Figure 3
Regional geological map and the total horizontal derivative (THD) of the simple Bouguer anomaly. (a) Topographic map indicating the extents of tectonostratigraphic terranes and granite bodies28,29,30. The generalized geological map of the research area was modified after The Geology Map of China [1:2,500,000]. Primarily Neoproterozoic metamorphic rocks are exposed in the Bikou block, and the granites exposed in the southwestern Songpan-Ganzi terrane include A, I and S types. (b) Except for the rigid Sichuan basin, the Minjiang fault zone and Longriba fault zone are associated with smaller THD values of the simple Bouguer anomaly than other areas shown on this map. These observations may indicate that the strain within the crust is released through the faults. Therefore, the Huya fault and Longmen Shan fault zones still pose a considerable risk of disastrous earthquakes. The digital elevation data were downloaded from http://srtm.csi.cgiar.org/SELECTION/inputCoord.asp. The topographic map was prepared using Generic Mapping Tools (GMT) (http://gmt.soest.hawaii.edu/). The map was drafted by X.X. using the CorelDRAW software package (http://www.coreldraw.com/en/product/graphic-design-software/).
