<p>The Tibetan Plateau, known as the roof of the Earth, is considered as the &#8220;Golden Key&#8221; for understanding plate tectonics, continental collisions and continental orogenic formation. A reliable Moho structure is also vital for understanding the deformation mechanism of the Tibetan Plateau.</p><p>In this study, we use improved Parker&#8722;Oldenburg&#8217;s formulas that include a reference depth into the exponential term and employ a Gauss-FFT method to determine Moho depths beneath the Tibetan Plateau. The synthetic models demonstrate that the improved Parker&#8217;s formula has higher accuracy with the maximum absolute error less than 0.25 mGal.</p><p>Two inversion parameters, namely the reference depth and the density contrast are essential for the Moho estimation based on the gravity field, and they need to be determined in advance to obtain correct results. Therefore, the Moho estimates derived from existing seismic studies (Stolk et al., 2013) are used to reduce the non-uniqueness of the gravity inversion and to determine these parameters by searching for the maximum correlation between the gravity-inverted and seismic-derived Moho depths.</p><p>Another critical issue is to remove beforehand the gravity effects of other factors, which affect the observed gravity field. In addition to the topography, the gravity effects of the sedimentary layer and crystalline crust are removed based on existing crustal models, while the upper mantle impact is determined based on the seismic tomography model.</p><p>The inversion results show that the Moho structure under the Tibetan plateau is very complex with the depths varying from about 30 ~ 40 km in the surrounding basins (e.g., the Ganges basin, the Sichuan basin, and the Tarim basin) to 60 ~ 80 km within the plateau. This considerable difference up to 40 km on the Moho depth reveals the substantial uplift and thickening of the crust in the Tibetan Plateau.</p><p>Furthermore, two visible &#8220;Moho depression belts&#8221; are observed within the plateau with the maximum Moho deepening along the Indus-Tsangpo Suture and along the northern margin of Tibet bounding the Tarim basin with the relatively shallow Moho in central Tibet between them. The southern &#8220;belt&#8221; is likely formed in compressional environment, where the Indian plate underthrusts northwards beneath the Tibetan Plateau, while the northern one could be formed by the southward underthrust of the Asian lithosphere beneath Tibet.</p><p>Stolk, W., Kaban, M., Beekman, F., Tesauro, M., Mooney, W. D., & Cloetingh, S. (2013). High resolution regional crustal models from irregularly distributed data: Application to Asia and adjacent areas. Tectonophysics, 602, 55-68. https://doi.org/10.1016/j.tecto.2013.01.022</p>
Abstract. The sea level rise contributed from ice sheet melting has been accelerating due to global warming. Continuous melting of the Greenland ice sheet (GrIS) is a major contributor to sea level rise, which impacts directly on the surface mass balance and the instantaneous elastic response of the solid Earth. To study the sea level fingerprints (SLF) caused by the anomalous acceleration of the mass loss in GrIS can help us to understand drivers of sea level changes due to global warming and the frequently abnormal climate events. In this study, we focus on the anomalous acceleration of the mass loss in GrIS at the drainage basins from 2010 to 2012 and on its contributions to SLF and relative sea level (RSL) changes based on self-attraction and loading effects. Using GRACE monthly gravity fields and surface mass balance (SMB) data spanning 13 years between 2003 and 2015, the spatial and temporal distribution of the ice sheet balance in Greenland is estimated by mascons fitting based on six extended drainage basins and matrix scaling factors. Then the SLF spatial variations are computed by solving the sea level equation. Our results indicate that the total ice sheet mass loss is contributed from few regions only in Greenland, i.e., from the northwest, central west, southwestern and southeastern parts. Especially along the north-west coast and the south-east coast, ice was melting significantly during 2010–2012. The total mass loss rates during 2003–2015 are −288±7 Gt/yr and −275±1 Gt/yr as derived from scaled GRACE data and SMB respectively; and the magnitude of the trend increased to −456±30 Gt/yr and to −464±38 Gt/yr correspondingly over the period 2010–2012. The residuals obtained by GRACE after removing SMB show a good agreement with the surface elevation change rates derived from pervious ICESat results, which reflect a contribution from glacial dynamics to the total ice mass changes. Melting of GrIS results in decreased RSL in Scandinavia and North Europe, up to about −0.6 cm/yr. The far-field peak increase is less dependent on the precise pattern of self-attraction and loading; and the average global RSL was raised by 0.07 cm/yr only. Greenland contributes about 31 % of the total terrestrial water storage transferring to the sea level rise from 2003 to 2015. We also found that variations of the GrIS contribution to sea level have an opposite V shape (i.e., from rising to falling) during 2010–2012, while a clear global mean sea level drop also took place (i.e., from falling to rising).
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