Seismicity and major geologic structures of Tiran and Sanafir islands and their surroundings in the Red Sea

Tiran and Sanafir islands and their surrounding areas are very important due to their location within the Red Sea, which is in a triple junction among the African and Arabian plates and the Sinai Peninsula microplate. Consequently, this area should be studied from a geological point of view, particularly because there is a plan to construct King Salman’s bridge connecting Egypt and Saudi Arabia. Freely available potential field data, such as magnetic and gravity data, were integrated with seismological data from nearby seismic stations to understand the regional structure and seismic activity in the area. Potential field data were analysed using edge detection techniques (Tilt DeRivative and horizontal gradient) for qualitative interpretation and 2D inversion modelling for quantitative interpretation. Seismological data were analysed geostatistically to identify many epicentre locations and estimate the focal depths. The results of the potential field data analysis indicate that Tiran and Sanafir islands are located along a subsurface geological edge trending NW, parallel to the Red Sea. A similarity in potential field anomalies between both islands and the southern Sinai Peninsula indicates that these islands were separated from the Sinai Peninsula during the formation of the Gulf of Aqaba via Dead Sea Transform fault. The analysis of the seismic data indicates that a specific motion characterizes each focal depth solution. The seismic events are related to main structural trends NW–SE and NE–SW.     

The Arabian Plate: unique fit of the earth's surface jig saw puzzle

The Arabian Plate is important and unique in many ways. The worker wants to highlight the important features characterizing the Arabian Plate. It is a unique fit of the earth's surface jig saw puzzle, different than all other lithospheric plates. It has the three known main tectonic plate boundaries, divergent, convergent and conservative ones. These boundaries are the Red Sea and Gulf of Aden, Zagros-Taurus and Dead Sea, respectively. It has three main well-defined and sharp plate boundaries, and it is surrounded by three major plates, African, Eurasian and Indian plates. The Red Sea and Gulf of Aden form the divergent boundary and spreading center. The Dead Sea Transform Fault (the Gulf of Aqaba Transform Fault) represents the conservative boundary and transform fault system. The Zagros-Taurus Thrust (Zagros-Taurus-Bitlis Thrust and Fold Belt) represents the convergent boundary and collision zone. The Arabian Plate incorporates a wide range and variety and subvariety of all three rock types, igneous, metamorphic and sedimentary rocks, this in addition to all kinds of structures. Among these are folding with major fold belts, faulting, foliation, lineation and diapirism. Transform, transcurrent, normal, graben, reverse, thrust faults are all represented one way or another. The tectonics of the Arabian shield, which forms a major part of the Arabian Plate, has long tectonic history prior to the formation of the Red Sea. After the opening and formation of the latter, the tectonics of the Arabian shield became affected and controlled by its tectonics. The Arabian Plate includes the Arabian Platform which has a relatively different setting of tectonics represented by the Central Arabian Graben. The Arabian Plate contains one of the best representative outcropped ophiolite sequences in the world. The Arabian Plate most importantly incorporates most of world oil reserve. Seismic and volcanic activities are also manifested and affected many areas in the Arabian Plate.     

“Shock event”, an impact phenomenon observed in water wells around the Arabian Gulf coastal city Dammam,Saudi Arabia: possible relationship with Sumatra tsunami event of December 26, 2004

A sudden disturbance in water level was recorded by hydrographs monitoring wells in the coastal city Dammam, Saudi Arabia on December 26, 2004. The water level was being recorded from the shallow (1–3 M deep) coastal aquifer at that time. In two wells, this disturbance was observed ~12 h after the Sumatra earthquake/tsunami event of December 26, 2004. The timing of this event is synchronous in two wells near the coast, but an inland well away from the coast line did not show any such disturbance. It is hypothesized that this disturbance, we call it the “shock event”, is resulted by sudden impact of tsunamis traveling in the Arabian Gulf from southeast toward northwest. As the tsunamis propagated, they suddenly impacted the coastal shallow groundwater aquifer resulting in the “shock event”.     

Deterministic seismic hazard assessment for Sultanate of Oman

The Sultanate of Oman forms the southeastern part of the Arabian plate, which is surrounded by relatively high active tectonic zones. Studies of seismic risk assessment in Oman have been an important on-going socioeconomic concern. Using the results of the seismic hazard assessment to improve building design and construction is an effective way to reduce the seismic risk. In the current study, seismic hazard assessment for the Sultanate of Oman is performed through the deterministic approach with particular attention on the uncertainty analysis applying a recently developed method. The input data set contains a defined seismotectonic model consisting of 26 seismic zones, maximum magnitudes, and 6 alternative ground motion prediction equations that were used in four different tectonic environments: obduction zone earthquake (Zagros fold thrust belt), subduction zone earthquakes (Makran subduction zones), normal and strike-slip transform earthquakes (Owen and Gulf of Aden zones), and stable craton seismicity (Arabian stable craton). This input data set yielded a total of 76 scenarios at each point of interest. A 10 % probability that any of the 76 scenarios may exceed the largest median ground acceleration is selected. The deterministic seismic hazards in terms of PGA, 5 % damped spectral acceleration at 0.1, 0.2, 1.0 and 2.0 s are performed at 254 selected points. The ground motion was calculated at the 50th and 84th percentile levels for selected probability of exceeding the median value. The largest ground motion in the Sultanate of Oman is observed in the northeastern part of the country.     

Relocation processing of selected earthquakes in the Gulf of Aqaba region

Earthquakes in the Gulf of Aqaba were compiled from the Jordan Seismological Observatory bulletins, Saudi Arabia (SNSN, King Abdulaziz City for Science and Technology), and Egypt (National Research Institute of Astronomy and Geophysics, Helwan) sources and were relocated after reexamining the P and S arrival times, testing the efficiency of stations used to determine the location of Aqaba events, calculating the average value of V _p/V _s, and choosing the best crustal model for the study area. The earthquake epicenters are distributed along the eastern side of the Gulf of Aqaba.     

Overview of some geological hazards in the Saudi Arabia

The Saudi Arabia has harsh environmental conditions which enhance some geomorphologic/geological processes more than in other areas. These processes create different geological hazards. The general physiography of the Saudi Arabia is characterized by the Red Sea coastal plains and the escarpment foothills called Tihama, followed by the Arabian Shield Mountains, the Arabian Shelf plateau and finally the Arabian Gulf coastal plains. These types of geological hazards can be categorized into sand accumulations, earth subsidence and fissures, flash floods, problematic soils, slope stability problems, and karst problems. The current study gives an overview of all these hazards with examples, as well as develops a geo-hazard map for the Saudi Arabia. Our findings indicate that the desert environment needs much concern and care. National and international agencies have to join together with other people to keep the system balanced and to reduce the resulting geological hazards. Also, remedial measures should be proposed to avoid and reduce these natural hazards.     

The seismic hazard assessment of the Dead Sea rift, Jordan

The Dead Sea fault system and its branching faults represent one of the most tectonically active regions in the Middle East. The aim of this study is to highlight the degree of hazards related to the earthquake activities associated with the Dead Sea rift, in terms of speculating the possible future earthquakes. The present investigation mainly is based on available data and vertical crustal modeling of Jordan and the Dead Sea model for the Dead Sea basin with particular emphasis of the recent earthquake activities, which occurred on December 31st, 2003 (Mc = 3.7), February 11th, 2004 (strongest Mc = 4.9 R), and March 15th, 2004 (Mc = 4). The present research examines the location of the strong events and correlates them with the various tectonic elements in the area. The source mechanism of the main shock and the aftershock events is also examined. The analyses were based on the available short period seismogram data, which was recorded at the Natural Resources Authority of Jordan, Seismological Observatory. The seismic energy appears to have migrated from the south to the north during the period from December 31st up to March 12th, where the released seismic energy showed a migration character to the southern block of the eastern side of the Dead Sea, which led the seismic event to occur on March 15th.     

Earthquake generation in Cyprus revealed by the evolving stress field

Strong earthquake occurrence (M ≥ 6.0) onshore and offshore the Cyprus Island constitutes significant seismic hazard because they occur close to populated areas. Seismicity is weak south of the Island along the Cyprean Arc and strong events are aligned along the Paphos transform fault and Larnaka thrust fault zone that were already known and the Lemessos thrust fault zone that defined in the present study. By combining the past history of strong (M ≥ 6.0) events and the long-term tectonic loading on these major fault zones, the evolution of the stress field from 1896 until the present is derived. Although uncertainties exist in the location, magnitude and fault geometries of the early earthquakes included in our stress evolutionary model, the resulting stress field provides an explanation of later earthquake triggering. It was evidenced that the locations of all the strong events were preceded by a static stress change that encouraged failure. The current state of the evolved stress field may provide evidence for the future seismic hazard. Areas of positive static stress changes were identified in the southwestern offshore area that can be considered as possible sites of future seismic activity.     

Magnetic and seismic refraction survey for site investigation of an urban expansion site in Abha District,Southwest Saudi Arabia

Arabian Journal of Geosciences - Ground magnetic and seismic refraction survey is carried out on an urban extension site in the southwest of Ahud Rufeidah town, southwest Saudi Arabia. The purpose...     

Diagenesis of Holocene beachrocks: a comparative study between the Arabian Gulf and the Gulf of Aqaba,Saudi Arabia

Beachrocks occur in present-day intertidal zones of the Arabian Gulf and the Gulf of Aqaba, on the eastern and northwestern coasts, respectively, of Saudi Arabia. The beachrocks occur as linear patches within beach deposits, which have variable grain size and detrital compositions. The Arabian Gulf beachrocks are composed of sand-sized bioclasts and siliciclastic grains, whereas the Gulf of Aqaba beachrocks are composed of sand- to pebble-size grains, which are dominated by igneous rock fragments and small amounts of skeletal carbonate grains. The cement includes micritic high-magnesian calcite and isopachous acicular/bladed aragonite. In addition to cements, intergranular pores are locally filled by a lime–mud matrix. Radiocarbon dating of beachrock samples from the Arabian Gulf yielded ages from ca. 655 to 2185 year bp, whereas the Gulf of Aqaba samples range in age between 2745 and 5075 year bp.     

Seismic Hazard Assessment in the Tihamat Asir Region, Southwestern Saudi Arabia

The occurrence of earthquakes, faulting of Pleistocene sediments, uplifting of Pleistocene coral reefs, recent incised wadis and lava effusions in addition to hot springs all clearly indicate that southeastern Saudi Arabia is tectonically active. This paper reviews the tectonic features of southwestern Saudi Arabia and provides new approaches and maps for the interpretation of old and recent earthquake data for improved assessment of the regional tectonics. A regionalized variable approach is used to develop earthquake groundmotion hazard maps for the region, based on geostatistical methods using the kriging technique. This hazard must be considered in any design/construction of engineering structures in the region. The application of kriging for estimating the ground shaking in the study region succeeded clearly in accomplishing its ultimate aim where the generated groundmotions are well correlated with the instrumental magnitude and historical intensity of any earthquake occurrence in the study region.     

Lithostratigraphy,deformation history,and tectonic evolution of the basement rocks,Republic of Yemen: an overview

Basement rocks of presumed Precambrian age, in Yemen Republic (105,000 km²), are exposed in the northwestern and southeastern parts of the country. The basement rocks of southern Saudi Arabia and northern parts of Yemen are almost continuous and similar in the lithostratigraphic succession. In spite of the presence of such common basic characteristics for each, there are slight differences of local structural framework and major tectonic events. The structural complexity, great variety of rock units and types, multi-intrusive environments, and multiplicity of metamorphic events in the study basement rocks make the main target of lithostratigraphic analyses, in particular, daunting in the southern Arabian Shield. As reported here, accepting that the southern shield consists of five terranes and suture zones requires a limitation of such tectonic modifications. This led to the renaming of certain formations and groups and the revision of the lithostratigraphic successions for some regions. As a result, new lithostratigraphic relationships and names as well as tectonic events are proposed. Based on field and space image data, the basement rocks in Yemen exhibit at least six major phases of deformation (D1 to D6) including intensive brittle and ductile deformations that trend NW–SE and NNE–SSW (in major). Neoarchean rocks are well developed and restricted in the southeastern exposures (Al Bayda, Al Mahfid, and Al Mukalla terranes), whereas the final Pan-African cratonization of several rock units is widespread on all terranes, in which the major tectonic events and deformation history were concentrated during pre-Pan-African and early to late Pan-African orogenies. A correlation and evolution of the Precambrian rocks in Saudi Arabia and Egypt are taken into consideration.     

Structural mapping from high resolution aeromagnetic data in west central Arabian Shield, Saudi Arabia using normalized derivatives

Aeromagnetic data covering an area of about 40,000 km² at the west central Arabian Shield, Saudi Arabia has been collected and interpreted to provide structural map of the area. A number of normalized derivatives were used to help interpret the signature of magnetic data so that weak and small amplitude anomalies can be amplified relative to the stronger and larger amplitude anomalies. The interpretations obtained from these geophysical techniques of the field data demonstrated a strong correlation between magnetic anomalies and mapped subsurface geology. Based upon the variation in magnetic lineaments, shape amplitude, and trend structural map of the west central Arabian Shield on Saudi Arabia were obtained.     

http://www.sciencedirect.com/science/article/pii/S1674987112001247

The Sinai Peninsula has been recognized as a subplate of the African Plate located at the triple junction of the Gulf of Suez rift, the Dead Sea Transform fault, and the Red Sea rift. The upper and lower crustal structures of this tectonically active, rapidly developing region are yet poorly understood because of many limitations. For this reason, a set of P- and S-wave travel times recorded at 14 seismic stations belonging to the Egyptian National Seismographic Network (ENSN) from 111 local and regional events are analyzed to investigate the crustal structures and the locations of the seismogenic zones beneath central and southern Sinai. Because the velocity model used for routine earthquake location by ENSN is one-dimensional, the travel-time residuals will show lateral heterogeneity of the velocity structures and unmodeled vertical structures. Seismic activity is strong along the eastern and southern borders of the study area but low to moderate along the northern boundary and the Gulf of Suez to the west. The crustal V_p/V_s ratio is 1.74 from shallow (depth ≤ 10 km) earthquakes and 1.76 from deeper (depth > 10 km) crustal events. The majority of the regional and local travel-time residuals are positive relative to the Preliminary Reference Earth Model (PREM), implying that the seismic stations are located above widely distributed, tectonically-induced low-velocity zones. These low-velocity zones are mostly related to the local crustal faults affecting the sedimentary section and the basement complex as well as the rifting processes prevailing in the northern Red Sea region and the ascending of hot mantle materials along crustal fractures. The delineation of these low-velocity zones and the locations of big crustal earthquakes enable the identification of areas prone to intense seismotectonic activities, which should be excluded from major future development projects and large constructions in central and southern Sinai.     

Pan-African plates: Additional evidence from igneous events in Saudi Arabia

The chemical and geological nature of thec. 600 m.y. igneous complex of the Al-Hadah escarpment of Saudi Arabia is fitting to that of a modern subduction environment. It appears that plate motions were occurring during this Pan-African tectonic event but the scale of both plates and motions was smaller than that of the present time.     

Improving seismotectonics and seismic hazard assessment along the San Ramón Fault at the eastern border of Santiago city,Chile

The San Ramón Fault is an active west-vergent thrust fault system located along the eastern border of the city of Santiago, at the foot of the main Andes Cordillera. This is a kilometric crustal-scale structure recently recognized that represents a potential source for geological hazards. In this work, we provide new seismological evidences and strong ground-motion modeling from hypothetic kinematic rupture scenarios, to improve seismic hazard assessment in the Metropolitan area of Central Chile. Firstly, we focused on the study of crustal seismicity that we relate to brittle deformation associated with different seismogenic fringes in the main Andes in front of Santiago. We used a classical hypocentral location technique with an improved 1D crustal velocity model, to relocate crustal seismicity recorded between 2000 and 2011 by the National Seismological Service, University of Chile. This analysis includes waveform modeling of seismic events from local broadband stations deployed in the main Andean range, such as San José de Maipo, El Yeso, Las Melosas and Farellones. We selected events located near the stations, whose hypocenters were localized under the recording sites, with angles of incidence at the receiver <5° and S–P travel times <2 s. Our results evidence that seismic activity clustered around 10 km depth under San José de Maipo and Farellones stations. Because of their identical waveforms, such events are interpreted like repeating earthquakes or multiplets and therefore providing first evidence for seismic tectonic activity consistent with the crustal-scale structural model proposed for the San Ramón Fault system in the area (Armijo et al. in Tectonics 29(2):TC2007, 2010). We also analyzed the ground-motion variability generated by an M _w 6.9 earthquake rupture scenario by using a kinematic fractal k ^?2 composite source model. The main goal was to model broadband strong ground motion in the near-fault region and to analyze the variability of ground-motion parameters computed at various receivers. Several kinematic rupture scenarios were computed by changing physical source parameters. The study focused on statistical analysis of horizontal peak ground acceleration (PGAH) and ground velocity (PGVH). We compared the numerically predicted ground-motion parameters with empirical ground-motion predictive relationships from Kanno et al. (Bull Seismol Soc Am 96:879–897, 2006). In general, the synthetic PGAH and PGVH are in good agreement with the ones empirically predicted at various source distances. However, the mean PGAH at intermediate and large distances attenuates faster than the empirical mean curve. The largest mean values for both, PGAH and PGVH, were observed near the SW corner within the area of the fault plane projected to the surface, which coincides rather well with published hanging-wall effects suggesting that ground motions are amplified there.     

Seismic hazard assessment and rheological implications: a case study selected for cities of Saudi Arabia along the eastern coast of Red Sea

A probabilistic approach is used to evaluate the seismic hazard for 12 strategic cities in Saudi Arabia along the eastern coast of Red Sea. The focal depth variations controlled by rheological characteristics are taken into account for hazard calculations, and its creditability is tested through sensitivity analysis for hazard results. This study presents a neo-probabilistic seismic hazard assessment methodology in which the focal depth distribution of earthquakes within seismogenic layer is divided into three depth slices. These depth slices are based upon rheological characteristic of seismogenic layer. The hazard results are obtained using this depth-slice methodology and conventional approach in which uniform distribution of seismicity within seismogenic layer is assumed. The sensitivity analysis culminated in underestimation of hazard values in higher frequencies for uniform distribution of seismicity within seismogenic layer. Foregoing the observations recorded above, it can be concluded that the exploitation of depth-slices biased by the rheology to calculate hazard is relatively preferable in the situations demanding safety measures.     

Implementation of integrated multi-channel analysis of surface waves and waveform inversion techniques for seismic hazard estimation

In this study, an integrated multi-channel analysis of Surface Waves (MASW) technique is applied to explore the geotechnical parameters of subsurface layers at the Zafarana wind farm. Moreover, a seismic hazard procedure based on the extended deterministic technique is used to estimate the seismic hazard load for the investigated area. The study area includes many active fault systems along the Gulf of Suez that cause many moderate and large earthquakes. Overall, the seismic activity of the area has recently become better understood following the use of new waveform inversion method and software to develop accurate focal mechanism solutions for recent recorded earthquakes around the studied area. These earthquakes resulted in major stress-drops in the Eastern desert and the Gulf of Suez area. These findings have helped to reshape the understanding of the seismotectonic environment of the Gulf of Suez area, which is a perplexing tectonic domain. Based on the collected new information and data, this study uses an extended deterministic approach to re-examine the seismic hazard for the Gulf of Suez region, particularly the wind turbine towers at Zafarana Wind Farm and its vicinity. Alternate seismic source and magnitude-frequency relationships were combined with various indigenous attenuation relationships, adapted within a logic tree formulation, to quantify and project the regional exposure on a set of hazard maps. We select two desired exceedance probabilities (10 and 20 %) that any of the applied scenarios may exceed the largest median ground acceleration. The ground motion was calculated at 50th, 84th percentile levels for both selected probabilities of exceeding the median.     

Trace analysis of hydrocarbons in coral cores from Saudi Arabia

As part of a long-term environmental assessment of the impact of the 1991 Gulf War on coral reefs, the Australian Institute of Marine Science (AIMS) conducted growth and chemistry studies on coral cores from the Arabian Gulf. Twenty-eight cores were collected from four coral reefs located offshore from Saudi Arabia.Annual coral growth bands surrounding the 1991 oil spill were analysed in selected cores. Additionally, in cores that extended to the early 1980s, annual layers from 1980 to 1986 were analysed for possible residues from the 1983–4 oil spill caused by the Nowruz oil field blowout during the Iraq–Iran war. Both major spill events were targeted to provide additional confidence in relating oil concentrations to specific pollution events. We detected petroleum biomarkers in several coral annual bands related to the major pollution events. However, the oil remaining in these cores has been altered over time and the biomarker ratios found in these oil residues differed from Gulf crude oils.The concentrations of hydrocarbons were compared with the growth parameters of the coral cores. Only one sample may have recorded an “impact” of oil exposure. There was no other correspondence between slight changes in growth parameters between years and the trace chemistry. Therefore, chemical analysis enabled detection of the exposure incident, but provided no insight into the amount of oil to which the coral had been exposed. The chemical data can only infer biological impact if growth was significantly decreased.The average coral growth characteristics of Porites from the four sites in the Arabian Gulf were normal, as predicted from the average water temperatures of the region. There was an indication of an overall decline in growth over time, which should be monitored in the future.     

Drought and human adjustment in Saudi Arabia

Drought is one of the natural hazards which causes death and damage for property particularly in drylands of the world. Drought as a natural hazard tends to limit and disrupt human activities. On the other hand, man has tried to adjust his living conditions to this hazard. The adjustment to drought is different from one country to another. Adjustment to drought is affected by culture, income, and by the political system in the country. In the case of Saudi Arabia adjustment to drought hazard is usually the work of both individuals, and government. The Saudi Arabian government has spent large sums of money to reduce impact of drought hazard.