T42B-01 INVITED
The East Anatolian Fault: Structural pattern and relationship with the Dead Sea Transform
The NE-SW trending left lateral East Anatolian transform fault (EAF), is a major plate boundary, accommodates most of the active deformation between the Arabian and Anatolian plates. It is connected to the Dead Sea transform fault (DSF) at the southwestern continuation. However, relationship between EAF and DSF is still under discussion. In this paper, we present geometry of the EAF in the regional active fault pattern especially in the Kahramanmaras-Adana-Antakya region. The EAF is about 580 km-long between Karliova triple junction and Antakya. It was formed in the late Pliocene and has achieved a maximum offset 15-17 km. GPS data indicate that recent slip rate is about 10 mm/y along the EAF. It is divided into seven main geometric sections. While trend of the fault is almost ENE-WSW between Turkoglu and Karliova, general strike of the fault is N30E along the Turkoglu-Antakya section having approximately similar orientation with northern section of the DSF. Our new data suggest that the EAF divides into two main strands west of Celikhan as the southern and the northern. The Southern strand is the main fault connecting to the DSF. The northern strand bifurcates from the main strand at the west of Celikhan and extends parallel to the Taurus orogenic belt forming a large bend convex to the south between Surgu and Adana basin. Total length of this strand is about 350 km. From east to west, the eastern part of the strand consists of the Surgu, Elbistan and Goksun fault segments, trending E-W. General strike of the strand turns into from E-W to NE-SW at the west of the Goksun bend and the strand divides into several splay in NE-SW trending in the Adana basin. Our data reveal that the northern strand of the EAF also is played an important role in the active deformation of the Eastern Mediterranean. GPS measurements indicate that slip rate along the EAF increase from southwest to northeast. We can speculate that there might be a slip partitioning between the southern and northern strands of the EAF west of Celikhan. The southern and northern strands accommodate ratio of the 2/3 and 1/3 slip-rate of the fault zone respectively. We also suggest that EAF and DSF connected to each other by the Turkoglu bend at the north of the Karasu rift valley.
T42B-02
New insights into the northern Dead Sea Fault Zone (Karasu Rift and Hatay Graben), Southern Turkey.
The Karasu Rift forms the northernmost segment of the Dead Sea Fault Zone (DSFZ), trending northwards from the Amik Plain. To the south of the Amik Plain, the Gharb Rift forms the southwards continuation of the DSFZ, while to the east the Hatay Graben trends NE-SW from the Amik Plain to the present Mediterranean coast. Recent fieldwork in the area shows a markedly different style of deformation across the Amik Plain. The northern Gharb fault is a narrow (<10 km wide) structure that is flanked by numerous fault strands, large strike-slip faults have negligible vertical offset. Small-scale faulting accompanying the large faults is uncommon, although the Late Miocene and Pliocene sediments are pervasively fractured, with two sets of joints orientated between 010°-060° and 090°-130°. This may imply that motion along the DSFZ is accommodated along the main faults and internally fault blocks do not undergo any faulting. By contrast, the southern Karasu Rift is 15-20km wide and the bounding faults have a significant vertical component of motion. Palaeozoic to Upper Miocene sediments have been exhumed in the footwall and are faulted as well as jointed, two main populations of faults have been identified, those trending NE-SW (010°- 060°) and those trending ~ N-S (320°-005°), although in some areas there is also a third subset of faults that trend E- W. These differences suggest that the structural controls on the two areas differ, implying that there is no continuity of structure across the Amik Plain. The Hatay Graben is also 15-20km wide; the flanks of the graben are dominated by normal faults mainly striking parallel to the graben (0-180°). In contrast, the graben axis exhibits numerous strike-slip faults, trending from 100° - 200°, and normal faults striking 040°- 060° and 150°-190° (with a subset striking 110°-130°). Normal faults of similar orientation occur in Upper Cretaceous to Quaternary sediments, whereas strike-slip faults are mostly identified within Pliocene and Quaternary sediments exposed near the graben axis. Syn-sedimentary relationships indicate that initial faulting occurred during the Middle Miocene Stress analysis of mostly Pliocene sediments at eleven suitable locations shows that sigma 3 directions are uniform in the northeast and orientated at a high angle to the graben, parallel to the maximum extension direction. Analysis of faulting shows that the Hatay Graben developed due to transtension, whereas the Karasu and Gharb Rifts experienced strike-slip deformation. It is suggested that the orientation of these grabens were probably influenced by pre-existing zones of crustal weakness, related to Early Mesozoic rifting of Neotethys. Then, during the Plio-Quaternary the main tectonic controls were E-W left-lateral ‘tectonic escape' of Anatolia and N-S left- lateral movement along the propagating DSFZ, which lead to extension in the area. This composite origin contrasts with previous models for basin formation where the grabens are considered simply Pliocene to recent structures.
T42B-03
New GPS observations on fault slip rate and locking depth for the northern Dead Sea Fault System in western Syria: Implications for tectonics and earthquake hazards
The Dead Sea fault system (DSFS) is the transform plate boundary between the Arabian and Sinai plates in the eastern Mediterranean region. Along part of the northern DSFS in northwestern Syria, paleoseismic and historical studies document repeated large earthquakes over the past 2000 years, although the region has not experienced a large (magnitude > 7) earthquake in more than 800 years. We present new Global Positioning System (GPS) measurements that provide the first direct observations of near-field deformation associated with the DSFS in northwestern Syria. A network of 34 stations, including a closely spaced profile across the fault, was surveyed in 2000 and 2007. Preliminary velocities demonstrate left-lateral shear with 1-sigma uncertainties less than 1 mm/yr. These velocities are consistent with an elastic dislocation model involving a slip rate of 1.4 – 2.0 mm/yr and a locking depth of 10 – 22 km. This geodetically determined slip rate is less than that reported farther south along the central section (Lebanese restraining bend) and southern section (Dead Sea and Wadi Araba) of the transform and consequently requires some deformation to occur away from the transform. One possibility may be north-south shortening within the southwestern segment of the Palmyride fold belt of central Syria. This difference in slip rates along the transform is also consistent with differing estimates of total fault slip that have occurred since the mid Miocene: 20 – 25 km along the northern DSFS versus about 45 km along the southern DSFS. These new GPS measurements, when viewed alongside the paleoseismic record and the modest level of present-day seismicity, suggest that the reported recurrence rate of large earthquakes along the northern section of the DSFS may be overestimated owing to temporal clustering of large historical earthquakes. Hence, a revised estimate of the earthquake hazard may be needed.
T42B-04
Active Thrusting Offshore Mount Lebanon: Source of the Tsunamigenic A.D. 551 Beirut-Tripoli Earthquake
On July 9, AD 551, a large earthquake, followed by a tsunami destroyed most of the coastal cities of Phoenicia (modern-day Lebanon). This was arguably one of the most devastating historical submarine earthquakes in the eastern Mediterranean. Geophysical data from the Shalimar survey unveils the source of this Mw=7.5 event: rupture of the offshore, hitherto unknown, 100?150 km-long, active, east-dipping Mount Lebanon Thrust (MLT). Deep-towed sonar swaths along the base of prominent bathymetric escarpments reveal fresh, west facing seismic scarps that cut the sediment-smoothed seafloor. The MLT trace comes closest (~ 8 km) to the coast between Beirut and Enfeh, where as 13 radiocarbon-calibrated ages indicate, a shoreline-fringing Vermetid bench suddenly emerged by ~ 80 cm in the 6th century AD. At Tabarja, the regular vertical separation (~ 1 m) of higher fossil benches, suggests uplift by 3 more comparable-size earthquakes since the Holocene sea-level reached a maximum ca. 7-6 ka, implying a 1500?1750 yr recurrence time. Unabated thrusting on the MLT likely orchestrated the growth of Mt. Lebanon since the late Miocene. The newly discovered MLT has been the missing piece in the Dead Sea Transform and eastern Mediterranean tectonic scheme. Identifying the source of the AD 551 event thus ends a complete reassessment of the sources of the major historical earthquakes on the various faults of the Lebanese Restraining Bend of the Levant Fault System (or Dead Sea Transform).
T42B-05
GPS measurements of present day crustal deformation within the Lebanese restraining bend along the Dead Sea Fault System
The Lebanese restraining bend is a 200 km long bend with a left lateral sense of slip located along the Dead Sea fault system (DSFS) between 33.2 and 34.6 degrees north latitude. The DSFS is a transform plate boundary fault system accommodating the differential northward movement of Arabian and Sinai plates relative to the Eurasian plate. Within the Lebanese Restraining bend, The DSFS splays into several major left-lateral strike-slip faults, forming a positive flower structure. This study combines GPS measurements from Lebanon where surveys span for about 5.5 years with sites from the Anti Lebanon Mountains in SW Syria for a more complete view of crystal deformation in the Restraining bend. The GPS network includes Continuous GPS sites and 27 campaign sites: 14 sites in Lebanon installed in 2002, 8 sites in Lebanon installed in 2005, and 5 sites in southwestern Syria. Preliminary velocities for older campaign sites have uncertainties less than 1 mm/yr, whereas newer sites have around 1.5 mm/yr uncertainties. The improved spatial coverage and reduced uncertainties allow constructing elastic fault models that explore strain partitioning between two strike slip faults (representing the Yammouneh and Serghaya faults) and a generalized thrust fault to accommodate convergence in the Restraining bend. Preliminary velocities suggest around 4 – 4.5 mm/yr along the Yammouneh fault. This study provides an essential tool for assessing tool for assessing the seismic hazard in the vicinity of the Lebanese restraining bend.
T42B-06
Deciphering the Paleoseismic History of the Yammouneh Fault (Lebanon)
North of the Hula basin, the main branch of the 1000 km-long Dead Sea transform veers eastwards, forming a 160 km-long restraining bend responsible for the uplift of Mount Lebanon. The corresponding transpression is partitioned between the offshore Mount Lebanon Thrust and the Yammouneh fault, whose Late-Pleistocene- Holocene slip rate has been estimated to be 5.1 +/- 1.3 mm/yr from offset alluvial fans. Paleoseismic trenches in the Yammouneh basin have shown that the fault produces large earthquakes (M > 7) with a recurrence time of 1127 +/- 135 years, and that the last such event occurred in AD 1202. The new study we present here is from a trench in the Jbab el-Homr basin, 20 km north of Yammouneh. The chief goal is to compare the succession of events at both sites, to obtain evidence for simultaneous or asynchronous earthquake rupture, a key question to assess seismic hazard in Lebanon. The 4 m-deep trench reveals a succession of very thin palustrine and lacustrine layers, ruptured by 10 to 12 earthquakes. Given the dearth of radiocarbon dates, we rely for now on regional paleoclimatic variations to infer a tentative stratigraphic chronology. We identify cycles that might correspond to a solar cycle of 1500 years, but the most striking features are yearly varves that likely formed when a permanent lake flooded the basin. This episode may be correlated with the Early Holocene Climatic Optimum, from 9.8 to 6.8 ka B.P., a particularly humid period recorded by various proxies in the Middle-East, during which the Yammouneh lake level was also high. Based on such a correlation, 9 earthquakes would have occurred at Jbab el-Homr in the last 9.8 ka, providing a recurrence interval of about 1100 years, in keeping with paleoseismic results at Yammouneh. Sedimentological and chemical analyses are in progress to try to date at least a few of these earthquakes.
T42B-07
Seismic Evidence for Neogene and Active Shortening Offshore Lebanon (SHALIMAR Cruise)
Lebanon is located on a 160 km long transpressional bend of the left-lateral Levant (Dead Sea) Fault. The main objective of the SHALIMAR (2003) marine survey was to characterize and map active deformation offshore Lebanon using a range of geophysical techniques, particularly seismic reflection profiling. The cruise results clearly establish the presence of submarine thrust faults - likely the source of one of the most devastating submarine historical earthquakes that happened along the Levantine shores - and clarify the structure of this part of the Levant margin. A submarine fold-belt, bounded by thrusts and lateral ramps and extending in places to at least 30 km from the shoreline, is interpreted as the foreland thrust system of the actively growing Mount Lebanon range. There is no large fault extending into the Levant Basin towards Cyprus, which indicates that thrusting only absorbs local transpression resulting from the Lebanese restraining bend. Both the Miocene and Plio-Quaternary sedimentary sequences are affected by shortening, with landward-dipping blind thrusts and associated growth strata. The presence of the Messinian evaporites creates complex deformation patterns, including normal faults due both to folding accommodation and gravity spreading, all well imaged in the seismic reflection profiles. Because the evaporite layer acts as a decollement level, deformation extends farther out seawards through a series of thrust imbricates or duplexes. Shortening is strongest between Beyrut and Batroun and decreases towards the south between Saida and Tyre. North of Tripoli, the passive margin is not affected by Neogene deformation, and is well preserved. We propose that, since the Miocene, the northward propagating Levant Fault interacted with margin structures inherited from the Mesozoic rifting phase, and was deviated away from the more rigid oceanic crust flooring the Levant basin, a process which led to the formation of the Lebanese restraining bend, and consequently to the offshore shortening we document here. Such coastal transpression has resulted in inversion of a ~100 km long segment of the passive margin, which might eventually evolve into a new subduction zone.
T42B-08 INVITED
The Dead Sea Transform and the Dead Sea Basin – Structure and dynamics
DESERT and DESIRE, two multi-national, interdisciplinary research efforts by teams from Germany, Israel, Jordan and Palestine focused on the Dead Sea Transform (DST) and the Dead Sea Basin (DSB), respectively. The DST has accommodated left-lateral transform motion of 105 km between the African and Arabian plates since early Miocene (ca. 20 My), creating during this process also the prime example of a pull-apart basin, the DSB. Within DESERT the DST segment between the Dead Sea and the Red Sea called Arava/Araba Fault (AF) was studied with the following results. On plate tectonic scale the AF is a narrow, sub-vertical zone cutting through crust and lithosphere to more than 50 km depth, while the Moho depth increases smoothly from 26 km to 39 km from W to E under the DST. Several faults exist in the upper crust in a ca. 40 km wide zone around the AF, but none has kilometer-size zones of decreased seismic velocities/zones of high electrical conductivities typical for damage zones. Across the sub-vertical AF abrupt changes in lithology can be identified to a depth of 4 kilometers. The AF also acts as a barrier to fluids. The AF is the main active fault of the DST system but it has only accommodated a limited part (up to 60 km) of the overall 105 km of sinistral plate motion. Now inactive fault strands in the vicinity of the present day AF took up lateral motion until about 5 Ma ago, when the main, active fault trace shifted ca. 1 km westward to its present position. In the top few hundred meters of the AF a locally transpressional regime occurs in a 100 to 300 m wide zone of deformed and displaced material, bordered by sub-parallel faults forming positive flower structures. The damage zones of the individual faults are only 5 to 20 m wide. This narrow width is significantly smaller than at other major strike-slip faults of similar magnitude. Most of these findings are corroborated by thermo-mechanical modeling that show shear deformation in the lithosphere under the DST/AF first localizes in a 20 to 40 km wide zone with a mechanically weak decoupling zone extending sub-vertically through the entire lithosphere. As time progressed upper crustal deformation became quickly focused in a few faults. Within DESIRE the DSB, the largest basin along the DST, is studied using again a multi-disciplinary and multi- scale approach. Some of the open questions presently being addressed in the DESIRE project which started in 2006, are: (1) What is the fault pattern of the DSB at depth? and (2) What is the deep structure of the DSB and the depth and configuration of the major crustal interfaces, e.g. the Moho beneath the basin? We will also report results of DESIRE, with an emphasis on the findings from geophysical studies and modeling.