Toland Road Seismic Analysis - Peak Ground Acceleration
Dynamic Site Response Analysis And Design Methodology Of A Geosynthetic Liner System For A Municipal Solid Waste Landfill Located In A High Seismic Risk Zone - A Case Study

Peak Ground Acceleration

In California, the PGA is evaluated in accordance with California Code of Regulations (CCR) Title 27, Sections 20370 and 21750 (f)(5) which require Class II landfills to be constructed to withstand the Maximum Credible Earthquake (MCE) and Class III landfills to be constructed to withstand the Maximum Probable Earthquake (MPE). The MCE is defined as the largest possible earthquake, whereas the MPE is defined as the earthquake likely to occur in 100 years, but not less than the largest historic earthquake. For this project, EBA used the MPE to evaluate temporary fill slopes; and at the request of the client, the larger MCE to conservatively evaluate permanent or long-term conditions.

Probabilistic Approach

EBA used a probabilistic approach to determine the PGA associated with the MPE. The annual probability, P, that an event with a likelihood of exceedance of q, will occur within the next, n years is given by:
P=1-(1-q) 1/n
Use of this equation requires an interpretation of California's Title 27 definition of "...likely to occur in 100 years" which will determine the variable q. For this project, we assumed "likely" meant a 70% probability of exceedance and determined the PGA associated with the calculated annual probability, P (0.01 for the MPE), from the acceleration-reoccurrence relationship (Figure 1) prepared previously for the site. This relationship was developed using various methods (i.e., strain accumulation observed on faults, statistical analyses of historical seismicity, etc.) and attenuation curves (Figure 2) relating earthquake magnitude and distance to PGA (Campbell, 1997).

Deterministic Approach

The deterministic approach was used to evaluate the PGA associated with the MCE. The earthquake source capable of producing the strongest level of ground shaking was determined to be a major active fault located less than one mile from the site. The MCE was estimated based on rupture mechanisms and geometry (i.e., fault length, slip rate, rupture area, dip angle, depth, etc.) developed by several researchers (Slemmons, 1977; Wells and Coppersmith, 1994; and Youngs and Coppersmith, 1985). Attenuation curves were used to determine the PGA which was applied in the slope stability analysis to evaluate the pseudo-static factor of safety.

References

  • Campbell, K.W., 1997, Empirical Near-Source Attenuation Relationships for Horizontal and Vertical Components of Peak Ground Acceleration, Peak Ground Velocity, and Pseudo-Absolute Acceleration Response Spectra, Seismological Research Letters, Vol. 68, No. 1, January/February 1997.
  • Slemmons, D.B., 1977, Faults and Earthquake Magnitude, Miscellaneous Paper S-73-1, Report 6, U.S. Army Corps of Engineers Waterways Experimental Station, Vicksburg, Mississippi, 129 pp.
  • Wells, D.L., and Coppersmith, K.J., 1994, New Empirical Relationships among Magnitude, Rupture, Length, Rupture Width, Rupture Area, and Surface Displacement, Bulletin of the Seismological Society of America, Vol. 84, No. 4, pp. 974-1002.
  • Youngs, R.R., and K.J. Coppersmith, 1985, Implications of Fault Slip Rates and Earthquake Recurrence Models to Probabilistic Seismic Hazard Estimates, Bulletin of the Seismological Society of America, Vol. 75, pp. 939-964.

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