USACE defines the following criteria:
1. Maximum credible earthquake (MCE).
This earthquake is defined as the greatest earthquake that can reasonably be expected to be generated by a specific source on the basis of seismological and geological evidence. Since a project site may be affected by earthquakes generated by various sources, each with its own fault mechanism, maximum earthquake magnitude, and distance from the site, multiple MCE’s may be defined for the site, each with characteristic ground motion parameters and spectral shape. The MCE is determined by a DSHA.
2. Maximum design earthquake (MDE).
The MDE is the maximum level of ground motion for which a structure is designed or evaluated. The associated performance requirement is that the project performs without significant failure, such as uncontrolled release of a reservoir, although severe damage or economic loss may be tolerated. For critical features, the MDE is the same as the MCE. For all other features, the MDE shall be selected as a lesser earthquake than the MCE which provides economical designs meeting appropriate safety standards. The MDE can be characterized as a deterministic or probabilistic event.
3. Operating basis earthquake (OBE).
The OBE is an earthquake that can reasonably be expected to occur within the service life of the project, that is, with a 50-percent probability of exceedance during the service life. (This corresponds to a return period of 144 years for a project with a service life of 100 years.) The associated performance requirement is that the project functions with little or no damage, and without interruption of function. The purpose of the OBE is to protect against economic losses from damage or loss of service, and therefore alternative choices of return period for the OBE may be based on economic considerations. The OBE is determined by a PSHA
Published FEMA guidelines are generally in accordance with FERC guidelines, but do include terminology definitions similar to USACE, as follows:
1. Maximum Credible Earthquake (MCE).
The MCE is the largest earthquake magnitude that could occur along a recognized fault or within a particular seismotectonic province or source area under the current tectonic framework. The loading resulting from the MCE can and often is exceeded for Probabilistic Methods for high return period faults close in, such as the San Andreas Fault in California.
2. Maximum Design Earthquake (MDE) or Safety Evaluation Earthquake (SEE). This is the earthquake that produces the maximum level of ground motion for which a structure is to be designed or evaluated. The MDE or SEE may be set equal to the MCE or to a design earthquake less than the MCE, depending on the circumstances. Factors to consider in establishing the size of MDE or SEE are the hazard potential classification of the dam (FEMA 1998), criticality of the project function (water supply, recreation, flood control, etc.), and the turnaround time to restore the facility to operability. Guidance on selecting the MDE and SEE is contained in paragraph C.3. In general, the associated performance requirement for the MDE or SEE is that the project performs without catastrophic failure, such as uncontrolled release of a reservoir, although significant damage or economic loss may be tolerated. If the dam contains a critical water supply reservoir, the expected damage should be limited to allow the project to be restored to operation in an acceptable time frame.
3. Operating Basis Earthquake (OBE). The OBE is an earthquake that produces ground motions at the site that can reasonably be expected to occur within the service life of the project. The associated performance requirement is that the project functions with little or no damage, and without interruption of function. The purpose of the OBE is to protect against economic losses from damage or loss of service. Therefore, the return period for the OBE may be based on economic considerations.
Note FEMA defines the SEE as the same as the MDE
출처: Site-specific seismic hazard study plan Section 16.6, Study Completion Report. Attachment 7, Discussion of MCE and OBE
https://www.arlis.org/docs/vol1/Susitna2/2/SuWa289/SuWa289sec16-6att7.pdf
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