A ∼28-kyr Continuous Lacustrine Paleoseismic Record of the Intraplate, Slow-Slipping Fuyun Fault in Northwest China

Abstract

The Fuyun Fault is a typical intraplate, slow-slipping fault, but has been repeatedly ruptured by surface wave magnitude (Ms) ≥ 8.0 earthquakes. The 11 August 1931 Ms 8.0 Fuyun earthquake resulted in more than 10,000 casualties in the sparsely populated Fuyun area. Cosmogenic 10Be dating of offset landforms produced by prehistoric Ms ≥ 8.0 earthquakes yields an average recurrence interval of 9,700 ± 3,300 years, much longer than previously estimated 2,000–4,500 years, clouding our understanding of the timing and recurrence behavior of past earthquakes originating from the Fuyun Fault. Reflection seismic data reveal widely distributed subaquatic faults in Yileimu Lake, implying high sensitivity of the lake sediments to paleoearthquakes originating from the Fuyun Fault. Two new long sediment cores (Y20A: 267 cm; Y20B: 890 cm) together with previously published two short cores (Y19: 71 cm; Y20: 31.5 cm) from the depocenter and nearshore zone of Yileimu Lake are used for stratigraphic correlations and analyses of sedimentary structures, grain-size distributions, magnetic susceptibility, elemental composition and carbon content. The mass-wasting deposits with underlying soft-sediment deformation structures (SSDS) in the Y20B core indicate six siliciclastic-enriched sandy sediment fluxes from earthquake-triggered landslides of granitic rocks, and isolated SSDS record three additional earthquake-induced in situ deformations. Turbidite-like deposits with sorting indices >3 and Si contents >700 counts per second (cps) are comparable to those of the seismic mass-wasting deposits, and are thus interpreted as seismites from earthquake-induced re-deposition of nearshore sediments. There are a total of 20 seismic events recorded by the Y20B core. Seismic intensity calculation results, combined with historical seismic data, provide potential magnitudes of Ms ≥ 8.0, Ms ≥ 7.0, and Ms ≥ 5.5 for the earthquake-triggered mass-wasting deposits, SSDS, and turbidite-like seismites, respectively, in Yileimu Lake, generally consistent with previously published magnitude thresholds. Radiocarbon dating and stratigraphic correlations constrain the timing of these past earthquakes to ∼28 cal kyr BP. This unique, long lacustrine paleoseismic record suggests a weakly periodic pattern with recurrence intervals between 2,317 and 7,830 years and an average of 5,303 years for potential Ms ≥ 8.0 earthquakes, and reveals an unprecedented high frequency of potential Ms ≥ 7.0 earthquakes originating from the Fuyun Fault in the last 5 kyr, demonstrating the urgent need for an improved assessment of seismic hazards and risks in the Fuyun Fault zone.

Millennial‐ to centennial‐scale anti‐phase relationship between the Westerlies and the East Asian summer monsoon and its cultural response along the Silk Roads after a great earthquake in southern Altay ~ 3500 cal a BP

“…In addition, the percentages of the >63-µm fraction, Mz and Si content of the seismic layer at 267-225 cm depth of the Y20A core in the depocenter of the lake are correlated well with those at 73-57 cm depth of the Y20B core in the shallow water zone of the lake (Fig. 1c) (Fan et al 2022), demonstrating that a large earthquake could have caused significant changes in the sediments of the whole lake (Howarth et al 2014, Fan et al 2022.…”

“…During this depositional event, exceptionally high percentages of the >63-µm fraction and high values of Si content (Figs 3a and S3) suggest that these coarse sediments were probably sourced from earthquake-induced extensive landslides of quartz-enriched granitic rocks around the lake (Fig. 1c) (Fan et al 2022). Exceptionally low Rb/Sr ratios (Fig.…”

“…In a recent paleoseismic study, an 890-cm-long sediment core (Y20B) from the shallow water zone of Yileimu Lake (Fig. 1c) was used to reveal prehistoric earthquakes from Fuyun Fault spanning the past 28 cal ka (Fan et al 2022). In this study, a continuous 267-cm-long sediment core (Y20A: 47.176°N, 89.740°E) was retrieved from the depocenter of Yileimu Lake using a Canadian Wink S5 sonic drill system (Fig.…”

“…3e). These sediments were interpreted as potentially rapid seismic deposits transported by debris flows surrounding the lake without experiencing significant hydrodynamic sorting (Fan et al 2022, Howarth et al 2014. The relatively wellsorted silty sand was interpreted as rapid seismic deposits transported by hyperpycnal flows along the Irtysh River (Fan et al 2022).…”

A Continuous 13.3-Ka Paleoseismic Record Constrains Major Earthquake Recurrence in the Longmen Shan Collision Zone

“…Lacustrine paleoseismology can capture long continuous records of strong seismic shaking, which integrate the activity of all significant seismic sources in a region and allow a reliable determination of recurrence patterns (Moernaut, et al, 2018;Ghazoui et al, 2019;Lu et al, 2020;Oswald et al, 2021), including soft-sediment deformation (SSD, co-seismic) and seismites (postseismic). Among them, in-situ SSD structures can record a seismic event (Xu et al, 2015;Jiang et al, 2016;Lu et al, 2017Lu et al, , 2020Zhong et al, 2019;Zhang et al, 2021;Fan et al, 2022). Some seismites overlay the SSD, others lack an underlying SSD but are temporally correlated with a historic earthquake (Lu et al, 2017).…”