Holocene Slip Rate Along the Beng Co Fault and Dextral Strike‐Slip Extrusion of Central Eastern Tibet

Abstract

The dearth of quantitative studies of Holocene fault slip‐rates makes kinematic modeling of crustal deformation across SE Tibet debatable. The ∼230 km long, WNW‐striking, dextral Beng Co fault (BCF) is the most prominent strike‐slip fault of southern Tibet. Using new UAV topographic data and OSL/14C dating of geomorphic markers, we measure horizontal offsets and ages of fluvial terraces/fans and lacustrine shorelines at eight sites west and east of the Beng Lake pull‐apart. Along the eastern BCF's northern branch, our measurements at two different locations are consistent with offsets of ∼4.7 ± 1.1 and ∼8.7 ± 0.7 m during the past ∼3.1–3.6 and 3.6–5.2 ka, respectively. Along the southern branch, ∼25 ± 5 m of slip have accrued since ∼9 ka. The total Holocene slip‐rate across both faults (4.2–5.4 or 4.8 ± 0.5 mm/yr), consistent with GPS/InSAR values, implies that the BCF contributes significantly to the eastward extrusion of eastern‐central Tibet. This rate is slightly larger than the lower bound of the extension rate (∼6 ± 1.8 mm/yr) recently determined across the middle Gulu rift normal fault, which splays off southwards from the southeastern tip of the BCF's southern branch. Empirical relationships suggest that the reported ∼90 km length of the Mw 7.7, 1951 Beng Co earthquake surface rupture is too short, which implies that the eastern BCF is immature, or requires additional, partly deep slip, along other branches of the eastern BCF. That there is no field evidence of rupturing along the western BCF in the last ∼1,000 yr indicates that the Bange County area, west of Beng Co, may be at risk of an Mw ≈ 7.4? event.

Lake Level Changes and Holocene Extension Rate Across the NS‐Trending Peiku Co‐Gyirong Faults, Southern Tibet

“…(f) Profiles P2 and P3 show 5.8 ± 0.1 and 4.7 ± 0.1 m vertical offsets of F2 across fault north and south of fluvial valley, respectively. The positions and dips of the normal fault observed in the field, which are consistent with the positions of the profile‐deduced maximum slope values (e.g., Z. F. Li et al., 2022) are shown at the 1/1 scale.…”

“…For comparison, the similarly sized, 1959, Mw 7.2, Hebgen Lake earthquake (USA) produced two main surface ruptures (the ∼10‐km Hebgen and ∼23‐km Red Canyon ruptures), with maximum offsets of 6.8 and 6.5 m, respectively (Johnson et al., 2018). Also, the 1952, Mw 7.4, Gulu event (CENC/USGS) along the Gulu normal fault (northeastern front of Nyainqentanglha Shan), had a rupture length of ∼60 km (e.g., Armijo et al., 1986; K. Li et al., 2022; Wu et al., 1992).…”

“…Active faults are from K. Li et al. (2022). GPS velocity vectors, relative to stable Eurasia, are from M. Wang and Shen (2020).…”

Discrete Element Modeling of Southeast Asia's 3D Lithospheric Deformation During the Indian Collision

“…For instance, Schellart et al.’s simulations (2019) generate strike‐slip faulting mostly in areas where little or none exist, or with offsets opposite to those observed. Sternai et al.’s models (2016) cause ≈NS extension in areas of northeastern Tibet (Qilian Shan) where only ≈NE shortening has prevailed since the Miocene (e.g., Meyer et al., 1998; Zuza et al., 2018; Z. Li et al., 2021, 2022).…”

The shape of the Himalayan “Arc”: An ellipse pinned by syntaxial strike-slip fault tips

“…That contrast and the ≈ EW extension have long been interpreted ( 9 ), and subsequently modelled ( 22 ), as a consequence of divergent thrusting atop the rigid, subducting Indian plate. North of the Tsangpo suture, extrusion-related strike-slip faulting along the Karakorum fault ( 23 ), Damxung fault ( 9 , 21 ), Beng Co fault ( 24 , 25 ), and Gyaring Co fault ( 24 , 26 , 27 ) further complicates the kinematic deformation pattern across the central part of the plateau.…”