Velocities of P and S waves calculated from the observed travel times of the Long Beach earthquake*

1936 ◽  
Vol 26 (2) ◽  
pp. 159-171 ◽  
Author(s):  
Cornelius G. Dahm
Keyword(s):  
Travel Times ◽  
Long Beach ◽  
S Waves

Stability of P an S velocities from Central California quarry blasts

1974 ◽  
Vol 64 (2) ◽  
pp. 343-353 ◽  
Author(s):  
T. V. McEvilly ◽  
L. R. Johnson
Keyword(s):  
Strike Slip ◽  
Travel Times ◽  
Mean Values ◽  
Central California ◽  
S Waves ◽  
Source Regions ◽  
Reading Errors ◽  
The Mean ◽  
Velocity Variations

abstract Travel times of crustal P and S waves from 70 quarry blasts in Central California between July 1961 and June 1973 have been measured for seven paths 46 to 168 km long passing in several cases within 10 km of hypocenters of moderate (ML 4.5 to 5.4) earthquakes. All P and S times and their ratios TS/TP lie within 2.3 per cent of the mean values and over 97 per cent of the TS/TP ratios lie within 1 per cent of the mean values. Variations can be explained by reading errors and uncertainties in source times and locations. There are no indications of velocity variations related to earthquake occurrences. Mean VP/VS ratios range from 1.73 to 1.84 for the various paths. The phenomenon of premonitory dilatancy accompanied by a 10 to 20 per cent reduction in VP or VP/VS cannot be reconciled with these observations unless the affected source regions have lateral dimensions less than about 5 km for these moderate strike-slip earthquakes.

Travel times and amplitudes of S waves from nuclear explosions in Nevada

1969 ◽  
Vol 59 (1) ◽  
pp. 385-398 ◽  
Author(s):  
Otto W. Nuttli
Keyword(s):  
Stress Field ◽  
Body Wave ◽  
P Wave ◽  
Travel Times ◽  
S Wave ◽  
Low Velocity ◽  
Time Curve ◽  
Regional Stress ◽  
S Waves ◽  
Regional Stress Field

Abstract The underground Nevada explosions HALF-BEAK and GREELEY were unique in creating relatively large amplitude and long-period body S waves which could be detected at teleseismic distances. Observations of the travel times of these S waves provide a surface focus travel-time curve which in its major features is similar to a curve calculated from the upper mantle velocity model of Ibrahim and Nuttli (1967). This model includes a low-velocity channel at a depth of 150 to 200 km and regions of rapidly increasing velocity beginning at depths of 400 and 750 km. Observations of the S wave amplitudes suggest that a discontinuous increase in velocity occurs at 400 km, whereas at 750 km the velocity is continuous but the velocity gradient discontinuous. Body wave magnitudes calculated from S amplitudes are 5.3 ± 0.2 for GREELEY and 4.9 ± 0.2 for HALF-BEAK. These are about one unit less than body wave magnitudes from P amplitudes as reported by others. The shape and orientation of the radiation pattern of SH for both explosions are consistent with the Rayleigh and P-wave amplitude distribution of BILBY as given by Toksoz and Clermont (1967). This suggests that the regional stress field is the same at all three sites, and that the direction of cracking as well as the strain energy release in the elastic zone outside the cavity is determined by the regional stress field.

An analysis of the travel times of S waves to North American stations in the distance range 28° to 82°

1967 ◽  
Vol 57 (4) ◽  
pp. 761-771 ◽  
Author(s):  
H. A. Doyle ◽  
A. L. Hales
Keyword(s):  
United States ◽  
Upper Mantle ◽  
Univariate Analysis ◽  
Western United States ◽  
Travel Times ◽  
Eastern United States ◽  
S Waves ◽  
Distance Range ◽  
Time Term ◽  
Mantle Velocity

abstract The travel times of S waves from 20 earthquakes to stations in North America in the distance range 28° to 82° have been studied. The deviations from J-B times were analyzed into station, source and distance components using the least-squares time-term approach of Cleary and Hales. Station anomalies had a range of about eight seconds, as compared to three seconds for the P anomalies, and are believed to be caused largely by variations in the upper mantle velocity distribution. S residuals, like the P residuals, were generally positive in the western United States, and negative in the central and eastern United States. P and S residuals at the same station correlated with a coefficient of 0.75, the slope of the regression of S anomaly on P anomaly being 3.72. Corrections to J-B times for S were of the order of the standard errors of the determinations. Within the distance range of 28° to 82° large changes of the S travel times, such as were required by the lower mantle velocities proposed by MacDonald and Ness (1961), are not permitted by the present data. The analysis was checked by carrying out a univariate analysis of variance of the same data.

scholarly journals A study of the Northwestern Pacific upper mantle

1965 ◽  
Vol 55 (5) ◽  
pp. 925-939
Author(s):  
Daniel A. Walker
Keyword(s):  
Upper Mantle ◽  
Fundamental Problem ◽  
Body Wave ◽  
Lower Boundary ◽  
P Wave ◽  
Northwestern Pacific ◽  
Travel Times ◽  
Low Velocity ◽  
S Waves ◽  
Wave Channel

abstract A fundamental problem of earthquake seismology is the occurrence of the upper mantle low-velocity channel. This study is intended to examine its existence in the upper mantle below the Northwestern Pacific on the basis of body-wave arrivals at a bottom-mounted hydrophone near Wake Island. A comparison of the observed travel times and the Jeffreys-Bullen travel times shows an extreme anomaly in the 21- to 33-degree range for both P and S waves. Assumed linear paths suggest a P-wave-channel upper boundary between 165 km and 185 km, and a lower boundary between 290 km and 542 km. Travel times for P and S waves indicate that the velocities in the channel remain constant at 8.1 km/sec and 4.65 km/sec respectively.

scholarly journals Travel times, apparent velocities and amplitudes of body waves

1968 ◽  
Vol 58 (1) ◽  
pp. 339-366
Author(s):  
Bruce R. Julian ◽  
Don L. Anderson
Keyword(s):  
Surface Wave ◽  
Travel Time ◽  
Velocity Gradient ◽  
Body Wave ◽  
Travel Times ◽  
S Waves ◽  
The Earth ◽  
Geometric Spreading ◽  
First Arrival ◽  
Wave Models

abstract Surface wave studies have shown that the transition region of the upper mantle, Bullen's Region C, is not spread uniformly over some 600 km but contains two relatively thin zones in which the velocity gradient is extremely high. In addition to these transition regions which start at depths near 350 and 650 km, there is another region of high velocity gradient which terminates the lowvelocity zone near 160 km. Theoretical body wave travel time and amplitude calculations for the surface wave model CIT11GB predict two prominent regions of triplication in the travel-time curves between about 15° and 40° for both P and S waves, with large amplitude later arrivals. These large later arivals provide an explanation for the scatter of travel time data in this region, as well as the varied interpretations of the “20° discontinuity.” Travel times, apparent velocities and amplitudes of P waves are calculated for the Earth models of Gutenberg, Lehmann, Jeffreys and Lukk and Nersesov. These quantities are calculated for both P and S waves for model CIT11GB. Although the first arrival travel times are similar for all the models except that of Lukk and Nersesov, the times of the later arrivals differ greatly. The neglect of later arrivals is one reason for the discrepancies among the body wave models and between the surface wave and body wave models. The amplitude calculations take into account both geometric spreading and anelasticity. Geometric spreading produces large variations in the amplitude with distance, and is an extremely sensitive function of the model parameters, providing a potentially powerful tool for studying details of the Earth's structure. The effect of attenuation on the amplitudes varies much less with distance than does the geometric spreading effect. Its main effect is to reduce the amplitude at higher frequencies, particularly for S waves, which may accunt for their observed low frequency character. Data along a profile to the northeast of the Nevada Test Site clearly show a later branch similar to the one predicted for model CIT11GB, beginning at about 12° with very large amplitudes and becoming a first arrival at about 18°. Strong later arrivals occur in the entire distance range of the data shown, 1112°. to 21°. Two models are presented which fit these data. They differ only slightly and confirm the existence of discontinuities near 400 and 600 kilometers. A method is described for predicting the effect on travel times of small changes in the Earth structure.

scholarly journals SH travel times and lateral heterogeneities in the lower mantle

1973 ◽  
Vol 63 (6-1) ◽  
pp. 2035-2046
Author(s):  
Mansour Niazi
Keyword(s):  
Travel Time ◽  
Lower Mantle ◽  
Angular Distance ◽  
Travel Times ◽  
S Waves ◽  
The North ◽  
Lower Shear ◽  
Core Boundary ◽  
Mid Atlantic Ridge ◽  
The Difference

Abstract The horizontal long-period seismograms of two shallow earthquakes in Turkey and Iran recorded in selected azimuths are combined for travel-time studies of the SH wave beyond the angular distance of 40°. The observed travel times along two profiles which sample the deep mantle in the vicinity of Iceland and the North Pole show monotonically increasing differences beyond 65°, indicating lateral heterogeneity in the lower mantle. The travel-time difference becomes as large as 7 sec at 95°, implying a variation as much as 0.06 km/sec, or about 1 per cent, in the shear-wave velocity near 2,500 km depth. Inversion of observations, adjusted to surface foci, results in an average lower mantle structure with lower shear velocities than those given by Jeffreys. The difference exceeds 0.1 km/sec at the core boundary. The arrival time and signature of S waves recorded in Greenland show anomalous features which may be related to deep seated anomalous zones associated with the Mid-Atlantic Ridge system.

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