Three Kamchatka earthquakes

1960 ◽  
Vol 50 (3) ◽  
pp. 347-388
Author(s):  
William Stauder
Keyword(s):  
Fault Plane ◽  
Focal Depth ◽  
Analytical Techniques ◽  
Aftershock Sequence ◽  
Great Earthquake ◽  
S Wave ◽  
Fault Plane Solutions ◽  
S Waves ◽  
Double Couple ◽  
First Motion

ABSTRACT Three earthquakes, two with previously determined fault-plane solutions, are selected in order to study the relation between the S waves and the source mechanism. The S waves are observed at favorable epicentral distances at stations distributed in all quadrants about the epicenter. The earthquakes are of a focal depth of 40 to 60 kilometers and belong to the aftershock sequence of the great earthquake of November 4, 1952. The direction of first motion and the plane of polarization of S are determined by the construction of particle-motion diagrams. In the case of the two earthquakes for which the fault-plane solutions have been published, no correspondence is found between the observed S wave data and the character of the S motion expected on the basis of the given nodal planes of P, whether the source be considered as a single couple or as a double couple. For the third earthquake it is found that the first motion of P is compressional along all rays leaving the focus downward and that the S waves are strongly SV polarized. No faulting mechanism can explain this distribution of the motion in the initial P and S phases. The motion is explained as corresponding to that generated by a simple force acting almost vertically downward. Graphical and analytical techniques of analysis determine the trend of the force at the source to be N 12° W, with a plunge of 85°. A reconsideration of the other two shocks shows that these, too, are better explained by a simple force source than by a faulting mechanism.

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.

Rampart seismic zone of central Alaska

1983 ◽  
Vol 73 (3) ◽  
pp. 813-829
Author(s):  
P. Yi-Fa Huang ◽  
N. N. Biswas
Keyword(s):  
Main Shock ◽  
Fault Plane ◽  
B Value ◽  
Aftershock Sequence ◽  
Strike Slip ◽  
Lithospheric Plate ◽  
Normal Faults ◽  
Seismic Zone ◽  
The West ◽  
Fault Plane Solutions

abstract This paper describes the characteristics of the Rampart seismic zone by means of the aftershock sequence of the Rampart earthquake (ML = 6.8) which occurred in central Alaska on 29 October 1968. The magnitudes of the aftershocks ranged from about 1.6 to 4.4 which yielded a b value of 0.96 ± 0.09. The locations of the aftershocks outline a NNE-SSW trending aftershock zone about 50 km long which coincides with the offset of the Kaltag fault from the Victoria Creek fault. The rupture zone dips steeply (≈80°) to the west and extends from the surface to a depth of about 10 km. Fault plane solutions for a group of selected aftershocks, which occurred over a period of 22 days after the main shock, show simultaneous occurrences of strike-slip and normal faults. A comparison of the trends in seismicity between the neighboring areas shows that the Rampart seismic zone lies outside the area of underthrusting of the lithospheric plate in southcentral and central Alaska. The seismic zone outlined by the aftershock sequence appears to represent the formation of an intraplate fracture caused by regional northwest compression.

A computer program for focal mechanism determination combining P and S wave data

1969 ◽  
Vol 59 (2) ◽  
pp. 503-519
Author(s):  
Agustin Udias ◽  
Dieter Baumann
Keyword(s):  
Computer Program ◽  
Focal Mechanism ◽  
Total Error ◽  
Source Model ◽  
Polarization Angle ◽  
S Wave ◽  
Period Range ◽  
S Waves ◽  
Double Couple ◽  
The Relationship

abstract A computer program has been developed to find the orientation of a double couple source model for the mechanism of an earthquake which best satisfies the data from P and S waves. The relationship between the two axes of the solution given by the equations for the polarization angle of S is used in order to rapidly find the orientation of the source model for which a total error value involving the error of S and P data is a minimum. The program gives best results for data from homogeneous instruments of similar period range. Solutions for three earthquakes, selected because of the orientation of the source, are presented and the reliability of their solutions under ideal conditions is discussed.

Analysis of Shallow Microearthquakes in the South Sebec Seismic Zone, Maine, 1989–1990

1992 ◽  
Vol 63 (4) ◽  
pp. 557-566 ◽  
Author(s):  
William E. Doll ◽  
Carol D. Rea ◽  
John E. Ebel ◽  
Sandra J. Craven ◽  
John J. Cipar
Keyword(s):  
New England ◽  
Satellite Images ◽  
Fault Plane ◽  
Seismic Zone ◽  
Fault Plane Solutions ◽  
Motion Data ◽  
First Motion ◽  
High Level ◽  
Surface Geology

Abstract Fifteen years of regional monitoring by the New England Seismic Network indicated a locally high level of seismicity near South Sebec, between the towns of Milo and Dover-Foxcroft in central Maine. Most of the events were located in a diffuse zone south of the distinctive, ENE trending Harriman Pond Fault (HPF) which is indicated by brittle deformation in outcrop and is represented as a depression in topographic maps and satellite images. A portable network consisting of both digital and analog instruments was deployed during the summers of 1989 and 1990 in order to characterize the pattern of the microearthquakes and to determine high-resolution epicenters, depths, and fault plane solutions. Seventy-three events were detected during the experiment, of which 28 could be located. Many of the events south of the fault lie along a NNW trending line which has no major expression in the surface geology. Only, a few of the events are subparallel to the HPF. The first motion data were insufficient for the determination of any fault plane solutions.

First motions from seismic sources

1960 ◽  
Vol 50 (1) ◽  
pp. 117-134 ◽  
Author(s):  
Leon Knopoff ◽  
Freeman Gilbert
Keyword(s):  
Radiation Pattern ◽  
Fault Plane ◽  
Displacement Vector ◽  
Strain Tensor ◽  
Dislocation Model ◽  
Double Couple ◽  
First Motion ◽  
Sudden Release ◽  
Deep Focus ◽  
Dynamic Dislocation

ABSTRACT An application of dynamic dislocation theory gives the elastodynamic radiation resulting from the sudden occurrence of an earthquake due to faulting. The fault plane is visualized as a geometrical discontinuity across which there exists a sudden discontinuity in either one component of the strain tensor or one component of the displacement vector. It is shown that there are eight independent models, if unilateral faulting is assumed; and an argument is presented to demonstrate the likelihood that unilateral faulting does not exist in nature. For bilateral faulting the eight independent models are reduced in number to five. Of these five, two are more likely to occur in nature than the others. One of these, the displacement dislocation model, has a first-motion radiation pattern formally identical with that of a double couple in an unfaulted medium. The second, the shearstrain dislocation model, has a first-motion radiation pattern formally identical with that of an isolated force in an unfaulted medium. The latter type of mechanism may occur in deep-focus earthquakes. Another type of radiation, corresponding to the single couple in an unfaulted medium, results from the sudden release of shear strain in a laminar region.

Model studies of effects of near-source velocity discontinuities on first-motion patterns

1963 ◽  
Vol 53 (5) ◽  
pp. 933-954
Author(s):  
P. M. Lavin ◽  
B. F. Howell
Keyword(s):  
High Velocity ◽  
Radial Force ◽  
Low Velocity ◽  
Motion Patterns ◽  
S Waves ◽  
Model Studies ◽  
Circular Model ◽  
Double Couple ◽  
First Motion ◽  
Single Force

Abstract Directions and amplitudes of first compressional and shear motions were measured in two-dimensional plastic models from a simulated explosion, a unidirectional-force, a single-couple and a double-couple source. Patterns for a uniform circular model are compared with those for the source located on a boundary, near a boundary, in a low-velocity zone, and near a high-velocity region. In general, the patterns for the uniform models are consistent with theory except that weak S waves were noted from the simulated explosion. Reversals of the first motions of P due to the presence of velocity discontinuities were observed within 30° of the boundary running through the double-couple source. Amplitude reduction in the high-velocity medium of the non-uniform models leads to the possibility of missing the first motions. Under these conditions, “first-motion” patterns may be undependable as a means of determining the source mechanism. Thus, a single couple, double couple, and radial force may produce a single-force distribution and the single force may give a single-couple pattern.

A refined slip distribution of the 2013 Mw 6.7 Lushan, China earthquake constrained by GPS and levelling data

2020 ◽  
Vol 222 (1) ◽  
pp. 572-581
Author(s):  
Yunguo Chen ◽  
Kaihua Ding ◽  
Qi Wang ◽  
Ping He ◽  
Shuiping Li ◽  
...  
Keyword(s):  
Fault Plane ◽  
Near Field ◽  
Focal Depth ◽  
Aftershock Sequence ◽  
Slip Distribution ◽  
Fault System ◽  
Gps Data ◽  
2008 Wenchuan Earthquake ◽  
Spatial Coverage ◽  
Tectonic Settings

SUMMARY The 2013 Lushan Mw 6.7 earthquake is the largest blind thrust event ever occurred on the southern segment of the Longmen Shan fault system. It has attracted extensive attention since it occurred 5 yr later following the 2008 Mw 7.8 Wenchuan destructive earthquake in this region. However, its slip distribution is still on debate due to the complex tectonic settings and limited near-field observations. In this study, we added some near-field GPS data, together with previously published GPS data and levelling data, and take consideration of possible coseismic and post-seismic effects caused by the 2008 Wenchuan earthquake, to construct a more accurate horizontal and vertical coseismic surface displacement field associated with the 2013 Lushan earthquake with a better spatial coverage. Then we invert for a refined slip distribution based on a flat-ramp-flat fault suggested by the relocated aftershock sequence and seismic imaging. Our preferred fault plane is striking southwest with 211° and dipping at varying angles of 4°, 35° and 12° separately for such a flat-ramp-flat geometry. The main rupture is roughly characterized by two asperities, including a round disk on the ramp with larger slips and an adjoining oval asperity on the shallow flat with smaller slips. The maximum slip is 1.2 m at 14.3 km focal depth, located at ∼20 km to the northwest of the GCMT epicentre. The released geodetic moment is 1.50 $\ \times $ 1019 Nm, equivalent to a Mw 6.7 earthquake. The slips on the fault plane clearly illustrate that this event is dominated by the thrusting and minor striking, which is consistent with its tectonic settings. Furthermore, if we assume the 2013 Mw 6.7 Lushan event to be the characteristic earthquake on the southern section of the Longmen Shan thrust zone, the accumulated strain should not be fully released by this strong event, and a potential seismic risk still exists in this region.

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.

Single-station fault plane solutions

1982 ◽  
Vol 72 (3) ◽  
pp. 729-744
Author(s):  
Charles A. Langston
Keyword(s):  
Fault Plane ◽  
Fault Plane Solutions ◽  
Waveform Data ◽  
Motion Study ◽  
Single Station ◽  
Source Mechanisms ◽  
First Motion ◽  
Motion Studies ◽  
Using Data ◽  
Pattern Information

abstract Fault plane solutions are derived from systematic trial-and-error (“grid”) testing of three-component body waveform data from a single station. Modeling P and SH waveform data from five shallow events recorded teleseismically demonstrates that radiation pattern information contained within the interference of the direct wave and surface reflections and the overall relative amplitude between P and SH waveforms is sufficient to discriminate between fault type (e.g., strike-slip versus dip-slip) and often agrees with well-constrained first-motion studies. Events studied are the 9 April 1968 Borrego Mountain, California; 20 June 1978 Thessaloniki, Greece; 13 August 1978 Santa Barbara, California; 20 May 1979 Alaska; and 6 August 1979 Coyote Lake, California, earthquakes. It is also shown using data from the 27 July 1980 Sharpsburg, Kentucky, earthquake that inclusion of pP/P and sP/P polarity and amplitude information to an otherwise unconstrained first-motion study can significantly improve the quality of the fault plane solution. Although there are many potential problems (source multiplicity, directivity, etc.) which can prohibit finding a good model with these techniques and inclusion of data from many stations is clearly desirable, the results of this study suggest that sparse, high-quality waveform data sets may be as or more useful for obtaining source mechanisms than standard first-motion studies. At a minimum, they should be performed together as a consistency check. This procedure would be most useful in the common situation where only a few receivers are available for a particular event.

S-wave studies of earthquakes of the North Pacific, Part II: Aleutian Islands

1963 ◽  
Vol 53 (1) ◽  
pp. 59-77
Author(s):  
William Stauder ◽  
Agustin Udias
Keyword(s):  
Aleutian Islands ◽  
Aleutian Island ◽  
Stress System ◽  
S Wave ◽  
The North ◽  
Double Couple ◽  
First Motion ◽  
Good Determination ◽  
The North Pacific

Abstract The polarization of the S wave at stations distributed azimuthally about the source is examined for each of twenty-five Aleutian Island earthquakes. A combination of data from the first motion of P and from the polarization of S is then used to study the focal mechanisms of the earthquakes. This combination of P and S wave data is found to make possible a good determination of the focal mechanism in cases where data from the first motion of P alone do not suffice. The earthquakes are divided into three groups according to three basic patterns of S wave polarization. The first group (fourteen earthquakes) corresponds to a double couple. The second group (five earthquakes) and the third group (six earthquakes) are conformable to conjugate shears and may therefore be explained by single couple sources of opposite moment, respectively. It is shown that a uniform principal stress system predominates in the region and that the axis of greatest compressive stress is normal to the trend of the island arc.

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