| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
U.S. Geological Survey Branch of Earthquake and Landslide Hazards, Denver, Colorado 80255
Abstract
Following the 1989 Loma Prieta earthquake, a dense array of seven digitally recorded, three-component seismograph stations was deployed on Robinwood Ridge 7.3 km northwest of the epicenter. The purpose of this array was to investigate the cause of high levels of structural damage and ground cracking observed on the ridge crest. Aftershocks recorded by the array allow a comparison of ground motion up the slope of the ridge from the base to the crest. The data present an extremely complicated pattern of ground motion that demonstrates the importance of the three-dimensionality of the problem. Slowness analysis of P wave trains show initial arrivals propagating away from the source with small angles of incidence and large apparent velocities, consistent with direct arrivals. After 0.5 sec, propagation azimuths become more random and apparent velocities drop, indicating nearly horizontal wave propagation and multiply reflected and diffracted phases within the ridge. Slowness analysis and particle motion diagrams of horizontal components of motion show dramatic variations in ground motion with changes in azimuth of the source and a complicated interaction between body waves and Rayleigh and Love waves. Results suggest that the larger amplitude, more coherent arrivals at the array stations favor a propagation direction parallel to the ridge axis. An amplification factor of from 1.5 to 4.5 is seen for frequencies from 1.0 to 3.0 Hz with wavelengths comparable to the base of the ridge, part of which may be caused by local site effects and part by topographic amplification. In addition, amplifications of up to a factor of 5 are seen at higher frequencies and are attributed to local site effects. These effects are most notable from 4 to 8 Hz on the vertical components, and from 6 to 9 Hz on the horizontal components. The entire Robinwood Ridge area may also have been situated in a region of heightened mainshock ground motion due to source directivity and radiation pattern effects.
This article has been cited by other articles:
|
|
 |
|
  S. Ma, R. J. Archuleta, and M. T. Page Effects of Large-Scale Surface Topography on Ground Motions, as Demonstrated by a Study of the San Gabriel Mountains, Los Angeles, California Bulletin of the Seismological Society of America, December 1, 2007; 97(6): 2066 - 2079. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G.-Q. Wang, G.-Q. Tang, C. R. Jackson, X.-Y. Zhou, and Q.-L. Lin Strong Ground Motions Observed at the UPSAR during the 2003 M 6.5 San Simeon and 2004 M 6.0 Parkfield, California, Earthquakes Bulletin of the Seismological Society of America, September 1, 2006; 96(4B): S159 - S182. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
W. Z. Savage An Exact Solution for Effects of Topography on Free Rayleigh Waves Bulletin of the Seismological Society of America, October 1, 2004; 94(5): 1706 - 1727. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Anomalous Concentrations of Seismically Triggered Rock Falls in Pacoima Canyon: Are They Caused by Highly Susceptible Slopes or Local Amplification of Seismic Shaking? Bulletin of the Seismological Society of America, December 1, 2002; 92(8): 3180 - 3189.
|
|
|
|
|
|
S. Hartzell, E. Cranswick, A. Frankel, D. Carver, and M. Meremonte Variability of site response in the Los Angeles urban area Bulletin of the Seismological Society of America, December 1, 1997; 87(6): 1377 - 1400. [Abstract] [PDF]
|
|
|
|
|
|
F. J. Chavez-Garcia, M. Rodriguez, E. H. Field, and D. Hatzfeld Topographic site effects. A comparison of two nonreference methods Bulletin of the Seismological Society of America, December 1, 1997; 87(6): 1667 - 1673. [Abstract] [PDF]
|
|
|
|
|
|
S. A. Ashford and N. Sitar Analysis of topographic amplification of inclined shear waves in a steep coastal bluff Bulletin of the Seismological Society of America, June 1, 1997; 87(3): 692 - 700. [Abstract] [PDF]
|
|
|
|
|
|
J. S. Barker, M. Campillo, F. J. Sanchez-Sesma, D. Jongmans, and S. K. Singh Analysis of wave propagation in the Valley of Mexico from a dense array of seismometers Bulletin of the Seismological Society of America, December 1, 1996; 86(6): 1667 - 1680. [Abstract] [PDF]
|
|
|
|
|
|
Z. Xu, S. Y. Schwartz, and T. Lay Seismic wave-field observations at a dense, small-aperture array located on a landslide in the Santa Cruz Mountains, California Bulletin of the Seismological Society of America, June 1, 1996; 86(3): 655 - 669. [Abstract] [PDF]
|
|
|
|
|
|
M. Bouchon and J. S. Barker Seismic response of a hill: The example of Tarzana, California Bulletin of the Seismological Society of America, February 1, 1996; 86(1A): 66 - 72. [Abstract] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
