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Volume 29 (1981)
- Issue 6 Pages 487-
- Issue 5 Pages 377-
- Issue 4 Pages 267-
- Issue 3 Pages 173-
- Issue 2 Pages 89-
- Issue 1 Pages 1-
Volume 29, Issue 2
Displaying 1-7 of 7 articles from this issue
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Janice REGAN, George A. MCMECHAN1981 Volume 29 Issue 2 Pages 89-95
Published: 1981
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSRay parameters as well as the travel times of all arrivals observed at any distance are functions of focal depth and can be used in focal depth estimates. Ray parameters of many arrivals can contribute to stable depth estimates in a number of station-source geometries. The precision to which ray parameters can currently be measured is sufficient that alternative focal depth algorithms that use ray parameters are competitive with current methodsView full abstractDownload PDF (792K) -
Naoya MIKAMI, Kazuro HIRAHARA1981 Volume 29 Issue 2 Pages 97-117
Published: 1981
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSA large number of WWSSN long-period P-wave records from 41 inter- mediate- and deep-focus earthquakes have been analyzed aiming at investigating global variations of attenuative properties in the upper mantle, with statistical treatments using a damped least squares method. The present results reveal significant regional variations of attenuation over the world. High Q is observed along the Pacific coastal region and the eastern part of the United States, India, Indochina, and Australia, most of which are located in stable shield region. On the other hand, low Q is observed in the western United States and a part of Europe, which are in tectonically active region. There appears to be some correlation between the obtained differential attenuation and heat flows, suggesting that high heat flow regions are characterized by low Q and vice versa. However, there is no clear relation between travel-time residuals and attenuation. A large number of the data used in this study generally give support to the SL8 model as an average Q model in the earth's mantle.View full abstractDownload PDF (1790K) -
Jose A. CANAS1981 Volume 29 Issue 2 Pages 119-129
Published: 1981
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSUsing the two-station-method, average fundamental mode surface-wave velocities and attenuation coefficients have been determined in the Atlantic Ocean. The average Rayleigh-wave attenuation coefficients decrease from 3.04×10-4km-1 at a period of 15sec to about 0.40×10-4km-1 at the longer periods. The average Love-wave attenuation coefficients, in the period range 26 to 100sec, vary from a value of about 2.20×10-4km-1 at the shorter periods to a minimum value of 0.92×10-4km-1 at the longest period.
Backus-Gilbert inversion theory applied to the attenuation data yields an average Q-1β model for the Atlantic that shows a clear and well-developed low-Q zone situated approximately between 40 and 220km depth. The maximum Q-1β value (-13×10-3) occurs at 100km depth.View full abstractDownload PDF (873K) -
Hideki SHIMAMURA1981 Volume 29 Issue 2 Pages 131-144
Published: 1981
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSA single mobile observation was made in Hokkaido to complement its crustal structure which had been poorly known. A swarm of Usu volcanic earthquakes, whose source region was concentrated within a diameter of 1km, was used as a "source". Because of the small size of the source region and the good time keeping, errors in travel times are as little as 0.2sec, which is enough for travel time studies. Thirty-nine stations were temporarily operated on two profiles, whose length was 320km and 100km, respectively.
The seismometer was basically an ocean bottom seismometer which was slightly modified for the land use. The small size, the wide dynamic range, the low power drain and the sturdiness were helpful for the efficient observations.
The obtained crustal structure illustrates: (1) The granitic layer, with the velocity of 5.8km/sec, is shallow at the top and the thickness is about 20km. (2) The basaltic layer, with the velocity of 6.6km/sec, is immediately beneath the granitic layer. Its thickness is also about 20km. Hence the crust is thicker than usual compared to other regions in Japan. (3) The upper mantle velocity is 7.8km/sec.
The profiles were inherently not reversed, however one of them is so planned as to be reversed by possible future earthquake swarms of Teshikaga region, which have occurred recurrently in the past.View full abstractDownload PDF (1257K) -
Robert C. BOSTROM1981 Volume 29 Issue 2 Pages 145-161
Published: 1981
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSFlexure of the mantle by the east-west M2 wave imposes non-reversing small body torques. The stress and displacement have been evaluated for the plausible range of the elastic quality factor Q. The non-cancelling stresses are of the order 5×10-7dyn/cm2, varying as the magnitude of Q-1. The displacement varies as Q-2 and is correspondingly minute, but is cumulative through geologic time. The role of the lithosphere becomes dominant, because stress diffusion causes it to act as a transmission channel. Stress acting on isostatic lithosphere is additive horizontally, as wind stress is additive across a floating ice sheet. In respect to oceanic lithosphere, within a period of about 106 years the stress reaches a value of tens of bars and its displacement rate several cm/yr. It is surmised that the values reached are limited by imperfect elasticity of the lithosphere. The energy consumption based upon gravimetric values of the phase lag, between 1.3 and 2.3×1026erg/yr, is a fraction of the dissipation astronomically observed but not found in the seas. The effect of lithosphere creep is compared with Pacific and Atlantic tectonic features.View full abstractDownload PDF (1437K) -
Yoshio FUKAO, Akihiko YAMAMOTO, Kyozo NOZAKI1981 Volume 29 Issue 2 Pages 163-166
Published: 1981
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSDownload PDF (312K) -
Shigeo MORI, Motoo UKAWA, Yoshio FUKAO1981 Volume 29 Issue 2 Pages 167-172
Published: 1981
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSDownload PDF (417K)
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