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TIME-SPACE DISTRIBUTION OF CODA Q IN...

HUANG, ZHONGXIAN.

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TIME-SPACE DISTRIBUTION OF CODA Q IN FAULT ZONES AND SURFACE WAVE DISPERSION IN EASTERN CHINA (EARTHQUAKES; HAWAII; ALEUTIANS).

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	TIME-SPACE DISTRIBUTION OF CODA Q IN FAULT ZONES AND SURFACE WAVE DISPERSION IN EASTERN CHINA (EARTHQUAKES; HAWAII; ALEUTIANS)./
作者:	HUANG, ZHONGXIAN.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 1987,
面頁冊數:	165 p.
附註:	Source: Dissertations Abstracts International, Volume: 48-07, Section: B.
Contained By:	Dissertations Abstracts International48-07B.
標題:	Geophysics. -
電子資源:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=8723469
ISBN:	9798206124972

TIME-SPACE DISTRIBUTION OF CODA Q IN FAULT ZONES AND SURFACE WAVE DISPERSION IN EASTERN CHINA (EARTHQUAKES; HAWAII; ALEUTIANS).
HUANG, ZHONGXIAN.

TIME-SPACE DISTRIBUTION OF CODA Q IN FAULT ZONES AND SURFACE WAVE DISPERSION IN EASTERN CHINA (EARTHQUAKES; HAWAII; ALEUTIANS). - Ann Arbor : ProQuest Dissertations & Theses, 1987 - 165 p.

Source: Dissertations Abstracts International, Volume: 48-07, Section: B.

Thesis (Ph.D.)--University of Colorado at Boulder, 1987.

This item must not be sold to any third party vendors.

Coda-Q were studied to search for temporal and spatial variations related to the November 16, 1983 Hawaii earthquake (M$\\sb {\\rm s}$6.6) and the May 7, 1986 Aleutian earthquake (M$\\sb{\\rm s}$7.7). More than 300 microearthquakes in each case, recorded by local networks, were used. The Q values were calculated from the coda decay rate using Aki's single back-scattering model. One-year average Q values were stable within the $\\pm$10% range for six years before the Hawaii earthquake and for five years before the Aleutian earthquake. No precursory change was detected in either case. After the 1986 Aleutian earthquakes, coda-Q decreased about 10% in the aftershock zone. In both cases the coda-Q showed spatial variations in the pre-mainshock stage. In the Hawaiian case, the region northwest of the mainshock epicenter yielded an average Q about 15% higher than that of the southeast region. The lower-Q region also showed higher seismicity and higher b-value, suggesting that the lower Q is due to a more fractured crust in that region. In the Aleutian case, the coda-Q within the mainshock rupture zone was about 20% higher than in the region to the west. The Q difference may be related to a difference in stress levels within and outside the rupture zone. Our study shows the difficulty in using coda-Q for earthquake prediction. The early part of the coda is so sensitive to the path and source effects that the random fluctuation of the measurements is relatively large compared to the possible precursory change. The later part of the coda is insensitive to Q changes in a small volume. The long-period recordings from three WWSSN stations were used to derive the Love and Rayleigh wave group velocity dispersion curves along paths which cross eastern China. The inverted velocity structures indicate a low shear velocity in the upper mantle in comparison to stable continental areas. The structure of the South China Block is relatively uniform. The North China Block, which is tectonically more active, is laterally more heterogeneous. In the coastal region, a north-northeast trending discontinuity in the crustal structure is inferred from the non-great-circle propagation paths.

ISBN: 9798206124972Subjects--Topical Terms:

535228
Geophysics.

TIME-SPACE DISTRIBUTION OF CODA Q IN FAULT ZONES AND SURFACE WAVE DISPERSION IN EASTERN CHINA (EARTHQUAKES; HAWAII; ALEUTIANS).
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500 $a Source: Dissertations Abstracts International, Volume: 48-07, Section: B.
500 $a Publisher info.: Dissertation/Thesis.
502 $a Thesis (Ph.D.)--University of Colorado at Boulder, 1987.
506 $a This item must not be sold to any third party vendors.
506 $a This item must not be added to any third party search indexes.
520 $a Coda-Q were studied to search for temporal and spatial variations related to the November 16, 1983 Hawaii earthquake (M$\\sb {\\rm s}$6.6) and the May 7, 1986 Aleutian earthquake (M$\\sb{\\rm s}$7.7). More than 300 microearthquakes in each case, recorded by local networks, were used. The Q values were calculated from the coda decay rate using Aki's single back-scattering model. One-year average Q values were stable within the $\\pm$10% range for six years before the Hawaii earthquake and for five years before the Aleutian earthquake. No precursory change was detected in either case. After the 1986 Aleutian earthquakes, coda-Q decreased about 10% in the aftershock zone. In both cases the coda-Q showed spatial variations in the pre-mainshock stage. In the Hawaiian case, the region northwest of the mainshock epicenter yielded an average Q about 15% higher than that of the southeast region. The lower-Q region also showed higher seismicity and higher b-value, suggesting that the lower Q is due to a more fractured crust in that region. In the Aleutian case, the coda-Q within the mainshock rupture zone was about 20% higher than in the region to the west. The Q difference may be related to a difference in stress levels within and outside the rupture zone. Our study shows the difficulty in using coda-Q for earthquake prediction. The early part of the coda is so sensitive to the path and source effects that the random fluctuation of the measurements is relatively large compared to the possible precursory change. The later part of the coda is insensitive to Q changes in a small volume. The long-period recordings from three WWSSN stations were used to derive the Love and Rayleigh wave group velocity dispersion curves along paths which cross eastern China. The inverted velocity structures indicate a low shear velocity in the upper mantle in comparison to stable continental areas. The structure of the South China Block is relatively uniform. The North China Block, which is tectonically more active, is laterally more heterogeneous. In the coastal region, a north-northeast trending discontinuity in the crustal structure is inferred from the non-great-circle propagation paths.
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