JOURNAL OF THE EARTH
Year:2007 | Volume:2 | Issue:2|Papers Count:9

The Mw 6.4 (Ms 6.5) Dahuiyeh (Zarand) earthquake occurred on February 22, 2005 in Kerman province in south Iran. The earthquake ruptured an intra-mountain reverse fault, striking E-W and dipping north at about 60 degree to a depth of about 10 km. It produced a series of coseismic scarps with up to 1m vertical displacement over a total distance of about 13 km, continuous for a 7 km. The line of the coseimic ruptures followed a known geological fault of unknown, but probably pre-late cenozoic age and involved bedding-plane slip where scarp were continuous at the surface. Faults of this type represent serious seismic hazard in Iran and are difficult to assess, because their geomorphologic expression is much less clear than the range-bounding reverse faults, which are common and have been better studied. The intense shaking in Zarand city and neighbouring villages, killing about 612 people of inhabitants of the earthquake area.

Bauxite is a sedimentary rock which is formed by weathering of various rocks in tropical climate with considering proper drainage and morphology. The Jajarm bauxite ore deposit is considered as Mediterranean karstic ores Lenticular-Layer type. Mineral in Jajarm ore deposit contains two separate zones, A zone (older) and B zone (younger), which overlies karstic - surface of the Elikah Formation and underlies sandstone and shale of the Shemshak Formation.The studied area is Tagoee part of the Jajarm area, which contains Diaspora and Chamosite mineralogical composition.Due to weaker tectonic influence in this region, integrity and continuity of bauxite layer were maintained. Extension of ore deposit in Tagoee area is about 4.8 km and thickness of bauxite is low and near the outcrop it is at lowest (1.5 m). With considering initial studies, in situ supply of ore mineral in Tagoee is expected about 2.5 million tones in hard bauxite zone (Al2O3 44.87 % and SiO2 12.52 %). Major observed textures in bauxite mineral are ooid and piezoid, microclastic and fine grain clastic, which reveal to be reworked. Another witness for being reworked is bauxite follows Karstic morphology in lower part while upper part of Bauxite layer is nearly tabular and suggests that a fluid solution or mixture has been transported to karsts and filled them. On the other hand, cracks made by jelly agglomeration in piezoides, present their formation insitu and show two probable bauxitization steps.

The Zarab Mountain is located in south of Baft and northern margin of Sanandaj_Sirjan Zone that contains of metamorphic rocks include orthogenesis, marble and aricw schists. The field studies indicate imbrication's structure with thrusts for this region. The folds of studied area can be subdivided into two branches: a) Flexural slip folds and vengeances. b) Flowed folds or similar folds which their vergens confirmed the movement direction major thrust of this region. The field studies indicate five stage of structural deformation in the studied are an as follows:1) The earliest tention which caused the earliest bodings (as that exist in the fold limb)2) Stage two with compressional stress which caused the major thrust and folds in this region. 3) The operation of recompressional stress and caused of drag folds in the limbs of earliest folds.4) The operation of tention stresses for second times which caused normal fault in the region.5) The late stage of deformation in the region caused the shear joint and tension fracture whit orientation of normal to thrusting and react thrust fault in the our region operating as compressional stress.

Garmabdar Anticline, located between 51o 30’-51o 45’ eastern longitudes and 35o 55’-36o northern latitude, with an area of 220 Km2 and E-W axis, is one of the structural sub-zones in the south of central Alborz range. Garmabdar Anticline, situated between Garmabdar overthrust in north and Mosha fault in south component of Paleozoic and Mesozoic older formation. Field mapping accompanied by structural interpretation of the study area shows that thrust fault with minor strike component that toward north and south (back thrust), are the main structures that control deformation in the sub-zones. kinematic analysis shows that it was developed by propagation of thrust fault. Therefore, it was classified as fault propagation fold. The thrust sequence of these study area is correlated with forward-breaking sequence.

It is common that the around of seismic energy that was released could be estimated by aftershocks activity. This study is local station data of aftershocks, nearly 40 years in Iran. Reduce trend number of aftershocks analyze for eight earthquakes. Then time decay rate of aftershocks in the region was indicated. Next, decay curves of aftershocks for Omori, Utsu, Mogi and Kisslinger models were indicated. This study analyzed the aftershocks of the 1962 Buin-Zahra, the 1968 Dasht-e-Bayaz, the 1990 Rudbar, the 1990 Fork, the 1997 Ardabil, the 2002 Avaj, the 2004 Baladeh and the 2005 Zarand earthquakes. Aftershocks decay was indicated and it was obtained that the Omori model is the best model in Iran.

Rock physics has an important role in reservoir characterization. An attempt is made to study one of the oil reservoirs in south west of Iran. Petrophysical properties such as bulk density, grain density, porosity, compressional and shear wave velocities were measured on 10 carbonate core samples taken from one well. Elastic wave velocity measurements conducted in both dry and saturated samples under reservoir condition. This study is made on the effect of some parameters such as saturation, pressure, porosity and density on elastic wave velocities.

Alborz is a narrow, long and high elevated mountain belt that participates in a part of motion between Arabia and Eurasia. Central Alborz is the site of historical and recent large earthquakes. Considering fast expansion of the cities located in this zone and their socio-economical activities, there is a great need for different seismicity studies. Several active faults that are usually from mountain bordering type and are parallel to the mountain belt trend have been already identified. These faults are mostly compressional or have a great compressional component, so with longer return periods and thus stronger earthquakes. In this paper a short but clear geoscientific picture of Central Alborz will be given and then some seismicity characteristics just like spatio-temporal distribution and changes, b-value changes and fractal dimension will be studied. Based on the results b-value reduces with depth and also before some great regional earthquakes. Meanwhile fractal dimension is near 2 that may reflect the planer distribution of seismic sources in this region.

Geophysical prospecting methods such as geo-electric, Seismic refraction and seismic borehole methods are significant in engineering geophysics studies. The fast and easy application of those methods accompanies with high accuracy and high resolution cased more popularity of them. The main purpose of my thesis is investigation of geological setting underneath of a high rise building in mega city of Tehran using inverse modeling of geophysical data. Geo-electric data have measured along 5 points based on Shulemberger array while the seismic data were measured along 9 refraction profiles. Moreover, the down- hole seismic data is surveyed through two holes with a depth of 20 meters. Results of data analysis and interpretation show three layers of alluvium beneath the studied site. The least seismic velocities for P and S waves are derived as follows: Vpmin=700 m/s and Vsmin=380 m/s. The maximum seismic P and S velocities are determined as Vsmax=880 m/s and Vpmax=2435 m/s. The minimum and maximum average resistivity is determined about 64 Ohm-meter and 250 Ohm-meter, respectively. The studied penetration depth is about 25 m which is good enough for such a limited area.