This proposal seeks to understand how shallow slip occurred during the Tohoku earthquake by determining the frictional strength of the fault before the rupture initiated and during slip. Using samples collected from the fault during IODP exp 341 (JFast), the PI?s will undertake:
1) Organic thermal maturity measurements to identify the rupture plane and quantify the frictional temperature anomaly induced by coseismic slip. 2) Microstructure observations to identify and characterize the fault that hosted the earthquake, including the identification of textures that indicate frictional weakening. 3) Friction measurements to constrain the steady-state frictional stress of the faults.
These results are crucial for understanding tsunami genesis in shallow subduction zones and will provide critical information for tsunami prediction and hazard mitigation. Importantly, only direct observation and measurement of the fault physical properties can determine these parameters. The Tohoku quake was a surprise, previous work had indicated that such a quake was unlikely in region, especially one in which large amounts of slip occurred in ?weak? shallow accretionary prism sediment. Understanding this quake requires understanding frictional characteristics of rocks in fault zone. There are three plausible scenarios: First, the fault could have undergone dramatic frictional weakening during rapid slip resulting in very low stress coseismically. Alternatively, stress prior to the earthquake was low and changes on the fault were small coseismically, with slip driven by stress transferred from the deeper part of the fault Finally, slip could have propagated through a velocity-strengthening region of the fault with little fault weakening on average.
Broader impacts: Information relating to how a major (and unexpected) tsunami-generating quake was hosted in shallow sediments. A better understanding of tsunamigenic earthquakes has great societal importance.
