We present a dynamic rupture model of the 2016 Mw 7.8 Kaikōura earthquake to unravel the event’s riddles in a physics-based manner and provide insight on the mechanical viability of competing hypotheses proposed to explain them. Our model reproduces key characteristics of the event and constraints puzzling features inferred from high-quality observations including a large gap separating surface rupture traces, the possibility of significant slip on the subduction interface, the non-rupture of the Hope fault, and slow apparent rupture speed. We show that the observed rupture cascade is dynamically consistent with regional stress estimates and a crustal fault network geometry inferred from seismic and geodetic data. We propose that the complex fault system operates at low apparent friction thanks to the combined effects of overpressurized fluids, low dynamic friction and stress concentrations induced by deep fault creep.

Extension deficit builds up over centuries at divergent plate boundaries and is recurrently removed during rifting events, accompanied by magma intrusions and transient metre-scale deformation. However, information on transient near-field deformation has rarely been captured, hindering progress in understanding rifting mechanisms and evolution. Here we show new evidence of oblique rift opening during a rifting event influenced by pre-existing fractures and two centuries of extension deficit accumulation. This event originated from the Bárðarbunga caldera and led to the largest basaltic eruption in Iceland in >200 years. The results show that the opening was initially accompanied by left-lateral shear that ceased with increasing opening. Our results imply that pre-existing fractures play a key role in controlling oblique rift opening at divergent plate boundaries.

Large earthquakes often do not occur on a simple planar fault but involve rupture of multiple geometrically complex faults. The 2016 Mw 7.8 Kaikoura earthquake, New Zealand, involved the rupture of at least 21 faults, propagating from southwest to northeast for about 180 km. Here we combine space geodesy and seismology techniques to study subsurface fault geometry, slip distribution, and the kinematics of the rupture. Our finite‐fault slip model indicates that the fault motion changes from predominantly right‐lateral slip near the epicenter to transpressional slip in the northeast with a maximum coseismic surface displacement of about 10 m near the intersection between the Kekerengu and Papatea faults. Teleseismic back projection imaging shows that rupture speed was overall slow (1.4 km/s) but faster on individual fault segments (approximately 2 km/s) and that the conjugate, oblique‐reverse, north striking faults released the largest high‐frequency energy. We show that the linking Conway‐Charwell faults aided in propagation of rupture across the step over from the Humps fault zone to the Hope fault. Fault slip cascaded along the Jordan Thrust, Kekerengu, and Needles faults, causing stress perturbations that activated two major conjugate faults, the Hundalee and Papatea faults. Our results shed important light on the study of earthquakes and seismic hazard evaluation in geometrically complex fault systems.

The 1600-km-long left-lateral East Kunlun fault (EKF) defines the northern boundary of the Bayan-Har Block, which is one of the most seismically active regions in the Tibetan Plateau, China (Li et al., 2011;. Over the past century, three destructive earthquakes (M > 7) ruptured some segments of the EKF, including the 1937 M7.5 Huashixia, 1963 M7.0 Dulan, and 2001 𝐴𝐴 Mw 7.8 Kokoxili earthquakes (Figure 1a), leaving two seismic gaps. One is the Maqin-Maqu seismic gap (Wen et al., 2007), where large earthquakes are expected to occur in the near future. Yet no related sign has been observed. In addition, the EKF is somewhat straight to the west of 98°E but bends ∼45° toward the southeast from 98°E to 99.5°E. Across such a fault geometry bending, the slip rate of the EKF decreases from ∼10 mm/yr in the west section of 98°E to ∼5-6 mm/yr along the Maqin-Maqu segment (Kirby et al., 2007;Van Der Woerd et al., 1998, 2002. Such a slip rate decrement suggests that the deformation is accommodated by some nearby structures and faults. Hence, some faults around the Maqin-Maqu segment, even though the slip rate is low, can be the location of large earthquakes. On May 22, 2021, an 𝐴𝐴 Mw 7.4 earthquake struck the Maduo county of Guoluo prefecture in Qinghai province, western China. This earthquake is another large earthquake (M > 7) that occurred in the Bayan-Har block since the 1947 M7.7 Dari earthquake. Until 30 May 2021, a total of 2979 aftershocks have been recorded by the China earthquake administration (Wang et al., 2021). This event caused severe damages to local buildings and