Collaborative Research: Probing the frictional behavior of the Tohoku megathrust using GPS, seismicity, and physics-based models

GSTDTAP

项目编号	1620507
	Collaborative Research: Probing the frictional behavior of the Tohoku megathrust using GPS, seismicity, and physics-based models
	Kaj Johnson
主持机构	Indiana University
项目开始年	2016
	2016-08-01
项目结束日期	2019-07-31
资助机构	US-NSF
项目类别	Continuing grant
项目经费	109301(USD)
国家	美国
语种	英语
英文摘要	The largest earthquakes in the world occur in subduction zones, such as the Cascadia Subduction Zone in the northwestern US, where oceanic plates dive into Earth's mantle. The devastating magnitude 9, 2011 Tohoku-oki earthquake in northern Japan is a notable example, and by far the best instrumented giant earthquake in history. The data from this quake presents a unique opportunity to understand what controls the frequency and size of subduction zone earthquakes. Prior to 2011 it was known that the northern Japan subduction zone exhibited both slow sliding (fault creep without earthquakes) which relaxes stress, as well as rapid slip in earthquakes. It had been, erroneously, thought that the creeping zones would limit the area that could slip in large earthquakes such that magnitude 9 events were not possible. The researchers past work has shown that, contrary to expectation, the same part of the fault can exhibit both creep and earthquakes. This new project develops a rigorous physics-based understanding of the mechanical properties that control how and when fault creep occurs. Models will be tested against precise GPS measurements, which quantify how rapidly stress builds up, as well as small earthquakes which track fault creep. Previous analysis of GPS data recorded in Japan showed that fault creep accelerated in the decades leading up to the magnitude 9; remarkably this was confirmed by independent data from small repeating earthquakes. We will test the hypothesis that creeping areas expand with time as stress builds up on the plate boundary. P.I. Segall will participate in the Geoscape Bay Area Professional Development program for middle and high school science teachers. He will develop a module to translate science from the Tohoku earthquake in Japan to earthquake hazards in the U.S., which has particular relevance to the Cascade subduction zone. This project explores models to explain unique interseismic and post-seismic observations from northeast Japan, constrained by repeating earthquakes and GPS data, both before and after the 2011 Mw 9 earthquake. Our hypothesis for accelerating interseismic creep as well as afterslip overlapping historical ruptures is that while earthquakes nucleate in velocity weakening regions, they rupture into velocity strengthening regions due to strong dynamic weakening. In the interseismic period, creep penetrates into velocity strengthening zones, eroding locked asperities with time. The simulations include rate-state friction and thermal pressurization, and test predictions against GPS and repeating-earthquake data. Time dependent asperity erosion appears to be a promising mechanism to explain the long-duration strain transient. Elastic models with locked asperities restricted to seismogenic depths cannot explain coastal subsidence documented over the last century; these data require either deep coupling (60? 100 km) or mantle relaxation. GPS and seafloor geodetic measurements, post-Mw 9, require some combination of afterslip and deep mantle flow. The Tohoku coast underwent Holocene uplift, yet at present it is unknown whether postseismic processes alone will even recover the observed inter- and co-seismic subsidence. We will use coupled viscoelastic and physics-based afterslip models to examine relative contributions of mantle flow and interface coupling to interseismic deformation and further test the eroding asperity hypothesis. These physics-based models of fault friction and earthquake-cycle deformation are able to integrate diverse datasets and provide a comprehensive model of the mechanical behavior of this unique plate boundary. This project mentors a SURGE (Summer Undergraduate Research in Geoscience and Engineering) student to analyze GPS vertical time series from Tohoku and use these results to constrain interseismic slip rate on the plate boundary. The student will participate in workshops on preparing for the GRE, applying to graduate school, and understanding geoscience careers.
来源学科分类	Geosciences - Earth Sciences
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/69889
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Kaj Johnson.Collaborative Research: Probing the frictional behavior of the Tohoku megathrust using GPS, seismicity, and physics-based models.2016.