First-generation site-response maps for the Los Angeles region based on earthquake ground motions

Abstract Ground-motion records from aftershocks of the 1994 Northridge earthquake and mainshock records from the 1971 San Fernando, 1987 Whittier Narrows, 1991 Sierra Madre, and 1994 Northridge earthquakes are used to estimate site response relative to a rock site for the urban Los Angeles area. Site response is estimated at 232 mainshock and 201 aftershock sites relative to a low-amplitude site in the Santa Monica Mountains. Average amplification values are calculated for the frequency bands: 1 to 3, 3 to 5, and 5 to 7 Hz. These bands are chosen based on limitations in aftershock recording equipment at lower frequencies and reduced significance to the building inventory at higher frequencies. Site amplification factors determined at the instrumented locations are grouped by the surficial geology and contoured to produce a continuous spatial estimation of amplification. The maps in this article represent the first attempt to produce estimates of site amplification based on observations of ground motion for such a large areal extent of the Los Angeles region. These maps are expected to evolve as more data become available and more analysis is done.

[1]  S. Harmsen Estimating the diminution of shear-wave amplitude with distance: Application to the Los Angeles, California, urban area , 1997, Bulletin of the Seismological Society of America.

[2]  J. Tinsley,et al.  Evaluation of the relation between near-surface geological units and ground response in the vicinity of Long Beach, California , 1979, Bulletin of the Seismological Society of America.

[3]  R. Borcherdt Effects of local geology on ground motion near San Francisco Bay , 1970 .

[4]  S. Hartzell,et al.  Site-Response Maps for the Los Angeles Region Based on Earthquake Ground Motions , 1996 .

[5]  John G. Anderson,et al.  A MODEL FOR THE SHAPE OF THE FOURIER AMPLITUDE SPECTRUM OF ACCELERATION AT HIGH FREQUENCIES , 1984 .

[6]  R. F. Yerkes,et al.  Geology of the Los Angeles Basin, California: an introduction , 1965 .

[7]  Roger D. Borcherdt,et al.  A comparative ground response study near Los Angeles using recordings of Nevada nuclear tests and the 1971 San Fernando earthquake , 1984 .

[8]  Roger D. Borcherdt,et al.  Estimates of Site-Dependent Response Spectra for Design (Methodology and Justification) , 1994 .

[9]  Margaret Hellweg,et al.  Directional topographic site response at Tarzana observed in aftershocks of the 1994 Northridge, California, earthquake: Implications for mainshock motions , 1996, Bulletin of the Seismological Society of America.

[10]  David Carver,et al.  Urban seismology—Northridge aftershocks recorded by multi-scale arrays of portable digital seismographs , 1996 .

[11]  Jamison H. Steidl,et al.  Site amplification in the San Fernando Valley, California: Variability of site-effect estimation using the S-wave, coda, and H/V methods , 1997, Bulletin of the Seismological Society of America.

[12]  William H. K. Lee,et al.  Shallow velocity structure and poisson's ratio at the Tarzana, California, strong-motion accelerometer site , 1996, Bulletin of the Seismological Society of America.

[13]  Kenneth W. Campbell,et al.  A note on the distribution of earthquake damage in Long Beach, 1933 , 1976, Bulletin of the Seismological Society of America.

[14]  Paul M. Davis,et al.  Localized Amplification of Seismic Waves and Correlation with Damae due to the Northridge Earthquake: Evidence for Focusing in Santa Monica , 1996 .

[15]  W. B. Joyner,et al.  ESTIMATION OF RESPONSE SPECTRA AND PEAK ACCELERATIONS FROM WESTERN NORTH AMERICAN EARTHQUAKES: AN INTERIM REPORT PART 2 , 1993 .

[16]  D. Perkins,et al.  Nuclear event time histories and computed site transfer functions for locations in the Los Angeles region , 1980 .

[17]  David Carver,et al.  Variability of site response in the Los Angeles urban area , 1997, Bulletin of the Seismological Society of America.

[18]  S. Harmsen Determination of site amplification in the Los Angeles urban area from inversion of strong-motion records , 1997, Bulletin of the Seismological Society of America.

[19]  Mihailo D. Trifunac,et al.  Recorded Ground and Structure Motions , 1995 .

[20]  Susan E. Hough,et al.  The Variability of PSV Response Spectra across a Dense Array Deployed during the Northridge Aftershock Sequence , 1997 .

[21]  A. Shakal,et al.  CSMP strong-motion records from the Northridge, California Earthquake of 17 January 1994 , 1994 .

[22]  W. B. Joyner,et al.  Seismic velocities and geological conditions at twelve sites subjected to strong ground motion in the 1994 Northridge, California, earthquake , 1996 .

[23]  Mihailo D. Trifunac,et al.  A note on distribution of uncorrected peak ground accelerations during the Northridge, California, earthquake of 17 January 1994 , 1994 .

[24]  Arthur Frankel,et al.  Site response for urban Los Angeles using aftershocks of the Northridge earthquake , 1996, Bulletin of the Seismological Society of America.