Moho undulations beneath Tibet from GRACE-integrated gravity data

Abstract

SUMMARY Knowledge of the variation of crustal thickness is essential in many applications, such as forward dynamic modelling, numerical heat flow calculations, seismologic applications and geohistory reconstructions. We present a 3-D model of the Moho undulations over the entire Tibetan plateau derived from gravity inversion. The gravity field has been obtained by using the Gravity Recovery and Climate Experiment (GRACE) potential field development which has been integrated with terrestrial data, and is presently the best available in the studied area. For the effective use of the global geopotential model that has no height information of observation stations, upward continuation is applied. The Moho model is characterized by a sequence of troughs and ridges with a semi-regular pattern, which could reflect the continent‐continent collision between the Indian and Eurasian plates. The three deep Moho belts (troughs) and shallow Moho belts (ridges) between them are clearly found to have an E‐W directional trend parallel to the border of the plateau and tectonic lines, while variation of the directionality is observed in central to southeast Tibet. To describe the distinctive shape of the Moho troughs beneath Tibet, we introduce the term, ‘Moho ranges’. The most interesting aspects of the Moho ranges are (1) that they run in parallel with the border and tectonic sutures of the plateau, (2) that the distances between ranges are found at regular distances of about 330 km except in northeast Tibet and (3) that the splitting of the ranges into two branches is found as the distance between them is increasing. From our study, we conclude that the distinctive undulations of the Tibetan Moho have been formed by buckling in a compressional environment, superimposed on the regional increase in crustal thickness. According to our analysis, the GRACE satelliteonly data turns out to have good enough resolution for being used to determine the very deep Moho beneath Tibet. Our Moho model is the first one that covers the entire plateau.