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Stability of coda wave attenuation during the Loma Prieta, California, earthquake sequence
4A
GEOLOGY:EARTHQUAKES
Then, a statistical discrimination of foreshocks from earthquakes of other types of clusters is explored. (from Authors)
Johnson Valley fault. A relatively low resolution could be an explanation for these differences. (from Authors)
961025 Spatial correlation of earthquake ground motion: nonparametric estimation I-I.-P. Boissieres & E. H. Vanmarcke, Soil Dynmnics & Earthquake Engineering, 14(1), 1995, pp 23-31. A non-parametric method, called multidimensional correlation mapping (MCM), is used to describe the local spatial correlation of different components of earthquake ground acceleration. The method estimates spatial correlation without presuming homogeneity or isotropy of the phasealigned local ground motion fields. For selected events recorded by the SMART1 accelerograph array, we obtain contour plots of equal correlation of ground acceleration, with respect to the center of the array. Displacement timehistories are also computed from the accelerograms and the spatial correlation of the displacements is estimated for comparison with that of the accelerations. (Authors)
961029 Stability of coda wave attenuation during the [arena Prleta, California, earthquake sequence G. C. Beroza, A. T. Cole & W. L. Ellsworth, Journal of Geophysical Research, 100(B3), 1995, pp 3977-3987. The Lama Prieta, California, earthquake occurred in a densely instrumented region with a history of microearthquake recording beginning more than a decade before the October 1989 mainsbock. This affords an unprecedented opportunity to detect changes in seismic wave propagation in the Earth's crust associated with a major earthquake. This study uses pairs of nearly identical earthquakes (doublets) to search for temporal changes of coda attenuation in the vicinity of the Lama Prieta earthquake. The observations place an upper bound of about 5% on preseismic, coseismic, and postseismic changes of coda Q in the epicentral region of the Lama Prieta earthquake. Even at this low level, the changes are neither spatially coherent nor correlated between adjacent frequency hands. The only hint of a signal is in the preseismic data where there is a possible precursory increase in coda Q of approximately 5% in the two eyars before the mainshock. The stabifity of coda Q throughout the Lama Prieta sequence is in sharp contrast to other studies that have reported much larger precursory changes in coda Q for other earthquakes. (from Authors)
961026 Earthquakes in the Vancouver area G. C. Rogers, Bulletin - Geological Survey of Canada, 481, 1994, pp 221-229. Vancouver and the densely populated Lower Mainland region of southwest British Columbia are situated over an active subduetion zone. The dynamic geological setting makes this region subject to frequent seismic activity and contributes to a higher risk of large damaging earthquakes than in other parts of Canada. While Vancouver has not experienced a damaging earthquake in its short history, large earthquakes nearby have been strongly felt and there is paieoseismic evidence for very strong shaking in prehistoric time. Most of the region is placed in Seismic Zone 4 in the 1990 edition of the National Building Code of Canada. (from Author) %1027 Catalogue of US Geological Survey strong-motion records, 1992 J. C. Switzer & R. L. Porcella, US Geological Survey Circular, 1114, 1994, 57 pp. During January to December 1992 nearly 720 accelerograph records were recovered at stations operated by the US Geological Survey's National Strongly-Motion Program; approximately 50% of these records are from the main shocks of the June 28 Landers and Big Bear earthquakes in southern California. Nine earthquakes of M = 5.0 or greater occurred in California during 1992, including Landers, Big Bear, and the Ms = 7.1 Petrolia earthquake in northern California on April 25. Additional strong-motion records were recoverd at USGS accelerograph stations located in Hawaii and Nevada during this report period. (from Authors) 961028 Frequency domain inversion of strong motions: application to the 1992 Landers earthquake F. Cotton & M. Campillo, Journal of Geophysical Research, 100(B3), 1995, pp 3961-3975. The paper presents a frequency domain inversion in which the observed earthquake strong ground motions are used to constrain the space-time dependence of slip on a fault. Green's functions are numerically evaluated and the parameters describing the rupture are the local slip, rupture time and rise time. These parameters are simultaneously evaluated without additional constraints. This procedure allows for large variations in the local rupture velocity. The June 28, 1992 Landers earthquake (Mw -- 7.3) offers an exceptional opportunity to apply this technique to a major strike-slip event. The rupture evolution is modelled, including local differences in slip durations and variations in rupture velocity. The results are in good agreement with other inversion studies, geodetic and surface observations. The main discrepancies occurred at depth and at the end of the
%1030 Ground motions during the 1994 Northridge earthquake W. D. L. Finn, C. E. Ventura & N. D. Schuster, Canadian Journal of Civil Engineering, 22(2), 1995, pp 300-315. Some major damage centres coincided with alluvial basins. Generation of surface waves within the basins during the main shock contributed to increased amplification and duration. Surface waves were detected at the site of the collapse of the 1-10 interchange and in the damaged area of Sherman Oaks using afLershock data. Cedar Hill seismographic station in Tarzana recorded the highest accelerations of the earthquake. These are currently attributed to topographic effects of the hill on which the station is located. After shock data from two major arrays found that the low amplitude motions were magnified significantly at the crest of the hill. (from Authors)
961031 The 1994 Northridge earthquake: 3-D crustal structure in the rupture zone and its relation to the aftershock locations and mechanisms Dapeng Zhao & H. Kanamori, Geophysical Research Letters, 22(7), 1995, pp 763-766. A detailed 3-D P-wave velocity structure of the crust in the epicentral area of the 17 January, 1994 Northridge earthquake is determined. Regions with high aftershock activity are generally associated with faster P-wave velocities. The velocity is high around the main south-dipping fault of the 1994 Northridge earthquake and the north-dipping fault of the 1971 San Fernando earthquake. A linear distribution of strike-slip aftershocks was found along a NE-SW boundary between high-velocity and low-velocity structures. To the west of this boundary a cluster of large shallow aftershocks with mixed mechanisms occurred in or near the border of a low-velocity area, while to the east aftershocks with thrust mechanisms occurred in a high-velocity area. These observations suggest that lateral variations of crustal properties are closely related to the fault segmentation in the Transverse Ranges. (from Authors) 961032 On the variability of aftershock ground motions in the San Fernando Valley S. E. Hough, C. Dietel, G. Glassmoyer & E. Sembera, Geophysical Research Letters, 22(6), 1995, pp 727-730.
GEOLOGY:EARTHQUAKES
Then, a statistical discrimination of foreshocks from earthquakes of other types of clusters is explored. (from Authors)
Johnson Valley fault. A relatively low resolution could be an explanation for these differences. (from Authors)
961025 Spatial correlation of earthquake ground motion: nonparametric estimation I-I.-P. Boissieres & E. H. Vanmarcke, Soil Dynmnics & Earthquake Engineering, 14(1), 1995, pp 23-31. A non-parametric method, called multidimensional correlation mapping (MCM), is used to describe the local spatial correlation of different components of earthquake ground acceleration. The method estimates spatial correlation without presuming homogeneity or isotropy of the phasealigned local ground motion fields. For selected events recorded by the SMART1 accelerograph array, we obtain contour plots of equal correlation of ground acceleration, with respect to the center of the array. Displacement timehistories are also computed from the accelerograms and the spatial correlation of the displacements is estimated for comparison with that of the accelerations. (Authors)
961029 Stability of coda wave attenuation during the [arena Prleta, California, earthquake sequence G. C. Beroza, A. T. Cole & W. L. Ellsworth, Journal of Geophysical Research, 100(B3), 1995, pp 3977-3987. The Lama Prieta, California, earthquake occurred in a densely instrumented region with a history of microearthquake recording beginning more than a decade before the October 1989 mainsbock. This affords an unprecedented opportunity to detect changes in seismic wave propagation in the Earth's crust associated with a major earthquake. This study uses pairs of nearly identical earthquakes (doublets) to search for temporal changes of coda attenuation in the vicinity of the Lama Prieta earthquake. The observations place an upper bound of about 5% on preseismic, coseismic, and postseismic changes of coda Q in the epicentral region of the Lama Prieta earthquake. Even at this low level, the changes are neither spatially coherent nor correlated between adjacent frequency hands. The only hint of a signal is in the preseismic data where there is a possible precursory increase in coda Q of approximately 5% in the two eyars before the mainshock. The stabifity of coda Q throughout the Lama Prieta sequence is in sharp contrast to other studies that have reported much larger precursory changes in coda Q for other earthquakes. (from Authors)
961026 Earthquakes in the Vancouver area G. C. Rogers, Bulletin - Geological Survey of Canada, 481, 1994, pp 221-229. Vancouver and the densely populated Lower Mainland region of southwest British Columbia are situated over an active subduetion zone. The dynamic geological setting makes this region subject to frequent seismic activity and contributes to a higher risk of large damaging earthquakes than in other parts of Canada. While Vancouver has not experienced a damaging earthquake in its short history, large earthquakes nearby have been strongly felt and there is paieoseismic evidence for very strong shaking in prehistoric time. Most of the region is placed in Seismic Zone 4 in the 1990 edition of the National Building Code of Canada. (from Author) %1027 Catalogue of US Geological Survey strong-motion records, 1992 J. C. Switzer & R. L. Porcella, US Geological Survey Circular, 1114, 1994, 57 pp. During January to December 1992 nearly 720 accelerograph records were recovered at stations operated by the US Geological Survey's National Strongly-Motion Program; approximately 50% of these records are from the main shocks of the June 28 Landers and Big Bear earthquakes in southern California. Nine earthquakes of M = 5.0 or greater occurred in California during 1992, including Landers, Big Bear, and the Ms = 7.1 Petrolia earthquake in northern California on April 25. Additional strong-motion records were recoverd at USGS accelerograph stations located in Hawaii and Nevada during this report period. (from Authors) 961028 Frequency domain inversion of strong motions: application to the 1992 Landers earthquake F. Cotton & M. Campillo, Journal of Geophysical Research, 100(B3), 1995, pp 3961-3975. The paper presents a frequency domain inversion in which the observed earthquake strong ground motions are used to constrain the space-time dependence of slip on a fault. Green's functions are numerically evaluated and the parameters describing the rupture are the local slip, rupture time and rise time. These parameters are simultaneously evaluated without additional constraints. This procedure allows for large variations in the local rupture velocity. The June 28, 1992 Landers earthquake (Mw -- 7.3) offers an exceptional opportunity to apply this technique to a major strike-slip event. The rupture evolution is modelled, including local differences in slip durations and variations in rupture velocity. The results are in good agreement with other inversion studies, geodetic and surface observations. The main discrepancies occurred at depth and at the end of the
%1030 Ground motions during the 1994 Northridge earthquake W. D. L. Finn, C. E. Ventura & N. D. Schuster, Canadian Journal of Civil Engineering, 22(2), 1995, pp 300-315. Some major damage centres coincided with alluvial basins. Generation of surface waves within the basins during the main shock contributed to increased amplification and duration. Surface waves were detected at the site of the collapse of the 1-10 interchange and in the damaged area of Sherman Oaks using afLershock data. Cedar Hill seismographic station in Tarzana recorded the highest accelerations of the earthquake. These are currently attributed to topographic effects of the hill on which the station is located. After shock data from two major arrays found that the low amplitude motions were magnified significantly at the crest of the hill. (from Authors)
961031 The 1994 Northridge earthquake: 3-D crustal structure in the rupture zone and its relation to the aftershock locations and mechanisms Dapeng Zhao & H. Kanamori, Geophysical Research Letters, 22(7), 1995, pp 763-766. A detailed 3-D P-wave velocity structure of the crust in the epicentral area of the 17 January, 1994 Northridge earthquake is determined. Regions with high aftershock activity are generally associated with faster P-wave velocities. The velocity is high around the main south-dipping fault of the 1994 Northridge earthquake and the north-dipping fault of the 1971 San Fernando earthquake. A linear distribution of strike-slip aftershocks was found along a NE-SW boundary between high-velocity and low-velocity structures. To the west of this boundary a cluster of large shallow aftershocks with mixed mechanisms occurred in or near the border of a low-velocity area, while to the east aftershocks with thrust mechanisms occurred in a high-velocity area. These observations suggest that lateral variations of crustal properties are closely related to the fault segmentation in the Transverse Ranges. (from Authors) 961032 On the variability of aftershock ground motions in the San Fernando Valley S. E. Hough, C. Dietel, G. Glassmoyer & E. Sembera, Geophysical Research Letters, 22(6), 1995, pp 727-730.