Crustal structure in Xiaojiang fault zone and its vicinity

Abstract

Based on the integrative interpretation of travel-time data and amplitude information obtained from the deep seismic sounding experiment on the Chuxiong-Luoping profile, eastern Yunnan province, carried out in January of 2005, we present a 2-D P wave velocity structure along the profile. The crustal structure shows remarkable contrasts between the two sides of the Xiaojiang fault zone, although the whole profile is situated within the Yangtze platform. The average P wave velocities of the crust on the west and east sides of the fault zone are 6.21 km/s and 6.32 km/s, respectively, and the crustal thicknesses are 41 km and 45 km, respectively. These results imply that the crust to the east of the Xiaojiang fault zone presents characteristics of crustal structure in a stable platform, while the crust to the west is complicated with a lower velocity zone in middle of the upper crust. The average velocity of 6.21 km/s is lower than the global continental crustal average (6.30 km/s), indicating that the region is tectonically active. According to the lateral variation of velocity and depth of interfaces (including the Moho), it is inferred that the Xiaojiang fault zone has cut through the whole crust. It is also deduced that existence of low velocity zone in middle of the upper crust is conducive to the south-southeastern sliding of the SichuanYunnan (Chuan-Dian) rhombus block.

Characteristics of Deep Crust Structure Beneath Western Yunnan

“…However, the eastern branch of the Xiaojiang fault penetrates crust down to a depth about 6 km, deeper than the western branch. Besides, below this fault, interfaces C1-C4 look like buckling, same as previous seismic sounding in the north [20] . But our work did not find obvious differences in crustal thicknesses between the two sides of this fault as suggested by the previous sounding to the north [20] .…”

“…It also implies that the crustal thickening in this region is primarily attributed to the lower crust. This feature has been found in previous seismic sounding [17,20] . Zhang et al [17] thought that it might be associated with subduction of Tethys, collision orogenies, and crust-mantle interaction.…”

“…Xiaojiang fault. Compared with the global average P velocity (6.39±0.25 km/s) [37] , the P velocity of this region is obviously low, also smaller than the probing result in the north of this survey line by 0.1∼0.2 km/s [20] , also consistent with intense tectonic activity in this region. The S wave velocity model from joint inversion of receiver functions and surface waves indicates that the S wave velocities below the three stations (Simao, Tonghai, and Mile), from southwest to northeast, are 3.42, 3.49, and 3.49 km/s, respectively.…”

Structural Geological Characteristics of Karst Caves and Shilin Stone Forest of the Lunan County, Yunnan, China

“…The Quaternary tectonic activity of the xiaojiang Fault zone is characterized by strong sinistral strike slip (Wang et al 2009). …”

“…The crust to the east of the xiaojiang Fault zone presents characteristics of crustal structure in a stable platform, while the crust to the west is complicated with a lower velocity zone in middle of the upper crust. It is inferred that the xiaojiang Fault zone has cut through the entire thickness of the crust (Wang et al 2009).…”