Site Effects in the Loma Prieta Earthquake and Comparison with an Earthquake Intensity Prediction Method

Strong motion records of the Loma Prieta Earthquake of October, 17, 1989 have been analyzed in comparison with epicentral distances and types of soil deposits, and site effects and attenuation relations have been studied. Site effects are significantly recognized in the earthquake, as usually found in Japanese earthquakes. And validity of the U.S. seismic intensity prediction method that Association of Bay Area Governments (ABAG) adopted to prepare some earthquake preparedness maps has been examined on the basis of the Loma Prieta Earthquake data. Finally, soil damping of San Francisco Bay Area has been evaluated from the strong motion records

Numerical and Experimental Simulation of Seismic Site Responses

Prediction of seismic site responses has been one of the most important tasks in geotechnical earthquake engineering. Since Kanai used the multiple wave reflection theory to compute horizontal ground movements against seismic shaking, a number of researchers have extended the basic concept proposed by Kanai. Performance of seismic site response methods, however, has always invited open questions for problems involving extreme seismic shaking and large deformation of soils due, for example, to liquefaction and lateral spreading. A new numerical method SRANG3D (Site Response Analysis of Non-linear Ground in 3 Dimensions) has been developed to improve our prediction capabilities for seismic site responses. SRANG3D computes seismic site responses that involve vertical propagation of two horizontally polarized S waves and one P wave. The most distinct feature of SRANG3D is that the stress-strain relationships of soil can be represented by a combination of various elasto-plastic constitutive soil models and discrete element models. This paper introduces the new site-response analysis method SRANG3D and the paper highlights results obtained from this new method. Our study demonstrated that SRANG3D yields improved predictions of the large-scale experimental data than currently available site-response analysis methods

Large-Scale Shake Table Test on Lateral Spreading of a Sheet-Pile Wall Model and Its Centrifuge Simulation

The purpose of this test was to realistically reproduce soil liquefaction and the lateral spreading of saturated sand deposits behind the sheet-pile quay walls and the consequent deformation and translation of neighboring pile foundations. Therefore, a shake table test was carried out using a large-scale laminar box on the large-scale shake table in Tsukuba. The inside dimensions of the model were 11.6 m in length, 3.1 m in width and 4.5 m in depth. Next, a dynamic centrifuge test on the behavior of a sheet-pile wall and a soil pile system was conducted to simulate that of a large-scale shake table test as a prototype. The shake table test was performed under a centrifuge acceleration of 15g． The large-scale test results showed that the lateral displacement of the sheet-pile is increased by about 5 seconds during the shaking, while the sheet-pile showed significant lateral spreading for about 200 seconds after the shaking. The centrifuge study generally confirmed that it is possible to simulate a large-scale test for lateral spreading of a sheet-pile wall and its backfill

Considerations to Damage Patterns in the Marina District During the Loma Prieta Earthquake Based on Rayleigh Wave Investigation

Rayleigh wave investigation is made in the Marina District to study geotechnical factors controlling the damage patterns in the Loma Prieta earthquake. A portable system has been developed for determining a Rayleigh wave dispersion curve based on the measurements of artificially induced ground vibration or microtremor. Five sites are selected along a line crossing the hydraulic fill zone in which structures and/or buried utilities were significantly damaged. An inverse analysis on the measured dispersion curves results in a cross section of shear wave velocity profiles in the District. Site amplification and liquefaction potential of each site are estimated and discussed based on the Vs-profiles. It is shown that soil liquefaction is likely to have occurred throughout the fill zone, and that the predominant period of ground motions in the zone of structural damage is longer than and closer to the natural period of structures with soft first story than that in the non-damaged zone. These results appear to be consistent with the damage patterns in the District, indicating that the proposed investigation is effective for seismic zonation