دانلود رایگان مقاله انگلیسی زلزله ی 2016 کاکورا: گسیختگی همزمان سطح مشترک فرورانشی و گسل های بزرگ - الزویر 2018

abstract

The distribution of slip during an earthquake and how it propagates among faults in the subduction system play a major role in seismic and tsunami hazards, yet they are poorly understood because offshore observations are often lacking. Here we derive the slip distribution and rupture evolution during the 2016 Mw 7.9 Kaikoura ¯ (New Zealand) earthquake that reconcile the surface rupture, space geodetic measurements, seismological and tsunami waveform records. We use twelve fault segments, with eleven in the crust and one on the megathrust interface, to model the geodetic data and match the major features of the complex surface ruptures. Our modeling result indicates that a large portion of the moment is distributed on the subduction interface, making a significant contribution to the far field surface deformation and teleseismic body waves. The inclusion of local strong motion and teleseismic waveform data in the joint inversion reveals a unilateral rupture towards northeast with a relatively low averaged rupture speed of ∼1.5 km/s. The first 30 s of the rupture took place on the crustal faults with oblique slip motion and jumped between fault segments that have large differences in strike and dip. The peak moment release occurred at ∼65 s, corresponding to simultaneous rupture of both plate interface and the overlying splay faults with rake angle changes progressively from thrust to strike-slip. The slip on the Papatea fault produced more than 2 m of offshore uplift, making a major contribution to the tsunami at the Kaikoura ¯ station, while the northeastern end of the rupture can explain the main features at the Wellington station. Our inversions and simulations illuminate complex up-dip rupture behavior that should be taken into consideration in both seismic and tsunami hazard assessment. The extreme complex rupture behavior also brings new challenges to the earthquake dynamic simulations and understanding the physics of earthquakes.

4. Discussion and conclusions

Simultaneous rupturing of the subduction interface and its splay faults (Fig. 6) explains the highly-segmented uplift pattern along the coast, which may result from the slip partitioning among the high-dipping angle splay faults (Fig. 6). During the earthquake, the block bounded by two fault systems parallel to the coast was likely squeezed out by the oblique westward slip south of the Kekerengu fault (Fig. 2a). When the mini-block south of the Jordan Thrust fault and the upper Kowhai fault was extruded by the westward motion (Figs. 2a and 6), the slip was partitioned into uplifting and southeastward motion between the Kaikoura ¯ Peninsula and the Papatea fault (Fig. 2a). By contrast, the region near the Hope fault shows minor horizontal motion, but only uplifting to the south. This is because of the nearly fault-perpendicular updip thrust along its subvertical fault plane. The southward motion between the Papatea and Kekerengu Faults can be explained by the shallow northwest-dipping (∼45◦) of the Jordan Thrust fault during the extrusion, but it can be alternatively interpreted as a result of thrust faulting occurred offshore (Clark et al., 2017). Distinguishing these two kinds of models will need evidence from seafloor surveys after the earthquake. The vertical coastal displacement pattern demonstrates that geomorphological features in a single event, such as stepped river terraces, can be overprinted on smooth vertical displacement produced by slip on the subduction interface. Such overprinted deformation driven by aforementioned simultaneous rupture slip within a complex multi-splay fault system will significantly change how the coastal uplift rate is interpreted.