Geomorphic offsets along the creeping Laohu Shan section of the Haiyuan fault, northern Tibetan Plateau

Abstract

High-resolution topographic or imagery data effectively reveal geomorphic offsets along faults that can be used to deduce slipper event of recurrent rupture events. Documentation of patterns of geomorphic offsets is scarce on faults that undergo both creep and coseismic rupture. In this paper, we used newly acquired high-resolution light detection and ranging (LiDAR) data to compile geomorphic offsets along the Laohu Shan section of the Haiyuan fault, in the northern Tibetan Plateau, where interferometric synthetic aperture radar (InSAR) data suggest creep presently occurs over a 35-km-long stretch at a rate comparable to the long-term geological slip rate, despite evidence for past coseismic fault rupture. Numerous offset gullies identified using the LiDAR data yield a range of offsets from less than 2 m up to 50 m. These offsets have well-separated probability density peaks at 2-3 m, ~7 m, and ~14 m, with increments of 2-3 m, 4-6 m, and 5-7 m. The sequence of paleoseismic events along the Laohu Shan section indicates that the gullies with offsets of 2-3 m are likely related to surface rupture of the historical 1888 Jingtai earthquake, plus subsequent creep. Offset increments of 4-6 m and 5-7 m may represent coseismic slip in past paleoseismic events plus creep during the interseismic period. The creeping Laohu Shan section preserves numerous discrete cumulative offsets, with an offset clustering pattern indistinguishable from that on a locked fault with recurrent earthquake ruptures. Association of offset increments with known paleoseismic events yields a slip rate of 3-5 mm/yr during the past 200 years, roughly similar to the ~5 mm/yr creep rate. If the ratio of surface creep rate to the total fault slip rate has been continuous, then seismic moment release by brittle ruptures, and thus seismic hazard, would be much reduced on the Laohu Shan section of the Haiyuan fault. Alternatively, the current high creep rate may be a transient phenomenon, perhaps after slip following the 2000 Jingtai Mw 5.6 earthquake or in response to the adjacent 1920 M ~8 Haiyuan earthquake rupture that terminated immediately to the east.

Systematic Search for Repeating Earthquakes Along the Haiyuan Fault System in Northeastern Tibet

“…There is some evidence for the surface-breaking rupture of paleoearthquakes in this section. In addition, the cumulative slip offset in this region is similar to noncreeping brittle faults (Chen et al, 2018). Based on these observations, Chen et al (2018) inferred that either the fault is capable of switching between creeping and brittle faulting over time or the fault is partially creeping.…”

“…In addition, the cumulative slip offset in this region is similar to noncreeping brittle faults (Chen et al, 2018). Based on these observations, Chen et al (2018) inferred that either the fault is capable of switching between creeping and brittle faulting over time or the fault is partially creeping. In the second possibility, the creep on the Laohushan section is a shallow phenomenon, with the fault remaining locked at depth, similar to the Ismetpasa segment of the North Anatolian fault in Turkey (Kaneko et al, 2013;Karabacak et al, 2011;Ozener et al, 2010) and the Hayward fault in northern California (Schmidt et al, 2005;Simpson et al, 2001).…”

“…In addition, the depth extent of the creep is not well constrained. It is still not clear whether creep on this section of the HYF is a transient phenomenon following the 1920 Haiyuan mainshock or reflects a long-term slip behavior (Chen et al, 2018).…”

Reevaluation of the Late Pleistocene Slip Rate of the Haiyuan Fault Near Songshan, Gansu Province, China

“…Between major events occurring every 800–1,000 years, moderate magnitude earthquakes also occurred in this section, the recent ones being 20 October 1990 Mw 5.8 Tianzhu earthquake and 2000 Mw 5.6 Jingtai earthquake (Committee for Chinese Earthquake Bulletin, ; Cai et al, ; US Geological Survey National Earthquake Information Center, ). The 35‐km‐long very eastern end of the Laohu Shan section is likely creeping at a rate of ~5 mm/year indicated by the analysis of interferometric synthetic aperture radar data (Cavalié et al, ; Jolivet et al, ), despite that numerous geomorphic offsets of gullies were found to cluster at amounts of sell‐separated increments, similar to the geomorphic offset pattern on noncreeping faults (Chen et al, ).…”

Paleoearthquakes and Rupture Behavior of the Lenglongling Fault: Implications for Seismic Hazards of the Northeastern Margin of the Tibetan Plateau

“…Liu‐Zeng et al () identified three or four seismic events on the Haiyuan fault since A.D. 1500 based on trench and historical records. In addition, Chen et al () systematically measured offset landforms along the Laohushan fault using lidar data. To the west of the Tianzhu Basin, the slip rates and paleoseismology of the fault segments are much less studied.…”