Seismic Structure of Local Crustal Earthquakes beneath the Zipingpu Reservoir of Longmenshan Fault Zone

Abstract

Three-dimensional P wave velocity models under the Zipingpu reservoir in Longmenshan fault zone are obtained with a resolution of 2 km in the horizontal direction and 1 km in depth. We used a total of 8589 P wave arrival times from 1014 local earthquakes recorded by both the Zipingpu reservoir network and temporary stations deployed in the area. The 3-D velocity images at shallow depth show the low-velocity regions have strong correlation with the surface trace of the Zipingpu reservoir. According to the extension of those low-velocity regions, the infiltration depth directly from the Zipingpu reservoir itself is limited to 3.5 km depth, while the infiltration depth downwards along the Beichuan-Yingxiu fault in the study area is about 5.5 km depth. Results show the low-velocity region in the east part of the study area is related to the Proterozoic sedimentary rocks. The Guanxian-Anxian fault is well delineated by obvious velocity contrast and may mark the border between the Tibetan Plateau in the west and the Sichuan basin in the east.

Seismic velocity changes in the epicentral region of the 2008 Wenchuan earthquake measured from three‐component ambient noise correlation techniques

“…Detailed seismic reflection data in our study region have shown that the depth of Precambrian basement is approximately 4 km [ Hubbard et al ., ]. In addition, a recent seismic tomography study [ Li et al ., ] using the same ZRSN data revealed a low‐velocity zone beneath the Zipingpu Reservoir up to 3.5 km, and the area between the Yinxiu‐Beichuan and Pengguan faults is mostly covered by Proterozoic sedimentary rocks. Their study also identified a low‐velocity zone extending up to 6 km around these active faults.…”