Survey of Historic Buildings Predating the 1811-1812 New Madrid Earthquakes and Magnitude Estimation Based on Structural Fragility

Abstract

Accurate estimation of the magnitudes of the 1811-1812 earthquakes is an important step in the assessment of earthquake hazard in the New Madrid seismic zone (NMSZ). Expert opinion on the magnitudes of these events has changed over time and currently varies from as low as M 7.4 to as high as M 8.1 (Johnston, 1996; Hough et al. , 2000; Bakun and Hopper, 2002). Historic damage reports and “felt” accounts are the primary sources of information on the extent of the 1811-1812 earthquakes. The distant date of the events, lack of earthquake experience and knowledge, poorly developed communication infrastructure, and locations of the epicenters in the scarcely populated area are among the factors that contribute to the ambiguity of the historic accounts. This ambiguity translates directly into uncertainty in the magnitude estimates of the events and the uncertainty of hazard estimates in the NMSZ. In an effort to better quantify and explain the degree of structural damage reported during the 1811-1812 earthquakes, an extensive historic building survey of structures that predated the events was conducted. The purpose of this survey was to document the construction methods and materials and building configurations typical for that time period. In addition, historic accounts depicting the aftermath of the events were examined for the types and extent of reported structural damage to supplement the results of the historic building survey. Using the compiled data, an improved, more consistent understanding of the performance of buildings during the 1811-1812 events can be achieved and the reported damage correlated with ground motions. In fact, these historic buildings represent surviving seismograph records. It is just that these seismographs are unusually large compared to modern instruments, have unique vibration characteristics, and use the language of damage instead of ink and paper or digital recordings. The remaining task …