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We considered various non‐uniformities such as branch faults, rotation of stress field directions, and changes in tectonic environments to simulate the dynamic rupture process of the 6 February 2023 Mw 7.8 Kahramanmaraş earthquake in SE Türkiye. We utilized near‐fault waveform data, GNSS static displacements, and surface rupture to constrain the dynamic model. The results indicate that the high initial stress accumulated in the Kahramanmaraş‐Çelikhan seismic gap leads to the successful triggering of the East Anatolian Fault (EAF) and the supershear rupture in the northeast segment. Due to the complexity of fault geometry, the rupture speed along the southeastern segment of the EAF varied repeatedly between supershear and subshear, which contributed to the unexpectedly strong ground motion. Furthermore, the triggering of the EAF reminds us to be aware of the risk of seismic gaps on major faults being triggered by secondary faults, which is crucial to prevent significant disasters. Plain Language Summary: On 6 February 2023, the south‐central Türkiye was hit by two major earthquakes with magnitudes of Mw 7.8 and Mw 7.6 respectively. Among them, the complex rupture process and unexpected ground motion of the Mw 7.8 event attracted the attention of seismologists. In this paper, the 3D dynamic rupture process of this mainshock is simulated based on complex multi‐fault system and heterogeneous initial stress. And the simulation results are in good agreement with the observations. Our results show that high initial stress is required for the EAF to be triggered. The supershear rupture occurred only in certain fault segments and is unable to sustain itself in a significant area on the fault due to the along‐strike variations in fault geometry and strength. More importantly, the dynamic model suggests that we must be alert to the risk of major fault being triggered by earthquakes on nearby small faults, especially when there are seismic gaps on the major fault. Key Points: The high initial stress accumulated in the seismic gap leads to the successful triggering of the East Anatolian FaultThe change of fault geometry in the southwest segment prevented the sustained supershear ruptureThe risk of earthquake nucleation on the secondary fault triggering the major fault rupture and the related disaster was highlighted [ABSTRACT FROM AUTHOR]

Abstract We considered various non‐uniformities such as branch faults, rotation of stress field directions, and changes in tectonic environments to simulate the dynamic rupture process of the 6 February 2023 Mw 7.8 Kahramanmaraş earthquake in SE Türkiye. We utilized near‐fault waveform data, GNSS static displacements, and surface rupture to constrain the dynamic model. The results indicate that the high initial stress accumulated in the Kahramanmaraş‐Çelikhan seismic gap leads to the successful triggering of the East Anatolian Fault (EAF) and the supershear rupture in the northeast segment. Due to the complexity of fault geometry, the rupture speed along the southeastern segment of the EAF varied repeatedly between supershear and subshear, which contributed to the unexpectedly strong ground motion. Furthermore, the triggering of the EAF reminds us to be aware of the risk of seismic gaps on major faults being triggered by secondary faults, which is crucial to prevent significant disasters.

Intersecting orthogonal strike‐slip faults with opposite senses of slip pose the question of what allows rupture to propagate through the junction and through both faults versus confining rupture to a single fault. I conduct dynamic rupture simulations on simplified orthogonal strike‐slip fault systems, to determine which conditions produce rupture on both component faults. In models with uniform initial tractions on both faults, slip on the first fault must reduce normal stress on the second fault for it to rupture. If the first fault ends at the cross fault, a stopping phase causes the cross fault to rupture. In models where I resolve a uniform regional stress field on the faults, only a narrow range of stress orientations allow multifault ruptures. These results will be helpful for evaluating hazard near orthogonal strike‐slip faults. Plain Language Summary: There are many examples around the world where two strike‐slip earthquake faults cross each other at nearly 90° angles. This is not remarkable when only one of the faults in a pair causes an earthquake, but it becomes notable when two or more crossing faults move at the same time. This raises the question of what causes the second fault to get involved, or not. To address this question, I use computer simulations of the physics of the earthquake process to test dozens of different fault configurations and earthquake starting points. I find that the location where the earthquake starts on the first fault controls whether the second fault is made stronger versus weaker, and therefore whether both faults can move together in one earthquake. These results can help us understand earthquake hazard around crossing faults. Key Points: Nucleation location effectively controls whether multifault rupture occurs on orthogonal strike‐slip fault systemsA stopping phase from rupture reaching the end of one fault is often required to initiate rupture on the cross faultOnly a narrow range of regional stress orientations allows both cross‐faults to rupture [ABSTRACT FROM AUTHOR]

Abstract Elastic dislocation models require large near‐trench slip to explain large tsunamigenesis, which is probably best exemplified in the 2011 M9 Tohoku earthquake. However, it is puzzling that the largest Tohoku tsunami heights occurred about 100 km north of the largest slip zone, where bathymetric surveys indicate no large slip at the trench or submarine landslides. Here we show that coseismic yielding of plentiful sediments in the northern Japan Trench margin can induce large inelastic uplift landward from the trench and diminish slip near the trench. The scarcity of sediments in the south leads to nearly elastic response with large slip at the trench and mostly horizontal seafloor displacement. Thus, the variations of sediments along the Japan Trench and sediment yielding can explain the puzzling variations of tsunamigenesis and near‐trench slip in this earthquake. Inelastic wedge deformation can be an important mechanism of tsunamigenesis in accretionary and other sediment‐filled plate margins.

Elastic dislocation models require large near‐trench slip to explain large tsunamigenesis, which is probably best exemplified in the 2011 M9 Tohoku earthquake. However, it is puzzling that the largest Tohoku tsunami heights occurred about 100 km north of the largest slip zone, where bathymetric surveys indicate no large slip at the trench or submarine landslides. Here we show that coseismic yielding of plentiful sediments in the northern Japan Trench margin can induce large inelastic uplift landward from the trench and diminish slip near the trench. The scarcity of sediments in the south leads to nearly elastic response with large slip at the trench and mostly horizontal seafloor displacement. Thus, the variations of sediments along the Japan Trench and sediment yielding can explain the puzzling variations of tsunamigenesis and near‐trench slip in this earthquake. Inelastic wedge deformation can be an important mechanism of tsunamigenesis in accretionary and other sediment‐filled plate margins. Plain Language Summary: The general consensus about the devastating 2011 Tohoku tsunami is that it was due to large slip at the trench. This can be somewhat misleading because the largest tsunami heights occurred about 100 km north of where the largest trench slip occurred. Using elastic dislocation theory, inversions of tsunami data require large trench slip ~30 m in the north (north of 39°N). However, the bathymetry data before and after the earthquake suggest no large trench slip or submarine landslides in the north. Here we present a mechanism that involves the yielding of sediments in the overriding wedge. Our inelastic wedge deformation model can explain the puzzling observations of large tsunami heights along the Sanriku coast in the north with no or small trench slip and small tsunami in the south with large trench slip. The amount of sediments in a subduction margin can be very important in evaluating tsunami hazard. Key Points: Inelastic wedge deformation can induce large seafloor uplift efficiently landward from trench and diminish near‐trench slip on the faultAlong‐arc variation of sediment thickness in the Japan Trench margin can lead to important along‐arc variations of tsunamigenesisThe large tsunami heights along the Sanriku coast in the 2011 Tohoku earthquake can be due to inelastic wedge deformation [ABSTRACT FROM AUTHOR]

The 2016 Kaikoura (New Zealand) earthquake is characterized as one of the most complex multifault rupture events ever observed. We perform dynamic rupture simulations to evaluate to what extent relatively simple forward models accounting for realistic fault geometry can explain the characteristics of coseismic observations. Without fine parameter tuning, our model reproduces many observed features including the multifault rupture, overall slip distribution, and the locations of the maximum slip and rupture arrest. In particular, our model shows spontaneous arrest of dynamic rupture at the both ends of the ruptured fault system due to smaller prestress levels expected from a regional tectonic stress field. Both the simulated and the observationally inferred source time functions show similar double peaks with a larger second peak. The results illuminate the importance of the 3‐D fault geometry in understanding the dynamics of complex multifault rupture. Plain Language Summary: The 2016 Kaikoura earthquake in the northern South Island of New Zealand was one of the most complex faulting events ever observed. Previous studies identified surface ruptures along at least a dozen major faults extending over 150 km. Here we use computer simulations to investigate how the complex three‐dimensional geometry of faults plays a role in the rupture propagation and termination during the Kaikoura earthquake. We find that our model can explain a number of observations associated with the earthquake. In particular, the model suggests that the termination of propagating rupture at the ends of faults was caused by the unfavorable orientations of these faults with respect to regional tectonic stresses. The results illuminate the importance of three‐dimensional fault geometry in understanding the dynamics of multifault earthquakes. Key Points: Dynamic model considering realistic fault geometry and regional stress field reproduces multifault rupture during the Kaikoura earthquakeModel shows spontaneous rupture arrest on the western Humps and Needles faults, which are unfavorably oriented in a regional stress fieldDynamic triggering of fault slip may have played an important role in transferring the rupture from the southern to northern faults [ABSTRACT FROM AUTHOR]