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The magnetotelluric (MT) data processing is often a time-consuming job due to the manual inspection of the time series and removal of noisy segments. Use of different data selection tools combined with the robust estimation of the impedances has enabled the automation of MT data processing to a large extent. In this paper, we introduce an open-source Python package, named 'SigMT' for the automated MT data processing. This Python package offers Python scripts to estimate MT impedances and tipper data from the raw time series data. The overview of the SigMT package explaining different steps involved in the processing is discussed in this paper. Different data selection tools such as Mahalanobis distance based-, coherency threshold based-, polarization direction based-selection tools are integrated in the package. The incorporation of different data selection tools with robust estimation technique delivers best estimates of the impedances. SigMT is applied to the MT data from Himalaya with different selection tools and found to be yielding satisfactory results. • Open-source Python package for magnetotelluric data processing. • Automated processing of data, no need of any manual time series editing. • Availability of different data selection tools. • Robust estimation of the magnetotelluric impedance values. [ABSTRACT FROM AUTHOR]

Abstract: Broadband (0.001–1000s) magnetotelluric soundings were carried out at 18 locations with a station interval of 5–8km across the Sikkim Himalaya (northern India) along a 120km long traverse from Siliguri in the south to Yumthang in the north. Magnetotelluric transfer functions were computed after robust processing of single site and remote reference sites. The two-dimensional (2D) model derived from the joint inversion of TE and TM mode data shows distinct electrical signatures of the Main Frontal Thrust (MFT), the Main Boundary Thrust (MBT) and the Main Central Thrust (MCT). The MFT and MBT zones are expressed by a conductive feature of about 10–40Ωm indicating, the presence of Siwalik molasse sediments of Gangetic foreland basin. An anomalously high conductive (2–5Ωm) in the crust in the depth range of 3–15km is observed to the north of MBT. This may indicate the presence of Siwalik molasse sediments together with lesser Himalayan sediments with trapped fluids in the fault zone. These sediments may act as a lubricant accommodating underthrusting of continental crust. The nature of the low resistivity associated with the Main Himalayan Thrust in the higher Himalayas (north of the MCT) might indicate presence of metamorphic fluids released due to under thrusting of the Indian plate. [Copyright &y& Elsevier]

Understanding the arc parallel variation on the geometry of the Main Himalayan Thrust (MHT) is as important as understanding the arc perpendicular variation in the Himalayas. The geometric variability of the MHT holds significant implications for the occurrence of major and great earthquakes. Three-dimensional magnetotelluric (MT) forward modeling enables the investigation of potential crustal models along the MHT in northwest Himalayas. MT impedance tensors were computed utilizing the 3D forward modeling code MTD3FWD. Previously established MT resistivity and seismic velocity models from various sectors of the northwestern Himalayas were employed as inputs for generating the resistivity mesh necessary for 3D forward modeling. The computed impedance tensors by 3D forward computation were cross-referenced with the original published MT data to validate their accuracy. A lateral resistivity cross section is also derived from the 3D forward model along the sub-Himalaya and lesser-Himalaya region to study the lateral heterogeneity. The lateral resistivity cross-section reveals significant heterogeneity within the crust, marked by both high and low-resistive structures and a possible lateral ramp along the MHT. The geometry of the lateral MHT showcases a gradual incline within the Himachal sector and a steep ramp within the Garhwal and Kumaun sectors in the northwestern Himalayas. The crustal architecture exhibits distinct nearly-vertical resistive and conductive features beneath the study area. Consequently, the crust within this region is characterized by considerable heterogeneity, influenced by a network of subsurface faults and ridges. The Delhi Haridwar Ridge, which exhibits high resistivity, plays a significant role in dictating the lateral dip of the MHT and exerting control over seismic activity patterns in the region. [Display omitted] • Lateral resistivity variation in geometry of the Main Himalayan Thrust (MHT) along the strike of the northwest Himalaya. • The MHT, showcases a gradual incline within the Himachal sector and a steep ramp within the Garhwal and Kumaun sectors. • The crust within this region is characterized by considerable heterogeneity, influenced by a network of subsurface faults and ridges. [ABSTRACT FROM AUTHOR]