The long- and short-term lateral slip and seismicity along the Dead Sea Transform: An interim evaluation

Recent advances in neotectonic, paleoseismic, and other studies of the Dead Sea Transform (DST) allow evaluating the lateral slip rate over different time periods, and also raise new questions. The long-term slip rate over time scales of millions of years represents continuous plate motions that are expected to vary slowly. GPS observations reveal the current plate motions which probably reflect the last 0.5-1 Ma. These results indicate that approximately 1-2 Ma ago the slip rate slowed to 4-5.5 mm/y, compared with the average rate of 6-7 mm/y over the last 5 Ma. At the same time the Euler pole of the Sinai-Arabia motion shifted eastward, continuing a longer term trend that began >5 Ma ago, which records an increase of the components of transverse motion along the N and S parts of the DST.The short-term slip rate over the last several kyr to tens of kyr is dominated by discrete earthquake-generating slip events that are distributed irregularly in space and time. These events relieve, to various extents, the shearing of the plate margins that is built up as a result of the continuing plate motions during the inter-seismic periods when the faults along the DST are locked. Offsets of various markers and variations in the earthquake distribution show that over the last ca. 2 kyr (perhaps more), which is not much longer than the recurrence times of the strongest earthquakes, the lateral slip rate varied irregularly along the DST. On short time scales, local slip rates could deviate by up to 50% from the plate motions in that period. Some findings raise the possibility that the magnitude-frequency relation deviated from the Gutenberg-Richter relation, an issue that requires further study.Offsets of geomorphic markers show that in the last 50 kyr and more, much longer than the recurrence times of the strongest earthquakes, the cumulative slip at any place was quite close to the plate motions during this period. Over this time scale the residual short-term variations of the slip become small compared with the total slip. This should be reconciled with the record of sediments disturbed by seismic shaking that suggests that the frequency of strong earthquakes varied considerably and was particularly low 15-40 kyr ago, at least in the Dead Sea basin. This raises questions regarding the magnitudes of past strongest earthquakes and the role of aseismic slip. Both of these issues require further study.