Radiation mode of S waves from a deep-focus earthquake as derived from observations

1963 ◽  
Vol 53 (3) ◽  
pp. 643-659
Author(s):  
Keichi Kasahara
Keyword(s):  
Fault Plane ◽  
Analog Computer ◽  
P Wave ◽  
Wave Form ◽  
Type I ◽  
Radiation Mode ◽  
S Waves ◽  
Plane Solution ◽  
Earthquake Mechanism ◽  
Deep Focus

Abstract Two representative hypotheses on earthquake mechanism (so-called force types I and II) have been examined in comparison with seismograms for the earthquake of February 18, 1956 (south off Honshu, Japan; h = 450 km). On the basis of the fault-plane solution derived from P-wave data, one can predict polarity and relative amplitude of shear wave phases for a given station. The prediction by both of the hypotheses is compared with the observations at Kiruna and several other stations, where the principal seismic phases have been recorded clearly. The comparison has proved that the force type I does not fit the present case. The second type, on the other hand, explains the observations more consistently, although there are minor disagreements with respect to later phases. Reduction of the recorded wave form by an analog computer has shown that the original seismic disturbance (S) from the source is very simple in its wave form and harmonizes very well with Honda's theory. If we accept his theory, the radius of the origin sphere is estimated at 30-40 km for the present case.

Note on the determination of the earthquake mechanism by S waves

1962 ◽  
Vol 52 (3) ◽  
pp. 683-688
Author(s):  
Sergio G. Ferraes
Keyword(s):  
Seismic Wave ◽  
Fault Plane ◽  
Computational Technique ◽  
Type I ◽  
S Waves ◽  
Direction Cosines ◽  
Earthquake Mechanism

abstract Various methods have been devised for determining the nature of the forces which give rise to the seismic wave motions. To determine the direction of motion along the fault-plane, the direct computational technique to be proposed in this paper is an analytical modification of Adams' technique (1958) by means of determinants. This paper is concerned with the derivation of equations for computing the direction cosines of the “direction of motion” for a type I source, i.e., a couple of two equal and opposite forces with moment acting at the focus of the earthquake.

An optimal strategy for searching the best fault-plane solution using wave-amplitude data

1977 ◽  
Vol 67 (5) ◽  
pp. 1355-1362
Author(s):  
Kailash Khattri
Keyword(s):  
Seismic Waves ◽  
Fault Plane ◽  
Source Parameters ◽  
P Wave ◽  
Spectral Amplitude ◽  
Fault Plane Solution ◽  
Amplitude Data ◽  
Earthquake Source Parameters ◽  
Plane Solution ◽  
Deep Focus

abstract This paper presents an optimum search procedure known as the Fibonacci Technique for abstracting the earthquake-source parameters from the amplitude data of seismic waves. The power of the method has been demonstrated by determining the fault-plane solution of a deep-focus earthquake using the P-wave spectral amplitude data.

Computer program for a fault-plane solution

1963 ◽  
Vol 53 (1) ◽  
pp. 1-13
Author(s):  
Keichi Kasahara
Keyword(s):  
Probability Function ◽  
Fault Plane ◽  
Successive Approximations ◽  
Standard Errors ◽  
Machine Time ◽  
The Past ◽  
First Approximation ◽  
Plane Solution ◽  
Earthquake Mechanism ◽  
Time Required

Abstract In its earthquake mechanism studies the Dominion Observatory has been producing solutions graphically, but a program based on a probability function defined by Knopoff has been written for the IBM 1620 which permits the best solution to be obtained by a series of successive approximations from a given first approximation. The program prints out the strike and dip of the two nodal planes, their standard errors, the azimuth and plunge of their line of intersection, and a list of the stations producing inconsistent data. Weights can be assigned to each station; in practice these weights would depend on the past reliablity of the station. The machine time required depends on the number of stations used, the accuracy of the first approximation and other factors; in general 20 to 30 minutes is required for a solution involving 30-40 stations.

The Peru-Bolivia border earthquake of August 15, 1963

1970 ◽  
Vol 60 (2) ◽  
pp. 639-646 ◽  
Author(s):  
Umesh Chandra
Keyword(s):  
Travel Time ◽  
Fault Plane ◽  
P Wave ◽  
Focal Mechanism Solution ◽  
Event Analysis ◽  
Rupture Propagation ◽  
Fault Propagation ◽  
Amplitude Data ◽  
First Motion ◽  
Deep Focus

abstract The seismograms of the deep focus Peru-Bolivia border earthquake of August 15, 1963 reveal the presence of a number of conspicuous phases occurring within 15 seconds of the first P onset. These phases cannot be explained on the basis of known travel-time curves. Accordingly, the earthquake is interpreted to have occurred in a series of jerks during the course of fault propagation, or in other words it is composed of multiple events. Only one of these events, following the first event, at which the amplitude of the recorded motion becomes suddenly very large, has been located in this study. The focal mechanism solution of this earthquake has been determined from the P wave first motion and amplitude data. Consideration of the direction of rupture propagation determined from the multiple event analysis makes it possible to identify the fault plane in the mechanism solution. The parameters of the fault plane, length and speed of rupture between the two events have been determined.

Elastic waves from a spherical source: Aperiodic solutions for Scholte's model

1964 ◽  
Vol 54 (3) ◽  
pp. 897-908
Author(s):  
Tomowo Hirasawa
Keyword(s):  
Time Variation ◽  
Elastic Waves ◽  
Step Function ◽  
Wave Form ◽  
Type I ◽  
Type Ii ◽  
Spherical Coordinates ◽  
Force System ◽  
Spherical Source ◽  
S Waves

Abstract The radiation patterns of P and S waves from a spherical cavity, in an infinite elastic medium on which the stress similar to a single couple force acts, were obtained by J. G. J. Scholte and A. R. Ritsema (1962). In this paper the solution for their model is presented in the case when a step function is assumed as the time variation of the stress. As a result, it is found that the wave form of S waves depends on θ in spherical coordinates (r, θ, ø). Generally speaking, the orbit of the particle motion of S waves is not linear. Also the radiation pattern of S waves is similar to that for Type II rather than for Type I force system.

A study of earthquake mechanism using S wave data

1958 ◽  
Vol 48 (3) ◽  
pp. 201-219
Author(s):  
Wm. Mansfield Adams
Keyword(s):  
Wave Motion ◽  
P Wave ◽  
Wave Method ◽  
Wave Analysis ◽  
Poor Agreement ◽  
S Wave ◽  
Tectonic Earthquake ◽  
S Waves ◽  
The World ◽  
Earthquake Mechanism

Abstract The purpose of this paper is to determine from the seismograms of a tectonic earthquake the line of the motion which generated the observed S waves (tectonically, the A axis). By noting certain geometrical relationships between the faulting motion and the emitted S waves, it is possible to derive a method which determines the line of the generating motion from observations of the generated S waves. The results of the application of the proposed method of S wave analysis should, theoretically, make it possible to determine which of the two solutions given by the P wave method of analyzing the tectonic mechanism of earthquakes is the correct solution. The proposed procedure is applied to data collected from the original seismograms of four earthquakes as recorded at seismic observatories throughout the world. There is such poor agreement between the S wave results and the previous P wave solutions that it is necessary to conclude that one or more of the following is true: either the mechanism assumed is not the type actually occurring; the phase identified as the S wave does not correspond to the first P wave motion; the P wave method is incorrect or inadequate; or the S wave method is incorrect or inadequate. To select among the various possibilities necessitates a discussion of the relative merits, defects, and potentialities of the two methods.

A comparison of some S-wave studies of earthquake mechanisms

1961 ◽  
Vol 51 (2) ◽  
pp. 277-292
Author(s):  
William Stauder ◽  
Adams W. M.
Keyword(s):  
Fault Plane ◽  
Analytical Techniques ◽  
P Wave ◽  
Graphical Methods ◽  
S Wave ◽  
Fault Plane Solutions ◽  
P Waves ◽  
S Waves ◽  
Analytical Technique ◽  
Direction Of Polarization

Abstract Graphical and analytical techniques for using S-waves in focal mechanism studies are compared. In previous applications the analytical technique has shown little or no agreement with the results of fault-plane solutions from P-waves, whereas for other groups of earthquakes the graphical methods have shown good agreement between the S-waves and the P-wave solutions. It is shown that the graphical and analytical techniques are identical in principle and that when the graphical methods are applied to the same three earthquakes to which the analytical technique had been applied the identical results are obtained. Closer examination of the graphical presentation of the data, however, shows that the disagreement between the S-waves and the fault plane solutions from P is largely apparent. The discrepancy follows upon the peculiar scatter in the S-wave data and the chance occurrence of observations of S at stations located along closely parallel planes of polarization of S. Once this is understood, it is seen that the direction of polarization of S-waves is in substantial agreement with the methods of analysis of focal mechanisms from P-waves, and that the data are consistent with a simple dipole as the point model of the earthquake focus.

S waves: Alaska and other earthquakes

1960 ◽  
Vol 50 (4) ◽  
pp. 581-597 ◽  
Author(s):  
William Stauder
Keyword(s):  
Focal Mechanism ◽  
Fault Plane ◽  
P Wave ◽  
Wave Analysis ◽  
Point Model ◽  
S Wave ◽  
S Waves ◽  
Wave Solutions ◽  
Single Force

ABSTRACT Techniques of S wave analysis are used to investigate the focal mechanism of four earthquakes. In all cases the results of the S wave analysis agree with previously determined P wave solutions and conform to a dipole with moment or single couple as the point model of the focus. Further, the data from S waves select one of the two nodal planes of P as the fault plane. Small errors in the determination of the angle of polarization of S are shown to result in scatter in the data of a peculiar character which might lead to misinterpretation. The same methods of analysis which in the present instances show excellent agreement with a dipole with moment source are the methods which in a previous paper required a single force type mechanism for a different group of earthquakes.

scholarly journals DETERMINATION OF FAULT PLANE SOLUTIONS USING WAVEFORM AMPLITUDES AND RADIATION PATTERN

2004 ◽  
Vol 36 (3) ◽  
pp. 1529
Author(s):  
D. A. Vamvakaris ◽  
C. B. Papazachos ◽  
E. E. Karagianni ◽  
E. M. Scordilis ◽  
P. M. Chatzidimitriou
Keyword(s):  
Radiation Pattern ◽  
Multiple Solutions ◽  
Fault Plane ◽  
Synthetic Data ◽  
P Wave ◽  
Original Version ◽  
Fault Plane Solutions ◽  
S Waves ◽  
Short Period

In the present work a modified version of the program FPFIT (Reasenberg and Oppenheimer, 1985) is developed, in order to improve the calculation of the fault plane solutions. The method is applied on selected earthquakes from short period waveform data in the Mygdonia basin (N. Greece) as recorded by the permanent network of the Seismological Station of Aristotle University of Thessaloniki during the period 1989-1999. The proposed modification of the FPFIT program was developed in order to minimize the derivation of multiple solutions, as well as the uncertainties in the location of Ρ and Τ axis of the determined fault plane solutions. Compared to the original version of FPFIT the modified approach takes also into account the radiation pattern of SV and SH waves. For each earthquake horizontal and vertical components of each station were used and the first arrivals of Ρ and S waves were picked. Using the maximum peak-to-peak amplitude of Ρ and S waves the ratio Pmax/(S/\/2max+SE2max)1/2 was estimated, where S/Vmax and SEmax are the maximum amplitudes of the two horizontal components (N-S, E-W) for the S waves and Pmax is the maximum amplitude of the vertical one for the P- waves. This ratio for the observed data, as well as the corresponding ratio Prad/iS/Aad+SlAad)1'2 of the synthetic data was used as a weight for the determination of the observed and theoretical P-wave polarities, respectively. The method was tested using synthetic data. A significant improvement of the results was found, compared to the original version of FPFIT. In particular, an improved approximation of the input focal mechanism is found, without multiple solutions and the best-estimated Ρ and Τ axes exhibit much smaller uncertainties. The addition of noise in the synthetic data didn't significantly change the results concerning the fault plane solutions. Finally, we have applied the modified program on a real data set of earthquakes that occurred in the Mygdonia basin.

scholarly journals Earthquake of July 1980 in Far Western Nepal

1982 ◽  
Vol 2 (2) ◽  
Author(s):  
Vinod Singh
Keyword(s):  
Wave Motion ◽  
Fault Plane ◽  
P Wave ◽  
Main Central Thrust ◽  
Nodal Plane ◽  
Nepal Himalaya ◽  
The Earth ◽  
Main Boundary Thrust ◽  
First Motion ◽  
Plane Solution

This paper is an attempt to study the seismicity of the Nepal Himalaya and the earth-quake of July 1980 of Magnitude 6.5 in western Nepal on its regional geological framework. A new fault plane solution is obtained for this earthquake from the study of P wave motion on WWSSN Seismograms at 34 stations. The solution given by Kanamori and Given is not in conformity with the observed P wave first motion. The damaged area is elongated in the azimuth of 110°-120°, which is parallel to the strike of the nodal plane obtained in this study. From the study of the seismicity of Nepal region it is observed that most of the seismicity in recent years is confined in between the Main Central Thrust and the Main Boundary Thrust.

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