Hierarchical and structural complexities on the diffuse fault system associated with the 2000 Tottori earthquake revealed by a hyperdense seismic observation
Abstract
Young faults display unique complexity associated with their evolution, but how this relates to earthquake occurrence is unclear. Unravelling the fine-scale complexity in these systems could lead to a greater understanding of ongoing strain localization in young fault zones. Here we present high-spatial-resolution images of seismic sources and structural properties along a young fault zone that hosted the Tottori earthquake (Mw 6.8) in southwest Japan in 2000, based on data from a hyperdense network of ~1,000 seismic stations. Our precise micro-earthquake catalog reveals conjugate faulting over multiple length scales. These conjugate faults are well developed in zones of low seismic velocity. The most prominent conjugate fault plane extends toward W20S from the main trend, with a horizontal length of ~5 km along strike. This prominent aftershock lineation occurs close to the distinct boundary between a low-velocity body and a high-velocity body, on the northwestern side of the mainshock epicenter. The boundary between the low- and high-velocity bodies trends W20SE20N, and the observed seismicity rate is higher along this boundary than in other areas. A vertically dipping seismic cluster of about 200 m length occurs within a width of about 10 m, consisting of several small sub-clusters. The fault-length of each sub-cluster is ~30 m and the sub-clusters are separated by ~15 m in the horizontal direction. High-accuracy focal mechanism solutions show that one of the nodal planes (NNWSSE trend) is parallel to the direction of the major alignment. The earthquake alignment and focal mechanisms clearly indicate that this seismic sequence was macroscopically produced by left-lateral strike-slip movement. Earthquake migrations in this cluster have a speed of about 30 m per day, which suggests that fluid diffusion plays a role. We suggest that fine structural complexities influence the pattern of seismicity in a developing fault system.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.S42B..04K