{'fraction_non_alphanumeric': 0.019391507856904047, 'fraction_numerical': 0.014376462721497826, 'mean_word_length': 5.448275862068965, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
3-D DENSITY DISTRIBUTION OF THE CRUST AND UPPER MANTLE BENEATH NORTHEAST CHINA BY JOINT INVERSION OF GRAVITY AND SEISMIC DATA

The Northeast China plate is composed of multiple micro-plates,so its geological structure is very complicated and there exist lots of fault zones.Although some investigations have been done in this area,less effort has been devoted to its three-dimensional(3-D)density structure that plays an important role in dividing tectonic unit and studying the evolution of this plate.In this study,considering the high lateral resolution of the gravity data and the vertical resolution of seismic tomography,we used both the gravity data and P-wave arrival time data to obtain the three-dimensional density structure of the crust and the upper mantle beneath the Northeast China area.We firstly obtained a 3-D P-wave velocity model at depths between 0and560 km by using the seismic tomography method and 12429P-wave arrival time data.Based on the relationship between seismic velocity and density,the obtained velocity model is then converted to a density model that can be used as the initial model in the gravity inversion.Then we calculate the anomaly field generated by the lower boundary of deposition,the Moho and the deep formation.When these calculated fields are removed from the Bouguer gravity anomaly,the5′× 5′residual gravity anomaly field can be used to invert for the 3-D residual density distribution.The density structure is finally converted to the velocity structure that is used as the initial model for the next seismic tomography.This process is repeated for several times until thedensity changes are small enough.As a result,we get the distribution of residual density at 9different depths of 10 km,30km,60 km,100km,150 km,210km,300 km,400km,and 500 km.The results show that(1)the joint inversion effectively not only improves the vertical resolution of gravity inversion but also stabilizes the seismic inversion results relative to the independent inversions by using only gravity or seismic data;and(2)the distribution of residual density anomalies in the crust and the upper mantle beneath the Northeast China area seems to be correlated with the tectonic units,in which the lower density anomalies correspond well to the orogenic belts while high density anomalies are related to the basins;and(3)a distinct lower density body exists beneath the volcanoes in this study area.Due to the seismic inversion result as the prior information,the vertical resolution of the density distribution is enhanced largely.The lower density anomalies associated with the orogenic belts and faults zones may be caused by the presence of magmatic rocks,and the higher ones associated with basin may be caused by the high density geologic structures underneath.In addition,combining with other previous results,we consider that the formation of volcanoes may be closely related to the stagnant Pacific slab in the mantle transition zone beneath Northeast China.