DEVELOPING A CLASSIFICATION SCHEME FOR SEISMITES

The term "seismite" is presently used for many features and deposits of inferred seismic origin, each of which requires varying types and amounts of data to support a seismic interpretation. Studies of modern earthquakes indicate that shaking causes sediment to lose cohesion and deform through several processes. Neither the processes or the sedimentary deformation features formed by the processes are necessarily diagnostic of seismogenic origin. Likewise, the criteria and methodology used by different investigators to interpret seismites varies. For major, modern earthquakes, strong shaking results in widespread deformation features along correlative horizons; features along correlative horizons commonly exhibit regional trends in intensity of deformation or scale relative to earthquake magnitude and duration, as well as site characteristics. These characteristics, as well as theoretical considerations, can be used to develop a classification scheme for sedimentary deformational features, which can be used to interpret seismites. The scheme is designed to qualify seismite interpretations by using a standardized methodology for interpreting deformational features. The intent of the proposed scheme is to classify features or groups of features based on the relative amount and type of corroborating data. The degree to which deformational features or groups of features meet the following criteria is evaluated: (1) could be formed by processes initiated by a seism, (2) occurs at correlative horizons of deformation, (3) exhibits widespread occurrence, (4) exhibits regional trends, and (5) could not be formed by other mechanisms. Four types of features are defined: Class I can be interpreted as seismites, class II as probable seismites, class III as likely seismites, and class IV as possible seismites.