Long-term decrease in plate coupling prior to the 2011 Tohoku, Japan earthquake : insights from GPS and seismicity data and physics-based models
Abstract/Contents
- Abstract
- Until the turn of the century, studies of crustal deformation had shown that strain around active fault zones, as measured by geodetic techniques, accumulates at a constant rate between large earthquakes. Over the past fifteen years, however, thanks to the rapid growth of continuous geodetic data, mainly using the Global Positioning System (GPS), a variety of transient deformation signals have been discovered. Mostly occurring in subduction zones, these transient events last for several days to a few years and manifest as anomalous deviations from the interseismic strain rate. In this thesis, I present evidence of a much longer-term deformation transient in northern Japan, over the 15-year period from 1996 to 2011, prior to the M 9 Tohoku-Oki earthquake. GPS position time series in the south-central Tohoku region exhibit nonlinear trends from 1996 to 2011, but in the period 2003--2011 the time series are heavily influenced from postseismic transients due to several M ∼ 6--7 earthquakes. In the first part of the thesis, I correct for these effects and quantify the residual change in interseismic strain rate. I find spatially coherent and statistically significant accelerations in the position time series at numerous stations throughout the Tohoku region. These accelerations can be explained by accelerating aseismic creep on the Japan trench plate interface in the decades before the 2011 Tohoku-Oki earthquake. In the second part of the thesis, I show that changes in the recurrence intervals of repeating earthquakes on the megathrust in the period 1996 to 2011 are consistent with accelerating slip preceding the Tohoku-Oki earthquake. All sequences of repeating earthquakes with statistically significant trends in recurrence interval (at 95% confidence) offshore south-central Tohoku occurred at an accelerating rate. Furthermore, estimates of the magnitude of slip acceleration from repeating earthquakes are consistent with the completely independent geodetic estimates. From joint modeling of the GPS and seismicity data, I infer that a substantial portion of the megathrust experienced accelerating slip, partly surrounding the eventual rupture zone of the M 9 earthquake. The inference of long-term accelerating creep challenges the conventional "asperity model" for the Japan Trench megathrust which, before 2011, posited that the fault was partitioned into fixed velocity-weakening patches (asperities) that are locked interseismically and velocity-strengthening regions that creep stably without accumulating stress. In the third part of the thesis, I use physics-based simulations of earthquake cycles with thermal pressurization to develop a physical model for shrinking asperities. This model may provide a viable physical mechanism for this surprising transient.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2017 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Mavrommatis, Andreas Petros |
|---|---|
| Associated with | Stanford University, Department of Geophysics. |
| Primary advisor | Segall, Paul, 1954- |
| Thesis advisor | Segall, Paul, 1954- |
| Thesis advisor | Beroza, Gregory C. (Gregory Christian) |
| Thesis advisor | Dunham, Eric |
| Advisor | Beroza, Gregory C. (Gregory Christian) |
| Advisor | Dunham, Eric |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Andreas Petros Mavrommatis. |
|---|---|
| Note | Submitted to the Department of Geophysics. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2017. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2017 by Andreas Petros Mavrommatis
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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