Atlas of Jordan|
Chapter one - Constraints and Resources
A Seismic Junction
1The Official Report of the United States Expedition to Explore the Dead Sea and the River Jordan (1852) marks the commencement of modern scientific investigation into the geology-topography of the area (Quennel 1956, p. 5). Blake drew the first geological map of Jordan in 1939. But the first preeminent geologist is A. M. Quennel who conducted fieldwork between 1946 and 1948 to prepare the 1: 250 000 geological map of East Jordan in collaboration with the Department of Land and Surveys (Quennel 1951).
2Jordan lies accross the northern rim of the African-Arabian Pre Cambrian granitic shield. Over the geological times, the shield has pulsated up and down in epeirogenic movements, allowing seas ingressions (and sedimentation when down) or huge erosion phases (when up) (Burdon 1959).
3On a Precambrian Basement Complex that appears in the southern and south-eastern parts of the country (Igneous and metamorphic rocks of the Nubo Arabian shield more than 600 million years in age), Paleozoic sandstone and shale sediments (570 – 280 my) are attaining 1800 meters in thickness of marine and continental origins. During the oldest Mesozoic phase (Lower Triassic age 224 my) marine sedimentation occured in in the northern and western parts of the country. At the end of the Triassic (190 my) the sea regressed and the whole area was subjected to erosion.
4During the Middle Jurassic (165 my) the sea transgressed again, marine sedimentation was restricted to the Jordan Valley side wadis in a region extending southwards about 20 kilometres from Wadi Zarqa. Erosion on the continent continued in the South and East. Beginning in the Late Cretaceous Epoch (100 my) regional transgression started to spread over extensive areas of Jordan depositing appreciable thickness of sediments accumulated in basins particularly along the Wadi Araba Jordan Rift Valley and in the al-Jafr and al-Azraq Wadi Es-Sirhan Basins.
5In the Cenozoic Era (65 my), the Tertiary marine sediments of the Paleocene and the major part of the Eocene were deposited in a similar “Gentle Swells and Basins Systems”. Along Wadi Araba - Jordan rift, coarse clastic weathering products from the bordering uplifted areas were deposited at the same time together with taphrogenic tectonism in the Oligocene Epoch (36 -26 my). Locally, in the central parts of the graben, thick rock salt was deposited in the Oilgo-Miocene to Pliocene (36-12 my). During the Cenozoic Era the Jordan Rift was either occupied by fresh water lakes draining west to the Tethys Sea, or formed an inland depression with terrestrial or lacustrine sediments or was entered by marine waters. Miocene transgression from the north reached to Azraq - Wadi Sirhan Depression and to northeast Jordan beyond Jebel al-Drouz basalt flow.
6During a time in the Miocene - Pliocene, the Mediterranean Sea may have linked with the Red Sea through the Gulf of Aqaba and Wadi Araba Jordan Rift and through the Beisan Depression.
7Throughout the Quaternary, detritus was transported into the Rift Valley, and the extension Azraq - Wadi Sirhan and al-Jafr depressions of East Jordan. These depressions were partly covered by fresh and brackish water lakes during fluvial periods of the Pleistocene, while fluviatile conglomerates of the same age spread over wide areas along the eastern slopes of the mountain ridges bordering the east side of the Wadi Araba - Jordan Rift (Jreisat 1995, p.3).
8Jordan covers the north-western part of the Arabian plate separated from the African Plate along the most profound tectonic event on the earth crust: the Aqaba - Dead Sea - Jordan Valley - Rift. This is an active pull-apart with left-lateral motion. The amount of left-lateral motion along the Transform in the Dead Sea Region is estimated at 105 km (Quennell 1958 ; Freund et al., 1970). But one must keep in mind that the African plate is going north, as the Red Sea is widening (fig. I.4).
Figure I.4 — Jordan Major Structural Features.
A. al-Diabat, NRA Geological Mapping Division, 2012
9The geological structure of Jordan shows the effect of several phases of deformation since the Cambrian period. The crystal movement that affected the country has resulted in gentle, regional tilting, uplift and subsidence and a combination of faulting and folding. According to the different kinds of structural deformation and pattern, the country has been divided into three major structural provinces:
The Nubo-Arabian Shield of South Jordan.
The Block-Faulted Platform of Jordan east of the Rift.
The Wadi Araba - Jordan Rift (fig. I.5 and I.6).
Figure I.5 — Geological Map of Jordan by F. Bender 1974.
Figure I.6 — Combined Profiles of Jordanian Highlands and Jordan Rift Valley.
10The East Mediterranean region is the place where three major tectonic plates : Africa, Arabia, and Eurasian Anatolian Sub plate, face each other. These tectonic plates are what sandwich the fragmented Palestine - Sinai sub-plate. Consequently, the region could be affected by a number of seismotectonic active sources distributed along the Dead Sea Transform (DST). This extends to about 1100 km and goes from the Gulf of Aqaba triple junction, up to the plate boundary between the Arabia and Anatolian sub- plate, the left lateral East Anatolian fault, the Carmel ruptures zone (that itself extends more than 130 km of the northwestern trend) and the Gulf of Suez divergent rift - that follows the same route as the Mid Red Sea spreading ridge (fig. I.7). Due to this tectonic setting, seismicity and topography, the East Mediterranean Region (EMR) has been subjected to earthquake disasters during the past two thousand years that has left great losses in terms of life and material damage. Earthquakes have been the main cause of past disasters and this is expected to continue in the future. ??. Seismic activity of the EMR is mainly associated with the northward movement of the Arabian plate.
11This aside, accumulated historical and instrumental data records since the establishment of seismic networks in the region reveal that the majority of the seismic activities are mainly associated to the tectonic features that compose the plate boundary of the Palestine - Sinai sub-plate (fig. I.8).
Figure I.8 — Earthquake distribution in Jordan and the Middle East from 1900 to 2005.
12Evidence found at archaeological sites in the East Mediterranean Region, as well as the major earthquake of July 11, 1927 - with epicenter next to the village of Dahmiya in the vicinity of Jordan river, bear witness to the fact that the region has to be considered highly vulnerable to earthquake hazards. In the 1980s, the Natural Resources Authority (NRA) took an important step in establishing an earthquake monitoring observatory now called the Jordan Seismological Observatory (JSO). The role of the observatory is mainly to monitor local and regional earthquake activities that could affect the country, undertake a variety of seismological studies and assess earthquake hazards of the Dead Sea Transform system. During the past two decades, JSO has deployed well trained and highly educated personnel to conduct polynomial seismic studies, including both a Probabilitistic Seismic Hazard Assessment (PSHA) and a Deterministic Seismic Hazard Assessment (DSHA) covering the whole country, whilst focusing on certain key areas. As a result of the PSHA project, a probabilistic seismic hazard zonation map of the country was released in 2005 (fig. I.9), along with strong advocacy to all construction-based stakeholders of the country to respect and to use the findings therein as a guide to their future activities.
13JSO instrumental recordings from the past two decades revealed that the Gulf of Aqaba, in addition to south of Cyprus segment of the East Anatolian fault, presents the most active tectonic activity in the region, illustrated by a major 1995 Mw = 7.2 in the Gulf of Aqaba and the 1996 Mw = 6.8 south west of Cyprus. However, more recent data accumulated since 1996 seems to show that the region could be entering a cycle of reduced seismic activity in terms of the number of major events occuring, although some moderate earthquakes have taken place in the region : the Wadi Araba ML = 4.5 and the Al-Guerra ML = 4.3 in 1999, that could be seen as a consequence of the 1995 major Gulf of Aqaba earthquake.
14A number of moderate events which occurred in the region during the last decade are also worth noting : the Dead Sea 2004 and 2007 of ML = 4.9 and ML = 4.7 respectively and the late Tyre 2008 of ML = 5.2. Data produced throughout the last 15 years of monitoring refer to activity migration heading northwards but remaining moderate up to today. The Dead Sea Transform is also characterized by the ‘stress long distance jump’ that occurred at least twice in the past 15 years (in 2003 and 2004). The 2003 stress jump shifted southward of Aqaba city for 67 km, while the 2004 shifted northward for 290 km from a starting point south of Aqaba. Until now, there is no scientific explanation for the long distance stress jump that the DST experienced in 2003 and 2004, although there is a an existence of scientific explanation for short distance stress jump that not exceed 10 km].
15The East Mediterranean Region is rich in archaeological sites and there is evidence of strong shaking found at almost all ancient structures of the region. Historical documents refer to more than 300 earthquakes that have taken place in the Dead Sea basin since 2150 BC, of which 10 have had a devastating impact (JSOC).
16On July 11, 1927, a devastating earthquake of Ml = 6.3 (with the epicenter confined at Lat. = 32.0o and Lon. = 35.5o) struck the region. This event left widespread damage in Jordan and Palestine with more than 300 lives lost. Since the beginning of the twentieth century many efforts were made to establish a complete historical earthquake catalogue for the region. The historical seismicity of the area (downward to 31○ latitude) was poorly documented due to the prevailing arid environment. The area was rarely inhabited northward of 31○ latitude, where historically felt earthquakes are well documented. Historically the East Mediterranean tectonic features were the main source of seismological activities that severely affect the region since the ‘slip’ movements along the Dead Sea rift valley started some 20 to 25 million years ago. All well documented earthquakes during the past 2000 years are of an estimated magnitude range 6.5 – 7.5 which coincides well with what is known today about the East Mediterranean tectonic features (fig. I.10).
Figure I.10 — Major historical earthquakes along the Dead Sea Transform during the past 2000 years.
17Seismic activities of the Gulf of Aqaba, Wadi Araba, Dead Sea, Carmel, Cyprus and the Gulf of Suez are the most well known seismogenic zones in the East Mediterranean region. Data obtained from these areas refer to the Gulf of Aqaba and Cyprus as the highest maximal expected earthquake magnitude in the region. Calculated seismic behaviour refers to the Gulf of Aqaba maximum expected local magnitude of M ≈ 6.4, while Cyprus is allocated a maximum expected earthquake local magnitude of M ≈ 7.1. On the other hand the lowest estimated maximum expected earthquake magnitudes are to be found in Wadi Araba M ≈ 5.1 and the Carmel M ≈ 5. The Dead Sea maximum expected earthquake is M ≈ 5.9.
Table des illustrations
|Titre||Figure I.4 — Jordan Major Structural Features.|
|Crédits||A. al-Diabat, NRA Geological Mapping Division, 2012|
|Titre||Figure I.5 — Geological Map of Jordan by F. Bender 1974.|
|Titre||Figure I.6 — Combined Profiles of Jordanian Highlands and Jordan Rift Valley.|
|Titre||Figure I.7 — The main east mediterranean tectonic features).|
|Titre||Figure I.8 — Earthquake distribution in Jordan and the Middle East from 1900 to 2005.|
|Titre||Figure I.9 — Seismic hazard zonation map of Jordan.|
|Titre||Figure I.10 — Major historical earthquakes along the Dead Sea Transform during the past 2000 years.|
© Presses de l’Ifpo, 2013
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