Iranian Journal of Earth Sciences
Volume:13 Issue: 2, Apr 2021

The Kohat Foreland Basin is an outcome of continental collision between Indian and Eurasian plates defining the southern edge of Himalayan Orogenic System in the north-western Pakistan. This study constrains the structural geometry and kinematics in 2-D and 3-D workflow, evaluation of the role of multiple detachments and the structural correlation between surface and sub-surface geology of the western Kohat Foreland Basin. The structural style of the western Kohat Foreland Basin evinces the thin skin deformation associated with a couple of structural detachments i.e.i) base-Eocene shale/ evaporite sequence ii) the upper interface of crystalline basement. These detachments separate the outcropping and buried stratigraphic sequence of the Kohat Foreland Basin into upper and lower structural-stratigraphic domains. The lower domain has a series of north-dipping or south-verging fold-thrust assemblages incorporating a rigid rock sequence of EoCambrian to Paleocene. The comparatively more ductile rocks of the upper domain comprising of Eocene to Pliocene are deformed into tight, overturned, doubly plunging and internally faulted anticlines intervened by broad synclines. The two domains dictate different deformational behaviour and structural style, deforming in total disharmony; hence the structural geometry of shallow units does not match the sub-surface rocks. The total 37% of shortening in the sedimentary cover was revealed by structural balancing in 2-D and 3-D kinematic modelling. Stress analysis of Gurguri Fault unveiled 40% failure susceptibility and recorded positive values of effective normal stress (σn) with an orientation of maximum principle stress (σ1) as N17°.

Seismic hazard for the central indo-gangetic plains (CIGP) is either available in terms of generalized hazard spectrum as per IS 1893:2016 or in terms of only Peak Ground Acceleration (PGA) at the city level. Also, the study region falls in the seismic gap region, which has a potential for an earthquake of Mw>8.0. Hence, in this study, the seismic risk is assessed for the first time at the district level in the seismically critical region of India, the CIGP. In addition, the relative contribution of parametric and model uncertainties is also quantified from sensitivity analysis. Seismic risk results reveal that mud mortar bricks with temporary roofing (MMB) have the highest collapse probability of ~0.6. Further, brick walls with stone roof (BSR) and brick walls with metal sheet roof (BMS) also have high extensive and collapse damage compared to other building groups. These building types need immediate retrofitting / replacement for effective disaster mitigation. Also, geo-unit Allahabad, even though lying in zone II as per IS 1893:2016, has the most number of homeless and uninhabitable dwellings. Further, for a future earthquake of magnitude in the range of Mw 7.5 and 8.5, the expected financial loss might vary from 60 to 150 billion dollars, and the human loss might vary between 0.8 and 2.8 lakhs, respectively. Finally, results from this study will create awareness in the general public, policymakers, and structural engineers for taking up necessary mitigation measures on the existing buildings of CIGP for better preparedness from a future strong earthquake.

The carbonate sequence of the Asmari Formation is the most important oil reservoir formed in the Zagros Basin, southwestern Iran. In order to interpret the sedimentary environment, the Makhmal-Kuh and Kaka-Reza sections in the Lorestan province were investigated. These sections were compared with some other outcrops in the Zagros Basin. Twenty one genera and species were identified in the Makhmal-Kuh section, and 20 genera and species in the Kaka-Reza section. Among foraminifera, Miogypsina sp ., Amphistegina sp., Elphidium sp., Operculina sp., Nephrolepidina sp., Eulepidina sp., Heterostegina sp., Nummulites fichtelli, Nummulites vascus and Nummulites intermedius are the most important species. Based on the identification of co-occurrence taxa, two assemblage zones are introduced in the Makhmal-Kuh section, and one faunal assemblage zone in the Kaka-Reza section. Petrographic analysis also led to the recognition of twelve microfacies types in the Makhmal-Kuh section and five microfacial types in the Kaka-Reza section. Based on these microfacial types, three sub-environments were determined in the Makhmal-Kuh section and two settings in the Kaka-Reza section: Outer ramp, in the aphotic zone, dominated by planktic foraminifera, bryozoan, and echinoids; the mid ramp, in the oligophotic zone, characterized with benthic foraminifera and planktic foraminifera; the shallower waters of the mesophotic-euphotic zone dominated by benthic foraminifera and coralline red algae in the inner ramp. Therefore, the depositional sub-environments along with biotic assemblages represent warm waters of tropical regions under photic variable conditions in a homoclinal ramp. Based on the distribution of co-occurrence fossils, the Asmari Formation is dated as Rupelian to the Aquitanian.

The Oligocene-Lower Miocene Asmari Formation shows considerable reservoir heterogeneity because of variations in the lithology, depositional facies and diagenesis. This paper aim to investigate reservoir heterogeneities using seismic, core and well logs data. Twelve carbonate microfacies and three siliciclastic petrofacies are identified in the Asmari Formation based on well log and core data from 7 wells in the Marun field, which generally indicate a shallowing-up profile. Microfacies changes suggest that the Asmari Formation was deposited in a restricted lagoonal and carbonate ramp setting with periodic clastic sediment supply due to relative sea level fall. Six third-order sequences are recognized in the Asmari Formation from studies of core and well log data, while interpretation of 3D seismic data shows that the formation consists of two second-order seismic sequences. The lowest sequence boundary between the Pabdeh and Asmari Formations (SBI) is a type-2 boundary, and the six others are type-1 sequence boundaries. Six distinct packages of reflectors are interpreted on seismic data through the Cenozoic. The Pabdeh and Asmari Formations can be divided into three packages. Package 1 corresponds to transgressive and highstand systems tract deposits, which mainly consist of shales, marls, and carbonates with interbedded sandstones. This package is overlain by mounded and lenticular seismic facies (package 2) and high-amplitude and continuous seismic reflectors (package 3). Package 2 is predominantly sandstone with interbedded shale, and package3 mainly consists of carbonates. Inversion of seismic data shows that high-porosity zones are present in the western and southern Marun field. A lower high-porosity zone corresponds to lowstand fluvial-deltaic sediments and the upper zone to the beach and shallow marine sandstones.

Sea cows are exceptional fossil vertebrates recently discovered in the deposits of the Qom Formation. Yet, the Sirenia-bearing limestones are still poorly understood in terms of detail paleoenvironmental and micropaleontological investigations. In order to distinguish the temporal and paleoenvironmental context of the Sirenia (sea cow) bearing deposits of the Qom Formation in central Iran, three stratigraphic sections were studied in Hamedan (Ivak and Shirinsu) and Isfahan (Chahriseh) provinces. A total number of 47 thin sections were studied for micropaleontology, biozonation and carbonate microfacies analysis, as well as sedimentary environment recounstruction. Biostratigraphical investigations suggest that the Sirenia-bearing deposits are Aquitanian/Burdigalian in age, which implies restriction of sea cows remains to the Lower Miocene. We recognized nine microfacies (n=8 correspond to carbonate; n=1 correspond to siliciclastic) in the study areas. They are systematically grouped into two microfacies settings, representing inner and middle ramp environments. This is based on the facies associations and the distribution of skeletal components and rock textures.  The Sirenia-bearing limestone consists of peloid/algae bearing wackstone/packstone/floatstone. A carbonate (inner) ramp system under shallow water conditions is interpreted as the habitats of the Sirenian mammals during the Aquitanian/Burdigalian in Central Iran. This paleoenvironmental setting could be utilized for further exploration of Qom Formation deposits for discovering sea cows.

The aim of this study is to investigate the strong ground motion generation of destructive earthquake in Kermanshah with the moment magnitude of 7.3 using Empirical Green’s function (EGF) method. To simulate the ground-motion can be helpful for understanding seismic hazard and reduce fatalities due to lack of real ground motion. We collected the seismograms recorded at seven strong motion stations with good quality to estimate the source parameters at frequencies between 0.1 and 10.0 Hz. By minimizing the root-mean-square (rms) errors to obtain the best source parameters for the earthquake. The earthquake fault was divided into seven sub-faults along the strike and seven sub-faults along the slope. The asperity of 21×10.5 km was obtained. The rupture starting point has been located in the northern part of the strong motion seismic area. The coordinates of the rupture starting point indicate that the rupture propagation on the fault plan was unilateral from north to south. The simulated ground motions have a good correlation with observed records in both frequency and time domain. The results are in well agreement with the Iranian code of practice for seismic resistant design of buildings, however, the calculated design spectrum of Sarpol-e Zahab station is higher than the design spectrum of the Iranian code which suggest that the Iranian code may need to be re-evaluated for this area.