Khaista Rehman

K -means cluster analysis and seismicity partitioning for Pakistan

Pakistan and the western Himalaya is a region of high seismic activity located at the triple junction between the Arabian, Eurasian and Indian plates. Four devastating earthquakes have resulted in significant numbers of fatalities in Pakistan and the surrounding region in the past century (Quetta, 1935; Makran, 1945; Pattan, 1974 and the recent 2005 Kashmir earthquake). It is therefore necessary to develop an understanding of the spatial distribution of seismicity and the potential seismogenic sources across the region. This forms an important basis for the calculation of seismic hazard; a crucial input in seismic design codes needed to begin to effectively mitigate the high earthquake risk in Pakistan. The development of seismogenic source zones for seismic hazard analysis is driven by both geological and seismotectonic inputs. Despite the many developments in seismic hazard in recent decades, the manner in which seismotectonic information feeds the definition of the seismic source can, in many parts of the world including Pakistan and the surrounding regions, remain a subjective process driven primarily by expert judgment. Whilst much research is ongoing to map and characterise active faults in Pakistan, knowledge of the seismogenic properties of the active faults is still incomplete in much of the region. Consequently, seismicity, both historical and instrumental, remains a primary guide to the seismogenic sources of Pakistan. This study utilises a cluster analysis approach for the purposes of identifying spatial differences in seismicity, which can be utilised to form a basis for delineating seismogenic source regions. An effort is made to examine seismicity partitioning for Pakistan with respect to earthquake database, seismic cluster analysis and seismic partitions in a seismic hazard context. A magnitude homogenous earthquake catalogue has been compiled using various available earthquake data. The earthquake catalogue covers a time span from 1930 to 2007 and an area from 23.00° to 39.00°N and 59.00° to 80.00°E. A threshold magnitude of 5.2 is considered for K-means cluster analysis. The current study uses the traditional metrics of cluster quality, in addition to a seismic hazard contextual metric to attempt to constrain the preferred number of clusters found in the data. The spatial distribution of earthquakes from the catalogue was used to define the seismic clusters for Pakistan, which can be used further in the process of defining seismogenic sources and corresponding earthquake recurrence models for estimates of seismic hazard and risk in Pakistan. Consideration of the different approaches to cluster validation in a seismic hazard context suggests that Pakistan may be divided into K = 19 seismic clusters, including some portions of the neighbouring countries of Afghanistan, Tajikistan and India.

Spatio-temporal variations of b-value in and around north Pakistan

The seismotectonic structure of north Pakistan has been formed by ongoing collision between the Eurasian and Indian plates. North Pakistan and the adjoining areas experienced many large earthquakes in the past, which resulted in considerable damages and loss of life. A magnitude-homogenous earthquake catalogue for north Pakistan and its surrounding areas for the instrumental period from 1964 to 2007 is used for analysis. We presented seismicity picture of the Hindukush–Pamir–Karakoram (HPK), Kohistan Island Arc (KIA) and Hazara–Kashmir–Himalayas (HKH) using various histograms and time series plots of the dataset. The b-value for each accreted domain is derived separately and investigated through a process of mutual correlation. Our computed temporal variation of b-value in Hazara region shows a significant decrease prior to 2005 Kashmir earthquake.

Tsunamigenic Analysis in and around Makran

The Makran region is only segment east of the Mediterranean and west of Andaman arc in which subduction of oceanic lithosphere is still an ongoing process. We applied statistical models for the possible explanation of earthquakes in and around Makran, and described a method of Fault Plane Solutions to present seismicity picture in the investigated region, and their possible tsunamigenic effects on Gwadar Coast. We also applied the Community Modeling Interface for Tsunami (ComMIT) for the estimation of tsunami hazard along the coast of Gwader due to the Arabian and Eurasian plate boundary earthquakes along the Makran subduction zone.

Effect of Shale Distribution on Hydrocarbon Sands Integrated with Anisotropic Rock Physics for AVA Modelling: A Case Study

Shales can be distributed in sand through four different ways; laminated, structural, dispersed and any combination of these aforementioned styles. A careful analysis of well log data is required for the determination of shale distribution in sand affecting its reservoir quality. The objective of this study is to characterize the effect of shale distribution on reservoir quality of sands using well log data. The correlation of well data in terms of lithology has revealed four sand and three shale layers in Lower Goru Formation acting as a major reservoir in the study area. Our results indicate that the laminated type of shale distribution prevails at the Basal sand level, which does not affect its reservoir quality greatly. The remaining layers of variable vertical extent show a variety of shale distribution models affecting their reservoir quality adversely. We also present anisotropic rock physics modelling for AVA analysis at Basal sand level.

Tectonic imprints of the Hazara Kashmir Syntaxis on the Northwest Himalayan fold and thrust belt, North Pakistan

Constraints from microscopic to mesoscopic structures and their relationship with the map scale macroscopic structures indicate a succession of two dominant deformation events for the rocks exposed in the western limb of the Hazara Kashmir Syntaxis. Regional scale NNE–SSW trending macro to meso scale fold axes and faults are distinctly deflected top to the NW with sinistral shear sense in the apex region of the Hazara Kashmir Syntaxis. Detailed analyses of micro, meso, to macro scale folds axes, stretching lineations and intersection planes indicate dominate NNE–SSW trending structures. The comprehensive study of en-echelon gash veins and NW verging asymmetrical to overturned folds with SE dipping axial planes show top to the NW sinistral shear sense. The gash veins overprint SE and SW plunging lineations and bedding across the region. The en-echelon gash veins and asymmetric to overturned limbs of the NNE–SSW trending folds that dominate the area developed during the last stage intense tectonism associated with the Hazara Kashmir Syntaxis within the Indian Plate. The Hazara Kashmir Syntaxis did not rotate the dominate NNE–SSW trending structures in the study area, due to shearing and rotation along the same axis.

Petrophysical evaluation and fluid substitution modeling for reservoir depiction of Jurassic Datta Formation in the Chanda oil field, Khyber Pakhtunkhwa, northwest Pakistan

Petrophysics coupled with rock physics studies are significant in the evaluation of well and field potential, and to construct subsurface models based on rock properties. This case study combines petrophysics and fluid substitution modeling for reservoir characterization of the producing Datta Formation in the Chanda oil field of Kohat Basin. The Datta Formation interval of two wells, Chanda-1, and Chanda Deep-1, is analyzed to calculate petrophysical parameters including gross thickness, net thickness, net to gross ratio (NGR), porosity (PHA), permeability (K), and water saturation (SW). The Datta Formation represents fair to good porosity in the range of 7–13%. Water saturation shows low values lying in the range of 31–36%. The formation is interpreted from gamma ray (GR) log trends, where sand packages dominantly represent a left box-car and irregular trend. Cross-plots, such as density porosity (RHOB-NPHI), gamma ray-density (GR-RHOB), gamma ray-porosity (GR-NPHI), and thorium–potassium (Th–K), were used for lithological identification in the studied wells, and indicated arkosic and micaceous sandstone as the dominant lithology with shale. Evaluation of petrophysical parameters shows that the Datta sands have high hydrocarbon saturation in the area. The fluid substitution modeling was applied to clastics of the Datta Formation for field development. One hydrocarbon-bearing zone (zone 1) was identified in Chanda-1, while four hydrocarbon-bearing zones (zones 1, 2, 3, and 4) were identified in Chanda Deep-1. Fluid substitution results at the Datta level showed that the P-wave velocity and density varied when the hydrocarbon phase was substituted completely with water. With the substitution of brine with oil, there was a change in compressional wave velocity (Vp) and a decrease in density (RHOB), while the shear wave velocity (Vs) was stable and unaffected by the change of fluid density and saturation. The results of this research could be used to predict saturation types of reservoir using seismic data and to identify pay-zones, and map reservoir saturation to drill for oil and gas.

Using larger benthic foraminifera for the paleogeographic reconstruction of Neo-Tethys during Paleogene

The biostratigraphic range distribution of larger benthic foraminifera (LBF) from the eastern part of Neo-Tethys in the Kohat Basin of Pakistan is compared with the Western and Central Neo-Tethys. The results are used to establish the migration pathways of LBF for the paleogeographic reconstruction of the Neo-Tethys that existed in the Paleogene. This comparison across the Neo-Tethys revealed that LBF species are mostly confined to the Gondwanan (Iran, Iraq, Pakistan, India, Indonesia) and Laurasian-derived blocks (Italy, France, and Spain), with only a few on the margin of the Gondwanan continents (Oman).