The effects of radiation patterns on magnitude estimates

1970 ◽  
Vol 60 (2) ◽  
pp. 503-516 ◽  
Author(s):  
David von Seggern
Keyword(s):  
Surface Wave ◽  
Radiation Pattern ◽  
Body Wave ◽  
Body Waves ◽  
Force System ◽  
Pattern Theory ◽  
Double Couple ◽  
Effects Of Radiation ◽  
Body Wave Magnitude ◽  
Selection Of

abstract With a double-couple force system as a model of an earthquake source mechanism, the radiation pattern theory of Ben-Menahem is employed to show that the far-field measurement of its strength can theoretically vary by more than a magnitude unit using either surface waves or body waves depending upon the angles of slip motion and fault dip for a source at a constant depth. The magnitude values determined by surface and body waves do not change linearly in relation to slip and dip angles nor do they change linearly in relation to one another. Random selection of locations within the radiation pattern is used to determine the extent of scatter in magnitude determinations which could be attributed to station distribution relative to the source. The scatter in surface-wave versus body-wave magnitude plots for earthquakes could be severe if only a few stations are used to obtain average magnitude values. A method of obtaining consistent estimates of surface-wave magnitude in practice is discussed.

A teleseismic body-wave analysis of the May 1980 Mammoth Lakes, California, earthquakes

1983 ◽  
Vol 73 (2) ◽  
pp. 419-434
Author(s):  
Jeffery S. Barker ◽  
Charles A. Langston
Keyword(s):  
Body Wave ◽  
Moment Tensor ◽  
Normal Fault ◽  
Strike Slip ◽  
Body Waves ◽  
P Wave ◽  
Moment Tensors ◽  
Double Couple ◽  
The Moment ◽  
Mammoth Lakes

abstract Teleseismic P-wave first motions for the M ≧ 6 earthquakes near Mammoth Lakes, California, are inconsistent with the vertical strike-slip mechanisms determined from local and regional P-wave first motions. Combining these data sets allows three possible mechanisms: a north-striking, east-dipping strike-slip fault; a NE-striking oblique fault; and a NNW-striking normal fault. Inversion of long-period teleseismic P and SH waves for the events of 25 May 1980 (1633 UTC) and 27 May 1980 (1450 UTC) yields moment tensors with large non-double-couple components. The moment tensor for the first event may be decomposed into a major double couple with strike = 18°, dip = 61°, and rake = −15°, and a minor double couple with strike = 303°, dip = 43°, and rake = 224°. A similar decomposition for the last event yields strike = 25°, dip = 65°, rake = −6°, and strike = 312°, dip = 37°, and rake = 232°. Although the inversions were performed on only a few teleseismic body waves, the radiation patterns of the moment tensors are consistent with most of the P-wave first motion polarities at local, regional, and teleseismic distances. The stress axes inferred from the moment tensors are consistent with N65°E extension determined by geodetic measurements by Savage et al. (1981). Seismic moments computed from the moment tensors are 1.87 × 1025 dyne-cm for the 25 May 1980 (1633 UTC) event and 1.03 × 1025 dyne-cm for the 27 May 1980 (1450 UTC) event. The non-double-couple aspect of the moment tensors and the inability to obtain a convergent solution for the 25 May 1980 (1944 UTC) event may indicate that the assumptions of a point source and plane-layered structure implicit in the moment tensor inversion are not entirely valid for the Mammoth Lakes earthquakes.

Effects of thin soft layers on body waves

1969 ◽  
Vol 59 (5) ◽  
pp. 2071-2078
Author(s):  
Tom Landers ◽  
Jon F. Claerbout
Keyword(s):  
Surface Wave ◽  
Upper Mantle ◽  
Body Wave ◽  
Wave Dispersion ◽  
Soft Material ◽  
Body Waves ◽  
Surface Wave Dispersion ◽  
Wave Data ◽  
Use Of Time ◽  
Surface Wave Data

abstract The inability of simple layered models to fit both Rayleigh wave and Love wave data has led to the proposal of an upper mantle interleaved with thin soft horizontal layers. Since surface-wave dispersion is not sensitive to the distribution of soft material but only to the fraction of soft material a variety of models is possible. The solution to this indeterminancy is found through body-wave analysis. It is shown that body waves are dispersed according to the thinness and softness of the layers. Three models, each of which satisfy all surface-wave data, are examined. Transmission seismograms calculated for these models show one to be impossible, one improbable and the other possible. Synthesis of the seismograms is accomplished through the use of time domain theory as the complicated frequency response of the models makes a frequency oriented Haskell-Thompson approach impractical.

scholarly journals Vertical force scaling in seismic source models of underground nuclear explosions

2020 ◽  
Vol 221 (1) ◽  
pp. 251-264
Author(s):  
Michael Howe ◽  
Göran Ekström ◽  
Paul G Richards
Keyword(s):  
Surface Wave ◽  
Body Wave ◽  
Scaling Factor ◽  
Body Waves ◽  
Burial Depth ◽  
Vertical Force ◽  
Underground Nuclear Explosions ◽  
Nuclear Explosions ◽  
Seismic Source Models ◽  
Force Scaling

SUMMARY We have reanalysed observations of body waves and surface waves for 71 well-recorded underground nuclear explosions (UNEs) that were conducted between 1977 and 1989 at the Balapan subregion of the Semipalatinsk Test Site in Kazakhstan. To reconcile differences between body-wave and surface-wave amplitudes, we solve for a scaling factor between vertical and horizontal forces in the explosion model. We find that the estimated scaling factor is anticorrelated with the scaled depth of burial for the subset of UNEs at Balapan that have published depths. The observed anticorrelation and the inferred variations in force scaling suggest that recorded surface-wave amplitudes are significantly influenced by UNE burial depth as well as by previously recognized tectonic release. As part of our analysis, we revisit the relationship between teleseismic mb(P) and yield for UNEs at Balapan, and discuss the physical basis for effectiveness of the mb–MS discriminant.

scholarly journals Teleseismic analysis of the 1980 Mammoth Lakes earthquake sequence

1982 ◽  
Vol 72 (4) ◽  
pp. 1093-1109
Author(s):  
Jeffrey W. Given ◽  
Terry C. Wallace ◽  
Hiroo Kanamori
Keyword(s):  
Surface Wave ◽  
Sierra Nevada ◽  
Body Wave ◽  
The Body ◽  
Body Waves ◽  
Earthquake Sequence ◽  
Local Data ◽  
Fault Plane Solutions ◽  
Principal Axes ◽  
Mammoth Lakes

abstract The source mechanisms of the three largest events of the 1980 Mammoth Lakes earthquake sequence have been determined using surface waves recorded on the global digital seismograph network and the long-period body waves recorded on the WWSSN network. Although the fault-plane solutions from local data (Cramer and Toppozada, 1980; Ryall and Ryall, 1981) suggest nearly pure left-lateral strike-slip on north-south planes, the teleseismic waveforms require a mechanism with oblique slip. The first event (25 May 1980, 16h 33m 44s) has a mechanism with a strike of N12°E, dip of 50°E, and a rake of −35°. The second event (27 May 19h 44m 51s) has a mechanism with a strike of N15°E, dip of 50°, and a slip of −11°. The third event (27 May, 14h 50m 57s) has a mechanism with a strike of N22°E, dip of 50°, and a rake of −28°. The first event is the largest and has a moment of 2.9 × 1025 dyne-cm. The second and third events have moments of 1.3 and 1.1 × 1025 dyne-cm, respectively. The body- and surface-wave moments for the first and third events agree closely while for the second event the body-wave moment (approximately 0.6 × 1025 dyne-cm) is almost a factor of 3 smaller than the surface-wave moment. The principal axes of extension of all three events is in the approximate direction of N65°E which agrees with the structural trends apparent along the eastern front of the Sierra Nevada.

Seismoelectric Surface-Wave Analysis for Characterization of Formation Properties, using Dispersive Relative Spectral Amplitudes

Geophysics ◽  
2021 ◽  
pp. 1-25
Author(s):  
N. Grobbe ◽  
S. A. L. de Ridder
Keyword(s):  
Surface Wave ◽  
Body Wave ◽  
Electrical Potential ◽  
Relative Strength ◽  
Body Waves ◽  
Fluid Viscosity ◽  
Near Surface ◽  
Em Field ◽  
Seismic Body Waves

We study seismoelectric (SE) surface-wave signals and find that they can be used to infer changes in the SE coupling properties at depth. Seismoelectric surface-wave signals have much higher amplitudes than seismoelectric body-wave signals. We propose to measure both the seismic and the electrical potential or electromagnetic (EM) field along the surface of the Earth. We use Dispersive Relative Spectral Amplitudes (DRSA) that measure the frequency-dependent relative strength of electrical signals versus seismic signals associated with seismoelectric surface-wave signals. We show that the DRSA have sensitivity to contrasts in the electrokinetic coupling coefficient and other relevant petrophysical properties at depth. Our discovery can mitigate the major limitation that plagues body wave-based SE methods: the relative weakness of the converted, EM signals from seismic body waves. We envision applications to characterize subsurface rock, fluid and fluid-flow properties (e.g. porosity, permeability, and dynamic fluid viscosity, salinity) in the near surface, for aquifers, and shallow geothermal reservoirs.

scholarly journals The source mechanism of the August 7, 1966 El Golfo earthquake

1978 ◽  
Vol 68 (5) ◽  
pp. 1281-1292
Author(s):  
John E. Ebel ◽  
L. J. Burdick ◽  
Gordon S. Stewart
Keyword(s):  
Surface Wave ◽  
Stress Drop ◽  
Gulf Of California ◽  
Body Wave ◽  
Source Parameters ◽  
High Stress ◽  
Plate Boundary ◽  
The Body ◽  
Body Waves ◽  
Wave Radiation

abstract The El Golfo earthquake of August 7, 1966 (mb = 6.3, MS = 6.3) occurred near the mouth of the Colorado River at the northern end of the Gulf of California. Synthetic seismograms for this event were computed for both the body waves and the surface waves to determine the source parameters of the earthquake. The body-wave model indicated the source was a right lateral, strike-slip source with a depth of 10 km and a far-field time function 4 sec in duration. The body-wave moment was computed to be 5.0 × 1025 dyne-cm. The surface-wave radiation pattern was found to be consistent with that of the body waves with a surface-wave moment of 6.5 × 1025 dyne-cm. The agreement of the two different moments indicates that the earthquake had a simple source about 4 sec long. A comparison of this earthquake source with the Borrego Mountain and Truckee events demonstrates that all three of these earthquakes behaved as high stress-drop events. El Golfo was shown to be different from the low stress-drop, plate-boundary events which were located on the Gibbs fracture zone in 1967 and 1974.

scholarly journals Seismic Characterization of the Nevada National Security Site Using Joint Body Wave, Surface Wave, and Gravity Inversion

2019 ◽  
Vol 110 (1) ◽  
pp. 110-126
Author(s):  
Leiph Preston ◽  
Christian Poppeliers ◽  
David J. Schodt
Keyword(s):  
Surface Wave ◽  
National Security ◽  
Surface Waves ◽  
Body Wave ◽  
Wave Dispersion ◽  
The Body ◽  
Body Waves ◽  
Gravity Inversion ◽  
Surface Wave Dispersion ◽  
Near Surface

ABSTRACT As a part of the series of Source Physics Experiments (SPE) conducted on the Nevada National Security Site in southern Nevada, we have developed a local-to-regional scale seismic velocity model of the site and surrounding area. Accurate earth models are critical for modeling sources like the SPE to investigate the role of earth structure on the propagation and scattering of seismic waves. We combine seismic body waves, surface waves, and gravity data in a joint inversion procedure to solve for the optimal 3D seismic compressional and shear-wave velocity structures and earthquake locations subject to model smoothness constraints. Earthquakes, which are relocated as part of the inversion, provide P- and S-body-wave absolute and differential travel times. Active source experiments in the region augment this dataset with P-body-wave absolute times and surface-wave dispersion data. Dense ground-based gravity observations and surface-wave dispersion derived from ambient noise in the region fill in many areas where body-wave data are sparse. In general, the top 1–2 km of the surface is relatively poorly sampled by the body waves alone. However, the addition of gravity and surface waves to the body-wave dataset greatly enhances structural resolvability in the near surface. We discuss the methodology we developed for simultaneous inversion of these disparate data types and briefly describe results of the inversion in the context of previous work in the region.

Precision of different varieties of magnitude

1972 ◽  
Vol 62 (3) ◽  
pp. 789-792
Author(s):  
B. F. Howell
Keyword(s):  
Surface Wave ◽  
Frequency Band ◽  
Wave Amplitude ◽  
Body Wave ◽  
The Body ◽  
Surface Wave Magnitude ◽  
Lower Standard ◽  
Standard Deviations ◽  
Body Wave Magnitude

Abstract The standard deviations of the body-wave magnitude, surface-wave magnitude and frequency-band magnitude of four shallow (H < 60 km) earthquakes are compared. For three out of four of these earthquakes, surface-wave magnitude exhibited lower standard deviations than either body-wave or frequency-band magnitude. In three out of the four cases, lower standard deviations were obtained by calculating surface-wave magnitude from the largest surface-wave amplitude than from time-correlated surface-wave phases.

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