Variability in magnitude of paleoearthquakes revealed by trenching and historical records, along the Haiyuan Fault, China

Abstract

Paleoseismology provides fundamental data for generalizing earthquake recurrence behavior, by revealing past surface‐rupturing events. Determining the size of paleoseismic events is notoriously more challenging than their timing. Paleoearthquakes exposed in trenches are vaguely defined as large enough to break to the surface and often assumed to be similar in size. Here we show an example where the paleoseismic record includes events of both moderate and large magnitudes. At the Salt Lake site on the active left‐lateral Haiyuan Fault, northern Tibetan Plateau, a high‐resolution stratigraphic sequence recorded three and possibly four events since A.D. 1500, constrained by accelerator mass spectrometry 14C dating. Historical accounts of earthquake damage in the study region suggest that several earthquakes exposed in the trenches markedly differ in magnitude. With the exception of the most recent M~8 earthquake that occurred in A.D. 1920, two earlier events, which occurred in A.D. 1760 (or 1709) and 1638, respectively, are considerably smaller, with magnitude M < 7 and more likely M~6 or less. Thus, this section of the Haiyuan Fault that broke during moderate‐magnitude events failed again after a short interval during a large Mw 7.8–8.3 earthquake, as part of a larger multisegment rupture. Our study shows that moderate‐magnitude events can be preserved in the stratigraphy and exposed by paleoseismic trenching under ideal conditions, for instance, if sedimentation is fast enough and there is no hiatus in deposition. Eventually, the data presented add to the growing body of paleoseismic records containing events of different magnitudes with a large variability in rupture length and coseismic slip.

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

“…Zhang et al (2005) and Ren et al (2015) found that the Haiyuan fault may rupture in segments. Liu-Zeng et al (2015) 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 (2018) systematically measured offset landforms along the Laohushan fault using lidar data.…”

“…Studying paleoseismology of the fault can provide important information to understand strain release process and recurrence behavior of the fault and possibility of next large earthquake (Akciz et al, ; Berryman et al, ; Scharer et al, ; Shimazaki & Nakata, ). The paleoseismic history and rupture pattern of the Laohushan and Haiyuan faults have been studied in detail (Y. Li et al, ; B. C. Liu et al, ; Liu‐Zeng et al, , ; Ran et al, ; P. Z. Zhang, Molnar, Zhang, et al, ; ). In contrast, the LLLF is located in a high‐altitude and remote area, with difficult access, and thus, relatively few studies have focused on the LLLF.…”

Paleoseismic Investigation of the Aksay Restraining Double Bend, Altyn Tagh Fault, and Its Implication for Barrier‐Breaching Ruptures

“…Channels have steep longitudinal profiles, transporting coarse sediment from mountain to piedmont, building boulder alluvial fans or cutting deep canyons. In this steep environment, few geomorphic settings in the study area are optimal for paleoseismology, like pull‐apart basins (e.g., Daëron et al, ; Liu‐Zeng et al, ; Rockwell et al, ; Scharer et al, ), shutter ridges, or other large morphological depressions (e.g., Fumal et al, ; Lienkaemper & Williams, ; Sieh, ) or distal fans (e.g., Grant & Sieh, ; Klinger et al, ) of fine‐grain deposits. Nonetheless, we found a pair of sites with local ponding of sediments caused by oblique slip along the fault.…”

Late Pleistocene‐Holocene Slip Rate Along the Hasi Shan Restraining Bend of the Haiyuan Fault: Implication for Faulting Dynamics of a Complex Fault System

“…In addition, paleoseismological trenches along the Haiyuan fault suggest that six events of different magnitude ruptured the central Haiyuan strand in the last 3,500–3,900 years (Liu‐Zeng et al, ). Historical medium‐size earthquakes have also been documented along the 1920 rupture section (Liu−Zeng et al, ).…”