in seismic exploration. The stacked body-wave image clearly shows a geological structure similar to that revealed by the shear-wave velocity model. This study, which is the first of its kind in Antarctica, possibly reveals a near-vertical intrusive rock covered by an ice sheet with a horizontal extent of 4 km. Our results help to improve the understanding of the subice environment and geological evolution in the Larsemann Hills, Prydz Bay, East Antarctica.

Attenuation of short-period body waves in Northwestern Himalayan Region, India

2018 ◽  
Vol 114 ◽  
pp. 555-562
Author(s):  
Priyamvada Singh ◽  
Sushil Kumar ◽  
Pitam Singh
Keyword(s):  
Body Waves ◽  
Himalayan Region ◽  
Short Period
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