Crustal study based on integrated geophysical techniques in the Northwestern Himalayas, Pakistan

Abstract

The present research aims to explicate the tectonics of the northwest Himalayas, Pakistan, based on integrated gravity, magnetic and earthquake data. The raw gravity and magnetic data were processed, and seven isoanomaly maps were prepared for qualitative interpretation, whereas a gravity model was prepared along the selected profile for quantitative interpretation. The local earthquake data have also been used to identify the various seismogenic layers in the subsurface and to understand how seismicity relates to regional structural features. Three northwest-trending thickskinned blind basement faults are identified from the present study, namely the Indus Kohistan Seismic Zone (IKSZ), Bagh Basement Fault and Hazara Lower Seismic Zone. The IKSZ is the tectonically most active among them and responsible for the 2005 Kashmir earthquake (Mw = 7.6) and 1974 Pattan earthquake (Mw = 6.2) in the region. The present study also delineated the prominent location of the Main Central Thrust in which the high-grade metamorphic rocks of Higher Himalayan Crystalline thrust over low-grade metamorphic rocks of Lesser Himalayas along this thickskinned fault. The field evidence such as ductile deformation, zone of inverted metamorphism, and brittle deformation also confirm this location. The sharp bending of the crystalline crust, as well as deep basement just south of Kohistan Island Arc (KIA), indicate that the high density and susceptibility rocks of this arc thrust on the leading margin of the Indian Plate along the Main Mantle Thrust. This thrust fault is a major suture zone separating the KIA in the north from the Indian Plate in the south. The other faults in the region exist in the sedimentary/meta-sedimentary wedge and are thin-skinned. It is inferred from the current investigation that the study area exhibits a composite style of deformation. Moreover, the gravity model combined with earthquake data suggested the existence of multiple décollement zones below the Hazara-Kashmir Syntaxis. The model envisaged an increase in the thickness of the Indian Plate continental crust in the northeast direction.

Analysis of Formation Ronggojalu Spring and Probolinggo Active Fault Continuity with Satellite Data Gravity Method

“…By doing several corrections in Gravity data processing is obtained the CBA (Complete Bouguer Anomaly) value through, assuming that the density value of the research area is the same as the density of the continental crust (2.67 g/cc) (Hameed, 2023). Through the concept of the FHD (First Horizontal Derivative) and SVD (Second Vertical Derivative) methods, it will be able to show the results of the interpretation of the fault structure, where the results of the slicing through the fault will show the contrast of values that occur between a peak derivative of the Gravity anomaly value indicating differences in structural patterns and interpretation of depth deposition of sediment or pyroclastic (Aziz et al, 2018;Rosid & Siregar, 2017) Remote sensing processing consist lineament extraction from Digital Elevation Model (DEM) data processed in Hillshade form.…”