A Board of Inquiry was appointed by the Governor of California to investigate the 1989 Loma Prieta Earthquake. The formation of the Board was prompted by earthquake damage to bridges and freeway structures and the desire to know not only what happened, but how to prevent such destruction in future earthquakes. The Board made fifty-two specific findings and eight recommendations. They identified three essential challenges that must be addressed by the citizens of California, if they expect a future adequately safe from earthquakes: 1) ensure that earthquake risks posed by new construction are acceptable; 2) identify and correct unacceptable seismic safety conditions in existing structures, and; 3) develop and implement actions that foster the rapid, effective, and economic response to and recovery from damaging earthquakes The Loma Prieta earthquake should be considered a clear and powerful warning to the people of California. Although progress has been made during the past two decades in reducing earthquake risks, much more could have been done, and awaits doing. More aggressive efforts to mitigate the consequences of future, certain earthquakes are needed if their disastrous potential is to be minimized and one of the most fundamental of responsibilities of government is to be fulfilled—to provide for the public safety. The Governor signed an Executive Order implementing the principal recommendations of the Board that may prove to be the most significant step to improve seismic safety within the State taken in the last several decades. It establishes the policy that all state owned and operated structures are to be seismically safe and that important structures are to maintain their function after earthquakes.

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.

SummaryThe Thiel–Zsutty (TZ) model predicts mean and the probability distribution function for earthquake damageability of building as a function of peak ground acceleration. ATC‐13‐1 provides an alternate damageability model based on modified Mercalli intensity characterization of ground motion and a beta distribution function for selected building types. This paper provides a reconciliation of the TZ and Applied Technology Council (ATC) methods. It is shown that the beta distribution can provide a continuous representation of the step‐wise TZ Markov distribution function. When the TZ model uses a compression factor for the standard deviation to represent the degree of uncertainty in the parameters, then the TZ results are found to be consistent with the ATC‐13‐1 distribution function for a specific compression factor of 0.40. This paper provides a new, simply applicable method to determine the damage distribution function for a given site, building type, and site conditions; using a beta distribution and allowing inclusion of the degree of confidence the assessor has in the determination of the parameters. New equations are provided to estimate the mean, standard deviation, and upper confidence limit of the damage ratio.

Bridges affected by the Northridge earthquake were examined to evaluate the performance of Caltrans bridges, retrofit and peer review programs, and technical procedures. All structures in the region of strong shaking that had been retrofitted since 1989 performed adequately; if the seven bridges that collapsed had been retrofitted, they would be expected to have survived with little damage. The bridges subjected to strong shaking that had been constructed or retrofitted to current Caltrans criteria had, at most, minor damage; all remained in service. The Seismic Advisory Board concluded that the Caltrans seismic design procedures for new bridges and its retrofit procedures for existing hazardous bridges are technically sound. The Board found that the retrofit program is proceeding fairly well, but that the screening methods used to identify hazardous bridges could be improved as could the pace of retrofitting, particularly toll bridges. There were no construction projects underway in the Spring of 1994 for toll bridges, nor had preparation of retrofit designs begun. Twenty-one findings and seventeen recommendations are presented. Although much has been accomplished, much remains to be done. With some improvements, the Caltrans program should be continued with dispatch and determination. The major foreseeable impediments to a successful program are inadequate or fluctuating funding. The Seismic Advisory Board has confidence that the California highway system is progressing in an orderly fashion to one that is significantly more seismically safe.

Current earthquake casualty reduction measures are examined and recommendations made for needed changes. Key new approaches are outlined and a new framework for understanding casualty reduction measures presented. The framework considers both issues of demand for medical services and supply within primary, secondary and tertiary prevention aspects of each. It is used to assess current measures against recent empirical data and to suggest changes that incorporate new data and methods. Issues include the management of emergency medical services, messages for individual protective actions and assumptions about the nature of injuries. Research has tended to consider primarily the demand side of earthquake injury prevention, focusing on the injured rather than the uninjured. Case series investigations have tended to be descriptive rather than analytical and be undertaken from a clinical rather than an epidemiological perspective, documenting medical aspects of earthquake injuries. Linking these injuries to the risk factors associated with them has not been as systematically studied. Proposed here is an approach for casualty reduction research to fill knowledge gaps. It includes steps to integrate future casualty data and assessment efforts into casualty modeling and into ongoing earthquake policy formation.