The 1170 and 1202 CE Dead Sea Rift earthquakes and long-term magnitude distribution of the Dead Sea Fault zone

In combination with the historical record, paleoseismic investigations have provided a record of large earthquakes in the Dead Sea Rift that extends back over 1500 years. Analysis of macroseismic effects can help refine magnitude estimates for large historical events. In this study we consider the detailed intensity distributions for two large events, in 1170 CE and 1202 CE, as determined from careful reinterpretation of available historical accounts, using the 1927 Jericho earthquake as a guide in their interpretation. In the absence of an intensity attenuation relationship for the Dead Sea region, we use the 1927 Jericho earthquake to develop a preliminary relationship based on a modification of the relationships developed in other regions. Using this relation, we estimate M7.6 for the 1202 earthquake and M6.6 for the 1170 earthquake. The uncertainties for both estimates are large and difficult to quantify with precision. The large uncertainties illustrate the critical need to develop a regional intensity attenuation relation. We further consider the distribution of magnitudes in the historic record and show that it is consistent with a b-value distribution with a b-value of 1. Considering the entire Dead Sea Rift zone, we show that the seismic moment release rate over the past 1500 years is sufficient, within the uncertainties of the data, to account for the plate tectonic strain rate along the plate boundary. The results reveal that an earthquake of M7.8 is expected within the zone on average every 1000 years. ?? 2011 Science From Israel/LPPLtd.