Study on the crustal velocity structure of the Dunhua-Mishan fault based on the dense seismic array by ambient noise tomography

Abstract

The Dunhua-Mishan fault is a component of the Tanlu fault zone, and it is also a major regional fault structure in Liaoning area. The study area is located in Fushun area of the Dunhua-Mishan fault. In order to study the crustal velocity structure in this region, we used 60 sets of three-component short-period seismographs and lay out two temporary profiles in Fushun, Liaoning from Nov. 3 to 25, 2019. Each temporary profiles is about 12km long that is composed of 30 seismometers, which nearly vertically cross the Dunhua-Mishan fault where the survey lines are 6km apart. The installation stations spacing distance from 200 to 400m use the external GPS time service to record frequency range of 0.2 to 150Hz in the instrument. The crustal structure characteristics of the fault zone are studied by ambient noise cross-correlation method. In order to efficiently extract high and low frequency surface wave dispersion signals at the same time, we adopt the Extended Range Phase Shift (ERPS) method. Finally, we use ERPS method to process the collected data and invert the S-wave velocity structure. We initially obtained the S-wave velocity structure of the upper crust below 5 km in the area, which matches well with the local geological data. The S-wave velocity structure has significant lateral inhomogeneity of the Dunhua-Mishan fault in Fushun area. The S-wave velocity is obviously lower on the Dunhua-Mishan fault, while with the existence of ancient mixed granite the velocity on both sides of the fault is obviously higher.