Elisa J. Kagan, Hebrew University of Jerusalem, Institute of Earth Sciences, Jerusalem 91904, Israel; et al. Pages 261-264.
The long-term recurrence pattern of past earthquakes is of considerable consequence for hazard assessments with implications for earthquake physics. Kagan et al. introduce a dated record of earthquakes from well-preserved earthquake-damaged cave deposits (e.g., stalactites and stalagmites). The study caves are located 15 km from the city of Jerusalem (Israel) and 40 km from the active Dead Sea transform fault. During an earthquake, cave deposits can be broken and may fall. Subsequent to an earthquake, deposition continues on top of the damaged material. The boundary between the pre- and post-earthquake material can be dated precisely, bracketing the date of the earthquake. Kagan et al. dated a large number of rock falls inside the caves using Uranium-Thorium radiometric dating methods and stable isotope correlation with well-dated climatic events previously recognized in the deposits. Cave deposits are advantageous to this kind of study since they are potentially well dated up to about half a million years. This presents the opportunity to recreate a long-term earthquake record and include the largest earthquakes to have hit a region, which is usually unavailable by other methods. Within the last 185,000 years covered, they dated 38 damaged samples. They determined that these deposits were damaged during 13\ufffd18 earthquakes. The average recurrence interval of earthquakes causing damage at the study location is 10,000\ufffd14,000 years. Kagan et al. show that there is a correlation of the earthquakes dated in the study caves with independent earthquake records (mainly deformed lake sediments) near the Dead Sea. The earthquakes dated in their study are most likely large (M > 8), infrequent events, given the distance from the active fault. This opens up a significant new avenue of earthquake research that will provide precise dating and observational constraints on large, infrequent earthquakes.