This project will test earthquake recurrence and slip models for a major plate boundary fault, the Dead Sea Transform in Israel. Through high-resolution three-dimensional trenching and precise dating of past earthquakes, along with analysis of the exceptionally long historical record of earthquakes in this region, this work will determine the timing and sizes of past earthquakes along this simple fault system. This will provide a test of the repeatability of large earthquakes and whether their occurrence in time is predictable or more random. This issue is at the core of earthquake forecast models and yet there is no general agreement as to what direction or approach should be taken because there are very few long records of past earthquakes, and most lack information on displacement.
Understanding earthquake production along plate boundary faults is critical for seismic hazard assessment worldwide. Most studies on earthquake recurrence have been conducted along complex plate boundaries, such as in California where multiple parallel faults affect stress interaction, and on faults with high rates such that the production of large earthquakes is too frequent to precisely resolve unambiguous event ages without overlap in uncertainties. The Dead Sea Transform is a unique plate boundary fault with a very long historical record that slips at a moderate rate, and has a simple segmented geometry with no parallel interacting strands in Israel and Jordan. It is therefore uniquely set to address questions of earthquake recurrence and its variability. Thus, this project will provide much needed information to test the fundamental behavior of continental transform systems, and will lead to better methodology in the forecasting of future destructive earthquakes worldwide.
This project tested earthquake recurrence and slip models for a major plate boundary fault, the Dead Sea Transform in Israel. Through high-resolution three-dimensional trenching and precise dating of past earthquakes, along with analysis of the exceptionally long historical record of earthquakes in this region, we determined the timing and sizes of past earthquakes along the Jordan Gorge section of this simple fault system for the past 2,000 years. The overall purpose is to test the repeatability of large earthquakes and whether their occurrence in time is predictable or more random, an issue that is at the core of earthquake forecast models. Understanding earthquake production along plate boundary faults is critical for seismic hazard assessment worldwide. Our new paleoseismic results show that, in addition to the previously recognized earthquakes of 1202 and 1759 AD, we observe direct stratigraphic evidence for 8 surface-rupturing earthquakes, with all of them occurring between the 1st century BC and about 1000 AD. We also determined slip for channels that bracket the historically known AD 749 earthquake, which also apparently extended rupture into this section of fault. In contrast, the past millennium appears deficit in strain release with the occurrence of only 2 large ruptures, when compared with the preceding 1200 years. With current strain accumulation rates at about 5 mm/yr, as determine by GPS (short term) and geology (long term), between 4 and 5 m of slip has accrued along most of the DST between the Red Sea and Syria that could be released in future earthquakes. As determined in this study on the delta of the Jordan River near the northern shore of the Sea of Galilee, the inter-event time of surface rupturing earthquakes has varied by a factor of two to four during the past 2kyr, and the fault’s behavior is neither time- nor slip-predictable. The Jordan Gorge section of the Dead Sea Fault Zone seems to rupture in conjunction with both its southern and northern neighboring segments, and there is evidence that earthquakes nucleating in the Jordan Valley (e.g. 749 AD) could either rupture through the step-over between the faults or trigger a smaller event on the Jordan Gorge Fault. We offer a model of earthquake slip for this segment in which the long-term slip rate remains constant while differing earthquake sizes can occur, depending on the segment from which they originated and the time since the last large event. The rate of earthquake production in this model does not produce a time predictable pattern over a period of 2kyr as a result of the interplay between fault segments to the south and north of the Jordan Gorge Fault. It does, however, indicate that the fault may be due for one or more large earthquakes in the near future. Large earthquakes that occur in densely populated regions can have devastating effects on the local and regional population and economy, especially when these regions have an aging or poorly built environment or are politically unstable. The Middle East is both politically and economically unstable, with active conflicts in Syria (high level) and Lebanon (low level), and a built environment that is at significant risk from strong ground shaking, should a large earthquake occur. The Dead Sea fault system transects the Middle East from the Red Sea (adjacent to Egypt and Saudi Arabia) northward through Israel and Jordan (generally along or near their common border), into Lebanon and Syria. Large historical earthquakes along this fault have occurred in the past, with the most recent large earthquake in the north being the November 1202 M7.6 earthquake, which caused enormous damage over a very broad area. This was one of several large earthquakes in a sequence that occurred between the 11th and 13th centuries (AD 1033, 1068, 1202, 1212) that released strain along the plate margin between the Red Sea and Lebanon. A repeat of such a sequence could have devastating affects on the people and economy of the Middle East, and a new sequence may have been initiated with the 1995 M7.3 earthquake in the Gulf of Aqaba (arm of the Red Sea between Egypt and Saudi Arabia). This makes understanding short and long-term earthquake generation on plate boundary faults all the more critical, not only for along the Dead Sea fault, but worldwide.
