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Volume 34, Issue 1
Displaying 1-6 of 6 articles from this issue
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Tamao SATO1986 Volume 34 Issue 1 Pages 1-18
Published: 1986
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSA method of simultaneously estimating hypocenter parameters, station corrections, and velocity parameters has been developed for a velocity model with an arbitrary dipping layer boundary. The seismic ray is traced two-dimensionally by defining an equivalent ray path in a flat-layered velocity model for each combination of source and receiver. The partial derivatives of the travel time with respect to the perturbations in the hypocenter parameters and velocity model parameters are found to be expressed in analytical forms. These advantages are utilized in developing a time-saving computational procedure for the simultaneous estimation. The computer program coded according to the above procedure is tested for an artificial data set. The arrival-time data are stably inverted for true hypocenters and a true velocity model. Thus, it is concluded that the method works well, at least for an ideal data set. The present method may be used in estimating the gross image of the lateral variation in the crust of the velocity structure.View full abstractDownload PDF (1247K) -
Emile A. OKAL, Jacques TALANDIER1986 Volume 34 Issue 1 Pages 19-42
Published: 1986
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSWe present a study of the duration, Θ, of T wave trains propagating over teleseismic distances in the ocean, and recorded at island stations, in relation to the various magnitudes (mb, Ms, Mw) of the parent earthquake. Theoretical models based on scaling laws predict relations of the form log10 Θ = a+bM, with the slope b equal to 1/3 at low magnitudes, but increasing to 1/2 (and eventually to 1) because of the effect of saturation of the magnitude scales. The investigation of an extensive dataset using records of more than 400 Pacific earthquakes shows a remarkable agreement with these theoretical slopes. In the case of truly large earthquakes (Mw>7), such relations allow an estimation of the earthquake's seismic moment at ultra-long periods within 1 to 2 hr of the origin time, with important applications to efficient tsunami warning.View full abstractDownload PDF (2316K) -
Timothy L. NIEMAN, Kazuya FUJITA, William J. JR. ROGERS1986 Volume 34 Issue 1 Pages 43-70
Published: 1986
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSThree-dimensional seismic ray tracing through thermally derived slab models is used to investigate the effects of subducting lithosphere on teleseismic earthquake locations in island arcs. Theoretical results show teleseismic mislocations are greatest in the thrust zone and become negligible seaward of the trench. Varying the thermal coefficient of seismic velocity and the depth of penetration of the model slab have pronounced effects on mislocations while variations in assumed slab thickness have only minor effects. Variations in station distributions used to locate island arc events can result in 10 km differences in determined epicenters for the same event.
Comparison with observed mislocations gives a range of conceivable models for the central Aleutian slab varying from a 360 km depth of penetration with a thermal coefficient of -0.0009 km/s-°C to a 600 km deep slab with∂v/∂T=-0.0005 km/s-°C. The best fit model extends to 360 km depth with a thermal coefficient of -0.0009 km/s-°C. Theoretical mislocations indicate that intermediate depth events are well located teleseismically. Spurious dips and thinning of the Benioff zone can result from mislocations of deeper events.View full abstractDownload PDF (2692K) -
Sergio G. FERRAES1986 Volume 34 Issue 1 Pages 71-83
Published: 1986
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSThe probabilistic estimation or prediction of future inter-arrival times (T) of strong earthquake magnitudes (M≥6.5, Richter scale), felt in Mexico City from 1908 to 1979, is considered in terms of Bayes theorem. P(Tr/M)={P(Tr)P(M/Tr)}/Σ(Tj)P(M/Tj). We require the posterior probability P(Tr/M), i.e., the conditional probability of the event Tr, given that M has occurred. T0 determine the prior probability P(Tj) and the likelihood function P(M/Tj), we use two fundamental assumptions: (i) Random occurrence with the associated equal prior probabilities, (ii) Binomial likelihood function. However, the discrete Bayesian analysis of our earthquake sample is evaluated on the basis of the proportion of successes (π), rather than in the number of successes. Thus, the Bayesian posterior distribution is the distribution of (π) conditional on observing the sample with X successes. The posterior distribution can be written in the form, where r stands for the specific midpoint earthquake magnitude class, s stand for the specific time-interval class. The discrete Bayesian analysis of strong earthquakes felt in Mexico City, suggests that the probabilistic estimation or prediction of strong earthquakes (magnitudes) felt in Mexico City as follows:
Observed Predicted
(Occurrence time)(Occurrence time)
October 25, 1981 (Ms=7.3) June, 1980 (M=7.3)
June 7, 1982 (Ms=7.0) January, 1982 (M=7.3)
September, 1985 (M=7.8) April, 1986 (M=7.8)
It should be noted that very strong agreement exists between the Observed occurrence time and the Predicted occurrence time.View full abstractDownload PDF (1222K) -
Toru MATSUZAWA, Norihito UMINO, Akira HASEGAWA, Akio TAKAGI1986 Volume 34 Issue 1 Pages 85-94
Published: 1986
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSThe spatial change in the focal mechanism of the intermediate-depth earthquakes in the Tohoku District, the northeastern part of Honshu, Japan, is investigated in detail. In addition to general features of the distribution of focal mechanisms revealed by the previous studies, it is found that normal fault type events are dominant in the upper seismic plane of the double-planed deep seismic zone beneath the volcanic front, where the upper seismic plane is bending downward. The bending of the descending oceanic plate is probably the cause of these normal fault type events.View full abstractDownload PDF (925K) -
Ichiro NAKANISHI, Daisuke SUETSUGU1986 Volume 34 Issue 1 Pages 95-99
Published: 1986
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSDownload PDF (341K)
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