Earthquakes recorded stratigraphically on carbonate platforms

Abstract

The longest records of earthquake activity¹ may be preserved near the edges of carbonate platforms where reefs have bordered active faults. Because the carbonate sediments build up almost to low tide level, because their character and lithification are very sensitive to deviations from that datum, and because they commonly lithify soon after deposition², strata can precisely record changes in lithospheric flexure³, which in turn record the buildup and release of elastic strain energy during stick–slip faulting. The approximate stratigraphy is predictable for a given history of faulting. Comparison of predictions with observations leads to an explanation for some of the hemicyclic sedimentary sequences common^4–6 on carbonate platforms. These records are important for characterizing the seismicity of Atlantic-type continental margins in general. After rifting, faults evidently remain active⁷, but major earthquakes are so rare that their recurrence times cannot be established from direct observations.