New Madrid Seismic Zone: Overview of Earthquake Hazard and Magnitude Assessment Based on Fragility of Historic Structures

摘要

Recent advances in seismic hazard characterization and earthquake engineering have culminated in the seismic design provisions of the International Building Code (IBC-2000) and the International Residential Code (IRC-2000). As both codes are currently being considered for adoption by local political jurisdictions across the United States, they have generated much concern and controversy as to the accuracy and validity of the new seismic provisions in the Central and Eastern United States (CEUS) and particularly in the New Madrid Seismic Zone (NMSZ). The design level of ground motion in the NMSZ exceeds that determined for many active seismic regions of California and represents a significant increase from historically used values. This study provides an overview of the seismic hazard characterization procedures used in the NMSZ and implemented in the IBC-2000 and IRC-2000. Furthermore, a series of structural fragility evaluations of historic accounts of building damage are conducted to provide additional and independent constraints on the magnitude estimates of the 1811-1812 earthquakes. This approach to magnitude assessment is particularly appealing given that the magnitude estimate is ultimately used for regulation of building construction through the use of seismic hazard maps that are integral with seismic design provisions in modern building codes. The specific objectives of the study are to: contribute to a constructive dialog between the seismic engineering community and the home building industry; review the seismic hazard assessment procedures for the NMSZ; communicate the level of uncertainties involved in the seismic hazard assessment procedures and their impact on the assignment of seismic design ground motions and categories; survey existing structures that survived the 1811-1812 earthquakes to better understand the seismic vulnerability of historic buildings; conduct probabilistic and deterministic structural fragility evaluations of historic structures to develop independent constraints on the magnitude of the 1811-1812 earthquakes; and, provide recommendations regarding implications associated with adoption or modification of newer seismic hazard provisions found in the IBC-2000 and IRC-2000.