SEISMIC HAZARD MAP OF THE CLEVELAND SOUTH (OHIO) 30X60-MINUTE QUADRANGLE

A seismic hazard map of the Cleveland South (Ohio) 30x60-minute quadrangle has been developed using a Geographic Information System (GIS). The map indicates areas of relatively high and low hazard as indicated by the potential for surface accelerations. This potential is determined by past regional seismicity and effects of the surficial geology. A catalog of earthquakes (M>2.5) within a 1000 km radius of the quadrangle was developed to determine the past influence of regional seismicity at each point within the quadrangle. At every location within the study area, the cumulative influence of all earthquakes within the catalog is calculated using the magnitude-distance relation of Donovan (1973). The weighting of early instrumental earthquakes (i.e., those recorded on at least one seismograph) in the cumulative influence is twice that of historical earthquakes (pre-seismograph), while the weighting of network-located earthquakes is three times that of historical events. The cumulative influence is modified by a surficial geology factor (an acceleration amplification) given by the reciprocal of the local shear-wave velocity (Borcherdt et al., 1991).

The variation in seismic hazard across the quadrangle due to proximity to regional epicenters is of the same order of magnitude as that due to heterogeneity in surficial geology. For example, Burton, located in the northeastern part of the quadrangle, has relatively high contribution to its seismic hazard from its proximity to the Ashtabula seismic zone. This contribution is less in the Cuyahoga River Valley, located in the central portion of the quadrangle. The acceleration amplification factor, however, is higher along the Cuyahoga Valley due to the lower shear-wave velocity of the sand and gravel and lacustrine deposits there as opposed to the till and Pennsylvanian bedrock found at Burton. The net effect is a seismic hazard in the Cuyahoga Valley that is three times that at Burton.

Further work planned in this study include exploring other magnitude-distance relations, obtaining more accurate shear-wave velocity estimates, and the incorporation of liquefaction and slope-failure potentials into the total seismic hazard.