GENERAL DISCUSSION AND CONCLUSIONS: IMPLICATIONS TO THE REGIONAL SEISMIC HAZARD

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Tectonic setting of Dead Sea Fault

General tectonic setting

The Dead Sea Fault (Figure I.1) can be subdivided into the north and the south zone connected to each other by the restraining Lebanese bend an active transpressive zone (Griffiths et al., 2000; Gomez et al., 2003). The main difference between its southern and northern zones is the difference in accumulated slip rate (25 – 35 km) between the north (70 – 80 km) and south (~105 km) of the DSF (Freund, 1970; Chaimov et al., 1990; Westaway, 1995; Westaway, 2003). Khair et al., (2000) divided the DSF into five major segments (Wadi Araba, Jordan Valley, Albeqa’a basin, Al-Ghab Basin and Karasu Valley). The segmentation was proposed due to the difference in geometry, geomorphology, geology and seismicity of each fault zone (Figure I.1). Sbeinati et al., (2010) divided the northern DSF into two main parts: 1) a 90±10 km long linear fault zone which is the Missyaf segment, limited by the Lebanese restraining bend and the Al-Ghab pull-apart basin and 2) the Al-Ghab pull-apart basin of ~10km wide and related complex system of fault branches in its northern termination where it reaches the Amik basin. Another division for the DSF was proposed by Ferry et al., (2011) who considered that the DSF is made of a transtensional system to the south (including the Hula, Dead Sea, and Gulf of Aqaba pull-apart basins), the Lebanese restraining bend (the Yamouneh, Rashaya, Serghaya, and Roum faults) in the middle, and a strike-slip system to the north (the Missyaf fault and the Ghab pull-apart basin). All of these segments have N-S trending in general with small deviation to the NNE for the central and the northern segment of the fault.
In this study, we will focus on the northern part of the Dead Sea fault which connects with the triple junction in south-east of Turkey and north-west of Syria. A detailed investigation of strain accumulation using GPS measurements will be carried out to determine the physical parameters of mapped active faults and understand the kinematics of this part of DSF. Furthermore, the new detailed information and more clear view on the kinematics can be used in the analysis of seismic hazard and risk of the region and have a better assessments.

Eastern Mediterranean geodynamics

The present-day geodynamics of the eastern Mediterranean region is controlled by the relative motions of three major plates, Eurasia, Africa, and Arabia (Figure I.2). A large part of deformation in the region is due to the interaction between these plates (Jackson and McKenzie, 1984; Spakman et al., 1988; Westaway, 1994; Le Pichon et al., 1995; Barka et al., 1997; Jolivet and Faccenna, 2000; McClusky et al., 2000; Doglioni et al., 2002; Piromallo and Morelli, 2003; Dilek, 2006; Reilinger et al., 2006). The Anatolian continental block which was a part from Eurasia plate, is acting as a micro plate between these three major plates since the middle Miocene, when it collided with Eurasia (Dewey et al., 1986).
Figure I‎.2: Map of the eastern Mediterranean region, illustrating the major plates (Africa, Arabia, Eurasia, and Anatolia) and their boundaries and important fault systems. Thick black arrows show the plates convergence directions. Abbreviations for some key tectonic features: EAF: East Anatolian Fault, DSF: Dead Sea Fault, NAF: North Anatolian Fault, PFB: Palmyride Fold Belt, BZFB: Bitlis–Zagros fold and thrust belt. Fault mapping is from (Dilek, 2010). Movement rates are from (McClusky et al., 2003; Reilinger et al., 2006).
The current Anatolian-African plate boundary is represented by a north-dipping subduction zone that has been part of a wide-ranging domain of regional convergence between Eurasia in the north and Africa and Arabia in the south since the late Mesozoic (Faccenna et al., 2003; van Hinsbergen et al., 2005; Jolivet and Brun, 2010). The convergence rate between Africa and Eurasia is greater than 40 mm/yr across the Hellenic Arc but decreases to ~10mm/yr across the Cyprus Arc. Based on plate-tectonic models (NUVEL-1, De Mets et al., 1990) and the global positioning system of present-day central movements in this collision zone (Reilinger et al., 1997b; McClusky et al., 2000; Reilinger et al., 2006), The Arabia-Eurasia convergence is estimated to ~20 mm/yr with NNW trending movement of the Arabia plate relative to Eurasia. This difference in convergence rate between Arabia, Africa and Eurasia can be translated into a slip rate along the Dead Sea fault. The NNW trending convergence of Arabia towards Anatolia produces thickening of the crust in south-eastern Turkey, implying compressional deformation along the Bitlis–Zagros fold and thrust belt (Saroglu and Yilmaz, 1990), and westward extrusion of the Anatolian block. The Anatolian plate is bounded by the dextral NAF and the sinistral EAF (McKenzie, 1972; Sengor, 1979; Sengor et al., 1985; Dewey et al., 1986; McClusky et al., 2000). GPS data indicate a mean extrusion rate for Anatolia, with respect to Eurasia, of about 25 mm/yr along the NAF (Straub and Kahle, 1994; Le Pichon et al., 1995; Straub and Kahle, 1995; McClusky et al., 2000).

Dead Sea Fault segments

Wadi Araba

Wadi Araba is the southern part of DSF. It starts from the Red Sea (Aqaba Gulf) at 29.5o N and extends for about 160 km till the Dead Sea basin at 31o N (Figure I.1). This valley is delimited by two plateaus from the east and west, respectively (Klinger et al., 2000b). Along this segment, the fault has a sharp morphological discontinuity that can easily be traced across the Quaternary deposits and alluvium sediments, excluding where the fault is covered with sand dunes or cuts across very recent alluvial terraces. The principal fault is rather straight, striking N20oE, and showing limited structural discontinuities, with a simple geometry reliable with basically pure strike-slip motion (Garfunkel et al., 1981; Klinger et al., 2000b).
The estimations of the slip rate along Wadi Araba segment are varying between 2.5 and 7.5 mm/yr. An estimation based on geodesic study (GPS) of 4.9±1.4 mm/yr was given by (Le Béon et al., 2008), this value relays on 6 years of time span and a locking depth of 12 km. Geodetic studies along this segment and other segments are described in details in paragraph (1.4.2.2), see Table I.3.
Regarding the historical catalogues, a few seismic events are reported during the last 2000 years along the Wadi Araba. The biggest reported events occurred in AD 1068, 1212, 1293 and 1458 (Abou Karaki, 1987; Ambraseys et al., 1994; Klinger et al., 2000b). These events seems to be smaller than the 1995 earthquake which struck the Aqaba Golf with a Mw~7.3 (Klinger et al., 1999) due to lack of seismicity and elapsed time since the most recent historical earthquakes which suggest that a tectonic loading has been accumulating along the fault (Ferry et al., 2011).

Jordan Valley

The trending N-S Jordan Valley extends ~180 km between the Dead Sea pull-apart basin at 30.7o N and the Hula Basin in the north before connecting with the Lebanese restraining bend at 33.1o N. The northern end of this segment attests on the division of the DSF into many fault branches trending toward the NNE, the Serghaya, Rashaya, Hasbaya, and Yammuneh faults (Figure I.1). This segment is connecting the two pull-apart basins of the Dead Sea and the Tabariya and was the object of paleoseismologic and geomorphologic studies which estimate its slip rate a 2.5 to 10 mm/yr (Marco et al., 1997; Galli, 1999). One of the last recent studies along Jordan Valley (Ferry et al., 2011) proposes a slip rate of 5 mm/yr. This study relies on paleoseismic, archaeoseismologic and historical data for 12 destructive earthquakes over the last 25 kyr.
The calculated average magnitude for the paleoearthquakes in the Jordan Valley segment is Mw 6.6 (Hamiel et al., 2009). However, Ferry et al., 2011 suggests that the length of fault segments and thickness of the seismogenic crust agree with Mw 7.2-7.4 as a reasonable maximum magnitude in the region. Studies of macroseismic damage from historical events and archaeological evidence conclude that 1–3 large earthquake (Ms>6) occurred in the northern Jordan Valley segment during the past 2000 yr (Ambraseys et al., 1994; Guidoboni et al., 1994; Marco et al., 2003).

Beqa’a Basin (Lebanese restraining bend)

The 200-km-long Lebanese restraining bend between 33.1o N and 34.7o N is the central part of the Dead Sea fault in Lebanon and southwestern Syria. This segment strikes 25◦–30◦ from the main trend of the transform fault (Gomez et al., 2007a). It shows NNE trending fault branches, i.e., the Serghaya, Rashaya, Hasbaya, and Yammuneh Faults and NW trending Al-Roum Fault in the south and the SE Akkar fault in the north. The Yamouneh Fault forms the main fault continuation on the Dead Sea Fault to the North and ends at the Lebanese border where the NS section starts in Syria. Al-Roum and Akkar faults are striking oblique to the DSF transform. They seems to serve as the structure linkages between the strike-slip faults of the Lebanese restraining bend and the horizontal shortening of the mountain Lebanon range (Gomez et al., 2006; Nemer and Meghraoui, 2006; Gomez et al., 2007a).
Recent geodesic studies gave a slip rate of 4-5 mm/yr along the main Yamouneh fault (Mahmoud et al., 2005; Reilinger et al., 2006; Gomez et al., 2007a). Other geomorphologic studies propose a slip rate of 5-10 mm/yr (Garfunkel et al., 1981; Daeron et al., 2004a). The historical seismicity of this segment being rich with several historical large events contradicts with the recent time of a general seismic quiescence. The large earthquakes that took place in the Lebanese restraining bend are 551 AD, 1202 AD, 1759 AD and 1837 AD (Ambraseys and Melville, 1988; Ambraseys and Barazangi, 1989; Beydoun, 1997; Sbeinati et al., 2005).

Table of contents :

I- THE DEAD SEA FAULT
I.1 Introduction
I.2 Tectonic setting of Dead Sea Fault
I.2.1 General tectonic setting
I.2.2 Eastern Mediterranean geodynamics
I.2.3 Dead Sea Fault segments
I.2.3.1 Wadi Araba
I.2.3.2 Jordan Valley
I.2.3.3 Beqa’a Basin (Lebanese restraining bend)
I.2.3.4 Al-Ghab basin
I.2.3.5 Karasu Fault
I.3 Seismicity of Dead Sea Fault
I.3.1 Historical seismicity
I.3.2 Instrumental seismicity
I.4 Kinematisc of Dead Sea Fault
I.4.1 Geodynamic of the Dead Sea Fault
I.4.1.1 Long term deformation
I.4.1.2 Short term deformation (GPS)
I.5 Conclusion
CHAPTER II
II- THE EAST ANATOLIAN FAULT
II.1 Introduction
II.2 Tectonic settings of the East Anatolian Fault
II.2.1 General View
II.2.2 East Anatolian Fault segments
II.2.3 The total offset
II.3 Seismicity of the East Anatolian Fault
II.3.1 Historical seismicity
II.3.2 Instrumental Seismicity
II.4 Kinematic of the East Anatolian Fault
II.4.1 Long term deformations
II.4.2 Short term deformations (GPS)
II.5 Conclusions
CHAPTER III
III- GPS NETWORK IN NORTH-WEST SYRIA AND SOUTH-EAST TURKEY
III.1 Introduction
III.2 Global position system and plate kinematics
III.2.1 What is GPS
III.2.2 GPS segments
III.2.2.1 Space segment
III.2.2.2 Control segment
III.2.2.3 User segment
III.2.3 GPS observables
III.2.3.1 The GPS code measurement
III.2.3.2 GPS carrier phase measurement
III.2.4 GPS linear combinations
III.2.4.1 Single-difference combination
III.2.4.2 Double-difference combination
III.2.5 Resolution of ambiguity
III.2.6 Plate kinematics
III.2.7 The International Terrestrial Reference Frame: ITRF2005
III.3 GPS network in the Hatay Triple Junction
III.3.1 GPS network installation
III.3.2 GPS campaigns in Syria and Turkey
III.3.2.1 Campaigns of 2009
III.3.2.2 Campaigns of 2010
III.3.2.3 Campaign of 2011
III.3.3 GPS measurement strategy
III.4 GPS Data processing with GAMIIT
III.4.1 GPS processing method in GAMIT
III.4.2 Stabilization: Permanent IGS sites
III.4.3 Time series, errors, RMS
III.5 Results
III.5.1 GPS velocity field in ITRF2005 reference frame
III.5.2 GPS velocity field in Eurasia reference frame
III.5.3 GPS velocity field in Arabia reference frame
III.6 Conclusions
CHAPTER IV
IV- BLOCK MODELING WITH GPS MEASUREMENTS
IV.1 Introduction
IV.2 Data and analysis
IV.2.1 Data selection and rejection
IV.2.1.1 GPS data obtain in this study
IV.2.1.2 GPS data from previous studies
IV.2.2 Combination of different GPS velocity solutions
IV.3 Inversion approach (Method)
IV.4 Faults
IV.5 Block model
IV.6 Modeling results
IV.6.1 Profiles across major faults
IV.6.2 Slip deficit, locking depth and variation of ɸ
IV.6.3 Fault slip rates
IV.6.3.1 The Dead Sea fault:
IV.6.3.2 The East Anatolian fault:
IV.6.3.3 The Karatas-Osmaniye fault:
IV.6.3.4 The Karasu fault
IV.6.3.5 The Cyprus Arc
IV.6.4 Block motions and rotation Euler poles
IV.7 Conclusions
CHAPTER V
V- GENERAL DISCUSSION AND CONCLUSIONS: IMPLICATIONS TO THE REGIONAL SEISMIC HAZARD
V.1 Introduction
V.2 GPS velocity field and block model results in the HTJ
V.3 Slip rate and seismic hazard in the Triple junction
V.3.1 The Dead Sea Fault
V.3.2 The East Anatolian Fault
V.3.3 The Karatas-Osmaniye Fault
V.3.4 The Karasu Fault
V.4 Conclusions

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