Earthquake Spectra

Recent foreign disasters reinforce the argument that it is past time to distinguish conceptually post-earthquake “urban heavy rescue” (UHR) from the generic “search and rescue.” It is especially important to appreciate the problematic operational environment of UHR and the political as well as the lifesaving implications of UHR successes and failures. Effective UHR requires complex inter-governmental, public-private, and civil-military preparedness planning. At this point in time, UHR remains the weak link in the entire response chain to the inevitable major urban earthquake in the United States.

A simple Markov distribution relates the probability of occurrence of five discrete damage states for a specific building type in an earthquake. Within the model the damage distribution depends on parameters that represent the building's structural system, the matching of the site and building periods, and the site materials, and the site's acceleration. The constants in the model were determined using a maximum likelihood formulation and damage observations for a series of California and Chinese earthquakes. Model predictions of damage distributions agree well with reserved damage data not used in determining the constants. A maximum likelihood method allows determination of ground motion, attenuation, and/or earthquake moment magnitude from observations of damage for different types of structures located at diverse sites. A simple relationship exists for average damage estimate that closely matches historical observations.

A twenty-two story, triangular in plan, symmetrical, reinforced concrete building on the beachfront in Vin~a del Mar, Chile, was temporarily instrumented in August 1985 following the 3 March 1985 Central Chile earthquake (M _s = 7.8) and aftershocks were recorded. Ambient and free vibration tests were also performed. The paper reports studies of the records of the responses of the building, the primary modes of vibration of the structure, its excellent performance during the earthquake and results from analyses using mathematical models and system identification techniques.

After many years of making progress slowly through ad hoc and piecemeal seismic safety measures adopted after damaging earthquakes, California has recently been moving toward more comprehensive seismic policy development, and in 1985 enacted the California Earthquake Hazards Reduction Act. The new law is a landmark in seismic policymaking, establishing a system of comprehensive and continuous planning, plan implementation, monitoring of results, and plan revision. It also adopted as a state policy goal the achievement of significant earthquake-hazard reduction by the year 2000. The program set up by the new law will further earthquake safety in six major areas: (1) existing development, (2) emergency preparedness and response, (3) new development, (4) long-term recovery, (5) education and public information, and (6) research and its application. The Seismic Safety Commission, an independent policy body that advises the Legislature and Governor on earthquake-related matters, was chosen to lead the program, working with other agencies representing a wide range of concerns. The first five-year program was published in September 1986, the “year 2” revision and progress report in September 1987, and the first follow-up supplement (for local government) in January 1988. The new program is already making respectable progress, although not as rapidly as the initial schedule called for.