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The Gulf of Aqaba forms the southernmost segment of the
1100 km long Jordan Dead Sea transform that links the Red
Sea floor spreading in the south to the plate convergence in
the north. With its 180 km length and 20–30 km width, it
forms a major plate boundary that separates between the
Arabian plate in the east and the Sinai-Palestine microplate
in the west. Its maximum depth is 1,850 m in its middle part
Historical information as obtained from old Arab literature confirms that more than ten destructive earthquakes (M≥6.0–6.5) were felt in this region during the last ten centuries
Some of these were felt quite strongly and were thus epicentered close to the gulf if not within it. Two more strong earthquakes that are known to have occurred in the northern part of Wadi Araba have also been felt in the Aqaba region.
Both historical and instrumental seismicity data that occurred
within the Gulf of Aqaba region are compiled from
all available sources. Detailed analyses are made to these
including frequency magnitude, seismic moment, and other
seismotectonics calculations. Final results are presented in
this article.
Changes in the trend of the regional strike-slip faults which resulted in the creation of large basins along this transform, such as the Dead Sea),have also produced three marine basins within the Gulf of Aqaba).These are from north to south Aqaba-Haqel, Nuabie, and Tiran- Maqna basins, Extensive uplifting along the whole transform is a haracteristic feature that increases southwards towards the Gulf of Aqaba and the Red Sea. This is believed to have started in Late Tertiary. Itscontinuation in the present is witnessed along the gulf by raised beaches that can be seen in many localities. Continental breakup was accompanied by widespread, predominantly basaltic volcanism that was mostly restricted to the eastern margin. Radiometric dating of these indicate that this activity began in the Oligocene 30–20 Myr ago and continued to Recent times in some localities..
Most of the hazards to people come from man-made structures themselves and the shaking.
They receive from the earthquake.
The real dangers to people are being crushed in a collapsing building, drowning in a flood caused by a broken dam or levee, getting buried under a landslide, or being burned in a fire.
We have compared the Haicheng foreshock sequence with several earthquake swarms which occurred in its neighborhood. The spatial distribution of the earthquakes is relatively concentrated. For the most part, the events occurred within a few kilometers of each other. The focal mechanisms are comparatively stable. However, there are several swarms in which the variations of focal mechanisms are quite obvious after the occurrence of the largest event of the sequence, which would allow it to be recognized as a swarm. However, there are also swarms whose focal mechanisms are no less stable throughout the sequence compared to the Haicheng foreshock sequence. This feature could thus not be used to identify a foreshock sequence. The temporal distributions of foreshocks and swarms are quite similar in some cases. This is again not a definite criterion for identifying foreshocks, but is worthy of further study. Thus, no definite criterion for identifying foreshock sequences has been found. However, some earthquake swarms may be recognized in their later stage.
figure 5 :
show
The seismicity of the
Gulf of Aqaba region Ml≥3.5
as compiled from the IRIS files
for the period 1983–2011
The Gulf of Aqaba is situated along the southern portion of the Dead Sea Transform (DST) fault zone, a 1100 km transform fault that forms the barrier between the African plate and the Arabian Plate (Arabian-Nubian Shield).It is a zone of left lateral displacement, signifying the relative motions of the two plates. Both plates are moving in a general north-northeast direction, but the Arabian Plate is moving faster, resulting in the observed left lateral motions along the fault of approximately 107 km. A component of extension is also present in the southern part of the transform, which has contributed to a series of depressions, or pull apart basins, forming the Gulf of Aqaba.
The Seismicity data
* The November 22, 1995, Aqaba earthquake demonstrated that
this region is an active seismic area characterized by several
strong earthquakes occurring at relatively short recurrence
intervals. It also showed that contrary to earlier observations,
these seismic events may occur without warning in the form of
foreshocks.
* The earthquake swarms increase the hazard potential 24% in the northern part of the Gulf, while it has increased to 53% and 46% in the central and southern part of the Gulf, respectively.
* For Aqaba city the Jordan Dead Sea transform seismic sources, mainly Wadi Araba and the Dead Sea, represent the second potential hazard sources, after the Gulf of Aqaba source.
figure 7 :
show
The seismicity of the
Gulf of Aqaba region Ml≥5.5
as compiled from the IRIS files for the period 1983–2011
The ground firms up again after the earthquake has past and the water has settled back down to its usual place deeper in the ground. Liquefaction is a hazard in areas that have groundwater near the surface and sandy soil.Buildings can also be damaged by strong surface waves making the ground heave and lurch. Any buildings in the path of these surface waves can lean or tip over from all the movement. The ground shaking may also cause landslides, mudslides, and avalanches on steeper hills or mountains, all of which can damage buildings and hurt people.
The Effect of Ground Shaking
The first main earthquake hazard (danger) is the effect of ground shaking. Buildings can be damaged by the shaking itself or by the ground beneath them settling to a different level than it was before the earthquake (subsidence).
Buildings can even sink into the ground if soil liquefaction occurs. Liquefaction is the mixing of sand or soil and groundwater (water underground) during the shaking of a moderate or strong earthquake. When the water and soil are mixed, the ground becomes very soft and acts similar to quicksand. If liquefaction occurs under a building, it may start to lean, tip over, or sink several feet.
A strong earthquake, Mw 7.3, occurred in the Gulf of
Aqaba on 22 November 1995. The epicenter of the earthquake
was off-shore, about 60 km from the head of the gulf
where the cities of Aqaba (Jordan) lie. In these cities a few buildings were damaged, and a small wave
swept the beach according to witnesses. More extensive destruction was reported in the city of Nuweyba (Sinai, Egypt)
on the central part of the western coast, where several modem
houses, built with reinforced concrete, were completely
destroyed. This earthquake is the largest event ever recorded
in the Gulf of Aqaba since the beginning of instrumentally
recorded seismicity.
On 22 November 1995 the largest earthquake iinstrumentally recordedin the area, with magnitude Mw 7.3, occurred in the Gulf of Aqaba. The main rupturecorresponding to the strike-slip mechanism is located within the gulf of Aqaba, which forms the marine extension of the Levantine fault, also known as the Dead Sea fault.
The Levantine fault accommodates the strike-slip movement between the African plate and the Arabian plate. The Gulf of Aqaba itself is usually described as the succession of three deep pull-apart basins, longated in the N-S direction. Concerning historical seismicity, only two large events have been reported for the last 2000 years, but they are still poorly constrained.
Search in the different seismicity sources revealed that for
the Gulf of Aqaba region in particular, historical seismicity
information appear to be scarce for the period preceding the
year 1000 AD. It is found that during the last 10 centuries,
12 historical earthquakes have affected the Gulf of Aqaba
region. It is possible therefore that at least some of the historical earthquakes, if not all have initiated along some of the gulf’s faults. Future similar earthquakes in this region will certainly affect the northern part of the Gulf of Aqaba.
Considering that all the 12 historical earthquakes of Table
(1) were felt in the Gulf of Aqaba region with intensities≥
VI–VII, i.e., Ml≥6.0, and accounting for the two instrumental
earthquakes of Table (1), then the overall average recurrence
period of feeling such earthquakes in this region is
about 71 years.
The Mercalli intensity scale is a seismic scale used for measuring the intensity of an earthquake. It measures the effects of an earthquake, and is distinct from the moment magnitude M_w usually reported for an earthquake (sometimes misreported as the Richter magnitude), which is a measure of the energy released. The intensity of an earthquake is not totally determined by its magnitude.
I. Instrumental
II. Weak III. Slight
IV. Moderate V. Rather Strong
VI. Strong VII. Very Strong
VIII. Destructive IX. Violent
X. Intense XI. Extreme
XII. Catastrophic
fig 10 :show Cumulative Temporal b-variation during 1983-2011
log N = a - bM
Aqaba city is located Southern of Jordan, within the Dead Sea Transform Fault (DSTF)
system, the source of medium to high seismic activity, as illustrated in figure 1.
DSTF is the major active tectonic and morpho-tectonic features of the region; it strikes in a
NNE direction.
Abdel-Fattah A, Hussein H, Ibrahim E, Abu El Atta A (1997) Fault plane solutions of the 1993 and 1995 Gulf of Aqaba earthquakes and their tectonic implications. Ann Geophys 40(6)
El-Isa Z (2011) Temporal Variations in the b-value of the Earthquake
Frequency-Magnitude-Distribution ( in preparation)
Kiinger, Y., J. P. Avouac, and N. Abou Karaki (1997). Seismotectonics of Wadi Araba fault (Jordan) (Abstract), in EGS 22th GeneralAssembly
21-25 April, Vienna, Austria, Annales Geophysica Sup., 15.
Al-Tarazi, E. 2000. The Major Gulf of Aqaba Earthquake, 22 November 1995-Maximum Intensity Distribution, Natural Hazards, 22: 17-27.
Gruenthal, G., and Wahlstroem, R. 2001. Sensitivity of Parameters for Probabilistic Seismic Hazard Analysis using a Logic Tree Approach, J. of Earthquake Engineering, 5 (3): 309-328.
fig 4 "a" Regional tectonics of the Jordan Dead Sea transform. Red stars represent possible epicenters of all historical earthquakes that have affected the Gulf of Aqaba region during the last 10 centuries. The two blue stars
represent the epicenters of the 1969 Gulf of Suez (M=6.9) and 1995 Gulf of Aqaba earthquakes ( M=6.1)
"b" Fault system and Miocene dykes ofthe Gulf of Aqaba region and the three basins resulting from the arrangement
of the en-echelon strike-slip faults within the gulf. The circles represent the epicentral locations of all instrumental earthquakes that occurred in the gulf region with Ml≥4.9 during the period 1982–2008
One it her side of the gulf,long early Neogene dykes trending NW parallel to each other and the Gulf of Suez are believed to have accompanied the initial stage of the development of the Red Sea–Gulf of Suez Faulting alongthis direction (NW) is also present in this area. This volcanism was followed by the shear along the Gulf of Aqaba. A system of faults subparallel to the gulf exists within a zone a few tens of kilometers wide on either side. Said (1962) mapped some of these faults and reported that these were contemporaneous with the faults of the Gulf of Suez, and older than those NE faults that determine the location of Aqaba Gulf. Later, these were found to be of left-lateral shear with displacements that range from several meters to cumulative amounts of 24 km in the west and some 20 km in the east al.). From a study of the tectonic development of the western margin of the Gulf of Aqaba. It is suggested that the whole shear along the Jordan transform could have happened with- in the last 5–10 Myr. Other geological studies confirm that the oldest movements along this transform are surely youn- ger than those in the Suez basin, suggesting the end of the extension of the Gulf of Suez and the transfer of the motion along the Aqaba Gulf to have occurred some 10–14 Myr ago .
figure 6 :
show
The seismicity of the
Gulf of Aqaba region Ml≥4.5
as compiled from the IRIS files for the period 1983–2011
The seismicity recorded since installation of regional networks in the early 1980s had been characterized by a low background level punctuated by brief swarmlike activity a few months in duration. Three swarms
have already been documented in the Gulf of Aqaba in 1983, 1990, and 1993, with magnitudes reaching at most 6.1 (Mw). We suggest that the geometry of the rupture for the 1995 event is related to the spatial distribution of these previous swarms.
Body-wave modeling of broadband seismograms from the global network, along with the analysis of the aftershock distribution, allow us to propose a well-constrained model for the rupture process. Northward propagation of the rupture has been found.
We have demonstrated that three successive subevents are necessary to obtain a good fit between observed and synthetic wave forms. The total seismic moment released was 7.42 × 1019 N-m. The location of the subevents shows that the three stages of the rupture involve three different segments within the gulf. Substantial surface breakage showing only normal motion (up to 20 cm) affecting beachrock was observed along the Egyptian coast. We show that these ruptures are only a secondary feature and are in no case primary ruptures. The stress tensor derived from striations collected in quaternary sediments shows radial extension. This result supports landsliding of the beach terraces under the action of the earthquake shaking.
Earthquake swarms are events where a local area experiences sequences of many earthquakes striking in a relatively short period of time.
They are differentiated from earthquakes succeeded by a series of aftershocks by the observation that no single earthquake in the sequence is obviously the main shock. Earthquake swarms are one of the events typically preceding eruptions of volcanoe.
* The Gulf of Aqaba region has been affected by some 12 historical earthquakes within the last 10 decades with average recurrence periods 70–90, 167–200, and 333–500 years for M≥6.0, 6.5, and 7.0, respectively. At least, the largest four of these have occurred very close
to the gulf or within it. Correlating historical with instrumental
seismicity data, it is concluded that the first appears to be incomplete and require further investigations,particularly for earthquakes with ≤6.5.
* The epicentral distribution of the instrumental seismicity data indicates that all regional faults of the gulf area are active in the present. Most of the activity of the study period was concentrated within the area bound by latitudes 28.2°–29.8° and longitudes 34.4°–35.2°. This implies that
the regional strike-slip and normal faults of the northern two basins Aqaba–Haqel and Nuwabie were the most active during this period. Their activity is at least twice that of the normal faults.
Earthquakes really pose little direct danger to a person. People can't be shaken to death by an earthquake. Some movies show scenes with the ground suddenly opening up and people falling into fiery pits, but this just doesn't happen in real life Seismic hazard refers to the study of expected earthquake ground motions at the earth's surface, and its likely effects on existing natural conditions and man-made structures for public safety considerations; the results of such studies are published as seismic hazard maps, which identify the relative motion of different areas on a local, regional or national basis. With hazards thus determined, their risks are assessed and included in such areas as building codes for standard buildings, designing larger buildings and infrastructure projects, land use planning and determining insurance rates. The seismic hazard studies also may generate two standard measures of anticipated ground motion, both confusingly abbreviated MCE; the simpler probabilistic Maximum Considered Earthquake or Event, used in standard building codes, and the more detailed and deterministic Maximum Credible Earthquake incorporated in the design of larger buildings and civil infrastructure like dams or bridges.
More extensive de- struction was reported in the city of Nuweyba (Sinai, Egypt) on the central part of the western coast, where several mod- em houses, built with reinforced concrete, were completely destroyed. This earthquake is the largest event ever recorded in the Gulf of Aqaba since the beginning of instrumentally recorded seismicity. The Gulf of Aqaba belongs to the Levantine fault sys- tem (also called the Dead Sea fault) and is located at its southern extremity. The Levantine fault is considered to be a plate boundary of the transform type between the African plate and the Arabian shield, which slides along this limit in its northward motion.
Further frequency-magnitude nalyses were made to the seismicity data
and the b values were calculated from the seismicity data of each year
of the whole period 1982–2008.
The results are plotted on Fig 11. which also shows the total number of earthquakes that occurred in each year with magnitudes≥2.5 and the
highest magnitude of that year.
The b value shows a clear temporal variation where it records
a minimum value (0.48) in the year 1987 and a maximum value
(1.49) in the year 2002. It varies for most years in the range 0.8–1.1.
The seismicity data for the years 1989 and 1992 showed minimum
number of earthquakes that did not allow precise b calculations.
Total yearly number of earthquakes (Ml≥2.5) show clear fluctuation
with time. Two maxima of 189 and 314 earthquakes are seen from the
1993 swarm and the 1995 sequence, respectively.
Two smaller maxima are seen from the 1983 and the 1999– 2003
swarms. These data show that the Gulf of Aqaba region was
seismologically quite during the periods 1985– 1992 and 2003–2008,
though two swarms have occurred during these years, namely the
1986 and the 1990–1991swarms
Finally, we introduced a magnitude sequence with gaps which can be used to see whether a large event is still forthcoming. This method (in conjunction with other methods) could be used in areas prone to large earthquakes, immediately before a large event, to improve the probability of predicting the occurrence of a large event. We also report that the temporal distribution of all the sequences showed a 12-hour recurrence pattern that corresponded with the earth tides, indicating that tidal forces might be influencing foreshocks and earthquake swarm occurrence.
Arab J Geosci (2013) 6:3437–3449
DOI 10.1007/s12517-012-0604-8
The second main hazard is flooding. An earthquake can rupture (break) dams or levees along a river. The water from the river or the reservoir would then flood the area, damaging buildings and maybe sweeping away or drowning people.
Tsunamis and seiches can also cause a great deal of damage. A tsunami is what most people call a tidal wave, but it has nothing to do with the tides on the ocean. It is a huge wave caused by an earthquake under the ocean. Tsunamis can be tens of feet high when they hit the shore and can do enormous damage to the coastline. Seiches are like small tsunamis. They occur on lakes that are shaken by the earthquake and are usually only a few feet high, but they can still flood or knock down houses, and tip over trees.
Nawaibia
Tiran- magna
fig 8 :The time distribution of the seismicity ( Ml≥3 ) of the Gulf of Aqaba region during the period 1983–2011
fig 3:show the general tectonuc of Gulf of Aqaba
"b" Fault system and Miocene dykes ofthe Gulf of Aqaba region and the three basins resulting from the
arrangement of the en-echelon strike-slip faults within the gulf. The circles represent the epicentral locations of all instrumental earthquakes that occurred in the gulf region with Ml≥4.9 during the period 1982–2008
Magnitued
Year
figure 12:
The locations of the swarms of 1995
IRIS for 1995 event
*