Surface Ruptures Induced by the Devastating 1068 AD Earthquake in the Southern Arava Valley, Dead Sea Rift, Israel

Tectonophysics 408 (2005) 79–99 www.elsevier.com/locate/tecto

Surface ruptures induced by the devastating 1068 AD earthquake in the southern Arava valley, Dead Sea Rift, Israel

E. Zilberman a,*, R. Amit a, N. Porat a, Y. Enzel b, U. Avner c

aGeological Survey of Israel, 30 Malkhe Israel St., Jerusalem 95501, Israel bInstitute of Earth Sciences, The Hebrew University, Israel cIsrael Antiquities Authority, Israel Received 20 May 2003; accepted 31 May 2005 Available online 19 August 2005

Abstract

The Elat fault (a segment of the Dead Sea Transform) runs along the southern Arava valley (part of the Dead Sea Rift, Israel) forming a complex fault zone that displays a time-dependent seismic behaviour. Paleoseismic evidence shows that this fault zone has generated at least 15 earthquakes of magnitude larger than M 6 during the late Pleistocene and the Holocene. However, at present the Elat fault is one of the quietest segments of the Dead Sea Transform, lacking even microsesimicity. The last event detected in the southern Arava valley occurred in the Avrona playa and was strong enough to have deformed the playa and to change it from a closed basin with internal drainage into an open basin draining to the south. Paleoseismological, geophysical and archaeological evidences indicate that this event was the historical devastating earthquake, which occurred in 1068 AD in the eastern Mediterranean region. According to the present study this event was strong enough to rupture the surface, reactivate at least two fault branches of the Elat fault and vertically displace the surface and an early Islamic irrigation system by at least 1 m. In addition, the playa area was uplifted between 2.5 and 3 m along the eastern part of the Elat fault shear zone. Such values are compatible with an earthquake magnitude ranging between M 6.6 and 7. Since the average recurrence interval of strong earthquakes during the Holocene along the Elat fault is about 1.2F0.3 ky and the last earthquake occurred more about 1000 years ago, the possibility of a very strong earthquake in this area in the future should be seriously considered in assessing seismic hazards. D 2005 Elsevier B.V. All rights reserved.

Keywords: Dead Sea Transform; Historical earthquakes; Earthquake magnitude; Recurrence interval

1. Introduction

The Dead Sea Transform (DST), which is one of * Corresponding author. Tel.: +972 2 5314268; fax: +972 2 5380688. the two ridge–trench boundary transforms in the E-mail address: [email protected] world, separates the African and Arabian plates and (E. Zilberman). connects the spreading centers of the Red Sea with the

Bitlis zone, the oblique collisional zone between the Garfunkel, 1981; Gardosh et al., 1990; Ginat et al., Anatolian and Arabian plates (Yeats et al., 1997). Its 1998) as well as plate tectonic models (McKenzie et morphology is well expressed all along its strike, by al., 1970; Joffe and Garfunkel, 1987; DeMets et al., the Dead Sea Rift (DSR), which is composed of 1994) suggest lateral slip rates of 1 to 20 mm/year. several major linear stretches separated by extensional Large earthquakes are known to have occurred pull-apart basins, among which the Dead Sea basin is along this fault zone, with earthquake magnitudes of the largest. Geological observations (Quennell, 1956; M 6–7 over the historical periods (Ambraseys et al.,

Fig. 1. Location map of study area. .Zlemne l etnpyis48(05 79–99 (2005) 408 Tectonophysics / al. et Zilberman E.

Fig. 2. Geomorphic map of the southern Arava valley in the Avrona basin. 81 82 E. Zilberman et al. / Tectonophysics 408 (2005) 79–99

1994; Amiran et al., 1994). Its seismic activity is earthquakes of 1068 and 1202, which damaged south- characterized by non-uniform spatial distribution of ern Israel. This would imply that the epicenters of earthquakes. Most of the current seismic activity is these historical events were located in the southern localised around the major pull-apart basins: the Gulf Arava area. of Elat–Aqaba and the Dead Sea basin in the south, and The decrease in earthquake magnitudes with time the Sea of Galilee and Hula valley in the north (Arieh combined with the present no-seismicity across the and Rotstein, 1985; Rotstein and Arieh, 1986; Shamir, Elat fault zone might signal locking of this segment. 1996, 1997)(Fig. 1). Between these extensional This possibility has significant implications for seis- basins, the DST is characterized by low seismicity mic hazard assessment in the southern Arava valley (Shapira, 1997). One of the most aseismic segments and the Elat–Aqaba region common to Israel and of the DST is the 40-km-long Elat fault zone that Jordan. extends from the western margins of the Gulf of Elat in the south to the Yotvata playa in the north (Fig. 1) (Garfunkel, 1970). Continuous seismic monitoring 2. Geological, geomorphic and climatic setting of along this segment during the past 15 years shows the study site insignificant to no seismic activity over this time (Sha- mir, 1997; Shapira, 1997; Shapira and Feldman, 1987). The southern Arava valley is crossed by the Elat Paleoseismic evidence shows that this presently non- fault zone, one of the segments of the DST, which active segment of the DST is capable of producing forms a shear zone several hundred meters wide and large earthquakes, but during the last 80 ka earthquake which is expressed as a clear tectonic line extending 50 magnitudes and recurrence intervals have appreciably km on land. (Garfunkel, 1970). It diagonally crosses decreased (Gerson et al., 1993; Amit et al., 1995; the DSR from the northwestern coast of the Gulf of Enzel et al., 1994, 1996; Amit et al., 2002). While Elat–Aqaba to the eastern margin of the rift in the the late Pleistocene earthquakes range in magnitude Yotvata Playa (Garfunkel, 1970, 1981). This part of from M 6.7 to 7 with recurrence interval of 2.8F0.7 the DSR is composed of the Elat and Avrona, pull-apart ka, the Holocene earthquakes range in magnitude structures, which are filled by alluvial sequence several from M 5.9 to 6.7 and recurrence interval of hundreds to several thousand meters thick (Ben Gai et 1.2F0.3 ky (Amit et al., 1995, 2002; Enzel et al., al., 1993; Frieslander, 1995, 2000). The youngest sur- 1994, 1996). These findings suggest that the Elat fault face ruptures along the trace of the Elat fault were zone displays a time-dependent seismic behaviour. detected in the Avrona playa, which occupies the cen- Historical documentation mentions only two large tral part of the Avrona pull-apart basins (Frieslander, seismic events that severely damaged the southern 2000). The Elat fault is composed of a narrow shear Arava area during the last 1500 years. The first was zone, several hundreds meters wide (Ben Gai et al., a devastating, strong earthquake, which occurred in 1993; Frieslander, 1995, 2000), which is accompanied 1068 AD and completely destroyed Aila, a major by a series of small pull-apart structures indicating a trade center, situated at the present site of Aqaba, sinistral movement (Zak and Freund, 1966; Fig. 1). Jordan (Fig. 2)(Avner, 1993; Ambraseys et al., Systems of dominantly normal faults are aligned on 1994). The second earthquake, which occurred in both sides of the Elat shear zone, displacing the alluvial 1212 AD, was weaker and was felt mainly in Aila fans along the margins of the DSR. The Elat fault (Ambraseys et al., 1994; Amiran et al., 1994; Avner, crosses the distal parts of the Roded, Shehoret and 1993; Abou Karaki et al., 1983). Raham alluvial fans in the western part of the DSR The aim of this study was to detect and analyse the and the distal parts of the Mahatadi alluvial fan in its most recent historical events that occurred in the eastern part. It crosses the Avrona playa and runs in Avrona playa and which were triggered by the Elat NNE direction along the eastern side of the Yotvata fault. Using paleoseismic methods, we examined the playa, close to the eastern mountain front (Figs. 1 and possibility that the young surface ruptures detected 2). At present the streams that drain to the Avrona basin along the trace of the Elat fault in the Avrona playa cross the Avrona playa and flow toward the Gulf of (Garfunkel, 1970) are related to the two historical Elat–Aqaba through the Elat coastal Sabkha. E. Zilberman et al. / Tectonophysics 408 (2005) 79–99 83

The climate in the southern Arava valley is extremely arid. The mean annual precipitation is 30 mm, usually falling in one or two rainfall events during the winter. Surface soil temperatures may reach 50 8Cat midday and drop by up to 30 8C at night (Ashbel et al., 1965). Mean annual temperature is 25 8C, with a mean daily range of 14 8C. The annual potential evaporation is 2600 mm (Atlas of Israel, 1985). The Avrona playa is partly covered by halophytic vegeta- tion, including tamarisks, rushes and doom palms, whereas the rest of the area is barren. The soils in the playa vary between fine desert alluvial soil in the vegetated areas to sterile Solonchaks (typical Sal- orthid) in the barren zone (Amiel and Freidman, 1971; Dan and Yaalon, 1982).

3. Methodology

3.1. Mapping

The geomorphological and morphostructural features of the Avrona playa area were mapped using 1:7000 airphotos and satellite images (Fig. 2). In addition to recent airphotos taken in 1995 and 1996, airphotos from the 1950s and 1960s were used to obtain information since lost due to intensive human activity. Detailed stream profiles and topographical cross sections (vertical error of F20 cm) across the playa area were drawn based on photogrametric maps. The present low gradient (0.1–0.15%) of the stream channels of Wadi Avrona and Wadi Raham, which drain the Avrona basin, serves as a reference line for estimates of the playa area deformation.

3.2. Geophysical survey

To characterize the structural pattern of the shallow Fig. 3. Air photo of the Avrona playa showing the traces of the subsurface fault system of the DST and to evaluate its photogrametric topographic profiles (circles) and the sites of the trenches and exposures (rectangles) described in the text. The relation to the playa surface morphology, a high reso- straight lineament that bounds and crosses the playa (dark area) lution seismic reflection survey was conducted across represents a NNE-trending fault of the Avrona Shear Zone. This the Avrona playa at three locations 3 to 5 km apart fault is trenched in T-20. The dark area bounded by straight linea- (GI-0061; GI-0065; GI-0074; Fig. 3). These geophy- ments corresponds to the uplifted sterile playa sediment. The light- sical lines followed a previous deep seismic reflection tone areas mark the wide braided Wadi Avrona stream, which occupies a structural depression in the north and splits into several survey at the same locations (Ben Gai et al., 1993). narrow and shallow streams within the playa area. The main faults The present survey included three P-wave seismic are designated A–E; the profiles are labelled GI-0061, GI-0065 and lines (GI-0061; GI-0065; GI-0074) and one S-wave GI-0074. 84 E. Zilberman et al. / Tectonophysics 408 (2005) 79–99

line (GI-0065). The lines were shot in a general east– eral do not contain authigenic CaCO3 that can be dated west direction using the conventional common mid- by 14C. Therefore, only a few charcoal samples were point technique (CMP) with 2.5 m spacing between 14C dated. Most sediments were dated using lumines- receiver stations. The source was applied at every cence methods and thus unless stated otherwise, all station using split-spread geometry (Shtivelman et ages presented in this study are luminescence ages. al., 1998). The energy source was an 8 kg sledge The luminescence technique dates the last expo- hammer. In most cases a single blow of the hammer sure of mineral grains in the sediment to sunlight, was sufficient to generate P- and S-waves. We used a which resets the luminescence signal (Aitken, 1998). 48-channel EG and G seismograph, model ES-2401X. After burial, the signals increase again with time as a PROMAX package was used for data processing. result of the natural ionizing radiation emitted by Since only the shallow information was needed, no radioactive isotopes (U, Th and K) and by cosmic static corrections were applied to the data (for more rays that penetrate the sediment. Minerals in the sedi- details see Shtivelman et al., 1998). ment, such as quartz and feldspar, have dosimetric properties; thus, the intensity of the accumulated sig- 3.3. Trenching and logging nal reflects both the time passed since solar resetting and the amount of environmental radiation. Two Information derived from geomorphic mapping values are required for age determination: the amount and from the shallow seismic reflection subsurface of radiation that the mineral has absorbed since it was data served as a basis for site selection for trenching last reset (the equivalent dose De), and the environ- across morphological elements. Three trenches were mental dose rate. opened and logged at a 1:20 scale (Fig. 3). The In this study the infrared stimulated luminescence trenches are 10 to 70 m long, up to 5 m deep and (IRSL) signal in alkali feldspars was used because it 1.5 m wide. Trench T-20 was excavated across a fault requires only several minutes of exposure to sunlight scarp. Trench T-21 was excavated perpendicular to a for complete zeroing of the signal and resetting of the morphological scarp in the northern part of the playa. luminescence bclockQ (Aitken, 1998; Clarke, 1994). Trench T-22 was excavated in the easternmost part of Samples were collected from holes drilled into natural the playa across a structural ridge composed of playa outcrops or trench walls, at a depth of ~30 cm. To deposits. One wall in each trench was selected for prevent exposure to daylight, the samples were imme- mapping. A metric horizontal datum line was estab- diately put in light-tight bags and all subsequent lished along the trench wall and vertical rod sections sample preparation was made under subdued orange were taken to delineate contacts of alluvial and collu- light. Field data, laboratory results and calculated ages vial units and pedogenic horizons. Two exposures of for the samples from the trenches in Avrona are listed the sedimentary sequence were also analysed: one at in Table 1. the central part of the playa (E-23) and a second (E- Fine-sand size alkali feldspars with densities less 24) at the southern part (Fig. 3). Alluvial and colluvial than 2.58 g/cm3 were extracted from the sediment units were differentiated on the basis of texture, struc- using routine laboratory procedures (Porat et al., ture, type of boundary, colour, type of salic horizons, 1997). About 10 mg of the extracted alkali feldspars degree of cohesion and pedogenic features (McCal- was deposited on aluminum discs using a silicon pin, 1996). The soils and paleosols exposed in the spray as adhesive and measurements were carried sedimentary sequences were described, sampled and out on a Risø reader (Bøtter-Jensen et al., 1991). De analysed after the Soil Survey Staff (1975). was determined by the single aliquot added dose protocol (Duller, 1994) roughly following the routine 3.4. Numerical dating outlined in Porat et al. (1996).

Two dating methods were applied in this study: 3.4.1. Water contents and dose rates conventional 14C and luminescence dating. The gypsic External g dose rates were measured in the field and salic soils and the sediments in this extremely arid using a portable calibrated g scintillator while external region only rarely contain organic material and in gen- a and h dose rates were calculated from the concentra- E. Zilberman et al. / Tectonophysics 408 (2005) 79–99 85

Table 1 and changed from a closed basin with an internal Field and laboratory data and age results of IRSL dating drainage system to an open basin–is presented in 14 13 14 14 C sample Depth CPDB C C calibrated Amit et al. (1999). number (m) age years ages The playa sediments are exposed along a broad A-8927 1.8 À10.8 1520F175 140–880 AD elongated deformation belt composed of low, long- F A-8930 0.8 À22 2335 150 800–60 BC itudinal, sub-parallel ridges (0.5–4 m high and up to 5 A-8931 1.2 À11.8 1470F110 340–790 AD km long). Shallow braided channels flow along and F Error estimates are at the 1r confidence level and include sys- across these ridges (Figs. 2 and 3). Wadi Raham flows tematic as well as random errors. from the west, cuts the northern edge of the playa, and then flows southward at its eastern edge along a tions of the radioelements. Present-day water contents gradient of 0.1–0.15%, forming steep and deep in the sediment range from 1% to 7% (Table 1). How- playa margins. Wadi Avrona, which drains the western ever, these values do not reflect water contents margin of the rift, crosses the entire width of the playa throughout the sediments’ burial history. Pedogenic and merges into Wadi Raham. The outlet of the analysis indicates that the water table at the Avrona Avrona playa is a narrow channel that flows along playa was at the surface several times in the past 10,000 the eastern margin of the steep (4–5%) alluvial fan of years and that in general the sediments were water- Wadi Roded, which separates the Avrona playa from saturated for most of their history. Therefore laboratory the Elat sabkha. experiments were conducted on several sediment types Several low ridges composed of sterile playa to estimate the saturation values, which are in the range deposits were trenched and their sedimentary of 20–30%. This range is assumed to represent past sequences were studied (for details see Amit et al., water content and ages were calculated using both the 1999). The upper part of the sequence is composed of current water contents and the laboratory saturation barren, sterile silty–clayey playa deposits, which value of 25F5% (Table 1). The ages presented on include a 1.2 m thick saline soil profile (Salorthids, the trench logs and soil profiles are those calculated Soil Survey Staff, 1975; or Solontchak, Duchaufour, using the saturation water contents. 1977). This soil is characterized by in-situ pedogenic gypsic nodules, salt efflorescence, and a well-cemen- 3.5. Solar resetting ted petrosalic horizon at a depth of 1 m. This horizon marks a stage of stability during which the basin was A sediment sample was collected from the present- probably closed and had a high water table. Playa day streambed of Wadi Avrona, to assess the degree of sediments at the base of the exposed sections date to solar resetting of the IRSL signal in a modern envir- the Early Holocene, whereas the upper 2 m of the onment. This sample had a low De value of sequence dates between 690F50 and 1400F100 0.28F0.01 Gy. Age calculations using the average years BP (Table 1). As a result of tectonic deformation dose rate for the Avrona sediments, ~2400 AGy/year, the saline soils and the playa deposits are at the high- give 115 years. This residual age implies that the ages est topographic position and at present are undergoing presented below could be about 115 years too old. intensive erosion (Amit et al., 1999).

4.2. The subsurface fault system and its relations to 4. Results morphostructural features

4.1. The geomorphology of the Avrona playa The results and interpretations of the geophysical survey are presented in Fig. 4. The three seismic The Avrona basin is at present externally drained, sections show a complex fault pattern identified as a its relief is inverted and it does not function as a flower structure, with converging and diverging NNE- closed basin with an endoreic fluvial system, as trending faults extending for several hundred meters. expected in playas. A detailed analysis of the tectonic Some of the interpreted faults coincide with surface history–during which the Avrona playa was deformed morphostructural elements, such as surface ruptures, 86 E. Zilberman et al. / Tectonophysics 408 (2005) 79–99

Fig. 4. Profiles of high-resolution seismic reflection lines across the Avrona playa shear zone. The location of trench T-20 is marked on top of section G-0061 (After Shtivelman et al., 1998). The location of the profiles marked in Fig. 3. E. Zilberman et al. / Tectonophysics 408 (2005) 79–99 87 lineaments, and small compression or structures that been conducted across the Avrona playa to a depth of permit correlation between the lines. The geophysical 25 m below the surface (Basson, 2000). It is possible to survey reveals that the Avrona fault is composed of consider the deformed belt of the Avrona playa as a several distinct sub-parallel branches; these are positive flower structure, which is typical of strike-slip marked A–E in Fig. 4. fault systems (Sylvester, 1988). The surface expression Zone A on line GI-0074 (Figs. 3 and 4) is asso- of the positive flower structure changes across the ciated with a NNE-trending morphological feature, shear zone of the Elat fault as a result of frequent which shows a compressional structure that is transitions from normal to reverse displacements (Shti- expressed as an elevated ridge built of uplifted playa velman et al., 1998; Basson, 2000; Amit et al., 2002). deposits. In some places the ridge forms a topographical step up to 4 m high. The western branch of 4.3. Paleoseismology of fault C zone A is expressed as a low, elongated depression occupied by braided shallow channels of Wadi The most recent seismic history of the Elat fault Avrona. The northern extension of the western fault was examined by the paleoseismic analysis of the of this shear zone displaces the playa surface, forming most prominent branch of this shear zone in the a sharp, 2 km long, east-facing fault scarp. Avrona playa (fault C). This fault trace, which is 10 Zone B appearing on lines GI-0074 and GI-0065 km long and about 1 m high, dissects a transitional (Figs. 3 and 4) is expressed by a row of low hills vegetated playa zone composed of sand to sandy-loam capped by a gypsic unit of groundwater origin, which sediment (Fig. 3; fault C). Based on its clear morphol- is now elevated above the western alluvial fans. The ogy and the high-resolution seismic reflection analy- eastern flank of the zone is related to an elongated sis, this fault is assumed to be the youngest in the ridge extending south of line GI-0065 and forming a playa area. A trench (trench T-20) excavated at this straight lineament about 3 km long and 100 m wide. A site exposes a multiple-event fault with normal dis- shallow depression occurs between the western and placement and one main fault plane (Fig. 5). No the eastern branches of flower structure B. This lateral displacement was detected on this fault. depression serves as the local base level of the east- Five partially preserved colluvial units were iden- flowing streams blocked by the low ridge in the east. tified adjacent to the fault plane (Fig. 5, units I–V). Zone C on line GI-0065 (Figs. 3 and 4) is related to This succession of vertically stacked colluvial wedges zone C of line GI-0061 and of line GI-0074. Zone C is maintains a constant thickness up to the fault contact situated along the most prominent lineament in the and terminates abruptly at the fault plane. The collu- Avrona playa. This lineament is about 10 km long. In vium is gravelly to sandy, depending on the composi- the southern part of the playa, it forms a low ridge tion of the sedimentary units from which it derived. bounded in the west by a short west-facing scarp; in Pedogenic features such as bioturbation, gypsic the northern part, it is expressed as an approximately nodules, and horizonation were detected in several 1-m high east-facing scarp. A clear discontinuity in of the colluvial wedges. The variation in the pedo- the reflectors coinciding with the surface scarp occurs genic features indicates that each wedge formed dur- in line GI-0061. A trench at this site (T-20, Fig. 5) ing a different time period. The shape of the wedge, exposed a normal fault. the different sedimentological character of each col- Zones D and E (Fig. 3) are expressed as series of luvial wedge, the absence of a fining upward trend in low hills composed of alluvial material cemented by the whole colluvial section, and the absence of corre- gypsum. These hills represent uplifted alluvial fan lative colluvial units on the upthrown block indicate sediments deposited at the western playa margins. that they were tectonically induced and not a result of The results of the high-resolution seismic reflection nontectonic slope processes (Amit et al., 1995; survey in the Avrona playa area enable us to relate McCalpin, 1996). surface structures to subsurface faults, hence confirm- According to data from unit 3, which overlies the ing the presence of several NNE-trending sub-parallel colluvial units and unit 1a at the base of the section, fault splays. These observations are confirmed also by five tectonic events occurred between 14,200F300 Ground Penetrating Radar (GPR) imaging, which has and 3700F300 years BP. Each of these events was 88 .Zlemne l etnpyis48(05 79–99 (2005) 408 Tectonophysics / al. et Zilberman E.

Fig. 5. Log of the southern wall of trench T-20 across a fault scarp in the Avrona playa. Its location is shown in Fig. 3. E. Zilberman et al. / Tectonophysics 408 (2005) 79–99 89 accompanied by displacements of at least 0.5 m. The Vertical changes along the ridge topographic pro- deposition of unit 3 marks the beginning of at least file reflect differential vertical uplift in relation to the 2000 years of quiescence. During this period, playa Avrona stream channel (Fig. 6). It reaches a height of sediments were deposited on the downthrown block 3.5–4 m in the central part of the Avrona basin and and later also over the up-thrown block (Fig. 5; units 3 about 1 m at the basin outlet (segment 9 in Fig. 6) and 5). Scour-and-fill sedimentary structures with fine close to the alluvial fan of Wadi Roded. The vertical cross-bedding, especially at the bottom of unit 5, indi- topographical differences between the stream-channel cate a north–south flow direction sub-parallel to the and the elevated playa ridge decrease from the central fault trace for a limited period. The deposition of fluvial part of the ridge northward and southward toward the sediments decreased during the last 2000 years and present outlet of the playa. Such a topographical changed into fluvial-eolian deposition of sand sheets situation could not have been achieved by fluvial (Fig. 5; unit 5b). A saline soil with a petrosalic horizon incision but only by the amount and pattern of a developed in the fluvial-eolian deposits in the entire tectonic uplift. The maximum incision that can be playa area (Fig. 5; unit 5). The soil marks a period of attributed to later fluvial erosion under such condi- stability with a low rate of sediment deposition and tions is 1 m, which is measured at the Avrona playa tectonic quiescence. Tectonic activity of this fault was outlet. This leaves a maximum tectonic uplift of about renewed later than 140–800 AD with vertical surface 2.5–3 m. rupture of about 1 m (Fig. 5; Table 2). A small remnant In summary, the topographic profiles of the chan- of unit 5b in which a soil with a petrosalic horizon was nels and the sub-ridges across the Avrona playa show preserved was left on the down-faulted block, enabling that the maximum amount of vertical uplift along the us to measure the amount of displacement of the last entire Avrona shear zone ranges between 2.5 and 3 m. tectonic event that occurred on this fault (Fig. 5; unit 5b The uplift of the playa area is reflected by the present on the down-faulted block). location of the saline soil, which must have formed during a former phase when the playa was a closed 4.4. Topogaphic profiles of the Avrona playa area and basin. As this soil is about 1000 years old, the uplift, the stream channel of Wadi Avrona which changed the soil location, happened about 1000 years ago. Two topographic profiles were drawn across the Avrona playa area. One follows the ridges scattered 4.5. Archaeological evidence for tectonic activity in across the elevated playa and the other follows the the Avrona playa area in historical times stream channel of Wadi Avrona (Fig. 6). The profile along the stream channel of Wadi Avrona, which A well-preserved Early Islamic ranch dated to flows sub-parallel to the trace of the Elat fault, can the 11th century AD was discovered at the western be used as a reference datum for estimating the part of the Avrona playa (Avner, 1993). This ranch, amount of deformation of the playa surface. The which provided fresh agricultural products to the ridges whose topographical elevations were measured town of Aila, was irrigated by a network of water are those on which a Salorthid soil was detected. This canals connected to a central water pool. The water soil represents the un-eroded playa surface which pool was fed by a Qanat system (subsurface tun- reached the same degree of development over the nel, marked on the surface by a row of vertical whole playa area while the playa was a closed basin shafts), which collected shallow groundwater deriv- with a shallow water table (Amit et al., 1999). The age ing from alluvial fans located along the western rift range of five soil profiles in the playa area located on margins (Fig. 7A). A roofed water canal (aqueduct) elevated sub-ridges (Fig. 6) is between 690F50 years connected the outlet of the Qanat system to the BP and 1400F100 years BP, with an average age of central irrigation pool. The farm was abandoned in about 1000 years (Fig. 6; Tables 1 and 2). With a the 11th century at the same time that Aila was known age and uniform degree of development this destroyed by an earthquake because of the destruc- soil can be used as a chronostratigraphic marker in tion of the irrigation system by surface deformation reconstructing the previous undeformed playa surface. (Avner, 1993). 90

Table 2 Laboratory data and age results for 14C ages Sample Depth Grain Water KKF K U Th External a External h Internal h External g+ Total dose De IRSL Age Age (m) size (%) (%)a sediments sediments sediments (AGy/year)c (AGy/year)c (AGy/year)d cosmic rays (AGy/year) (Gy)f (years) (years)g,* (Am) (%)b (ppm)b (ppm)b (AGy/year)e T20-3 3.3 177–212 4.0 7.7 0.43 1.59 2.51 140F37 557F17 420F39 659 1776F82 12.7F2.7 7150F1560 8700F1900 T20-4 3.1 177–212 3.5 8.1 0.82 1.12 1.85 101F27 772F28 443F41 668 1984F83 16.3F3.2 8220F1650 10,100F2100

T20-6 2.55 149–177 7.1 8.4 0.39 1.06 1.78 109F19 436F27 383F35 491 1419F65 4.54F0.33 3200F270 3700F300 79–99 (2005) 408 Tectonophysics / al. et Zilberman E. T20-8 1.6 177–212 1.3 10.1 0.79 1.11 1.88 105F27 771F24 549F50 600 2024F79 2.98F0.17 1470F100 2100F200 T20-9 1.1 149–177 1.2 8.5 0.76 1.00 2.00 120F31 748F25 390F35 633 1891F78 1.83F0.07 970F55 1200F80 T20-10 0.95 177–212 1.6 9.9 0.72 1.41 2.98 143F38 778F29 540F49 650 2111F82 1.83F0.11 870F60 1100F80 T20-11 2.65 125–177 18 9.9 1.10 2.25 5.66 240F72 986F75 421F72 897 2544F146 33.9F2.4 13,300F1200 14,200F1300 T20-12 1.7 177–212 1.5 8.0 0.84 1.44 2.35 134F34 858F25 438F41 615 2044F49 11.6F2.8 5680F1360 7100F1700 T20-13 0.9 177–212 1.3 9.9 0.66 1.39 3.02 144F37 734F24 545F47 618 2040F82 1.70F0.08 830F50 1020F70 T20-14 0.6 149–177 2.5 7.8 0.7 1.32 2.45 151F40 742F77 358F33 607 1857F108 1.04F0.05 560F40 690F50 T21-1 2.6 177–212 6.0 9.7 0.69 1.12 2.71 113F30 674F34 527F48 571 1885F82 5.84F0.39 3100F250 3600F300 T21-2 0.7 177–212 5.1 9.9 1.13 2.11 5.45 222F59 1172F44 538F49 904 2836F120 1.93F0.03 680F0830F40 T21-3 0.4 149–177 1.0 10.2 0.98 1.55 4.78 224F59 1052F27 467F41 773 2617F101 0.67F0.12 270F50 340F60 T22-1 2.3 149–177 (4) 8.8 0.79 1.98 4.01 228F60 909F33 403F36 772 2312F104 16.2F2.9 7010F1290 8700F1600 T22-4 0.45 125–177 (2) 7.4 0.97 1.83 3.89 239F68 1051F29 313F52 859 2462F109 0.59F0.06 240F30 300F30 T22-5 3.7 125–177 (3) 7.2 1.42 1.89 5.00 266F77 1405F45 305F51 1144 3120F142 7.69F0.41 2460F170 4100F300 T22-8 0.8 149–177 (4) 8.7 0.80 1.58 3.93 198F52 866F32 399F36 929 2391F113 2.7F0.13 1130F80 1400F100 E23-1 2.9 149–177 6.4 8.0 1.27 2.20 5.05 257F68 1269F51 365F33 909 2801F128 4.28F0.26 1530F120 1900F150 E23-2 2.3 149–177 0.8 8.2 1.21 1.73 3.93 218F57 1229F28 374F34 913 2735F111 3.38F0.13 1240F70 1600F100 E23-3 1.2 149–177 1.2 8.2 0.95 1.91 3.92 231F61 1052F27 378F34 981 2642F118 2.26F0.09 860F50 1100F70 E24-1 1.25 125–212 7.3 11.0 1.57 2.40 7.92 315F100 1546F78 522F120 1255 3638F178 4.39F0.35 1210F110 1500F150 E24-2 0.4 149–177 3.1 11.1 1.36 2.47 8.45 365F96 1502F37 509F45 1133 3509F152 2.54F0.18 720F60 910F80 SH-15 modern 177–212 ~2400 0.28F0.01 115 a K contents in extracted alkali feldspar fraction, measured using AAS. b U, Th and K contents in bulk sediments. U and Th measured by ICP-MS; K was measured using AAS. c Calculated from the concentrations of the radioelements, attenuated for moisture contents and grain size. d Calculated from K contents in extracted alkali feldspars measured by AAS, corrected for grain size and using an a value of 0.2F0.05 (Mejdahl, 1987). e Measured in the field using a portable g counter calibrated to include cosmic rays, error estimated at F10%. External g dose rates were also calculated from the concentrations of the radioelements and these match the measured field values to within F10% (Porat and Halicz, 1996). f Determined using the single aliquot IRSL technique; uncertainties calculated from the average of 6–12 measured aliquots. g Ages were calculated with saturation water contents of 25F5%. * The dates were measured and calibrated at the Laboratory of Isotope Geochemistry, Department of Geoscience, Tucson Arizona. .Zlemne l etnpyis48(05 79–99 (2005) 408 Tectonophysics / al. et Zilberman E.

Fig. 6. Composite topographic profiles of the Wadi Avrona stream-channel and the elevated sub-ridges across the playa area. Notice the nick-point at I, where the stream crosses the fault that displaces the alluvial fan, and the convex profile of the stream channel between points II and III, where the stream crosses the elevated ridge. Numbers refer to segments of the photogrametric profiles. The soil and sedimentary profiles represent the upper 1.5 m of the elevated playa deposits, showing similarity throughout the tectonically deformed area. Notice the petrosalic horizon, which serves as a chrono-stratigraphic marker for correlating the elevated playa surface. 91 92 E. Zilberman et al. / Tectonophysics 408 (2005) 79–99

A I N II

III Water reservoir

Subsurface tunnel II Deformation zone Vertical shaft Water canal

0 0 100 m III B Measured point II Water canal -0.5

Bottom of I reservoir Flow direction -1 Elevation (m) Elevation

Topographic profile of the Avrona water canal -1.5 400 300 200 100 0 Distance (m)

Fig. 7. Topographic profile of the water canal in the Avrona Islamic farm. The profiles were measured by EDM total station.

Topographic profiles of the roofed water canal 5. Discussion measured using Electro-Optical Distance Measure- ments (EDM) revealed that today the inlet of the 5.1. Location of the epicentral area of the 1068 AD canal to the pool is about 1 m higher than the Qanat earthquake outlet (Fig. 7B). Three points of deformation were detected along the canal: near the outlet of the Qanat, The catalogues of historic earthquakes in the Mid- at the middle part of the canal and near its inlet to the dle East document only two large seismic events in water pool. The inversion of the original southward the southern region of the eastern Mediterranean in gradient of the roofed canal is clearly related to an the last 1500 years: the strong 1068 AD earthquake uplift of the water pool area by more than the 1 m in and the moderate less destructive 1212 AD earthquake relation to the Qanat system. (Amiran, 1951; Ben-Menahem, 1981, 1991; Turcotte The deformed water system is located a few and Arieh, 1988; Ambraseys et al., 1994; Amiran et hundred meters west of the main lineament underlain al., 1994). According to the earliest account of the by the subsurface fault C (Fig. 3) and presumably 1212 AD earthquake it was strongest in the part of also underlain by fault D, which was detected further Aila that was by the sea (Ambraseys et al., 1994; to the northwest of fault C (Fig. 3). The deformation Amiran et al., 1994; Avner, 1993), suggesting that it of the irrigation system can be directly related to originated on the eastern fault of the Elat depression reactivation of these two branches of the Elat fault extending between Aqaba in the north and Nuwieba in during the historic earthquakes that occurred in the the south (Ben Avraham et al., 1979; Ben Avraham, 11th century. 1985; Abou Karaki et al., 1983). The 1068 earthquake E. Zilberman et al. / Tectonophysics 408 (2005) 79–99 93 was more damaging and caused the total destruction of the city of Aila and widespread damage throughout Iskanderun Rodos Aleppo the Middle East, resulting in thousands of casualties within a radius of more than 500 km from the Gulf of Cyprus Elat–Aqaba including north Hijaz, Sinai, Egypt, and 35o the Mediterranean coast (Fig. 8)(Ambraseys et al., Tripoli 1994). Reports indicate that it was felt all the way to I Beirut Baniyas AM N Damascus Baghdad (Ambraseys et al., 1994). This earthquake Mediterranean Sea TSU Tiberias was also associated with a tsunami at several sites Jarash along the Mediterranean coast (Willis, 1928; Amiran, Jaffa Jerusalem Amman 1951; Amiran et al., 1994; Ben-Menahem, 1977, Ramla Tinnis Gaza 1981, 1991; Poirier and Taher, 1980; Arieh et al., Alexandria Tanta 1985; Arieh and Feldman, 1985; Turcotte and Arieh, Petra DST 1988; Ambraseys et al., 1994). Such an event seems 30o Cairo Helwan more likely to have caused the severe damage and Aila surface rupture of the playa area than the weaker 1212 AD earthquake. ✱ It was previously demonstrated that a relief inver- Tabuk sion of the Avrona playa was triggered by tectonism 0 200km (Amit et al., 1999). The paleoseismic analysis reveals Red Sea Taima that at least six M N6 tectonic events have affected the Quseir playa during the last 14,000 years. The limiting age of 30o Luxor 35o the sedimentary sequence, the extent of the soil development and the longitudinal profiles of Wadi Avrona ✱ Epicenter of the 1068 earthquake according to Ambraseys et al., (1994) and Wadi Raham indicate that one of the faulting Epicenter of the 1068 earthquake according to the present study events of the playa, which was accompanied by com- Damaged area pression and uplift, occurred in the last 1000 years. Fig. 8. Extent of damage caused by the 1068 AD earthquake (based Supportive data for such an event were also obtained on Turcotte and Arieh, 1988; Ambraseys et al., 1994; Amiran et al., from a paleoseismic study in the nearby faulted Wadi 1994). The site of the epicenter near Tabuk suggested by Ambraseys Yutim fan complex at the head of the Gulf of Elat– et al. (1994) is compared to the epicenter site suggested by the present study. Numbers in parentheses indicate the approximate Aqaba (Mansoor and Niemi, 1999). The age of the number of casualties. tectonic event that deformed the playa is more accu- rately constrained to the 11th century by the archaeological evidence forthcoming from the deformed the observed surface rupture of the Avrona playa. Islamic irrigation system, which was damaged by an Measured dimensions of surface faulting detected in earthquake at the same time that Aila was destroyed. worldwide historic and recent earthquakes of various This tectonic event displaced the surface by at least 1 magnitudes revealed that the maximum length of sur- m and changed the morphology of the Avrona playa face rupture in a Mw 7.5 earthquake is 80 km followed from a closed system with internal drainage to an open by maximum displacement of 3 m (Wells and Copper- basin, resulting in relief inversion (Amit et al., 1999, smith, 1994). Taking this into account it is clear that 2002). Such amount of displacement is consistent Tabuk is too far from the Avrona playa area to have with an earthquake magnitude of M 6.6 (Wells and caused any surface ruptures. The only response to this Coppersmith, 1994). earthquake in the Tabuk area was three new springs, Using historical documents Ambraseys et al. which appeared at a place called al-Qur, and in Taima (1994) located the epicenter of the 1068 earthquake the ground was split open bto reveal buried treasures near Tabuk in Saudi Arabia, about 250 km southeast of gold and golden jewelleryQ (Ambraseys et al., of Aqaba. This places it at a distance of about 300 km 1994). Whereas the DST, is a well-known source of from the study area, making it unlikely to have caused strong earthquakes, in the Tabuk area in Saudi Arabia 94 E. Zilberman et al. / Tectonophysics 408 (2005) 79–99 there is no tectonic feature that could have produced In the Elat fault zone there are no measurable such a large magnitude earthquake (Bartov, 1990). geomorphic or stratigraphic markers for determining The total destruction of Aila further suggests that it lateral slip rates. As a result, only vertical displace- was situated in the near-field of the earthquake rup- ment can be used for slip rate evaluations. The aver- ture. Moreover, the damaged sites (the Baniyas area in age vertical slip rate of the normal faults is 0.2 mm/ the north and the Taima area in the southeast) fall year (Amit et al., 2002). This value changes through within the radius of about 500 km around the pro- time along different segments of the active shear zone posed surface rupture. and among clusters of events related to the same Taking into consideration the sparsely inhabited segment, with a range of 0.1 to 0.35 mm/year. The region one cannot obtain accurate data on natural value calculated for the Avrona playa fits the higher and artificial damage and the epicentral area of this value and reaches 0.3 mm/year (Amit et al., 2002). event must be sought, as proposed by Ambraseys et However, such average slip rate range is low in com- al., (1994, p. 31), between Aila and Taima. The results parison to the worldwide vertical slip rate for normal of this study suggest that it was located at the southern faults, which vary from b0.5 mm/year to N3 mm/year Arava area at the Avrona playa and not in the Tabuk (Yeats et al., 1997). The low vertical slip rate range area. can emphasize both the complexity of the Elat fault zone, which is composed of a large number of fault 5.2. Estimating the earthquake magnitude and slip branches and their dominant strike-slip character. The rate fault pattern of this segment is different from the pattern of the northern Arava segment. The latter is Several considerations indicate that the earthquake characterized by a narrower fault zone with clear and that deformed the Avrona playa was of very large measurable lateral components of motion. Estimates magnitude and that it was caused by the Elat fault. of its lateral slip rate range between 4F2 mm/year Using the maximum displacement parameter (Bonilla and 4.7F1.3 mm/year (Klinger et al., 2000b; Niemi et al., 1984; Wells and Coppersmith, 1994), the ver- et al., 2001). tical displacement of 1 m measured for the youngest fault in trench T-20 could have been produced by an earthquake with a magnitude of about M 6.6. A 6. Seismic modes along the Dead Sea Transform similar displacement was measured in the deformed irrigation canal in the Early Islamic ranch, which is Earthquake magnitudes and their recurrence inter- underlain by fault D (Fig. 3) and was also supported vals are two fundamental descriptors of paleoseismi- by GPR measurements (Basson, 2000). However, this city, and both are critical for seismic hazard amount of displacement may represent a minimum in assessment. Paleoseismic data from the different the area, as shown by the topographic profiles of the branches of the Elat fault zone shows that it consists elevated playa ridges. These represent the entire defor- of sub-zones in which several faults are active mation caused by the last earthquake in the southern together and at least two neighboring branches of Arava valley, and show an uplift of 2.5 to 3 m along a the irregular shear zone were tectonically active deformation belt, which is 10 km long and 0.5–0.2 km simultaneously during several of the detected earth- wide. Such uplift must correspond to an earthquake quakes (Amit et al., 2002). Such seismic behavior with a magnitude higher than M 6.6, which was was also detected in the present study area; the 1068 measured at trench T-20. The surface rupture length AD earthquake reactivated at least two branches, cannot be determined in the playa area because of fault C and fault D crossing an irrigation system erosional obscuring, burial by younger deposits of dated to the Early Islamic period. Furthermore, the the playa and fragmentation of the continuous fault Holocene period is characterized by intense tectonic line by incision of the alluvial fan. If the full 50 km activity at the central part of the Arava, followed by a length of the fault zone is assumed to have been active decrease in the tectonic activity at the western and during the studied event, the maximum magnitude is eastern margins (Amit et al., 2002). In the Holocene, expected to be M 7(Wells and Coppersmith, 1994). the faults composing the marginal fault zone of the E. Zilberman et al. / Tectonophysics 408 (2005) 79–99 95

Elat fault, which is capable of producing high-mag- active in respect to large events during the last 60 ka nitude earthquakes, seem not to have been active and including historical and present time (Fig. 9). This the faults at the central fault zone produced earth- behavior is supported by the subsidence rates calcu- quakes of magnitude M 5.9–6.7 only. Such evidences lated for the Dead Sea basin, which has been constant support the hypothesis that the behavior of the Elat during the last 700 ka (Begin and Zilberman, 1979). fault zone is time-dependent and is characterized by On the other hand the tectonic activity of the Elat changes in the faulting sequence with time and space. fault zone changed with time. This segment was At present the Avrona playa area, located in the highly active during the last 40 ka but its activity central part of the Elat fault zone, is the active area decreased with time until it almost stopped during although this segment of the Dead Sea Rift has been historical times. If the 1068 AD earthquake was the least seismically active segment during the past related to the Elat fault zone, as suggested in this 1000 years. paper, only two large events occurred on this fault The recurrence interval of large earthquakes during the last 2000 years, while during the same (M N6) in the Elat fault zone is much longer than period at least eight large historical events occurred the recurrence interval determined for the other seis- in the Dead Sea basin (Ken-Tor et al., 2001). More- mogenic zones along the DST (Fig. 9). The most over, the pattern of the earthquakes is also different active segment regarding large earthquakes of M N6 between these two seismogenic zones. Earthquakes is the Dead Sea basin with a recurrence interval of (M N5.5) in the Dead Sea basin appear to cluster in ~100–300 years supported by pre-historic and his- periods of 8–12 ky with relative quite periods of toric evidences (Ken-Tor et al., 2001; Marco et al., similar duration between the clusters. A period of 1996). The second most active segment is the Sea of 20 ky is likely to include a complete cycle of both Galilee and the Hula valley with recurrence interval active and non-active time periods (Marco et al., estimates of 230 and 340 years, respectively (Marco 1996). The southern Arava area shows a different et al., 1997; Ellenblum et al., 1998; Zilberman et al., seismic pattern with a non-homogeneous distribution 2000). In addition to the data on recurrence intervals of earthquakes in both time and space. The location of the different segments of the Dead Sea Rift, the of earthquakes with magnitudes larger than M 6.5 paleoseismic and historic evidences allow us some migrated with time over the Elat fault zone and in the insight of the general seismic pattern of these seg- Holocene most of the large events were located at the ments. The Dead Sea basin has been continuously central part of the fault zone, i.e. Avrona playa. In

Fig. 9. The distribution of prehistorically and historically earthquakes with magnitudes larger than M 6 in several segments of the Dead Sea Rift. In this figure we relate to tectonic events, which can rupture the surface. 96 E. Zilberman et al. / Tectonophysics 408 (2005) 79–99 addition, the earthquake magnitudes are larger and 3. The most active part of the Elat fault zone is the the recurrence intervals are longer on faults that were central part of the southern Arava valley, the active mainly during the late Pleistocene than those Avrona playa area, in which the most recent tec- that were active also or only during the Holocene tonic events have been detected. (Amit et al., 2002). 4. Paleoseismological, geomorphological and archae- The Arava valley, from the Dead Sea to the Gulf of ological evidences show that an earthquake that Aqaba, can be divided into a southern and a northern occurred about 1000 years ago deformed the segments. They differ from each other in their mor- Avrona playa surface. This earthquake was strong phology and in their seismic behavior. The distribu- enough to have uplifted the playa and change it tion of offsets along the northern Arava segment from a closed basin with an internal drainage sys- indicates repeated coseismic slip events with 1.5–2 tem into an open basin. It reactivated at least two m of displacement, which follows a stick-slip beha- branches of the fault zone, fault C and fault D, vior (Klinger et al., 2000a). These values are consis- vertically displaced the surface by at least 1 m and tent with fault rupture of 60–80 km in length and damaged the Early Islamic irrigation system. The moment magnitude of the order of Mw 7.2. The south- estimated minimum magnitude of this earthquake ern Arava segment behaves differently. It has a more is M 6.6. complex morphology with wide fault zone and no 5. The recurrence interval of large earthquakes (M 6) clear measurable lateral displacements and its seismic for the Elat fault zone is three to five times longer behavior is not of a stick-slip kind but was found to be than the recurrence interval determined for other closer to the bmode switchingQ model suggested by seismogenic zones along the Dead Sea Transform. Ben-Zion et al. (1999) and discussed in Amit et al. 6. The paleoseismic and historical evidences indicate (2002). that the seismicity of the Dead Sea basin is differ- Considering that the epicenter of the 1068 AD ent from that of the seismic behavior of the Arava earthquake was located in the Avrona playa area segment. The Dead Sea basin has been continu- and that the recurrence interval for the Holocene is ously active with respect to large events during the 1.2F0.3 ka, the probability for a large earthquake is last 60 ka, including historical and present times, relatively high in the central part of the Elat fault whereas the seismicity of the Elat fault zone mark- zone. edly decreased with time. 7. Historical records document two earthquakes, which damaged the ancient city of Aila at the 7. Conclusions southern Arava valley; the 1068 AD, and the 1212 AD earthquake. This study shows that The long record of seismicity along the Elat fault the 1068 earthquake was related to the DST as zone in the southern Arava valley provides an oppor- was the 1212 event. The location of the epicen- tunity to explore the temporal pattern of earthquakes ter of the 1068 AD earthquake in the Avrona in the southern part of the Dead Sea Transform. Our playa area means that an earthquake with a mag- main conclusions are: nitude of about M 7 occurred in the southern Arava valley about 1000 years ago. Since the 1. The Arava valley, one of the seismogenic zones of Holocene reoccurrence interval for this fault the Dead Sea Rift, has been seismically well mon- zone was determined to be 1.2F0.3 ka, this itored since 1986 and at present is seismically conclusion has important bearing on seismic inactive. hazard assessment of the southern Arava segment. 2. Paleoseismic evidence shows that this presently 8. The Elat fault zone is identified to be a site of non-active segment, called the Elat fault zone, is possible future earthquake of magnitude larger than capable of producing large earthquakes. However, M 6. This is augmented by the fact that the Avrona during the course of the last 80 ka earthquake fault is seismically inactive while no aseismic slip magnitudes and recurrence intervals have appreci- is known in this area. This raises the possibility that ably decreased. a seismic gap may exist in this area. An event of E. Zilberman et al. / Tectonophysics 408 (2005) 79–99 97

the magnitude inferred for the last earthquake (M Amit, R., Zilberman, E., Enzel, Y., Porat, N., 2002. Paleoseismic 6.6) in the Avrona playa would cause severe evidence for time-dependency of seismic response on a fault system in the southern Arava valley, Dead Sea rift, Israel. damage in the Arava Valley, including the two Geological Society of America Bulletin 114, 192–206. major cities of Elat and Aqaba. Arieh, E., Feldman, L., 1985a. Seismic intensities of earthquakes in Israel and adjacent areas during the last 2000 years, The Insti- tute of Petroleum Research and Geophysics, Report No. Z1 Acknowledgments (36), 20 pp. Arieh, E., Rotstein, Y., 1985b. Note on the seismicity of Israel (1900–1982). Bulletin of the Seismological Society of America This work was made possible through the financial 75, 881–887. support of the Earth Science Research Administration Arieh, E., Artzi, D., Benedik, A., Eckstein, A., Issakow, R., Reich, of the Ministry of National Infrastructures and the B., Shapira, A., 1985. Revised and updated catalogue of earth- CFS foundation. The authors thank Gideon Rosen- quakes in Israel and adjacent areas, 1900–1980, The Institute of baum, Orna Ben-Dov and Dina Stiber for the labora- Petroleum Research and Geophysics, Report No. Z6/1216/ 83(3), 38 pp. tory analyses, and Bat-Sheva Cohen and Nehama Ashbel, D., Eviatar, A., Doron, E., Ganor, E., Agmon, V., 1965. Soil Shragai for drawing the figures. We thank Mrs. Temperature in Different Latitudes and Different Climates. The Ximena Barrientos and Mrs. Bevy Katz for editorial Hebrew University of Jerusalem. 150 pp. assistance. Grateful acknowledgement extended to B. Atlas of Israel, 1985. 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