High- resolution Moho modeling in Makran subduction zone with spectral combination of seismic and gravity data

Document Type : Research Article


Department of Geodesy, Faculty of Geodesy and Geomatics Engineering, K. N. Toosi University of Technology, Tehran, Iran.


The Mohorovičić discontinuity, often known as the Moho, marks the boundary separating the Earth's crust from the mantle. Techniques such as isostatic-gravity and seismic methods can be used to determine this division. The Moho marks the boundary between the continental and oceanic crust and the upper mantle. Simply put, the Moho acts as a physical/chemical boundary between the mantle and the crust and causes significant changes in geophysical properties such as seismic wave velocity, density, pressure, and temperature (Mooney and Masters, 1998; Martinck, 1994; Bagherbandi, 2011 and Dashtbazi et al., 2023). An accurate and high resolution Moho depth model in fields such as geodesy, geology, geophysics, geodynamic modeling, seismic risk assessment, stress field modeling caused by mantle convection (Li et al., 2018; Behr et al., 2022; Singh and Yadav, 2023; Heilman and Becker, 2022; Hashima et al., 2016; Eshagh et al., 2020; Eshagh, 2015 and Gido et al., 2019), and understanding seismic source mechanisms is important, among other applications (Gido et al., 2019 and Dashtbazi et al., 2023). Furthermore, a reliable Moho model can reveal details of crustal structure that provide valuable insights into the complexities of deeper mantle layers; related to the calculations and detailed examination of gravity, geothermal, geomagnetic models (Stalk et al., 2013). Although there are several Moho models, their accuracy and resolution are insufficient in the complex tectonic geometry of the Makran subduction zone (Brizi et al., 2021 and Heilman and Becker, 2022), because these zones show a complex Moho configuration (Shad Manaman et al., 1390; Taghizadeh Farhamand et al., 2015 and Dashtbazi et al., 2023). As a result, the existing models lack the necessary accuracy for the Makran subduction zone, a region approximately 1000 km long located in southeast Iran and southwest Pakistan (Byrne et al., 1992; Shad Manaman et al., 1390, Penney et al., 2017; Dashtbazi et al., 1398; Dashtbazi. et al., 2023).
In geophysical and geodetic studies, hybrid methods are mainly used to determine the Moho depth when seismic data with appropriate distribution and abundance are not available. These techniques include the Parker-Oldenberg method and the Wenning-Mines-Moritz method. In an effort to strengthen the existing Moho depth models in the Makran subduction zone, two distinct models named BC and SC through the integration of gravity (VMM) and seismic (CRUST1.0) data, which are processed through the Butterworth filter, spectral combination approaches and the least squares technique, was developed (Bagherbandi , 2011 and Dashtbazi et al., 2023). The resulting models provide a resolution of 5' x 5' degrees of arc, corresponding to a grid size of 9 x 9 km (Dashtbazi et al., 2023). The accuracy of these models was evaluated against four separate regional and local models. The resulting RMS values were 5.28, 1.55, 4.18, and 1.27 km for the BC model and 5.59, 1.17, 3.74, and 3.04 km for the SC model. Also, the Moho depth model obtained for the west Makran region in Iran significantly improved the accuracy and resolution of the Moho depth models in the studied area. The SC Moho model exhibits improved RMS metrics compared to the combined BC model, so we recommend it as the first priority. While the Moho depth models in our research really bring significant improvements to the existing models of the Makran subduction Moho zone, the integration of more detailed seismic data with SC and BC Moho models can improve the developed model for the Makran subduction zone. In the end, we suggest that a similar approach be adopted for the analysis of the Moho model in the eastern Makran region in Pakistan, which allows a comparative evaluation of the Moho depth and structure between the western and eastern parts in order to obtain a better picture of the Moho depth model of the Makran subduction zone.


Main Subjects

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