Deep fault slip characteristics in the Xianshuihe-Anninghe-Daliangshan Fault junction region (eastern Tibet) revealed by repeating micro-earthquakes

Abstract

• 9 repeating earthquake sequences are identified in the Xianshuihe-Anninghe-Daliangshan Fault junction region in eastern Tibet . • The southern Xianshuihe Fault and the Gongyihai section of Daliangshan Fault is creeping, while the southern Anninghe Fault is locked. • The accumulated strain on the southern Anninghe Fault is large enough to form the next M7 earthquake. The Xianshuihe-Anninghe-Daliangshan Fault junction region in eastern Tibet marks the transition zone between the creeping Xianshuihe Fault and the locked Anninghe Fault. However, the role in slip partitioning of these three faults is unclear, mainly because the geodetic data lack the resolution to discriminate slip at depth. Repeating earthquakes, the seismic events rupture the same fault patch more than once, are recognized as the slip meters at depth and play an important role in the assessment of seismic hazard. In this study, repeating earthquakes in the Xianshuihe-Anninghe-Daliangshan Fault junction region are identified and the deep fault slip characteristics are investigated. First, a complete catalog (2013–2020) for the study region is achieved by using Matched Filter Technique detecting the continuous waveforms of the dense Xichang array. Second, waveform cross-correlation and double-difference location technologies are used to identify repeating earthquakes. Finally, by checking waveforms, focal depth and satellite images, mining expositions are excluded and 9 repeating earthquake sequences (RES) are obtained. RES indicate the deep slip at a rate of 8 mm/yr on the southern Xianshuihe Fault is partitioned to the northern Anninghe Fault and the Gongyihai section of Daliangshan Fault at rates of 1 mm/yr and 2–6 mm/yr, respectively. Aseismic slip on the southern Xianshuihe Fault and northern Anninghe Fault reach to 12 km depth. A large asperity on the Anninghe Fault from Liziping to Xichang is constrained by the back ground seismicity and the location of RES, which will form a M ∼ 7 potential earthquake when it ruptures.