Mechanische Eigenschaften des Störungsmaterials erosiver Subduktionszonen: Einfluß auf Erdbebenausbreitung und Slow Slip Events
Zusammenfassung der Projektergebnisse
The slip behavior of subduction megathrusts is of great interest due to their ability to generate large earthquakes, and the Japan Trench in particular after the devastation of the 2011 Tohoku earthquake. Laboratory friction experiments were conducted to further our understanding of how these faults behave. The results of the study are wide-ranging, and have resulted in important observations relevant to large coseismic slip during great subduction earthquakes, the origin of slow slip events, and also submarine landslides. Experiments on natural samples recovered by drilling during JFAST have shown that the plate boundary fault is clearly mechanically different from the wall rocks, exhibiting low strength and low cohesion. This difference clearly originates from its high smectite content and intense foliation. When sheared at the plate convergence rate of 85 mm/yr, slow slip events spontaneously occur in samples of the Tohoku fault zone. This is a first observation that is an unexpected result, but consistent with previous observations of slow earthquakes in the Japan Trench subduction zone. Tests on synthetic gouge composed of mineral standards, while not perfectly representative of the Tohoku region, show that slip-weakening behavior is prevalent at the same slip velocities exhibited by a slow slip event preceding the Tohoku earthquake. Collectively, these results suggest that the large coseismic slip that reached the trench during the Tohoku earthquake was probably facilitated by low strength, low cohesion, velocityweakening friction, and possibly an ongoing slow slip event. Further experiments with synthetic gouge examining the systematics of shear strength and cohesion were originally intended to be applied to faults, but instead proved to be useful and important for submarine landslides. These experiments have shown that overconsolidation strengthens sediment via enhanced cohesion, and that this additional strength may explain the relative lack of landslide failures in seismically active areas. Of note in this study is the successful implementation of plate-rate shear velocities in the laboratory, which yielded the surprising new observation of laboratory slow slip events.
Projektbezogene Publikationen (Auswahl)
-
(2015), Data Report : Rate- and state-dependent friction parameters of core samples from IODP Site C0019, IODP Expedition 343 (JFAST), in Chester, F.M. et al., Proc. IODP 343/343T: Tokyo (Integrated Ocean Drilling Program Management International, Inc.)
Ikari, M.J.
-
(2015), Strength characteristics of Japan Trench borehole samples in the high-slip region of the 2011 Tohoku-Oki earthquake, Earth Planet. Sci. Lett. 412, 35-41
Ikari, M.J., J. Kameda, D.M. Saffer and A.J. Kopf
-
(2015), The role of cohesion and overconsolidation in submarine slope failure, Mar. Geol. 369, 153-16
Ikari, M.J. and A.J. Kopf
-
Spectrum of slip behavior in Tohoku fault zone samples at plate tectonic slip rates, Nature Geoscience vol 8, pages 870–874, 2015
Ikari, M.J., Y. Ito, K. Ujiie and A.J. Kopf
