Seismic hazard analysis and seismic slope stability evaluation using discrete faults in northwestern Pakistan.

摘要

The Mw 7.6 earthquake that occurred on 8 October 2005 in Kashmir, Pakistan, resulted in tremendous number of fatalities and injuries, and also triggered numerous landslides. Although there are no reliable means to predict the timing of the earthquake, it is possible to reduce the loss of life and damages associated with strong ground motions and landslides by designing and mitigating structures based on proper seismic hazard and seismic slope stability analyses. This study presents the methodology and results of seismic hazard and slope stability analyses in northwestern Pakistan.;The first part of the thesis describes the methodology used to perform deterministic and probabilistic seismic hazard analyses. The methodology of seismic hazard analysis includes identification of seismic sources from 32 faults in NW Pakistan, characterization of recurrence models for the faults based on both historical and instrumented seismicity in addition to geologic evidence, and selection of four plate boundary attenuation relations from the Next Generation Attenuation of Ground Motions Project. Peak ground accelerations for Kaghan and Muzaffarabad which are surrounded by major faults were predicted to be approximately 3 to 4 times greater than estimates by previous studies using diffuse areal source zones. Seismic hazard maps for PGA and spectral accelerations at periods of 0.2 sec and 1.0 sec corresponding to 475-, 975-, and 2475-year return periods were produced for NW Pakistan. Based on deaggregation results, a discussion of the conditional mean spectra for engineering applications is presented.;The second part of the thesis proposes factors that affect distribution of shallow landslides triggered by an earthquake. Landslides are the most common consequence of earthquakes, resulting in significant amount of damages of structures and lives. Significant damage was induced from the landslides triggered by the 2005, Kashmir, Pakistan, earthquake. Therefore, predicting locations and severity of landslide is an essential part of earthquake engineering. However, the currently used seismic slope stability analysis cannot capture the actual trend of landslide distribution, especially high landslide concentration near field. This study proposes the effect of vertical ground acceleration, topographic effects, and bond break effects, in addition to the strong horizontal ground acceleration, as factors that contribute to the landslide distribution near earthquake source. Landslide database from four earthquake cases (1989 Loma-Prieta, U.S.; 1999 Chi-Chi, Taiwan; 2005 Kashmir, Pakistan; and 2008 Wenchuan, China) were selected to verify these factors for slope stability analysis.