| Discriminating Underground Explosions from Earthquakes Using Seismic Coda Waves |
15 JAN 95 |
35 pages |
| Authors:
Keiiti Aki; UNIVERSITY OF SOUTHERN CALIFORNIA LOS ANGELES CENTER FOR EARTH SCIENCES
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 | We successfully discriminated quarry blasts and earthquakes at local distance from the observed source power spectra by using the coda Q method. To extend this discrimination method to events at regional distances, we developed the energy transfer theory for a mixture of Rayleigh and S wave propagation in a random scattering and attenuation medium. Applying this theory to the quarry blast earthquake problem at local distance, we can explain the ... |
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| BOUNDARY INTEGRAL-GAUSSIAN BEAM METHOD FOR SEISMIC WAVE SCATTERING: SH WAVES IN TWO-DIMENSIONAL MEDIA |
JUL 89 |
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| Authors:
Rafael Benites; Keiiti Aki
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 | in this paper a new method is introduced based on gaussian beam superposition to calculate the scattering of plane sh waves by strong lateral heterogeneities buried in a two-dimensional (2-d) homogeneous half-space. the method was tested on three well-known problems of scattering plane sh waves and the results are in excellent agreement with the corresponding exact or other numerical solutions. the method was also used to calculate the effects of ... |
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| Surface Wave Ray Tracing and Ms:Yield Determination in a Laterally Heterogeneous Earth |
FEB 89 |
62 pages |
| Authors:
Yuehua Zeng; Ta-liang Teng; Keiiti Aki; UNIVERSITY OF SOUTHERN CALIFORNIA LOS ANGELES DEPT OF GEOLOGICAL SCIENCES
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| Pure path Rayleigh wave group velocities for 24 regional grids inside the Arctic have been obtained from 74 mixed path measurements. The vertical shear wave velocity structures under these 24 grids were then determined according to their pure path group velocity dispersion data. This result indicates that the crustal shear wave velocity in the Arctic region is generally lower than the world-wide average. In addition, a typical mid-ocean ridge structure ... |
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| Effects of Heterogeneities on the Propagation, Scattering and Attenuation of Seismic Waves and the Characterization of Seismic Source |
85 |
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| Authors:
Keiiti Aki; Vernon F. Cormier; M. N. Toksoz; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| During this reporting period work was completed on testing alternative measures of body wave magnitude. It was found that alternative measures of body waves magnitude often exhibit as much scatter as classical measures of magnitude, although coda magnitudes usually have slightly less scatter than spectral and classical magnitudes. In the cases investigated, these differences were usually not statistically significant. Another completed task was an investigation of the intrinsic attenuation of ... |
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| Source and Scattering Effects on the Spectra of Small Local Earthquakes |
DEC 1981 |
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| Authors:
Keiiti Aki; UNIDENTIFIED SOURCE
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| In order to separate the scattering effect from the source effect on high-frequency seismic waves, the spectra of S and coda waves are studied simultaneously for 900 small earthquakes (magnitude 3 to 4) in the Kanto region, Japan. The observed S-wave spectrum is the source spectrum modified by the attenuation and forward-scattering effect, while the coda spectrum is the source spectrum modified by the attenuation and back-scattering effect. From previous ... |
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| Discrete Wave-Number Representation of Seismic-Source Wave Fields |
APR 1977 |
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| Authors:
Michel Bouchon; Keiiti Aki; JOURNAL ARTICLE-UNIDENTIFIED SOURCE
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| A method based on a discrete horizontal wave-number representation of seismic-source wave fields is developed and applied to the study of the near-field of a seismic source embedded in a layered medium. The discretization results from a periodicity assumption in the description of the source. The problem is basically two-dimensional but its extension to three dimensions is sometimes feasible. The source is quite general and is represented through its body-force ... |
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| Research in Seismology. |
1975 |
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| Authors:
Frank Press; M. Nafi Toksoz; Keiiti Aki; Sean C. Solomon; MASSACHUSETTS INST OF TECH CAMBRIDGE
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| Among the topics included in this report are: studies in seismic source theory, inversion of seismic data for three dimensional earth structures, regional crust-upper mantle structures under LASA and in Asia, source mechanisms of Asian earthquakes, and attenuation and scattering of seismic waves. A list of published papers and theses completed during the contract period is given at the end of the report. |
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| Research in Seismology. |
1974 |
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| Authors:
Frank Press; M. Nafi Toksoz; Keiiti Aki; Sean C. Solomon; MASSACHUSETTS INST OF TECH CAMBRIDGE
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| The report summarizes work within four broad topics: (1) Theoretical and observational studies of source mechanisms of earthquakes and underground nuclear explosions; (2) Wave propagation in heterogeneous and anisotropic media; (3) Regionalization of earth structure; (4) Array and data processing techniques for event detection and location. All publications and theses completed during the contract year are listed. (Modified author abstract) |
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| Research in Seismology. |
15 AUG 1973 |
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| Authors:
Frank Press; M. Nafi Toksoz; Keiiti Aki; MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF EARTH AND PLANETARY SCIENCES
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| The report gives a summary of the projects conducted during the last year under the contract Research in Seismology. These investigations fall roughly under three broad headings: (1) Theoretical studies of source mechanisms of earthquakes and underground nuclear explosions; (2) Earth structure and path effects, especially the effects of lateral heterogeneities in velocity and in Q; (3) Studies of the capabilities of arrays for event detection and location. Lists of ... |
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| Research in Seismology. |
15 SEP 1972 |
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| Authors:
Frank Press; M. Nafi Toksoz; Keiiti Aki; Sean C. Solomon; MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF EARTH AND PLANETARY SCIENCES
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| The report gives a summary of the research projects conducted under this contract. These investigations can be grouped into three broad categories: (1) Wave propagation in laterally inhomogeneous media, including studies of body waves, surface waves and free oscillations; (2) Source mechanisms of earthquakes and underground nuclear explosions, including questions of the scaling of earthquake spectra, the tidal triggering of earthquakes, and the release of tectonic strain by explosions; (3) ... |
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| Post-Doctoral Research in Seismology. |
31 DEC 1971 |
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| Authors:
Frank Press; M. Nafi Toksoz; Keiiti Aki; MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF EARTH AND PLANETARY SCIENCES
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| Research has been carried out on observations of surface and body waves from explosions and earthquakes and the structure and dynamics of the earth crust and upper mantle. Wave spectra have been studied using the Large Aperture Seismic Array (LASA) in Montana and the M.I.T. tiltmeter. Shear waves generated by large underground explosions have been used to estimate the magnitude of tectonic strain release accompanying explosions. Near-field observations are fitted ... |
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| Research in Seismology. |
31 DEC 1971 |
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| Authors:
Frank Press; M. Nafi Toksoz; Keiiti Aki; MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF EARTH AND PLANETARY SCIENCES
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| A brief summary of the research efforts under this contract is provided. The areas of investigation fall under five categories: Seismic wave propagation in heterogeneous media; seismic source theory; study of structure, properties and heterogeneities of the earth's interior; utilization of seismic arrays; development and performance of long-period tiltmeters. (Author) |
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| Seismic Source Mechanisms. |
30 JUL 1971 |
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| Authors:
Keiiti Aki; Paul Reasenberg; MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF EARTH AND PLANETARY SCIENCES
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| The purpose of this project is to develop an instrument system capable of measuring and recording the seismic spectrum at short distances from a large underground explosion. A problem of geologic hazard of considerable interest exists concerning the interaction of explosion-generated shock waves with tectonic stress in the neighborhood of the explosion site. A wide-band measurement of the seismic spectrum at short distances and at various azimuths about the explosion ... |
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| POST-DOCTORAL PROGRAM IN SEISMOLOGY. |
30 JUN 1968 |
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| Authors:
Frank Press; M. Nafi Toksoz; Keiiti Aki; Paul E. Green; Edward J. Kelly Jr; MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF GEOLOGY AND GEOPHYSICS
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| The research efforts of the research associates supported by this program are described. These studies are divided into two groups: I. Continental size arrays and their application, and II. Theoretical seismograms and earth structure. A continental size array can be realized by considering individual seismic stations as array elements. The theoretical seismograms for P and S waves are computed for a model of point source in layered medium and matched ... |
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