Linking Active Source and Passive Ambient Noise Using Dense Array – Results from Several Experiments in China

Session: Recent Development in Ultra-Dense Seismic Arrays With Nodes and Distributed Acoustic Sensing (DAS)
Type: Oral
Date: 4/30/2020
Time: 03:45 PM
Room: 110 + 140
Description: 

The ultra-dense seismic array has been widely used recently for better imaging the shallow crust. In the past a few years, the Institute of Geophysics China Administration (CEA-IGP) has conducted several experiments to study the shallow crust structure using dense array. The traditional techniques, such as ambient noise tomography (ANT), HVSR, are used for passive imaging. Moreover, active sources are also used to build a comprehensive observation system. Several results will be summarized:

Case1: Binchuan Experiment. A dense array was deployed in Binchuan Basin Yunnan Province from March 25 to May 25 in 2017. This array is composed of 381 three component short period stations covering a 30x40 km area with average spacing about 2 km. The sediment depth is estimated using HVSR method and ANT is conducted for shallow S wave velocity. Body wave tomography using P and S travel times from 96 local earthquakes is used to obtain one 3D velocity model up to 10 km beneath the array. Moreover, one large volume airgun source is located in the center of the array. The P/S travel times of airgun signals are used to benchmark the accuracy of obtained 3D velocity models.

Case2: Zhuxi Experiment. In December 2017, one dense array of 178 short-period three component seismometers was deployed in Zhuxi County, Jiangxi Province to study the shallow structure of the mining area. This array covers 30×40km area with a station spacing of 1-2km. At the same time, four dense lines composed of 2311 single-component geophones were also laid with spacing about 10 m. Four kinds of active sources, i.e. airgun, vibroseis, methane detonation source and hammering, were used. The 3D high-resolution shallow velocity structure at depth 0-600m is obtained using 761,653 P-wave arrivals from active sources. The S wave structure from ambient noise tomography is also obtained for joint analysis.

Using the ultra-dense array, the passive source and active source can be linked together for a better imaging of the shallow crust.

Presenting Author: Weitao Wang

Authors