Field separation and anomaly feature extraction of mobile gravity data in Sichuan area

The mobile gravity measuring network for monitoring the Sichuan area gravitational field varying along with the time has made an overall transformation after the Wenchuan M_S8.0 earthquakes on 12 May 2008, forming a new closed loop with gravity observation to all of the point locations twice every year. Taking five-issue mobile gravity data in the period of 2010—2012 as the foundation, this paper detects dynamic change of gravitational field in multi-scale decomposition and extracts anomaly features by using wavelet multi-scale decomposition and the 3-D apparent density inversion, so as to search for dynamic change characteristics of gravity anomaly and the relationship between the range of density variation and the gravity field response within different depths before and after the earthquake in Sichuan measuring area. The results show that different order details chart got from wavelet decomposition on the same stage gravity data reveals dynamic change characteristics of gravity anomaly in the different depth. Decomposition results also show that changes of gravitational field are closely related with fracture structure framework, deep structure and characteristics of transitional zone in Sichuan measuring area. Comparison of 3-D apparent density inversions based on the differential gravity anomaly data of different periods suggests density change is different from shallow to deep depth before and after an earthquake. Variation of transverse density characteristics is obviously presented nearby the seismic region, and anomalous change difference in the density of shallow matter is especially prominent. The apparent density slice maps within the depth of the middle-upper crust of the testing area shows trend differences, which basically reflects the dynamic change process of underground substances before and after the earthquake. Therefore deep understanding of gravity dynamic evolution characteristics in the different depth bounds is of positive significance to study the matter density change in the crust and deep medium environment related to the pregnancy and development of the earthquake.