Sharp Changes of Crustal Seismic Anisotropy Across the Central Tanlu Fault Zone in East China

Abstract

Both seismic and geodetic data suggested that the ∼120‐km long Weifang segment of the Tanlu fault zone, a large‐scale active strike‐slip system at east China, is a seismic gap with no obvious along‐strike shear motion at surface. Measuring crustal deformation around the segment is crucial to constrain stress/strain buildup and potential seismic risk at the fault. We measured crustal and upper mantle seismic anisotropy using P‐to‐S converted waves at the Moho (Pms) and core‐mantle boundary (SKS) recorded by broadband arrays across the Weifang fault segment. The measured crustal anisotropy inside the fault zone shows a fast direction of ∼NNE, parallel to the fault orientation. Right east to the fault zone, the fast axis rotates by almost 90° to ESE. The crustal anisotropy within the fault zone could be caused by aligned microcracks and foliated minerals due to long‐lasting shear motion inside the fault zone.

Linear Array Double Difference Adjoint Ambient Noise Tomography of the Central Tanlu Fault Zone, Eastern China

“…Conversely, the lack of such secondary faults and the presence of solidified magma contribute to the tectonic activity of the eastern branch, leading to events like the Anqiu M7.0 earthquake in 70 BCE (Chao et al, 1994;Hu et al, 2014). The low-velocity anomaly beneath the eastern branch, as seen in our tomography results (Figure 6), could be indicative of activities of the AQ-JX fault, highlighting a significant earthquake hazard risk (Miao et al, 2023;Z. Wang et al, 2015;Xu et al, 2019).…”

Deformation microstructures and seismic anisotropy of Yeoncheon amphibolites in the Imjingang Belt, South Korea

“…The fast S-wave polarization direction parallel to the strike of the shear zone were reported from the various continental strike-slip shear zones (e.g. Hu et al, 2020;Miao et al, 2023;Poyraz, 2023;Sun et al, 2012). Considering that the type-II LPO of amphibole observed from the Yeoncheon amphibolite may have produced by the cataclastic flow, the LPO of amphibole may contribute to the seismic anisotropy of the continental strike-slip shear zones.…”

“…For the amphibolites with the type-II LPO of amphibole (samples 278 and 282), delay time produced by 10 km thick amphibolite was relatively large for the lateral shear geometry (0.1-0.11 s) (Table 3). The delay time and Moho depth were reported as 0.24-0.9 s and 32-71.1 km, respectively, in the southeastern margin of the Tibetan Plateau (Sun et al, 2012), and as 0.07-0.41 s and 31.0-36.8 km, respectively, in the Central Tanlu Fault Zone (Miao et al, 2023). Therefore, amphibolite exhibiting the type-II LPO of amphibole may significantly contribute to the large delay time in the continental strike-slip shear zones.…”