Modelling Fault Scarp Degradation to Determine Earthquake History on the Muztagh Ata and Tahman Faults in the Chinese Pamir

Lejun Lu,Peizhen Zhang,Xiao Cheng,Yu Zhou

doi:10.3389/feart.2022.838866

Abstract

The frequency of earthquakes on active faults is usually revealed by palaeoseismic trenching and geological dating. Nonetheless, field trenching and sampling are sometimes limited by difficulties in logistics, therefore impeding palaeoseismological studies. As surface rupture earthquakes create fault scarps that evolve with time, they may also provide important information about the timing of earthquakes. In this study, we provide a new approach to determine earthquake history based on the morphology of fault scarps. We select the Muztagh Ata and Tahman normal faults in the Chinese Pamir as a test area, on which fault scarps are well preserved but the earthquake history has not been quantified yet. We first simulate fault scarp degradation using a nonlinear transport model to obtain the empirical relationship between scarp width and its evolution time. We then measure 68 fault scarps from high-resolution topographic data derived from WorldView-2 stereo imagery. The measured fault scarps are clustered in four groups, each group possibly representing one earthquake event. Combining the time-width relationship and scarp width measurements, we infer that four earthquakes occurred at 0.1±0.4 kyrs before the present (BP), 2.1±0.5 kyrs BP, 2.9±0.4 kyrs BP and 4.9±0.5 kyrs BP, respectively. The first event is likely to be the most recent earthquake occurred on the faults, i.e., the 1895 Tashkurgan earthquake ( ∼0.13 kyrs BP). Based on the estimated earthquake recurrence intervals and vertical offsets, we obtain a vertical slip rate of 2.2±0.3 mm/yr on the Muztagh Ata and Tahman faults, conforming to previous geological rate estimates.

Highlights

IntroductionThe frequency of earthquakes that have occurred along a fault determines its seismic potential and is important for hazard assessment
We focus on the Muztagh Ata and Tahman faults in the southern part of the Kongur Shan extensional system (Figure 1)
The extracted point cloud was gridded with 1-m spacing to derive the WorldView-2 digital elevation model (DEM)

Summary

Introduction

The frequency of earthquakes that have occurred along a fault determines its seismic potential and is important for hazard assessment. Since earthquakes are recorded on the earth’s surface in the form of offset geomorphic features, such offsets can be used as an alternative method to characterise repeating earthquakes and fault slip behaviour. Under the assumption that similar-aged offset geomorphic features experienced the same number of Earthquake History Determined by Scarp Degradation earthquakes, offset measurements appear as groups, which can be used as an indicator of repeating earthquakes (Sieh, 1978; McGill and Sieh, 1991). This method, known as “cumulative offset probability distribution, COPD”, requires a large amount of offset measurements for statistical analysis (e.g., Zielke et al, 2015; Bi et al, 2018).

Results

Discussion

Conclusion