Thermal Correction for Moho Depth Estimations on West Philippine Basin: A Python Code to Calculate the Gravitational Eff
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Pure and Applied Geophysics
Thermal Correction for Moho Depth Estimations on West Philippine Basin: A Python Code to Calculate the Gravitational Effects of Lithospheric Cooling Under Oceanic Crust RENATA REGINA CONSTANTINO1,2 Abstract—The aim of this work is to present an easy-to-use Python code to calculate the gravitational effect due to lateral variations in the thermal structure of oceanic lithospheric plates, necessary to appropriately isolate the contribution of the variations in crustal thickness. The model is applied to calculate the Moho depth in the West Philippine Basin, and the results are compared with seismic data. The estimations of the Moho depth taking into account the thermal correction presented a better fit with the seismic data and smoother geographical variations than the model without thermal correction. Keywords: Lithospheric cooling, Thermal anomaly, Gravity.
1. Introduction The Moho interface marks the transitional boundary between the crust and mantle (Lewis 1983), representing an important density transition in the Earth’s interior. Mapping variations can be extremely important for understanding the tectonic evolution of a specific area. Although it is possible to accurately map the Moho depth through seismic surveys, gravity modeling can be considered a more practical and less expensive approach (Bai et al. 2014). To estimate variations in the Moho depth from gravity inversion, the observed gravity field must be free from certain major components such as
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00024-020-02581-2) contains supplementary material, which is available to authorized users. 1 Institute of Astronomy, Geophysics and Atmospheric Sciences, University of Sa˜o Paulo, Sa˜o Paulo, Brazil. E-mail: [email protected] 2 Present Address: Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, USA.
and VICTOR SACEK1 anomalies due to lateral changes in bathymetry, gravity effects of the sedimentary layers and the density variations due to thermal anomalies in the lithospheric plate (Kaban et al. 2002), thus isolating the gravity anomaly caused only by the Moho undulations. Neglecting one or more of those contributions might influence the accuracy of the estimated interface depth (Bai et al. 2014). Many works that estimate the Moho depth over oceanic areas through gravity modeling without taking into account the thermal correction can be found in the literature (e.g. Tiberi et al. 2001; Tirel et al. 2004; Tenzer and Chen 2014). Thermal contributions to the gravity anomaly gradually weaken with the age of the oceanic lithosphere (e.g. Lambeck 1972; Jonas et al. 1991; Kusznir et al. 2018). On the other hand, areas related to new oceanic lithosphere might have a significant thermal contribution to the gravity anomaly, which may reach up to 320 mGal (Chappel and Kusznir 2008). The thermal gravity anomaly in oceanic areas can be determined, assuming that the thermal structure of the lithosphere is essentially dep
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