دانلود رایگان مقاله انگلیسی شبیه سازی زلزله سونامیگنیک با استفاده از قوانین اصطکاکی مشتق شده تجربی - الزویر 2018

abstract

Seismological, tsunami and geodetic observations have shown that subduction zones are complex systems where the properties of earthquake rupture vary with depth as a result of different pre-stress and frictional conditions. A wealth of earthquakes of different sizes and different source features (e.g. rupture duration) can be generated in subduction zones, including tsunami earthquakes, some of which can produce extreme tsunamigenic events. Here, we offer a geological perspective principally accounting for depth-dependent frictional conditions, while adopting a simplified distribution of on-fault tectonic prestress. We combine a lithology-controlled, depth-dependent experimental friction law with 2D elastodynamic rupture simulations for a Tohoku-like subduction zone cross-section. Subduction zone fault rocks are dominantly incohesive and clay-rich near the surface, transitioning to cohesive and more crystalline at depth. By randomly shifting along fault dip the location of the high shear stress regions (“asperities”), moderate to great thrust earthquakes and tsunami earthquakes are produced that are quite consistent with seismological, geodetic, and tsunami observations. As an effect of depth-dependent friction in our model, slip is confined to the high stress asperity at depth; near the surface rupture is impeded by the rock-clay transition constraining slip to the clay-rich layer. However, when the high stress asperity is located in the clay-to-crystalline rock transition, great thrust earthquakes can be generated similar to the Mw 9 Tohoku (2011) earthquake.

5. Conclusion

In nature, subduction zone faults are more complicated than what is depicted in our numerical models (fault roughness, multiple asperities, off-fault inelastic deformation etc.). In particular, our choice of type of initial stress distribution (i.e. an ‘asperity’ model) only examines a small part of the potential stress models and it might not be compatible with stress profiles derived from the modelling of the whole seismic cycle. Therefore, future work should focus on the application of the model to a much wider range of heterogeneous initial stress conditions.

Nevertheless, our model based on lithological and depth dependent friction law tuned to the 2011 Tohoku fault region allows us to better understand and reproduce to the first order the different types of (tsunamigenic) earthquakes. Consistently with geophysical observations, the numerical simulations have shown that events with a number of characteristics resembling tsunami earthquakes were generated either near to or below the accretionary wedge. Their rupture area was constrained to remain there due to the fault strength and breakdown energy increasing with depth. We also found that standard thrust earthquakes, with relatively larger stress drops, shorter durations and faster rupture velocities occurred in crystalline rock where both the energy release rate and fault resistance are high. Finally, if the rupture initiated at the bottom of or just below the rock-clay transition and propagated towards the surface and into a zone characterised by low fault strength and frictional resistance, this leads to the production of great thrust earthquakes.