Modeling Post-Earthquake Restoration of the Los Angeles Water Supply System

Special Committee: Rachel A. Davidson, Thomas D. O'Rourke, Linda K. NozickThe purpose of this thesis is to develop a discrete event simulation model of post-earthquake restoration for the Los Angeles Department of Water and Power (LADWP) water supply system. Discrete event simulation, a new approach to modeling post-disaster lifeline restoration, offers many benefits for restoration modeling compared to alternative methods. The water supply system and restoration process are represented in great detail with few simplifications. The utility company's decision variables (e.g., number of repair crews, repair prioritization rules) are included explicitly, allowing exploration of their effects on the speed of the restoration. Restoration times are estimated separately for each region within the service area, and uncertainty in the process is modeled explicitly. With a service area of more than 1,200 km2 and 12,000 km of pipelines, the LADWP water supply system is the largest municipal system in the United States. Extensive review of the LADWP water organization, water supply system, and post-earthquake restoration process was conducted. This review provided the basis for the restoration model. Crews, tasks, and the different phases in the restoration process came directly from discussions with LADWP personnel and the water organization's emergency response plans. For a particular earthquake, the restoration model takes as input information about damage to the system and the resulting hydraulic flow, both of which are provided by the Graphical Iterative Response Analysis for Flow Following Earthquakes (GIRAFFE) model that was developed for the LADWP system (Shi 2006, Wang 2006). Throughout the restoration simulation, the model interacts with GIRAFFE periodically in order to receive updates of the system functionality at specific times as the restoration process proceeds and damage is repaired. The restoration model provides several different types of output including system and subregion restoration curves; spatial distribution of restoration; material usage; crew usage; average time each customer is without water; and time to restore the system and subregions to 90%, 98%, and 100%. It can also include damage uncertainty by combining the output from runs for multiple realizations of damage associated with a single earthquake. The model can be used to help estimate economic and societal losses due to water supply system outages, and to evaluate the effectiveness of possible restoration improvement strategies. Ten simulations of the restoration model were run using real damage data from the 1994 Northridge earthquake as input, and the results were compared to the actual restoration that took place following Northridge. The average spatial distribution of restoration roughly matches what occurred in 1994. As in real life, the areas experiencing longer outages in the model are mainly in the north of the system service area or around the San Fernando Valley. The system restoration curves did not match exactly, as the range of outputs from all 10 runs of the restoration model shows that the restoration occurs too quickly, especially during the first day after the earthquake. Possible future model modifications that may improve the calibration are discussed.This work was supported by the Earthquake Engineering Research Centers Program of the National Science Foundation through the Multidisciplinary Center for Earthquake Engineering Research under NSF Award Number EEC-970147

Posture-Induced Changes in Distortion-Product Otoacoustic Emissions and the Potential for Noninvasive Monitoring of Changes in Intracranial Pressure

Introduction Intracranial pressure (ICP) monitoring is currently an invasive procedure that requires access to the intracranial space through an opening in the skull. Noninvasive monitoring of ICP via the auditory system is theoretically possible because changes in ICP transfer to the inner ear through connections between the cerebral spinal fluid and the cochlear fluids. In particular, low-frequency distortion-product otoacoustic emissions (DPOAEs), measured noninvasively in the external ear canal, have magnitudes that depend on ICP. Postural changes in healthy humans cause systematic changes in ICP. Here, we quantify the effects of postural changes, and presumably ICP changes, on DPOAE magnitudes. Methods DPOAE magnitudes were measured on seven normal-hearing, healthy subjects at four postural positions on a tilting table (angles 90°, 0°, −30°, and −45° to the horizontal). At these positions, it is expected that ICP varied from about 0 (90°) to 22 mm Hg (−45°). DPOAE magnitudes were measured for a set of frequencies 750\u3cf 2\u3c4000, with f 2/f 1=1.2. Results For the low-frequency range of 750≤f 2≤1500, the differences in DPOAE magnitude between upright and −45° were highly significant (all p\u3c0.01), and above 1500 Hz there were minimal differences between magnitudes at 90° versus −45°. There were no significant differences in the DPOAE magnitudes with subjects at 90° and 0° postures. Conclusions Changes in ICP can be detected using the auditory-based measurement of DPOAEs. In particular, changes are largest at low frequencies. Although this approach does not allow for absolute measurement of ICP, it appears that measurement of DPOAEs may be a useful means of noninvasively monitoring ICP