Importance of intensity measure sufficiency for structural seismic demand hazard analysis

Seismic Intensity Measures (IM) are regularly used in demand hazard estimation of structures to mediate between seismological parameters such as magnitude, distance and the Engineering Demand Parameter (EDP). Conventionally, the quality of an IM is described by the IM's capability to predict an EDP (termed as efficiency) and render the EDP independent from seismological parameters (termed as sufficiency). While efficiency has received much attention in the past, sufficiency albeit being known as a sine qua non requirement has been overlooked. In this paper, we quantify sufficiency of IMs using a Total Information Gain metric (TIG- ) which represents the additional knowledge about the EDP from all the seismological parameters under consideration. We apply the (TIG - to a four-story steel moment frame building for several combinations of EDPs - IMs - ground motion record sets and find that record selection can have a considerable impact on IM sufficiency. Next, we show that the (TIG - generally represents changes in demand hazard curves when seismological parameters are included in computations. Finally, we explore the relation between efficiency and sufficiency of IMs and propose a unified metric for both sufficiency and efficiency of an IM.